Agricultural and Food Science in Finland 157 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Effects of band placement and nitrogen rate on dry matter accumulation, yield and nitrogen uptake of cabbage, carrot and onion Tapio Salo Agricultural Research Centre of Finland, Plant Production Research, Crops and Soil, FIN-31600 Jokioinen, Finland, e-mail: tapio.salo@mtt.fi ACADEMIC DISSERTATION To be presented, with the permission of the Faculty of Agriculture and Forestry of the University of Helsinki, for public criticism in Auditorium 1041 in Viikki Biocenter, Viikinkaari 5, Helsinki, on October 1st, 1999, at 12 noon. 158 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Supervisor: Professor Martti Esala Plant Production Research Agricultural Research Centre of Finland Reviewers: Professor Irma Voipio Department of Plant Production, Horticulture Section University of Helsinki, Finland Docent Johan Korkman Association of Rural Advisory Centres, SLF Helsinki, Finland Opponent: Dr. Albert L. Smit DLO – Research Institute for Agrobiology and Soil Fertility Wageningen, The Netherlands 159 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Preface The present study was carried out at the Agricultural Research Centre of Finland (MTT) during 1993–1999. I wish to extend my gratitude to the Directors of Crops and Soil, late Professor Paavo Elonen and his successor and my supervisor Professor Martti Esala, for offering me the financial and institutional framework for this investigation. I am also grateful to Dr. Antti Jaakkola, Professor of Agricultural Chemistry and Physics at the University of Helsinki, for his guidance and support dur- ing the work. I wish to thank Professor Irma Voipio and Dr. Johan Korkman for valuable advice and construc- tive criticism. The English manuscript was revised by Mrs. Sevastiana Ruusamo, M.A., and edited by Mrs. Sirpa Suonpää, M.Sc., to whom I express my appreciation for their work. I would also like to thank the Board of the Agricultural and Food Science in Finland for accepting this study for publica- tion in their journal. Special thanks are due to the technical staff of Crops and Soil, and especially to Mr. Risto Tanni for taking care of the field experiments and Mrs. Erja Äijälä for laboratory analyses and technical assistance. I also wish to thank my colleagues at MTT for providing advice and support over the years. Thanks are due also to the statisticians of MTT for giving advice when ever needed. Financial support by the Kemira Research Foundation and Scientific Foundation of Academic Agronomists is gratefully acknowledged. Finally, my warmest thanks to my dear Maria, my parents and all my friends, especially at the chess board or the badminton court, for support and periods of relaxation during my studies. Jokioinen, June 1999 Tapio Salo 160 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Contents Abstract ......................................................................................................................... 162 Introduction .................................................................................................................. 163 1.1 Nitrogen fertilization for vegetables ............................................................. 163 1.1.1 Nitrogen demand .................................................................................. 163 1.1.2 Nitrogen losses ..................................................................................... 164 1.2 Improving nitrogen recommendations and methods of application ........... 165 1.2.1 Fertilizer recommendations ................................................................. 165 1.2.2 Methods of application ........................................................................ 165 1.2.3 Response of experimental crops to nitrogen ..................................... 166 1.3 Objectives of the study ................................................................................... 167 2 Material and methods .............................................................................................. 168 2.1 Field experiments ............................................................................................ 168 2.2 Treatments ........................................................................................................ 169 2.2.1 Experimental design ............................................................................. 169 2.2.2 Application of fertilizers ..................................................................... 170 2.3 Management of field experiments ................................................................. 172 2.4 Soil and plant measurements .......................................................................... 174 2.4.1 Soil and root sampling ......................................................................... 174 2.4.2 Plant sampling and final yield ............................................................ 176 2.4.3 Laboratory analysis .............................................................................. 178 2.4.4 Apparent recovery of fertilizer nitrogen ............................................ 179 2.5 Statistical analysis ........................................................................................... 180 3 Results ...................................................................................................................... 181 3.1 Inorganic nitrogen in soil ............................................................................... 181 3.2 Plant growth ..................................................................................................... 185 3.2.1 Root length ............................................................................................ 185 3.2.2 Dry matter accumulation ..................................................................... 187 3.2.3 Final yield ............................................................................................. 194 3.2.4 Dry matter content ............................................................................... 197 3.3 Nitrogen uptake by plants .............................................................................. 197 3.3.1 Plant nitrogen concentration ............................................................... 197 3.3.2 Plant nitrogen uptake ........................................................................... 201 3.3.3 Apparent recovery of fertilizer nitrogen ............................................ 207 3.4 Interaction between nitrogen uptake and sample yield ............................... 210 3.5 Interaction between dry matter accumulation and nitrogen concentration 212 4 Discussion ................................................................................................................ 213 4.1 Inorganic nitrogen in soil ............................................................................... 214 4.2 Plant growth and final yield ........................................................................... 215 4.3 Nitrogen concentration ................................................................................... 220 161 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. 4.4 Nitrogen uptake ............................................................................................... 222 4.5 Apparent recovery of fertilizer nitrogen ....................................................... 224 5 Conclusions ............................................................................................................... 226 References .................................................................................................................... 227 Selostus ......................................................................................................................... 231 162 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Effects of band placement and nitrogen rate on dry matter accumulation, yield and nitrogen uptake of cabbage, carrot and onion Tapio Salo Agricultural Research Centre of Finland, Plant Production Research, Crops and Soil, FIN-31600 Jokioinen, Finland, e-mail: tapio.salo@mtt.fi Adequate nitrogen (N) nutrition is essential for producing high vegetable yields of good quality. Fertilizer N not taken up by the plants is, however, economically wasteful and can be lost to the environment. Therefore the efficient use of N fertilizer, involving accurate estimation of crop N demand, choice of application method and timing of N fertilization, is an important research area. The effects of band placement and rate of N fertilization on inorganic N in the soil and the dry matter accumulation, yield and N uptake of cabbage, carrot and onion were studied in a three-year field experiment between 1993 and 1995. The plants were sampled during the growing season to determine the dry matter accumulation and plant N concentration. The inorganic N in the soil was determined during the growing period and after harvest. The N uptake was 3.8 kg, 1.6 kg and 2.5 kg per ton of edible yield of cabbage, carrot and onion, respectively. At the highest yield levels the N uptake including crop residues was 300 kg ha-1, 150 kg ha-1 and 120 kg ha-1 in cabbage, carrot and onion, respectively. In cabbage, almost 50% of N was in crop residues, whereas in carrot and onion only about 30% of N was in crop residues. Nitrogen uptake from non-fertilized soil varied from 29 to 160 kg ha-1, depending on the growing season and the crop. Cabbage and carrot utilised soil N efficiently, usually taking up more than 100 kg ha-1 from non-fertilized soil. Onion, on the contrary, utilised soil N relatively poorly, usually less than 50 kg ha-1 from non-fertilized soil. The rate of N uptake was low with all crops in early summer. After one month, N uptake increased in cabbage and onion. This uptake continued until harvest, i.e. mid-August for onion and early Sep- tember for cabbage. Nitrogen uptake by carrot started rapidly only two months after sowing and continued until harvest at the end of September. High N rates often resulted in high N concentrations and N uptakes, but growth was not necessarily increased. One month after fertilization, most of the N placed was still near the original fertilizer band and at the depth of 5–10 cm. At that time, broadcast N was at a depth of 0–5 cm. After harvest the soil mineral N content was generally low, i.e. below 25 kg ha-1 at the depth of 0–60 cm. Onion was an exception with poor growth in 1994, when soil mineral N after the highest N rate was 80 kg ha-1 at a depth of 0–60 cm after harvest. © Agricultural and Food Science in Finland mailto:tapio.salo@mtt.fi 163 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. The placement distance in the cabbage experiment, 7.5 cm in the side and 7 cm below cabbage transplants, resulted in lower plant growth and N uptake than broadcasting of N at the beginning of the growing periods 1993 and 1994. Towards harvest differences between application methods de- creased, although in 1993, placement of N still led to 6% lower cabbage yields than broadcasting of N. In 1993, high N rates increased cabbage dry weight and N uptake towards harvest, and this effect was more pronounced when N was broadcast. In 1994, soil N mineralisation was high, and only non- fertilized cabbages took up less N than fertilized plants. Carrot was remarkably insensitive to N fertilization. Carrot yields were similar with and without N fertilizers. Band placement and N rate did not affect carrot growth and N uptake. In 1993, band placement and high rates of N increased onion growth and bulb yield more than broadcasting. In 1994, onion growth was poor and treatments did not affect plant N concentrations or growth. Apparent recovery of fertilizer N was increased in 1993 by low N rates or band placement. This result that band placement of N does not much affect vegetable growth is in agreement with most previous studies. With onion, probably due to the sparse root system, positive effects of N placement are most likely to be found. Keywords: Allium cepa L., application methods, Brassica oleracea var. capitata L., Daucus carota L., fertilization, growth, nitrogen content 1 Introduction caused a slight decrease in the recommended N rates in many countries, including Finland (Soil Testing Laboratory of Finland 1992, 1997), the effect of reduced N supply on yield levels should be studied. Vegetable crops comprise a widely differing species, with a range of N demand varying from less than 50 kg ha-1 for peas to more than 300 kg for white cabbage. In Finnish conditions, the short growing season prevents cultivation of sev- eral species and cultivars, and favours manage- ment practices, e.g. transplants, that shorten the growing period. In Finland, the total area of vegetables, in- cluding garden peas for the processing industry, has risen above 10 000 ha during the 1990’s (In- formation Centre of the Ministry of Agriculture and Forestry 1998). The most popular vegetable crops are garden pea (Pisum sativum L.), white cabbage (Brassica oleracea var. capitata L.), carrot (Daucus carota L.) and onion (Allium cepa L.). Although the total acreage of vegetable crops is not large, the value of production is high and production is usually concentrated on fertile soils. Nitrogen fertilizer recommendations for 1.1 Nitrogen fertilization for vegetables 1.1.1 Nitrogen demand Adequate nitrogen (N) nutrition is essential for producing high crop yields of good quality. As natural soil N supply is rarely sufficient, grow- ers usually apply fertilizer N each year. Unused fertilizer N is economically wasteful and can be lost to the environment. As public awareness of environmental quality increases, there is increas- ing pressure to improve N management (Below 1994). The general measures against N losses are classified as increased crop cover period, opti- mised application of animal manure and fertiliz- er to crops, minimum tillage and reduced appli- cation of N (Nordic Council of Ministers 1992). Plant N uptake is approved as a very important way of N removal from soil and mentioned as one of the important research areas (Nordic Council of Ministers 1992). Whilst efforts to re- duce leaching of N to the environment have 164 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion vegetable crops have been established in Finland for more than twenty years (Kurki 1974). The comparisons between the N fertilizer recommen- dations in different countries are often confus- ing, as expected yield, plant density, cultivars and crop management techniques vary consid- erably. In any case, this comparison (Table 1) can give us an idea of the average level of ex- pected N demand. According to Neeteson (1995), most of the current N recommendation systems are based on economically optimum application rates, i.e. they take into account the cost of N fertilizers and the expected price of the crop products. These recommendations do not con- sider N losses to the environment (Neeteson 1995). 1.1.2 Nitrogen losses In Finland, N losses caused by ammonia volatil- isation, denitrification and leaching have been estimated as an average 15 kg ha-1 per year for each of the loss mechanisms (Nordic Council of Ministers 1992). Whereas leaching can be con- sidered to cause major losses of N in Northwest Europe (Neeteson 1995), cold winters in Finland decrease the amount of leaching. However with certain crops, as for example cabbages, high fer- tilizer rates and crop residues rich in N can in- crease considerably the risk of N leaching (Everaarts 1993a). Denitrification occurs when soil is saturated with water. In vegetable production there are periods after harvest when large amounts of N and C in crop residues are in the field (Rahn et al. 1992), and rainfall is high. In Germany, Schlo- emer (1991) calculated denitrification of 44 kg ha-1 in 57 days from a cauliflower field where 30 tons of fresh crop residues had been ploughed in. Although most of the volatilisation of am- monium N results from animal production sys- tems, some volatilisation can result directly from plants or from decomposing plant residues. Whereas the losses directly from the plants are now estimated to be only 1–2 kg ha-1 y-1 (Matts- son et al. 1998), losses of ammonia from decom- posing plant mulch have been 17–39% of the N in the mulch (Larsson et al. 1998). Table 1. Fertilizer recommendations for white cabbage, carrot and onion in Austria, Germany, England and Finland. Expected yields (t ha-1) are given in parentheses after N recommendations if available. (Bundes- gemüsebauverband Österreichs 1995, Scharpf and Weier 1996, MAFF 1994, Soil Testing Laboratory of Finland 1997). N in soil (0–60 cm)+N fertilization N fertilization total (kg ha-1) total (kg ha-1) Crop Harvest Soil Austria Germany England Finland Cabbage early sand 250 (40) 300 120 (35) late sand 280 (50) 350 (80) 250 190 (50) Carrot early sand 170 (50) 60 90 (40) organic 0 80 (40) late sand 215 (70) 100 (60) 60 85–95 (50) organic 0 80–90 (50) Onion sand 170 (50) 160 (60) 90 90–95 (30) organic 30 80–85 (30) 165 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. 1.2 Improving nitrogen recom- mendations and methods of application 1.2.1 Fertilizer recommendations Different recommendation methods are classi- fied by Neeteson (1995) as follows: fixed rates, N min method, balance sheet method, plant analy- sis and simulation models. These methods are of different complexity. Fixed rates in their sim- plest form just depend on the expected N de- mands of crops. The N min method is based on soil inorganic N analysis at the time of fertilizer ap- plication. The balance sheet method attempts to include soil N mineralisation and atmospheric deposition in the N recommendation. Plant anal- ysis aims to determine a critical plant N concen- tration, below which N application is needed. Simulation models aim to calculate crop growth, N uptake, N supply to soil from different sources and losses of N to the environment. Most of the existing N recommendations in- clude expected yield level. However, correlation between yield and N uptake of the crop is often not thoroughly determined (Neeteson 1995). Crop N uptake that originates from N in the res- idues of the preceding crop and soil N minerali- sation is generally very difficult to estimate, al- though the balance sheet method and simulation models aim to do that. The rate of N uptake dur- ing the growing season is important for deter- mining the timing of top dressings. Considera- tion of root depth is important for determining the soil volume from which the plant can take up N. Finally some crops, as for instance cauli- flower, are supposed to need a certain level of soil N at the time of the harvest to produce a good yield (Welch et al. 1985b). Knowledge of the soil and crop properties discussed above should be increased in order to improve N recommen- dations. Dynamic simulation models, e.g. WELL-N (Rahn et al. 1996a) and N-Expert (Fink and Scharpf 1993), can be used for N recommenda- tions. Simulation models can be used alone or together with soil and plant analysis which can check and guide the modelling simulations. In addition, the more complicated versions of the models can be used by researchers to understand the behaviour of the agroecosystem. The prob- lem with the models is usually the large amount of data and parameters that is needed. Also the applicability of the models to conditions other than those they were developed for is often poor. 1.2.2 Methods of application Peterson and Frye (1989) classify seven differ- ent methods of application. Broadcast applica- tion is an even distribution over the field sur- face, after which the fertilizer is usually mixed into the topsoil. Injection and band placement involve subsurface placement of liquid or solid fertilizer before or during planting. In-row ap- plication places the fertilizer directly in the seed row. Side-dressing is applied beside the plant row after crop establishment. Top dressing is a broad- cast application over the top of the growing crop. Foliar fertilization means spraying of fertilizer solution directly onto the plant foliage. Band placement is the main fertilizer appli- cation method for cereals in Finland. Compound fertilizers (10–20% N, 2–8% P, 4–18% K) are placed in bands between every second seed row, 2–3 cm deeper than the seeds. The spacing of seed rows is 12.5 cm and thus the distance of the fertilizer from the seed is 6–7 cm. From the bands N dissolves easily in moist soil, and is rapidly available to the plants. The method has resulted in higher cereal yields in several exper- iments (Kaila and Hänninen 1961, Aura 1967). Band placement has produced the best results in climates with a dry early growing season (Esala and Larpes 1986). In Finnish outdoor vegetable production, band placement is not a widely used method of N compared to broadcasting. There are several reasons: lack of suitable machinery, risk of high salt concentrations when a high amount of nu- 166 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion trient is added close to the seed or transplant, and the aim of creating a large, tolerant root sys- tem by a uniform nutrient supply in the soil. Top dressings are recommended once or twice dur- ing the growing season depending on the crop (Soil Testing Laboratory of Finland 1997). Ac- cording to the recommendations, 30–50% of N rate should be applied as top dressing. Recom- mendations do not usually mention any differ- ence between band placement or broadcasting of N. Although vegetable yields were increased in early experiments with the band placement (Cooke et al. 1956), later research has not shown a clear advantage for band application in com- parison with broadcast application (Neeteson 1995). Recent studies in England have shown that side-dressing with a small amount of NP fertilizer might hasten plant development and increase plant yield (e.g. Rahn et al. 1996b). Everaarts (1993b) summarizes that beneficial effects of placement are likely to be greatest with crops having a large distance between plants, crops having a short growing period and in soils with low fertility. 1.2.3 Response of experimental crops to nitrogen In Finland, the three most cultivated vegetable crops, excluding garden pea, are carrot, onion and white cabbage (Information Centre of the Ministry of Agriculture and Forestry 1998). Ni- trogen recommendations for these crops (Table 1) are based on studies in the early 1980’s (Leh- tinen 1984, Aura 1985). As these studies includ- ed only the effect of N fertilizer on yield, there is a lack of knowledge concerning N uptake and the rate of N uptake in Finnish conditions. Al- though the recommendations have been revised to meet the yield levels of current cultivars (Soil Testing Laboratory of Finland 1992, 1997), there is still a need to optimise N application in re- spect of rate and timing and, in addition, to find out the effects of the application method. White cabbage, referred to below simply as cabbage, has a distance between plants of 25– 60 cm and the growing period in the field varies from 50 to 140 days in Finnish conditions, de- pending on the variety (Association of Rural Advisory Centres 1987b). The optimum range of N fertilizer, shown by several studies, has varied from 200 to 500 kg ha-1 (Everaarts and de Moel 1998). In Finnish studies, yields have in- creased up to the highest N rates used, 240 kg ha-1 (Lehtinen 1984) and 200 kg ha-1 (Aura 1985). As cabbage plants are wide apart and N demand is high, cabbage should benefit from N place- ment, especially with fast-growing varieties. Wiedenfeld (1986) in Texas, USA and Everaarts and de Moel (1998) in the Netherlands got no or varying effects on cabbage yield by band place- ment. Cauliflower responded well to placement in Denmark (Sørensen 1996), but Everaarts and de Moel (1995) in the Netherlands got positive effects from band placement in only two exper- iments out of seven. Considering placement of NPK fertilizer, Smith et al. (1990) in Pennsyl- vania, USA, found better yields in cabbage with band placement than with broadcasting. In Finland, carrot has been cultivated with a 45–65 cm row distance (Association of Rural Advisory Centres 1987a). According to Taival- maa and Talvitie (1997) there has been a change from flat bed to ridge cultivation, and based on their studies they recommended narrow ridges (base width 49 cm) for fresh market production and broad ridges (base width 75 cm) for indus- trial production. On the other hand, the growing period of carrot is long for late cultivars, from May to late September. In addition, carrot has a deep root system consisting of very fine roots with a high specific root surface area (Pietola 1995). This might be an additional reason why carrot yield has been relatively insensitive to experiments with water and nitrogen supply as assumed by Pietola (1995). But since placement of NPK fertilizer has resulted in higher carrot yields than broadcasting of NPK fertilizer both in Norway and Finland (Ekeberg 1986, Evers 1989), placement of N solely might also be ben- eficial for carrot growth. In Finnish studies con- 167 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. cerning N rates, the lowest N applications used, 60 kg ha-1 (Lehtinen 1984) and 80 kg ha-1 (Aura 1985), were sufficient for the highest carrot yields achieved. In Finland, onion is usually produced from sets, and the length of the growing period is 80– 100 days (Engblom 1993). The distance between onion rows is commonly about 30 cm, and as onion has a sparse root system (Portas 1973, Greenwood et al. 1982), it might be expected to benefit from placement of N. Placement of NPK fertilizers (Cooke et al. 1956, Dragland 1992) in England and Norway or NP fertilizers (Sø- rensen 1996) in Denmark has resulted in slight- ly higher onion yields compared to broadcast- ing. According to the results of Henriksen (1987), this effect might be caused mainly by phosphorous. Band placement of N solely has also increased yields slightly (Wiedenfeld 1986), especially when the amount of N fertilizer has been low (Sørensen 1996). Although optimum N rates have varied from 20 to 350 kg ha-1 in the Netherlands (De Visser et al. 1995), N rates of 50-100 kg ha-1 have been sufficient to achieve maximum yield in Finland (Aura 1985, Suojala et al. 1998). 1.3 Objectives of the study Field experiments were carried out in order to determine the effect of band placement and N rate on the growth response, plant N uptake and apparent recovery of fertilizer N. Three differ- ent model crops were cultivated in the same field area during three years. Cabbage cv. Castello F1 (Nickerson-Zwaan, the Netherlands) is used for autumn marketing and industrial purposes in Finland and has a growing period of approxi- mately 85 days (Association of Rural Advisory Centres 1987b). The characteristics observed in England, long field standing ability and high percentage marketable (NIAB 1997) have made Castello popular in Finland. The plant densities used should produce a head weight of 1.5–2.0 kg. The growth of transplanted cabbage contin- ues in the field with leaf development and then with head formation (Feller et al. 1995). The root system of cabbage has developed about 20 cm vertically when head formation begins (Portas 1973). Carrot cv. Narbonne F1 (Bejo Zaden, the Netherlands) is a late cultivar in Finnish condi- tions, and is used for storage (Pessala 1993). Narbonne has good resistance to breakdown and a good yield level (NIAB 1997). The growth stages of carrot in the field are germination, leaf development and finally root expansion (Feller et al. 1995). The root system of carrot is known to be deep and dense (Pietola 1995). Onion cv. Sturon (Sluis and Groot, the Netherlands) is suit- able for producing bulbs from sets. Good yield level and storage performance (NIAB 1997) have kept Sturon as one of the most popular onion cultivars in Finland despite its rather mixed size and shape distribution (NIAB 1997). As an on- ion set has a large reserve of stored assimilates, it rapidly develops into a large plant (Brewster 1990b). After root formation and green shoot emergence, leaf development begins and ceases when bulb development starts (Feller et al. 1995). Bulb development is controlled by tem- perature and radiation (Brewster 1990a). The root system of onion is unbranched and does not undergo secondary thickening (Langer and Hill 1991). In this study, these three model crops and culti- vars were assessed by the following questions: What is the relationship between yield and N uptake? What is the distribution of N between yield and crop residues? What are the potential yield and N uptake in conditions of low N supply? Can we determine the critical N concentra- tion? When is the most rapid period of N uptake? What is the apparent recovery of fertilizer N? Is growth increased due to band placement of N? Is the apparent recovery of fertilizer N in- creased due to band placement? 168 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion 2 Material and methods classified as Eutric Cambisol according to the FAO classification (Fitzpatrick 1980). Weather conditions Temperature, potential evaporation (determined by Class-A evaporation pan) and precipitation were measured at the Jokioinen Observatory (Table 3). In 1993, the temperature was slightly lower than long-time average. In 1994, July was extremely dry and warm, with only 1 mm of pre- cipitation and potential evaporation of 186 mm. In 1995, May and June were very rainy, but lat- er the rainfall was less than the long-time aver- age. Potential evaporation was high in May 1993, but decreased later below the long-time average. In 1994, potential evaporation was first low, but increased up to long-time average values due to warm July. 2.1 Field experiments The field site The field experiments were carried out in the same field area of the Agricultural Research C e n t r e o f F i n l a n d i n J o k i o i n e n ( 6 0 ° 4 9 ’ N , 23°28’E, 85 m a.s.l.). According to the soil clas- sification used in Finland (Juusela and Wäre 1956), the top soil was fine sand, except for the cabbage field in 1993 when the soil type was clay loam (Table 2). The subsoils of the experi- mental fields were sandy and silty clay. The or- ganic matter content (organic C multiplied by 1.94) indicates that the surface soil was medium (3–6%) in organic matter and the cabbage field in 1993 rich (6–12%) in organic matter (Aalto- nen et al. 1949). Both soils can tentatively be Table 2. Soil properties at the trial sites. Variation is presented in parentheses as standard error of the mean, if available. Experiments without cabbage 1993 Cabbage 1993 0–25 cm 25–50 cm 0–25 cm 25–50 cm Sand (0.2mm≤ ø <2.0 mm), % 29 (9) 16 (11) 12 (2) 8 (1) Finesand (0.02≤ ø <0.2 mm), % 35 (10) 37 (7) 22 (2) 18 (2) Silt (0.002mm≤ ø <0.02mm), % 10 (1) 12 (1) 26 (2) 26 (2) Clay (ø <0.002 mm), % 26 (3) 35 (4) 40 (3) 48 (2) Total porosity, % (v v-1) 48 (1) 40 (2) 53 (1) 49 (1) Field water capacity (pF=2), % (v v-1) 36 (2) 31 (2) 36 (1) 38 (2) Wilting point (pF=4.2), % (v v-1) 15 (1) 15 (1) 21 (1) 26 (2) Saturated hydraulic conductivity 14 (7) 2 (1) 26 (10) 4 (1) (cm h-1) Total Kjeldahl nitrogen (g kg-1) 2.0 (0.2) 0.6 (0.2) 2.2 (0.2) 0.7 (0.1) Total organic carbon (%) 2.6 (0.2) 0.5 (0.1) 3.3 (0.3) 1.4 (0.9) Phosphorus (mg dm-3) 35 3 47 (8) 10 (5) Potassium (mg dm-3) 300 180 260 (13) 220 (15) Bulk density (g cm-3) 1.38 (0.03) 1.59 (0.06) 1.31 (0.02) 1.35 Methods used: Particle size distribution by the pipette method (Elonen 1971), total porosity calculated from particle and bulk density (Danielson and Sutherland 1986), field water capacity by pressure plate extractor and wilting point by osmosis (Klute 1986), saturated hydraulic conductivity at the depth 0–25 cm by ring infiltrometer and at the depth 25–50 cm by the auger- hole method above water table (Youngs 1991), Kjeldahl N by autoanalyzer (Tecator 1981), organic carbon by a Leco analyzer at 1370°C (Sippola 1982), phosphorus and potassium extracted with acid ammonium acetate (Vuorinen and Mäki- tie 1955, Kurki et al. 1965) and bulk density by the core method (Blake and Hartge 1986). 169 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. 2.2 Treatments 2.2.1 Experimental design In 1993, factorial experiments were set up ac- cording to a split-plot design, where the main plot factor was N fertilization with three levels (N 1 , N 2 , N 3 ) and the subplot factor was broad- cast or band placement application (Table 4). The highest N level was estimated to be the optimum fertilizer N rate with respect to expected yield (Soil Testing Laboratory of Finland 1992) and soil N reserves. In addition, a treatment without N fertilizer was included in order to measure growth and N uptake produced by N mineral- ized from the soil and to calculate the apparent recovery of fertilizer N. In 1994, cabbage and Table 3. Monthly mean temperatures, monthly sums of potential evaporation, precipitation and irrigation during the growing seasons and 30 year averages at the Jokioinen Observatory. 1993 1994 1995 1961–90 Mean temperature (oC) May 13.6 7.8 8.7 9.4 June 11.4 12.1 16.7 14.3 July 15.6 19.0 15.3 15.8 August 12.9 15.1 15.1 14.2 September 5.7 10.0 10.3 9.4 Potential evaporation (mm) May 155 108 86 116 June 99 104 128 148 July 122 186 136 129 August 59 93 109 90 September 35 36 38 40 Precipitation (mm) May 1 34 87 35 June 56 66 121 47 July 107 1 53 80 August 136 54 65 83 September 13 105 45 65 Irrigation (mm) Cb Ca On Cb Ca On Cb Ca On May 20 20 10 June 10 10 July 20 10 10 85 71 77 40 23 60 August 61 36 10 September Sum 40 30 20 156 107 87 50 23 60 Cb=cabbage, Ca=carrot, On=onion. 170 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion onion experiments were conducted with a simi- lar split-plot design as in 1993. As carrot growth in 1993 was not influenced even by N rate, N rates were only broadcast in 1994. In 1995, car- rot and onion experiments were conducted only with a non-fertilized treatment and an estimated optimum N rate in order to obtain data for N min- eralisation and N uptake from the third year. With cabbage, placement and broadcast treatments were included to compare application methods also during the third experimental year. All ex- periments were made with four replicates, ar- ranged in separate blocks. Randomisation was done by the experimental design procedure of the MSTAT-C program (Michigan State Univer- sity 1989). Nitrogen fertilizer levels were first randomly assigned to the blocks and then the two application methods were randomised over each main plot. The locations of the experiments were changed from the previous year (Table 5) in or- der to decrease the risk of disease. As the avail- able field area for the experiments was small, the experiments were often established over the experiment of the previous year. The error caused by N application the preceding year was assumed to be small due to the leaching of N during the previous autumn and spring. 2.2.2 Application of fertilizers Autumn ploughed land was harrowed to a depth of 3–5 cm in order to decrease surface rough- ness. After that potassium and phosphorus were broadcast on the soil surface and the seed or planting bed was tilled. Nitrogen was applied as ammonium nitrate limestone (27.5% N, Kemira Agro Oy, Finland), potassium as potassium sul- phate (41.5% K) and phosphorus as triple su- perphosphate (20.1% P). Ammonium nitrate was used to protect part of the fertilizer N from pos- sible leaching at the beginning of the growing period. However, ammonium nitrate should maintain inorganic N in the soil at a high level right after planting or seeding. A high content of inorganic N would also test the effect of salt stress. Although experimental soils were as- sumed to contain enough other macronutrients and micronutrients, 500 kg ha-1 compound ferti- lizer (18.5% S, 5.0% Mg, 0.3% Fe, 0.3% B, 1.0% Cu, 4.0% Mn, 0.8% Zn and 0.05% Mo, Kemira Agro Oy, Finland) was applied to the experimen- tal fields each year. Table 4. Experimental details. Experiment Inorganic N Main plot Subplot Plant density Planting Final harvest before fertilization N rate Application method harvested / planned date date kg ha-1 kg ha-1 plants ha-1 Cabbage 1993 44 0, 125,188, 250 broadcast/band 62 000 / 67 000 25 May 7 September Cabbage 1994 27 0, 80, 120, 160 broadcast/band 36 000 / 44 000 1 June 7 September Cabbage 1995 16 0, 160 broadcast/band 33 000 / 50 000 16 June 3 October Carrot 1993 33 0, 30, 70, 100 broadcast/band 730 000 / 800 000 4 May 1 October Carrot 1994 44 0, 30, 70, 100 broadcast 785 000 / 800 000 6 May 30 September Carrot 1995 22 0, 70 broadcast 155 000 / 290 000 10 May 6 October Onion 1993 50 0, 30, 70, 100 broadcast/band 351 000 / 356 000 11 May 17 August Onion 1994 38 0, 30, 70, 100 broadcast/band 343 000 / 356 000 10 May 23 August Onion 1995 22 0, 100 broadcast 312 000 / 356 000 30 May 29 August Table 5. Crop rotation during the experiment. 1992 1993 1994 1995 Barley Cabbage Barley Barley Barley Carrot Cabbage Onion Barley Onion Carrot Cabbage Barley Barley Onion Carrot 171 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Cabbage Each year, 150 kg ha-1 potassium and 50 kg ha-1 phosphorus were applied according to the slight- ly higher yield expected than the 50 t ha-1 of the recommendations (Soil Testing Laboratory of Finland 1992). These fertilizers were broadcast and mixed in the 10 cm soil layer by a rotary harrow. The N fertilizer was band-placed using ferti- lizer drill (Juko Ltd., Finland) in four double rows for each 2 m wide experimental plot. The distance between double rows was 32 cm and the rows of the double row were 18 cm apart (Fig. 1). Fertilizer bands were placed about 12 cm below the soil surface. Broadcast treatment was made with the same fertilizer drill, first ap- plying fertilizer on the soil surface and then mix- ing the fertilizer with a harrow into the 8 cm top layer. Lower N rates (Table 4) were applied in 1994 than in 1993 because the N uptake of the non- Fig. 1. Locations of N fertilizer placement and soil samplings of placement treatments. 172 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion fertilized carrot crop had been over 100 kg ha-1 in this experimental field, and the density of cab- bage plants was lower in 1994 than in 1993. Carrot Each year, 80 kg ha-1 potassium and 50 kg ha-1 phosphorus were applied according to the rec- ommendations for the expected 50 t ha-1 yield (Soil Testing Laboratory of Finland 1992). These fertilizers were broadcast and mixed in the 20 cm soil layer by a rotary harrow. In 1993, band placement of N was done us- ing a potato planting machine (Juko Ltd., Fin- land) after loosening the soil by a rotary harrow to a depth of 20 cm. The potato planting ma- chine formed a ridge about 20 cm high, and placed the fertilizer band about 15 cm below the top of the ridge (Fig. 1). There were four ridges (Fig. 1) in the 3.0 m wide experimental plot. Broadcast treatment was made with a manually propelled fertilizer spreader working on the prin- ciple of an ordinary fertilizer drill (Tume Oy, Finland). The fertilizer was first applied on the soil surface, then mixed by a rotary harrow into the 15 cm top layer and finally ridges were formed with the potato planting machine. In 1994 and 1995, N fertilizer was broadcast with the manual fertilizer spreader (Tume Oy, Fin- land), and then mixed by a rotary harrow into the 15 cm top soil layer. Ridges were not formed in 1994 and 1995 in order to avoid problems of dry soil surface, which delayed emergence in 1993. Onion Each year, 60 kg ha-1 potassium and 60 kg ha-1 phosphorus were applied according to the slight- ly higher yield expected than the 25 t ha-1 of the recommendations (Soil Testing Laboratory of Finland 1992). These fertilizers were broadcast and mixed into the 8 cm soil layer by a harrow. The N fertilizer was band placed using a po- tato planting machine (Juko Ltd, Finland), in a single band with a distance of 30 cm between rows and at a depth of 10 cm (Fig. 1). There were four fertilizer bands in the 1.5 m wide experi- mental plot. Broadcast treatment was made with the manually propelled fertilizer spreader (Tume Oy, Finland). Fertilizer was applied on the soil surface and then mixed with a harrow into the 5 cm soil layer. 2.3 Management of field experiments In 1993, gypsum blocks were installed at depths of 10 and 20 cm in broadcast N 1 and N 3 and placed N 2 plots after planting or sowing. In 1994, gypsum blocks were installed at depths of 10, 20 and 30 cm in the broadcast N 2 plots and in the N fertilized plots in 1995. The gypsum blocks were usually recorded once a week. When the estimated tran- spiration was high and rainfall was low, the gyp- sum blocks were recorded 2–3 times per week. Ir- rigation was carried out when the plant-available water fell to 40–50%. Irrigation was applied at night by rotary sprinklers (radius 14 m and angle of irrigated sector 90°). The rate of irrigation was approximately 4 mm per hour. The amount of wa- ter given to the sprinkling sector was controlled by 6–9 plastic flasks equipped with funnels. These sprinklers have 15–25% variation within the sprin- kling sector (Pietola 1995). In spring 1993, irriga- tion was applied for all crops to secure start of growth after planting or sowing, as the rainfall in May was only 1 mm. In 1994, only the cabbage field was irrigated after planting. Plant protection was done according to the prevailing Finnish recommendations (Markkula 1993). The manufacturer’s instructions were fol- lowed in pesticide applications. Yellow traps were used to monitor the abundance of harmful insects. Early in the season weeds were control- led by herbicide applications, and later by hand- weeding. Protection measures against diseases and insects kept plant damage to a low level ex- cept for damage caused by carrot fly (Psila ro- sae F.) in autumn 1994. 173 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Cabbage The subplots were 2 m x 10 m. Cabbage spacing between rows was 0.5 m and the spacing within rows was 0.3 m in 1993, 0.45 m in 1994 and 0.4 m in 1995. The plant density was decreased in 1994 as the head weight the previous year had been less than 1.5 kg, which had been set as a target weight. In 1995, the plant density was slightly increased as the transplants were stressed due to delayed planting. The cabbage transplants were raised in cell trays (Plantek 144, Lännen Tehtaat, Finland) by a local farmer. The cell dimensions of this tray mod- el are 3.2 cm x 3.2 cm x 4 cm. In 1993 and 1994, four-week-old cabbage transplants were planted by hand after night temperatures had risen above 0°C (Table 4). Plant rows were positioned in the middle of the double fertilizer band in the placed treatments (Fig. 1). Thus N bands were 7.5 cm to the side and 7 cm below the cabbage transplants, as the cabbage pot inserted 1 cm below soil sur- face was 3 cm wide and 4 cm long. In 1995, the cabbage transplants were planted later in June, as high rainfalls had kept the soil too moist for plant- ing. As the transplants were delivered at the end of May, they were stored in a greenhouse and wa- tered with NP-solution (0.015% N, 0.015% P) for two weeks. This delayed planting seemed to stress the transplants, as root growth was excessive in the small cell of the tray. In 1993, the plants were irrigated twice with 10 mm after planting, and with 20 mm at the beginning of July when the plant-available wa- ter in the soil decreased rapidly. In 1994, the plants were irrigated seven times, the amount of water applied was altogether 156 mm (Table 3). In 1995, the soil was moist after high rainfall in early summer, and irrigation was applied only three times, altogether 50 mm. The cabbage transplants were watered with dimethoate after planting for protection against small cabbage fly (Delia brassicae L.) each year. In 1993, the cabbage field was kept under a non- wowen polypropylene cover (Lutrasil 17 g m-2, Freudenberg & Co., Germany ) between 26 May and 18 June in order to prevent damages by the European tarnished plant bug (Lygus rugulipennis Poppius). In 1994, plant bug was controlled by applying permethrin once in June, and in 1995 per- methrin and lambda-cyhalothrin were both applied once. Later during the growing period in 1993, both dimethoate and deltamethrin were applied twice against the small and large cabbage fly (Delia brassicae L. and Delia radicum L.). In 1994, del- tamethrin was applied twice, and in 1995 permeth- rin once against cabbage flies. Weeds were con- trolled in 1993 and 1994 by applying propachlor 4–5 days after planting, but in 1995 rain delayed application until two weeks after planting. Carrot The subplots were 3 m x 10 m. The plant spac- ing between rows was 0.75 m and the target plant density was 60 plants per row metre (800 000 plants ha-1). Seeds were sown 1–1.5 cm deep by a pneumatic sowing machine (Caspardo SV260, Italy) at the beginning of May in 1993 and 1994 (Table 4). In 1995, carrots were sown by a man- ually propelled cup-disc planter (Nibex, Nibe- verken AB, Sweden). In 1993, seeds were drilled in the middle of the ridge in double rows and in 1994 in double rows with no ridges. In 1995, seeds were sown in single rows with a planned density of 290 000 plants ha-1 (Table 4). In 1993, the plots were irrigated with 10 mm twice in May to improve plant establishment and once in July when plant-available water de- creased rapidly according to the gypsum block measurements. In 1994, crops were irrigated five times in July and August (Table 3). In 1995, ir- rigation was applied twice in July. Weeds were sprayed with metoxuron one month after sowing each year. In 1993, dimeth- oate and deltamethrin were first applied against European tarnished plant bug and carrot sucker (Trioza apicalis Förster) and later against carrot fly (Psila rosae F.), altogether four times. In 1994, plant bug and carrot sucker were controlled by permethrin four times, and carrot fly was con- trolled by permethrin and deltamethrin altogether four times. In 1995, plant bug, carrot sucker and carrot fly were controlled by permethrin and lamb- 174 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion da-cyhalothrin altogether five times. Although carrot fly was monitored by yellow traps, it dam- aged approximately 5% of the final yield in 1994. Onion The subplots were 1.5 m x 8 m. The onion rows were 0.3 m apart and the spacing within rows was 0.075 m. The edge rows of neighbouring subplots were 0.6 m apart. The sets, diameter 15–22 mm, were planted by hand in May (Table 4). The on- ion rows were 5 cm to the side of the fertilizer band in the placement treatments (Fig. 1). Plant- ing depth was approximately 3 cm and thus the vertical distance from the fertilizer band to the bottom of the onion set was approximately 7 cm. In 1993, the plants were irrigated twice with 5 mm of water to secure the start of growth after planting, and once with 10 mm in July. In 1994, the crops were irrigated five times (Table 3) ac- cording to the gypsum block measurements. In 1995, irrigation was applied three times in July. Before planting, the onion sets were soaked for 15 minutes in 0.1% benomyl and 0.1% dimethoate solution for protection against grey mould (Botrytis cinerea Pers.) and onion fly (Delia antiqua Meigen), respectively. Weeds were sprayed with prometryn two weeks after onion planting. A mixture of metalaxyl and man- cozeb was applied twice per growing season against downy mildew (Peronospora destructor Berk.). In 1993, two additional copper oxychlo- ride applications were given in order to stop an observed downy mildew infection. 2.4 Soil and plant measurements 2.4.1 Soil and root sampling Cabbage In 1993, the soil was sampled for inorganic N on 24 June (30 days after planting = dap) from three replicated plots (Table 6). From the broad- cast 250 kg ha-1 and placed 250 kg ha-1 treat- ments, additional depths of 0–10 cm and 10– 20 cm were sampled in order to assess vertical distribution of inorganic N and cabbage roots. Four subsamples per plot were taken a few cen- timetres to the side of the four sampled cabbage plants, and two subsamples between rows to as- sess the horizontal distribution of roots. All soil and root samples were taken using a core with 5 cm diameter. Individual subsamples were bulked and stored at –18°C until laboratory analysis. The second soil sampling was made on 27 July (63 dap, Table 6). Samples were taken both within (four subsamples) and between rows (two subsamples) to find out if there were horizontal differences in the distribution of soil inorganic N and cabbage roots. The third soil sampling was made after harvest, on 17 September (115 dap), in order to assess the residual amount of N after the cabbage crop. Eight subsamples were taken randomly from each plot. In 1994, the first soil sampling was made on 8 July (38 dap, Table 6). One core sample was taken at a few centimetres distance from each cabbage plant sampled and these four core sam- ples for each plot were bulked and stored at –18°C. From the treatment of placed 160 kg ha-1, three separate core samples were taken from a line perpendicular to the row, so that the middle coring was at the location of the sampled cab- bage plant and two corings were 5 cm to the side of the sampled plant (Fig. 1). These samples were taken from the location of two cabbage plants. This sampling was made to assess the horizon- tal and vertical distribution of soil inorganic N near the plants in the placement treatment. The second soil sampling was made on 13 September (105 dap) in order to assess the amount of residual N in the soil after harvest. Eight subsamples were taken randomly from each plot. Carrot In 1993, the soil was sampled for inorganic N on 21 July (106 days after sowing = das, Table 6) from three replicated plots. Soil samples were taken from the location where the sampled car- 175 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. rots were grown (Fig. 1). The soil samples were stored at –18°C until laboratory analysis. The second soil sampling was made on 15 October (164 das) and six subsamples were taken ran- domly from each plot. In 1994, soils were sam- pled on 14 October (161 das, Table 6). The sam- ples were treated and analyzed as in 1993. Table 6. Dates, depths and locations of soil samplings. Cabbage Date Treatment Depth (cm) Location 1993 24 June (30 dap) 0, B&P125, B&P188 0–20–40 plant row B&P250 0–10–20–40 plant row 27 July (63 dap) B&P188 0–10–20–40–60 plant row, interrow 17 September (115 dap) 0, B125, B188, B250 0–25–60 interrow 1994 8 July (38 dap) 0, B160 0–5–10–15–20–30–40 plant row P160 plant row, fertilizer row 13 September (105 dap) 0, B&P160 0–25–60 interrow Carrot 1993 21 July (106 das) 0, B&P30, B&P70, 0–10–20–40–60 plant row B&P100 15 October (164 das) 0, B100 0–25–60 plant row 1994 14 October (161 das) 0, B100 0–25–60 plant row Onion 1993 18 June (35 dap) 0, B&P30, B&P70 0–25–40 plant row, interrow B100 0–10–20–40 plant row, interrow P100 0–10–20–40 plant row, fertilizer row, non-fertilized interrow 20 July (70 dap) B&P70 0–10–20–30 plant row, interrow 20 September (132 dap) 0, B100 0–25–60 interrow 1994 15 June (36 dap) 0 0–20–40 plant row B100 0–5–10–15–20–30–40 plant row P100 0–5–10–15–20–30–40 plant row, fertilizer row, non-fertilized interrow 9 September (122 dap) 0, B100 0–25, 25–60 interrow dap = days after planting das = days after sowing B = Broadcast, P = Placement 176 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Onion In 1993, the experimental plots were sampled for inorganic N in soil on 15 June (35 dap, Table 6) from three replicated plots. Samples were taken both within (four subsamples) and between rows (two subsamples). From the broadcast 100 kg ha-1 and placed 100 kg ha-1 treatments three separate core samples were taken from a line perpendicu- lar to the onion row, so that the middle coring was at the location of sampled onion plants and two corings were 5 cm to the side of the onion row (Fig 1). These samples were taken at depths of 0–10 cm and 10–20 cm and four locations per plot were sampled. These samples were used to assess the spatial distribution of soil inorganic N near the plants and the root lengths. The subsam- ples were bulked, ground manually to pass a 20 mm sieve in the laboratory and roots were sepa- rated from the soil samples. The soil was then stored at –18°C until laboratory analysis. The second soil sampling was made on 20 July (70 dap, Table 6). Roots and soil inorganic N were determined as at the first sampling. The third soil sampling was made on 20 September (132 dap, Table 6) from three replicated plots. Six subsam- ples were taken randomly from each plot. In 1994, the first soil sampling was made on 15 June (36 dap, Table 6). From the placed 100 kg ha-1 treatment three separate soil samples were taken from a line perpendicular to the onion row, so that the middle sample was at the location of the onion row (Fig 1). Four subsamples were taken per plot and bulked as a single sample. The second soil sampling was made on 9 September (122 dap, Table 6) in order to assess the amount of residual N in the soil after har- vest. Six subsamples were taken randomly from each plot. 2.4.2 Plant sampling and final yield Cabbage In 1993, plant samples were taken on 22 June (28 dap), 19 July (55 dap), 10 August (78 dap) and 7 September (105 dap) which was the date of final harvest (Table 7). The date of final har- vest was decided according to the target head weight, 1.5 kg. Aerial parts of the cabbage plants were cut at ground level from the edges of the middle rows. Sampling locations were system- atically ordered so that the same location was used for each plot, and it was checked that there were no missing plants in the vicinity of the sam- pled plants. Heads and leaves were cut and weighed separately at two latter samplings. Part of the stem was included in leaf weight meas- urements but excluded from dry matter and N determinations. The stem of the cultivar studied is short and should not much affect the meas- urements. To determine the dry matter content, samples were sliced and maximum 500 g of sam- ple was dried to constant weight at 60°C. For the estimation of the final yield, heads were cut from the two middle rows from the total row length of 12 m. The heads were then weighed and their number was counted. The visible qual- ity of the heads was good each year, and the few distorted or damaged heads were also included in the final yield. In 1994 and 1995 plants were sampled four times during the growing period (Table 7). Plant samples and final yields in 1994 and 1995 were prepared and analyzed as in 1993. Carrot In 1993, plants were sampled on 21 July (78 das), 18 August (106 das) and 1 October (150 das) which was the date of final harvest (Table 7). The final harvest was scheduled as late as possi- ble in order to benefit from the growth in Sep- tember, as the cultivar studied maintained green leaves until October. Samplings were done sys- tematically from the edges of the middle rows, the same location of each plot, and checking that the sampled plant stand was uniform to the re- maining plot. The sampling methods were dif- ferent in order to obtain a sufficient amount of plant material for analysis and to preserve an intact area for the final harvest. Carrot storage roots and shoots were sampled separately on all plots. The fresh weights of the shoots and the washed, airdried storage roots were recorded. 177 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Then the storage roots were chopped by a food processor (Braun UK40, Braun, Germany) and a maximum of 500 g samples were dried to con- stant weight at 60°C. For estimation of the final yield, carrot storage roots were collected from 12 ridge metres. The storage roots were weight- ed and this weight was considered as the final yield. Then the storage roots were partitioned Table 7. Sampling dates and areas. Year Date Dap/Das Plants/ sample Area (m2) Cabbage 1993 22 June 28 4 1 19 July 55 4 1 10 August 78 4 1 7 September 105 4 1 1994 28 June 29 4 1 20 July 50 4 1 10 August 70 4 1 7 September 99 4 1 1995 19 July 33 4 1 2 August 47 4 1 22 August 67 4 1 3 October 109 4 1 Carrot 1993 21 July 78 55 0.75 18 August 106 22 0.30 1 October 150 15 0.21 1994 14 July 69 24 0.30 2 August 88 24 0.30 30 September 147 15 0.19 1995 2 August 84 13 0.45 22 August 104 13 0.45 6 October 149 13 0.45 Onion 1993 14 June 34 21 0.36 7 July 57 11 0.30 2 August 83 10 0.28 17 August 98 20 0.57 1994 14 June 35 10 0.29 4 July 55 10 0.29 27 July 78 10 0.29 23 August 105 10 0.29 1995 20 June 21 10 0.32 13 July 44 10 0.32 8 August 70 10 0.32 17 August 79 10 0.32 Dap/Das = days after planting or sowing 178 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion into the following classes by weight: < 50 g, 50– 250 g, > 250 g, and distorted and damaged stor- age roots were separated. The weight and number of storage roots in each class were determined. The class of 50–250 g storage roots was consid- ered as marketable yield. In 1994 and 1995, plants were sampled three times during the growing period (Table 7). Plant samples and final yields in 1994 and 1995 were prepared and analyzed as in 1993. Onion In 1993, plants were sampled on 14 June (34 dap), 7 July (57 dap), 2 August (83 dap) and 17 August (98 dap) which was the date of final har- vest (Table 7). Sampling locations, the edges of the middle rows, were systematically ordered so that the same location was used for each plot, and it was checked that the sampled plants grew at a plant density similar to the remaining plants. The sampling methods were different in order to obtain sufficient amount of plant material for analysis and to preserve an intact area for the final harvest. The foliage and bulbs were sam- pled separately from all plots. Foliage included leaf blades and sheaths. The fresh weights of the foliage and the washed, airdried bulbs were re- corded. Then the bulbs were chopped by a food processor (Braun UK40, Braun, Germany) and samples of a maximum of 500 g were dried to constant weight at 60°C. The final yield was collected when at least 70% of the shoots had fallen. Fertilized shoots fell first in both years, and non-fertilized shoots followed in a few days, after which the whole experiment was harvest- ed. Leaves were removed in the field and bulbs were collected from the two middle rows from a length of 6 metres. Then these bulbs were al- lowed to dry for 2 months in a greenhouse at a temperature of about 30°C. Then the onions were partitioned into the following classes by diame- ter: < 4.0 cm, 4.0–5.5, 5.6–7.0 and > 7.0 cm. The bulbs were then weighed and the number of bulbs in each class was counted. There were only a few damaged bulbs, and they were included in the corresponding size class. The sum of all classes was considered as final yield. In 1994 and 1995, plants were sampled four times (Table 7). In 1995, the yield was harvest- ed on 29 August (91 dap), while the shoots were already fallen on 17 August. Plant samples and final yields in 1994 and 1995 were treated and analyzed as in 1993. 2.4.3 Laboratory analysis Plant samples Plant samples dried at 60°C were ground to pass a 1 mm sieve. Nitrogen in the plant material was measured by the macro-Kjeldahl method in which copper is used as a catalyst and potassi- um sulphate is used to raise the digestion tem- perature. After digestion, Kjeldahl-N was meas- ured with a Kjeltec Auto 1030 Analyzer using alkaline distillation of NH 3 and determination of NH 4 by acidimetric titration (Tecator 1981). As the recovery of nitrate-N by the Kjeldahl method is not complete, estimation of the por- tion of nitrate-N in plant N uptake was done from the first and second onion and cabbage samplings of 1993. Nitrate-N was measured from dry foli- age samples with a nitrate-specific electrode (Orion 1983). At the first sampling of cabbage (28 dap), nitrate-N concentration averaged 2.9 g kg-1 DM and 9.5 g kg-1 DM in non-fertilized and 250 kg ha-1 fertilized treatments, respective- ly. At the second sampling (55 dap), cabbage nitrate-N concentrations were 0.1 g kg-1, 4.6 g kg-1 and 6.4 g kg-1 in the non-fertilized, broad- cast 250 kg ha-1 and placed 250 kg ha-1 treat- ments, respectively. Cabbage nitrate-N measured by a nitrate-selective electrode was at the first sampling a maximum 17% and at the second sampling 10–15% of the N measured by the Kjel- dahl method. Although nitrate-N concentration decreases during the growing period of cabbage (e.g. Riley and Guttormsen 1993a), during the first half of the growing period nitrate-N can have about 10% influence on N uptake. Onion nitrate-N concentration varied 34 days after planting from 0.3 g kg-1 DM for the non- 179 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. fertilized treatment to 0.9 g kg-1 DM in the broad- cast treatments and 1.6 g kg-1 DM in the place- ment treatments. At the second sampling (57 dap), onion nitrate-N concentrations varied from 0.2 g kg-1 DM for the non-fertilized treatments to 0.5 g kg-1 DM in the broadcast treatments and 0.9 g kg-1 DM in the placement treatments. On- ion nitrate-N measured by a nitrate-selective electrode was between 0.7% and 4.5% of the N measured by the Kjeldahl method. As nitrate-N concentration decreases later during the grow- ing period (Greenwood et al. 1992), it is possi- ble to assume that the nitrate-N content of onion foliage did not much affect the calculated plant N uptakes. Regarding carrot, Evers (1989) determined that carrot shoot nitrate-N concentration de- creased from 4–5 g kg-1 DM (66–75 das) to 0.5– 1.5 g kg-1 DM at harvest (116–121 das). Nitrate- N content was at first approximately 15% of the Kjeldahl-N and at harvest 2–8%. Thus actual N uptake can be underestimated at the first carrot sampling but later the underestimation is de- creased. Soil samples Soil samples were allowed to thaw at +4°C and 100 g of soil was extracted with 250 ml 2 M KCl for two hours (Esala 1995) and analyzed with a Skalar AutoAnalyser for NH 4 +-N and NO 3 - -N (Krom 1980, Greenberg et al. 1980). The dry matter content of the soil was determined by dry- ing 40 g moist soil overnight at 105°C. Root samples After taking 140 g of soil for soil inorganic N determination, soil samples from the first and second soil sampling for cabbage and the first soil sampling for carrot in 1993 were soaked in a solution of 0.015 M NaOH to disperse the clay and to wash the fibrous roots. The soil was washed from the soil samples with a hydropneu- matic elutriatior (Smucker et al. 1982) which separated any organic material which was less dense than the mineral fraction of the soil. Or- ganic debris associated with the root samples was manually removed from the root samples. Fi- brous roots were dyed with Malachite green oxalate and laid in a water bath. At this stage, samples from different replicates were bulked and fibrous roots were photocopied for each treatment. The photocopies were analyzed by an image analyzer (Olympus CUE-2, Japan). The area of fibrous roots in the photocopy was re- corded from the image analyzer data. The aver- age width of the fibrous roots in a sample was estimated from the photocopy and then the fi- brous root length was calculated dividing the measured fibrous root area by the estimated fi- brous root width. Onion roots from the first and second soil sampling in 1993 were placed in a flat glass dish containing water. A 1 cm grid was placed under the dish and the number of intersections between roots and the vertical and horizontal lines was calculated. The root length of the sample was calculated using the equation: Root length = 11/14 x number of intersections x grid unit (1) This method is described e.g. in Böhm (1979). Roots that were attached to the sampled onions were cut and their length was measured with a ruler. The length of these roots was in- cluded in the root length of the soil layer 0–10 cm from the location of the onion row. Data on root length is presented as cm per kilogram of dry soil. Carrot root length is additionally pre- sented as cm per cm2 of soil surface in order to compare root lengths between layers of differ- ent depths. 2.4.4 Apparent recovery of fertilizer nitrogen The apparent recovery of fertilizer-N in above- ground plant was calculated as the difference in above-ground plant N uptake between fertilized and non-fertilized plots, and divided by the amount of fertilizer applied. 180 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion 2.5 Statistical analysis Plant fresh weight, dry matter content and Kjel- dahl-N were determined, and plant dry weight and plant N uptake were calculated from these measurements. For each crop, plant dry weight included the following plant organs, cabbage head, leaves and small part of the stem, carrot storage roots and leaves and onion bulbs and foliage. The sampling data for cabbage and on- ion were converted to kilograms per hectare by multiplying the sampling results by the planting density. Only final yields and the numbers of cabbage heads and onion bulbs in the final yield were multiplied according to the actual plant density. The sampling data for carrot was con- verted to kilograms per hectare by multiplying the sampling results by the ratio of row length in one hectare (13 333 m ha-1) to the sampled row length. The sample of 15 carrots at harvest in 1993 and 1994 was multiplied by the actual plant density obtained from the 12 row metres harvested. The final yield and the number of car- rots in the final yield were also multiplied by the ratio of row length in one hectare to the har- vested row length. In addition, a sample yield was calculated from the plants in the last sam- pling in order to compare the yield of samplings to the final yield that contains more spatial var- iability. Plant dry matter accumulation, dry matter content, N concentration and N uptake of differ- ent plant organs were analyzed separately at each sampling by the SAS MIXED procedure (Littell et al. 1996). First the non-fertilized treatment was tested separately against broadcast or placed N rates using ANOVA for randomized complete block design. After this the non-fertilized treatment was excluded from the data, and the mixed model for split-plot design was used to test differences between N rates or application methods and in- teractions between them (Littell et al. 1996). The model was as follows: Y ijk = µ + B k + A i + AB ik + C j + AC ij + ε ijk (2) where Y ijk is the response from jth application method on ith N rate on kth block. The quan- tities µ, A i , C j and AC ij are fixed parameters. The B k terms are random effects of block that are assumed to be normally and independently dis- tributed with mean 0 and variance σ B 2 . Further- more, the interaction terms, AB ik , as well as the error terms, ε ijk , are considered random effects with AB ik ~ NID(0, σ AB 2 ) and ε ijk ~ NID(0, σε 2 ), respectively. A i was used as error terms for B k and e ijk was used as error terms for C j and AC ij . Assumptions of the model were checked by using graphical methods: box plot for nor- mality of errors and plots of residuals for con- stancy of error variance. Main and subplot effects with F test proba- bility values above 0.05 were considered non- significant, and probability values above 0.10 are not presented. If there was an interaction P < 0.10 between N rates and application methods, con- trasts were calculated to test differences between means of application methods at the same N rate and between means of N rates with the same application method using Satterthwaite’s approx- imation to correct degrees of freedom (Littell et al. 1996). If there was a main plot effect P < 0.05, contrasts of all means of N rates were estimat- ed, and their difference from zero was tested with the t test. The standard error of the mean was calculated for the soil samples, and they were treated in a descriptive way, without any statistical test between the treatments. The root lengths of on- ion were tested separately for each depth using the mixed model for split-plot design, with treat- ment as a main plot and sampling location as a subplot. It was not possible to test the root lengths of cabbage and carrot as the replicates were bulked during the analysis. Linear regression was calculated between plant N uptake and sample yield or dry matter accumulation, both determined from the last sampling. The regression was assumed to be lin- ear as the N rates were low or moderate and the intercept was fixed at the origin. The plant N concentration was related to the dry matter ac- cumulation of all samplings using the equation 181 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. of Greenwood and Draycott (1989): Critical N% = 1.35 x (1+ B x e-0.26 x Dry Weight ) (3) where B = species dependent coefficient, and dry weight is presented as t ha-1. Coefficient B was estimated separately for non-fertilized and fertilized plots with the NLIN- procedure of SAS software using Gauss-New- ton iteration for parameter estimation (Freund and Littell 1991). In addition, the 95% confi- dence interval for the estimated coefficient B was calculated. While discussing the above regres- sion analysis, we must have a certain doubt of the results, as individual samples are dependent on each other due to the treatments and year and also sampling date in the non-linear regression. Altogether three observations were exclud- ed from the analysis of N concentration and N uptake. One onion sample from the third sam- pling in 1993 was lost before N analysis. Two N concentrations from the second sampling of cab- bage in 1993 were considered outliers as their N concentrations were two and three times higher than the N concentrations of their replicates. From the first soil sampling of cabbage in 1993, all samples from the fourth replicate and two 20– 40 cm samples from the placed 250 kg ha-1 were lost during storage. Also three 20–40 cm soil samples from the first sampling of onion in 1993 were lost. Otherwise there were no missing ob- servations. 3 Results 3.1 Inorganic nitrogen in soil Cabbage In June 1993 (30 dap), most of the N was in the 10 cm top layer in the plots where the fertilizer was broadcast and in the 10–20 cm layer in the plots where the fertilizer was band-placed (Ta- ble 8). The measured N contents were higher than N fertilization, probably due to the measurement inaccuracy caused by the small number of sub- samples. At the end of July (63 dap), soil inor- ganic N had decreased to quite low values. There was clearly more N in the row than in the inter- row area in plots with band placement, whereas N was divided evenly in plots with broadcast fertilizer. After harvest (115 dap), the amount of soil inorganic N was rather low. There was less than 20 kg ha-1 N in the 0–60 cm layer, even in the broadcast 250 kg ha-1 treatment. In July 1994 (38 dap), samples taken from the 160 kg ha-1 fertilized plots indicated that most of the N was in the 0–5 cm top layer in plots with broadcast fertilizer and in the 10–15 cm layer in plots with placed fertilizer (Table 9). Horizontal distribution was also clear in plots with placed fertilizer. In these plots, samples tak- en with a 5 cm horizontal distance of each other contained 190, 301 and 139 kg ha-1 N in the 0– 20 cm layer in the locations of the plant row and two fertilizer rows, respectively. The small amount of N in one of the fertilizer rows indi- cates that another fertilizer band was actually less than 5 cm to the side of the cabbage row. After harvest (105 dap), the amount of soil inorganic N was again rather low. There was not more than 20 to 24 kg ha-1 N in the 0–60 cm layer of the broadcast or placed 160 kg ha-1 treatments. Carrot In July 1993 (106 das), on average 65% and 53% of the soil inorganic N contained in the 0– 20 cm layer was at the depth of 0–10 cm after N was broadcast and placed, respectively (Table 10). Thus it seems that when N was broadcast and the ridge was formed, more inorganic N was distributed in the top soil. The inorganic N in 182 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion the soil after harvest was less than 40 kg ha-1, in both years (Table 10). Onion In June 1993 (35 dap), the original location of the fertilizer band still contained twice as much N as the location of the onion row (Table 11). In the broadcast treatments, N was fairly evenly distributed between row and interrow areas. The interrow N contents of the placed 30 kg ha-1 and placed 70 kg ha-1 treatments are high because the N band was located 5 cm to the side of the onion row and thus the distance of the interrow samples was only 5–10 cm from the fertilizer band. It is not clear why the N content in the broadcast 100 kg ha-1 treatment was at the same level as the N content in the broadcast 70 kg ha-1 treatment. One reason could be the different sampling depths while according to the 1994 results, broadcast N was mainly in the 0–5 cm soil layer. Sampling of the 0–20 layer, when most of the N was in the 5 cm layer, could give rather heterogeneous material for laboratory analysis. This can also be noted from the high standard errors of plant row and interrow means, 21 and 32 kg ha-1 in the 0–20 cm layer of broadcast 70 kg ha-1 (Table 11). Table 8. Effect of N rate and application method on the soil inorganic N (NH 4 -N + NO 3 -N) contents in cabbage field in 1993. Standard error of the mean is in parentheses after the mean value. N rate Application Sampling Inorganic N kg ha-1 method location kg ha-1 24 June, 30 dap Depth (cm) 0–20 20–40 Sum (0–40) 0 plant row 36 (5) 17 (1) 50 (5) 125 Broadcast plant row 112 (18) 22 (4) 134 (16) 125 Placement plant row 142 (23) 42 (11) 184 (30) 188 Broadcast plant row 251 (38) 29 (9) 280 (30) 188 Placement plant row 216 (25) 29 (10) 245 (15) Depth (cm) 0–10 10–20 20–40 Sum (0–40) 250 Broadcast plant row 301 (47) 35 (1) 53 (12) 389 (56) 250 Placement plant row 64 (30) 248 (77) 35 (–) 347 (121) 27 July, 63 dap Depth (cm) 0–10 10–20 20–40 40–60 Sum (0–60) 188 Broadcast plant row 24 (6) 9 (2) 7 (1) 5 (<1) 45 (6) interrow 11 (4) 12 (4) 6 (1) 5 (1) 34 (8) 188 Placement plant row 48 (12) 15 (6) 11 (4) 6 (<1) 79 (14) interrow 4 (1) 4 (1) 6 (1) 5 (1) 18 (4) 17 September, 115 dap Depth (cm) 0–25 25–60 Sum (0–60) 0 interrow 6 3 9 (<1) 125 Broadcast interrow 7 4 11 (<1) 188 Broadcast interrow 8 4 12 (3) 250 Broadcast interrow 11 5 16 (3) dap = days after planting 183 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Table 9. Effect of N rate and application method on soil inorganic N (NH 4 -N + NO 3 -N) contents in cabbage field in 1994. Standard error of the mean is in parentheses after the mean value. N rate Application Sampling Inorganic N kg ha-1 method location kg ha-1 8 July, 38 dap Depth (cm) 0–5 5–10 10–15 15–20 20–30 30–40 Sum (0–40) 0 plant row 19 (5) 7 (1) 8 (1) 7 (1) 14 (1) 7 (1) 62 (6) 160 Broadcast plant row 100 (10) 38 (1) 25 (2) 15 (2) 24 (5) 13 (3) 216 (14) 160 Placement fertilizer row 14 (1) 48 (3) 159 (12) 80 (7) 337* (22) Placement plant row 15 (2) 35 (8) 93 (21) 46 (7) 26 (4) 9 (2) 225 (28) Placement fertilizer row 15 (1) 24 (7) 58 (28) 42 (14) 175* (54) 13 September, 105 dap Depth (cm) 0–25 25–60 Sum (0–60) 0 interrow 11 (1) 6 (1) 17 (1) 160 Broadcast interrow 13 (1) 11 (2) 24 (2) 160 Placement interrow 11 (1) 9 (1) 20 (1) * Sum of 0–40 cm is calculated assuming the content of soil inorganic N at the depth of 20–40 cm of each location to be the same as in the location of plant row. dap = days after planting Table 10. Effect of N rate and application method on soil inorganic N (NH 4 -N + NO 3 -N) contents in carrot field in 1993– 1994. Standard error of the mean is in parentheses after the mean value. N rate Application Inorganic N kg ha-1 method kg ha-1 21 July 1993, 106 das Depth (cm) 0–10 10–20 20–40 40–60 Sum (0–60) 0 19 (6) 13 (2) 25 (5) 18 (3) 75 (15) 30 Broadcast 29 (10) 16 (1) 23 (3) 11 (3) 79 (15) 30 Placement 35 (15) 31 (6) 24 (7) 15 (1) 104 (26) 70 Broadcast 47 (16) 25 (4) 28 (3) 17 (4) 117 (26) 70 Placement 70 (12) 54 (9) 44 (10) 17 (2) 185 (6) 100 Broadcast 58 (20) 28 (6) 34 (9) 22 (10) 142 (41) 100 Placement 49 (8) 46 (18) 22 (4) 36 (26) 153 (12) 15 October 1993, 164 das Depth (cm) 0–25 25–60 Sum (0–60) 0 9 (1) 5 (1) 14 (1) 100 Broadcast 12 (2) 19 (6) 31 (8) 14 October 1994, 161 das Depth (cm) 0–25 25–60 Sum (0–60) 0 9 (1) 8 (2) 17 (3) 100 Broadcast 13 (3) 22 (6) 35 (6) das = days after sowing 184 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion In 1993, soil inorganic N contents had fallen to 30 kg ha-1 in the placement treatments and approximately 45 kg ha-1 in the broadcast treat- ments in the 0–30 cm layer by July (70 dap). After harvest in 1993, soil inorganic N contents were below 10 kg ha-1 in the 0–60 cm layer. In June 1994 (36 dap), the vertical distribu- tion of N was different between the treatments. Most of the N in the placed 100 kg ha-1 treat- ment was at the depth of 5–10 cm (Table 12). In the broadcast 100 kg ha-1 treatment most of the N was at the depth of 0–5 cm. At the original Table 11. Effect of N rate and application method on the soil inorganic nitrogen (NH 4 -N + NO 3 -N) contents in onion field in 1993. Standard error of the mean is in parentheses after the mean value. N rate Application Sampling Inorganic N kg ha-1 method location kg ha-1 18 June, 35 dap Depth (cm) 0–20 20–40 Sum (0–40) 0 plant row 38 (9) 13 (2) 51 (8) interrow 24 (4) 16 (4) 40 (1) 30 Broadcast plant row 37 (6) 28 (5) 65 (10) Broadcast interrow 44 (11) 28 (5) 72 (14) 30 Placement plant row 109 (1) 24 (3) 136 (14) Placement interrow 64 (15) 23 (5) 87 (11) 70 Broadcast plant row 102 (21) 35 (16) 137 (14) Broadcast interrow 82 (32) 30 (8) 112 (30) 70 Placement plant row 167 (13) 36 (15) 203 (26) Placement interrow 69 (9) 18 (3) 88 (6) Depth (cm) 0–10 10–20 20–40 Sum (0–40) 100 Broadcast interrow 75 (9) 19 (3) 116* (12) Broadcast plant row 44 (6) 18 (3) 24 (2) 85 (8) Broadcast interrow 80 (5) 18 (1) 121* (7) 100 Placement fertilizer row 215 (20) 68 (13) 302* (19) Placement plant row 104 (13) 43 (10) 18 (3) 166 (13) Placement nonfertilized 17 (1) 16 (2) 53* (3) interrow 20 July, 70 dap Depth (cm) 0–10 10–20 20–30 Sum (0–30) 70 Broadcast plant row 21 (3) 6 (2) 8 (1) 35 (1) Broadcast interrow 34 (13) 9 (1) 10 (2) 53 (13) 70 Placement plant row 12 (1) 12 (1) 7 (1) 31 (2) Placement interrow 12 (2) 13 (2) 7 (1) 32 (2) 20 September, 132 dap Depth (cm) 0–25 25–60 Sum (0–60) 0 interrow 4 (<1) 4 (1) 8 (1) 100 Broadcast interrow 3 (1) 5 (2) 8 (2) * Sum of 0–40 cm is calculated assuming the content of soil inorganic N at the depth of 20–40 cm of each location to be the same as in the location of plant row. dap = days after planting 185 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. location of the fertilizer band there was 135 kg ha-1 N at the depth of 0–10 cm and at the loca- tion of the onion row 107 kg ha-1 in June 1994. After harvest there was 36 kg ha-1 less N in the 0–60 cm layer of the non-fertilized plots than in the broadcast 100 kg ha-1 plots. 3.2 Plant growth 3.2.1 Root length Cabbage One month after planting (30 dap), the fibrous root length was similar in the broadcast and placed 250 kg ha-1 treatments. Most of the fi- brous roots were at the depth of 0–10 cm below the plant row and with practically no fibrous roots below 20 cm and between rows (Fig. 2). Two months after planting (63 dap), the length of fibrous roots was similar to that in the first sampling at the depths of 0–10 cm and 10–20 cm (Fig. 2). In addition, there were fibrous roots at the depths of 20–30 cm and 30–40 cm in both treatments. Fibrous root length was higher be- tween rows in the broadcast 188 kg ha-1 treat- ment than in the placed 188 kg ha-1 treatment. Carrot There were slightly less fibrous roots at the depth of 0–10 than 10–20 cm at the end of July (106 das, Fig. 3). The length of fibrous roots varied from 150 to 250 cm kg-1 dry soil and from 150 to 400 cm kg-1 dry soil at depths of 0–10 and 10–20 cm, respectively. The amount of fibrous roots was still low at depths of 20–40 cm and 40–60 cm. Table 12. Effect of N rate and application method on the soil inorganic nitrogen (NH 4 -N + NO 3 -N) contents in onion field in 1994. Standard error of the mean is in parentheses after the mean value. N rate Application Sampling Inorganic N kg ha-1 method location kg ha-1 15 June, 36 dap Depth (cm) 0–20 20–40 Sum (0–40) 0 plant row 33 (4) 26 (3) 59 (5) Depth (cm) 0–5 5–10 10–15 15–20 20–30 30–40 Sum (0–40) 100 Broadcast plant row 48 (7) 11 (2) 7 (1) 9 (2) 29 (6) 18 (3) 122 (10) 100 Placement fertilizer row 51 (17) 84 (15) 39 (9) 12 (3) 215* (30) plant row 30 (8) 77 (11) 40 (12) 15 (3) 16 (1) 12 (2) 190 (16) nonfertilized 14 (2) 8 (1) 8 (1) 8 (1) 67* (6) interrow 9 September, 122 dap Depth (cm) 0–25 25–60 Sum (0–60) 0 interrow 17 (2) 27 (5) 44 (5) 100 Broadcast interrow 37 (4) 43 (6) 80 (8) * Sum of 0–40 cm is calculated assuming the content of soil inorganic N at the depth of 20–40 cm of each location to be the same as in the location of plant row. dap = days after planting 186 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Fig. 2. Effect of application meth- od of 250 kg ha-1 N on the cab- bage roots (cm kg-1 of dry soil) for 30 days after planting (dap) and of 188 kg ha-1 N on the distribu- tion of cabbage roots for 63 days after planting in 1993. Locations of plant row and interrow samples are explained in Figure 1. Fig. 3. Effect of treatments on fibrous carrot root length (cm cm-2 of soil surface) for 106 days after sowing in 1993. B = Broadcast, P = Placement. (Results have been trans- formed to cm of root length per cm2 of soil surface using the estimation based on soil bulk density and sampling depth. At the depths of 0–10 cm and 10–20 cm 1 kg of soil equals to 72.5 cm2 of soil surface and at the depths of 20–40 and 40–60 cm, 1 kg of soil equals to 31.4 cm2 of soil surface.) 250 kg/ha Broadcast 188 kg/ha Broadcast 187 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Onion Both 35 and 70 days after planting, most of the roots were at the depth of 0–10 cm (Figs. 4 and 5). One month after planting, at both depths most of the roots were below the onion sets. In addi- tion, there was an interaction between treatments and horizontal location of roots (P = 0.010). This interaction was caused by the low amount of roots in the location of the fertilizer band at the depth of 0–10 cm. Two months after planting, roots were spread further to the interrow area. There were still more roots below the onion set than between rows in the 0–10 cm layer (P < 0.001). But there were no statistically significant differ- ences between root lengths of plant rows and in- terrows at the depths of 10–20 cm and 20–30 cm. 3.2.2 Dry matter accumulation Cabbage The above-ground dry weight started to increase rapidly after the first sampling (28–33 dap) each year (Fig. 6). After the first sampling, N fertili- zation increased the dry matter accumulation compared to the non-fertilized treatment each year (Tables 13–15 ). In 1993, N rates higher than 125 kg ha-1 increased growth only between Fig. 4. Effect of application method of 100 kg ha-1 N on the onion root length (cm kg-1 of dry soil) for 35 days after planting in 1993. Sampling locations of placement treat- ment are explained in Figure 1 and interrow locations of broadcast treatment were taken 5 cm to the side of the on- ion row. Fig 5. Effect of application method of 70 kg ha-1 N on the onion root length (cm kg-1 dry soil) for 70 days after plant- ing in 1993. Sampling locations of the x axis are explained in Figure 1. 188 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion the third sampling (78 dap) and harvest (Table 13), whereas in 1994, N rates higher than 80 kg ha-1 did not increase growth (Table 14). At har- vest in 1993, the plant dry weights ranged from 6300 kg ha-1 in the non-fertilized plots to 14 800 kg ha-1 in the 250 kg ha-1 broadcast plots (Fig. 6). At harvest in 1994, the plant dry weights ranged from 9300 kg ha-1 in the non-fertilized plots to 13 500 kg ha-1 in the 160 kg ha-1 broad- cast plots. In 1995, dry matter accumulation at harvest without N fertilizer was 6200 kg ha-1 and on average 11 500 kg ha-1 with 160 kg ha-1 N fer- tilizer. Both in 1993 and 1994, broadcast applica- tion resulted in higher dry weight than band placement at the first (28–29 dap) and second (50–55 dap) sampling (Tables 13 and 14). At the third sampling (78 dap) of 1993, N rates of 188 and 250 kg ha-1 gave the highest head dry yields in broadcast application, but in placement ap- plication the N rate of 125 kg ha-1 produced the highest head dry yield (Table 13). Interaction effect was also observed in the 1993 harvest, when high N rates increased head dry yields more in broadcast applications than in placement applications (Table 13). In 1994, there were no differences between application methods after the second sampling (Table 14). In 1995, there were no differences between application meth- ods (Table 15). Carrot Dry matter accumulation in shoots and storage roots was similar between the treatments each year (Fig. 7). Dry matter accumulation in the Fig. 6. Dry matter accumulation rate for cabbage in 1993– 1995. Fig. 7. Dry matter accumulation rate for carrot in 1993– 1995. 189 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. treatments varied from 12 400 to 16 600 kg ha-1 in 1993, from 12 800 kg ha-1 to 14 000 kg ha-1 in 1994, and from 11 900 to 12 200 kg ha-1 in 1995. Non-fertilized treatments produced as high dry matter yields as fertilized treatments. Although plant density in 1995 was only one third of the preceding years, the individual storage roots grew larger than in the preceding years and thus dry matter production increased up to 12 000 kg ha-1. Table 13. Effect of N rate and application method on the dry weight of cabbage (kg ha-1) on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors Dap 0 125 188 250 (Method) N rate Method Interact. 28 Total dry weight 0 vs. N Broadcast 190 0.006 370 310 370 350 ns 0.007 ns Placement ns 220 230 250 473 Mean (N rate) 295 270 310 55 Total dry weight Broadcast 2210 0.001 4090 4020 4330 4150 ns 0.005 ns Placement 0.001 3490 3410 3760 3550 Mean (N rate) 3790 3715 4045 78 Leaf dry weight Broadcast 3210 0.037 4960 5680 4550 4440 ns ns ns Placement 0.022 5740 4720 4890 5120 Mean (N rate) 5350 5200 4720 Head dry weight Broadcast 1560 0.006 2310 3410 2840 2850 ns 0.006 0.001 Placement 0.025 2780 2200 2260 2410 Mean (N rate) 2545 2805 2550 105 Leaf dry weight Broadcast 3660 0.001 5740 5620 5900 5750 ns ns ns Placement 0.001 5630 5720 5430 5590 Mean (N rate) 5685 5670 5665 Head dry weight Broadcast 2660 0.001 6000 7110 8940 7350 0.031 ns 0.025 Placement 0.001 6470 7520 7740 7240 Mean (N rate) 6235c 7315b 8340a ns = not significant; P > 0.10. Means of N rates 125–250 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 125–250 kg ha-1. 190 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion The dry weight of storage roots increased rapidly from the middle of July until harvest, whereas shoot dry weight increased mainly from July until the middle of August. Method of ap- plication and N rate in 1993, and N rate in 1994 and 1995, did not affect the dry weights of car- rot storage roots or shoots (data not shown). Also the ratio of shoots to total dry weight was not affected by the treatments. Table 14. Effect of N rate and application method on the dry weight of cabbage (kg ha-1) on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors Dap 0 80 120 160 (Method) N rate Method Interact. 29 Total dry weight 0 vs. N Broadcast 40 0.002 90 110 110 100 ns 0.001 ns Placement ns 40 40 60 50 Mean (N rate) 70 70 80 50 Total dry weight Broadcast 1100 0.001 2360 2700 2460 2510 ns 0.002 ns Placement 0.001 1880 1930 1890 1900 Mean (N rate) 2120 2310 2180 70 Leaf dry weight Broadcast 3260 0.001 4060 4190 4500 4250 ns ns ns Placement 0.052 4050 3890 4050 3990 Mean (N rate) 4050 4030 4280 Head dry weight Broadcast 1280 0.021 1940 2120 2240 2100 ns 0.071 ns Placement ns 1750 1870 1830 1800 Mean (N rate) 1845 1990 2040 99 Leaf dry weight Broadcast 3980 0.001 5350 5980 5800 5710 ns ns ns Placement 0.006 5340 5420 5730 5500 Mean (N rate) 5340 5700 5760 Head dry weight Broadcast 5310 0.001 6870 7420 7740 7340 ns ns ns Placement 0.006 7120 7490 7090 7230 Mean (N rate) 6990 7450 7420 ns = not significant; P > 0.10. Means of N rates 80–160 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 80–160 kg ha-1. 191 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Onion In 1993, dry matter accumulation was low with- out N fertilizer, but in 1994 and in 1995, non- fertilized treatments produced similar growth to fertilized treatments (Tables 16 and 17, Fig. 8). The rate of dry matter accumulation was slower in 1994 than in 1993, and the final dry matter yield was also about 2000 kg ha-1 less in 1994 than in 1993. Bulb dry weight increased in an exponential manner, whereas foliage dry weight increased first rapidly and decreased between the third and fourth sampling in 1993 and 1994 (Ta- bles 16 and 17). In 1995, dry matter accumula- tion of 4000 kg ha-1 was low, compared to over 8500 kg ha-1 and 6500 kg ha-1 in 1993 and 1994, respectively (Fig. 8). The cause of the weak growth could be in the late planting. Because a long photoperiod tends to promote bulb initia- tion (Brewster 1990a), leaf growth ceased be- fore there were enough leaves for adequate pho- tosynthesis of the carbohydrates for the bulb. In 1993, foliage dry weight was increased with N fertilizer at the third (83 dap) and fourth sampling (98 dap). Nitrogen placing resulted in slightly higher foliage dry matter accumulation than broadcasting (Table 16). There were statis- tically significant differences at the first sam- pling (34 dap) and the fourth sampling. In 1994, there was only one statistically significant re- sult in foliage dry matter accumulation, at the fourth sampling (105 dap) placed 30 kg ha-1 gave a higher dry weight than broadcast 30 kg ha-1 (Table 17). At the first sampling (34 dap) in 1993, placed 70 kg ha-1 resulted in higher bulb dry weight than Table 15. Effect of N rate and application method on the above ground dry weight of cabbage (kg ha -1) on different days after planting (dap) in 1995. Days after planting N rate Application kg ha-1 method 33 47 67 109 0 130b 1020b 2930b 6160b 160 Broadcast 300ab 2670a 6030a 10830a 160 Placement 420a 2490a 5180a 11960a Probability* 0.048 0.010 0.013 0.003 * Significance of difference between treatments. Means of the same sampling date followed by a common letter do not differ significantly (P < 0.05). Fig. 8. Dry matter accumulation rate for onion in 1993– 1995. 192 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Table 16. Effect of N rate and application method on the onion foliage and onion bulb dry weights (kg ha -1 ) on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage dry weight 0 vs. N 34 Broadcast 150 ns 160 170 190 172 ns 0.010 ns Placement 0.029 210 250 220 225 Mean (N rate) 185 210 200 57 Broadcast 950 0.084 1220 1160 1270 1220 ns ns ns Placement 0.053 1290 1210 960 1150 Mean (N rate) 1250 1180 1120 83 Broadcast 1940 ns 1840 2270 2300 2140 0.029 0.081 ns Placement ns 2230 2210 2620 2350 Mean (N rate) 2030b 2240ab 2460a 98 Broadcast 810 0.011 1090 1290 1520 1300 0.002 0.009 ns Placement 0.004 1320 1550 1720 1530 Mean (N rate) 1200b 1420a 1620a Bulb dry weight 34 Broadcast 110 ns 110 90 110 105 ns ns 0.018 Placement ns 100 130 110 110 Mean (N rate) 105 110 110 57 Broadcast 600 ns 510 550 540 540 ns ns ns Placement ns 570 590 460 540 Mean (N rate) 540 570 500 83 Broadcast 3360 ns 3330 3420 3480 3410 ns 0.014 ns Placement 0.086 3850 3500 3650 3660 Mean (N rate) 3590 3460 3560 98 Broadcast 4580 0.003 5650 6050 7240 6320 0.078 ns ns Placement 0.001 6320 6790 6960 6670 Mean (N rate) 5990 6420 7100 ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 193 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Table 17. Effect of N rate and application method on the onion foliage and onion bulb dry weights (kg ha-1) on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage dry weight 0 vs. N 35 Broadcast 80 ns 90 90 90 90 ns ns ns Placement ns 100 80 110 100 Mean (N rate) 95 85 100 55 Broadcast 480 ns 490 480 540 500 ns ns ns Placement ns 580 490 540 540 Mean (N rate) 540 485 540 78 Broadcast 1 300 ns 1 450 1 430 1 460 1450 ns ns ns Placement ns 1 570 1 570 1 230 1570 Mean (N rate) 1510 1500 1340 105 Broadcast 870 ns 950 940 1 240 1050 ns ns 0.041 Placement ns 1 330 1 030 1 100 1160 Mean (N rate) 1140 990 1170 Bulb dry weight 35 Broadcast 110 0.098 100 100 110 100 ns ns ns Placement ns 110 110 110 110 Mean (N rate) 105 105 110 55 Broadcast 210 ns 200 190 210 200 ns 0.005 ns Placement ns 250 210 220 220 Mean (N rate) 225 200 215 78 Broadcast 2 490 ns 2 510 2 310 2 400 2410 ns ns ns Placement ns 2 550 2 440 2 250 2410 Mean (N rate) 2530 2370 2320 105 Broadcast 4 690 ns 4 920 5 700 5 770 5460 ns ns ns Placement ns 5 170 5 140 4 850 5050 Mean (N rate) 5040 5220 5310 ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 194 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion broadcast 70 kg ha-1. Later, at the third sampling (83 dap), placement resulted in higher bulb dry weight than broadcasting, but at the fourth sam- pling (98 dap) there was no difference (Table 16). Bulb dry weight was higher when fertilizer was band placed compared to broadcasting at the sec- ond sampling (55 dap) in 1994 (Table 17). 3.2.3 Final yield Cabbage In 1993, higher N rates resulted in clearly high- er final yields (P = 0.002, Fig. 9). Non-fertilized plots gave only about 30% yield compared to the lowest yielding fertilized treatments (P = 0.001). Also broadcasting of N resulted in high- er yields than band placement (P = 0.029). The number of heads per hectare varied from 61 300 to 63 300, without statistically significant dif- ferences. In 1994, only non-fertilized treatment resulted in a low final yield (P = 0.023, Fig. 9). Even with- out N, the final yield was 45 t ha-1. N rates above 80 kg ha-1 did not increase yield. The number of heads per hectare varied from 34 600 to 37 900, and the treatments did not affect head number. In 1995, non-fertilized treatment resulted in a low final yield of 15 t ha-1 compared to 34 t ha- 1 and 41.5 t ha-1 for the N fertilized treatments (P = 0.001). The number of heads per hectare var- ied from 28 300 to 38 300, but the treatments had no effect on head number (data not shown). The sample yields estimated from the four sampled cabbages resulted in yields 6% higher on average compared to the yields from the 6 m2 area in 1993 (data not shown). In 1994, there were more dead transplants which resulted in 14% higher yields on average from the samples of four cabbages than from the 6 m2 area. In 1995, high rainfall in June caused waterlogging of the soil and approximately 30% of the plants were lost. Due to this, the yield calculated from the fourth sample was 36% to 95% higher than the yield from the 6 m2 area. Carrot The yield varied between treatments from 76 to 89 t ha-1 in 1993, from 81 to 92 t ha-1 in 1994 and from 34 to 45 t ha-1 in 1995. Marketable yield averaged 61 t ha-1 in 1993, 66 t ha-1 in 1994 and only 9 t ha-1 in 1995. In 1994, N fertilizer in- creased the final yield (P = 0.015, data not shown), but marketable yield was not affected, Fig. 9. Effect of N rate and appli- cation method on the head yields of cabbage on fresh weight basis in 1993 and in 1994. B = Broad- cast, P = Placement. 195 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. as the proportion of too large and damaged stor- age roots increased with the N rate (P = 0.023, data not shown). In 1993, the proportions of branched, split, lift damaged and pest damaged storage roots were 7%, 3%, 2% and 1%, respec- tively. In 1994, the respective values were 9%, 1%, 0% and 8%. In 1995, the proportions of branched and split storage roots were 14% and 21%. This may have been caused by the soil moisture during the growing season, as initially very moist conditions changed to dry conditions towards harvest. The sampling yield was on av- erage 25% higher than the final yield in 1993, 10% higher in 1994 and 139% higher in 1995. In 1995, low marketable yield and the huge dif- ference between the sampling yield and the 12 row metre yield are explained by the much low- er plant density than in preceding years. Plant density was on average 730 000, 785 000 and 155 000 plants per hectare in years 1993, 1994 and 1995, respectively. In addition to the small- er planned plant density due to the single row in 1995, high rainfall in May eroded the seedbed and seeds were transported by the running wa- ter out from the seed row. Onion In 1993, final bulb yield was an average 16% higher when fertilizer was band placed compared to broadcasting (P = 0.002, Fig. 10). In addition, N rate increased bulb yields (P = 0.022). Accord- ing to the contrasts, final yield was higher with higher N rate when fertilizer was broadcast, but not when fertilizer was placed. In placed treat- ments, final yield was good even with the 30 kg ha-1 fertilization. In 1994, the N application method and N rate did not affect the bulb yield (Fig. 10). Even the non-fertilized treatment pro- duced the same bulb yield as the other treat- ments. The plant population density i.e. the number of bulbs was not affected by the treat- ments (Tables 18 and 19). In 1995, final yields were low, 14.7 t ha-1 without N and 18.1 t ha-1 with 100 kg ha-1 of N (P = 0.054). Calculated from the fourth sampling, the sample yield of bulbs was from 8 to 24% higher than the final yield calculated from 12 row me- tres in 1993, but only 1–10% higher in 1994 (data not shown). These differences were low as the bulbs from 12 row metres were dried for two Fig. 10. Effect of N rate and application method on the bulb fresh yields in 1993 and in 1994. B = Broadcast, P = Placement. 196 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion months in the greenhouse, which should result in lower yields in any case. In 1995, the final yield of bulbs calculated from 12 row metres was 7–11% higher than the yield calculated from the sample. The probable cause was that while the shoots had fallen the onions were kept for two weeks in the field, and there was translocation of dry matter from shoots to bulbs. In 1993, bulbs were larger with higher N rates and with band placement (Table 18). Without N fertilizer, the proportion of small (< 4 cm) bulbs was high, almost 10% of all bulbs. In 1994, the Table 18. Effect of N rate and application method on the size distribution of harvested onion bulbs in 1993. The number of bulbs is presented as 1000 bulbs ha-1. Diameter in cm N rate Application kg ha-1 method < 4 4.0–5.5 5.6–7.0 >7.1 Sum 0 29 173 134 1 337 30 Broadcast 16 119 205 2 342 30 Placement 7 83 240 11 341 70 Broadcast 10 86 219 6 321 70 Placement 7 62 253 16 338 100 Broadcast 5 60 258 18 341 100 Placement 5 49 261 29 344 Probability* N rate 0.018 0.012 0.065 0.021 ns Method 0.052 0.004 0.022 0.019 ns Interaction 0.073 ns ns ns ns ns = not significant, (P>0.10). *Significance of difference between N rates or application methods in each diameter class and total sum. Table 19. Effect of N rate and application method on the size distribution of harvested onion bulbs in 1994. The number of bulbs is presented as 1000 bulbs ha-1. Diameter in cm N rate Application kg ha-1 method < 4 4.0–5.5 5.6–7.0 >7.1 Sum 0 12 205 126 1 344 30 Broadcast 10 210 124 0 344 30 Placement 8 179 172 0 358 70 Broadcast 12 196 134 1 343 70 Placement 7 179 146 0 332 100 Broadcast 5 187 165 1 358 100 Placement 9 187 144 1 341 Probability* N rate ns ns ns ns ns Method ns ns ns ns ns Interaction ns ns 0.022 ns ns ns = not significant, (P>0.10). *Significance of difference between N rates or application methods in each diameter class and total sum. 197 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. proportion of small (< 4 cm) and large (> 7.1 cm) bulbs was low (Table 19). In 1994, place- ment increased bulb size when the N rate was low, but at a N rate of 100 kg ha-1 broadcasting resulted in larger bulbs than placement. In 1995, bulb distribution was not changed by N fertili- zation (data not shown). 3.2.4 Dry matter content Cabbage Leaf dry matter content varied from 8.1% to 16.3% during the growing seasons and there was no trend of dry matter content increasing towards harvest. Head dry matter content increased in the latter part of the growing season from an aver- age 7.7% to 9.9% in 1993 and 1994. The dry matter contents of both heads and leaves at harvest in 1993 were slightly lower when the N rate was high (data not shown). Leaf dry matter content was 13.0% in the 125 kg ha-1 fertilized treatments and 10.8% in the 250 kg ha-1 fertilized treatments, and head dry matter con- tent was 10.7% and 9.4% in the respective treat- ments. Otherwise there were no statistically sig- nificant differences between dry matter contents in 1993 and 1994 (data not shown). At the first sampling (33 dap) of 1995, dry matter content was higher in the placed treatment than in the others. At the second sampling (47 dap) in 1995 the dry matter content of non-fertilized cabbag- es was higher than the dry matter content of N fertilized (data not shown). Carrot The dry matter content of the storage roots var- ied from 10.0% to 14.1% during the three grow- ing seasons. At harvest the dry matter content of the storage roots was on average 11.3%. The dry matter content of the foliage increased towards harvest to 19.2% in 1993 and 1995, but was only 14.2% in 1994. Treatments did not affect dry matter contents (data not shown). Onion Bulb dry matter content increased from 8.0% at the first sampling to 14.0% at harvest in 1993, and to 19.0% in 1995. In 1994, bulb dry matter content at the first sampling (35 dap) was 10.0% and increased to an average 15.8% at harvest. Dry matter content of foliage decreased from 11.0% at the first sampling (34 dap) to 7.0% at harvest in 1993. In 1994, foliage dry matter con- tent varied from 8.3% to 9.5% in the different samplings, without any clear trend caused by time. Nitrogen rate decreased foliage dry matter content in the latter part of the growing period, but by only 0.5 percentage points in 1993 (data not shown). Placement compared to broadcast- ing led to 0.8 percentage points higher dry mat- ter content in bulb and 0.4 percentage points higher dry matter content in foliage at the first sampling (34 dap) in 1993. Also in 1994, place- ment resulted in slightly higher dry matter con- tents at the first (35 dap) and second (55 dap) samplings (data not shown). However, these changes in dry matter contents were less than 0.5 percentage points. In 1995, bulb dry matter content increased from 8.6% at the first sampling (21 dap) to 19.0% at harvest. Dry matter content of foliage in- creased from 8.2% to 10.8% to the third sam- pling (70 dap) and then decreased to 9.8% at harvest. N fertilization did not cause any statis- tically significant differences in 1995 (data not shown). 3.3 Nitrogen uptake by plants 3.3.1 Plant nitrogen concentration Cabbage Leaf N concentrations decreased clearly during the growing periods 1993 and 1994 (Tables 20 and 21). In 1995, leaf N concentration decreased from 50–56 g kg-1 DM to 27 g kg-1 DM in the N 198 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion fertilized treatments. Head N concentrations de- creased every year as in 1995, when the N con- centration of heads decreased from over 30 g kg-1 DM (67 dap) to nearly 20 g kg-1 DM at harvest. Both leaf and head N concentration were lower without N fertilizer than with N fertilizer in all years. At the first sampling (28 dap) in 1993, N con- centrations were still equal in all N fertilized treat- ments (Table 20). At the second sampling (55 dap) the highest N rate resulted in slightly higher N concentrations than lower N rates. In addition, placement application led to higher N concentra- tions than broadcasting of N. At the third sam- Table 20. Effect of N rate and application method on the total N concentration in cabbage tops, leaves or heads (g kg-1 DM) on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors Dap Sample 0 125 188 250 (Method) N rate Method Interact. 28 Tops 0 vs. N Broadcast 47.5 0.001 55.1 55.4 56.1 55.5 ns ns ns Placement 0.001 56.2 56.8 55.2 56.0 Mean (N rate) 55.6 56.1 55.6 55 Tops Broadcast 21.1 0.001 33.1 36.8 46.0 36.5 0.012 0.001 ns Placement 0.001 39.3 41.3 44.6 41.7 Mean (N rate) 36.2b 39.1ab 42.1a 78 Leaves Broadcast 13.0 0.001 17.6 26.8 28.0 24.1 0.001 ns 0.040 Placement 0.001 19.7 24.7 30.3 24.9 Mean (N rate) 18.7c 25.7b 29.1a Heads Broadcast 21.6 0.001 24.9 30.5 31.6 29.0 0.004 ns ns Placement 0.001 27.4 31.0 32.1 30.2 Mean (N rate) 26.1b 30.7a 31.8a 105 Leaves Broadcast 13.6 0.001 15.0 19.6 23.5 19.4 0.001 ns ns Placement 0.001 16.7 19.1 24.0 19.9 Mean (N rate) 15.9c 19.3b 23.7a Heads Broadcast 15.4 0.018 15.5 18.0 19.4 17.6 0.001 ns ns Placement 0.001 15.3 17.7 20.3 17.7 Mean (N rate) 15.4c 17.8b 19.8a ns = not significant; P > 0.10. Means of N rates 125–250 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 125–250 kg ha-1. 199 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. pling (78 dap) high N rates resulted in high N con- centrations both in the leaves and in the heads. At harvest the differences in N concentrations had increased further, and in the leaves of fertilized treatments varied from 15.0 to 24.0 g kg-1 DM and from 15.3 to 20.3 g kg-1 DM in the heads. In 1994, plant N concentrations were higher in broadcast treatments than in placement treat- ments one month after planting (Table 21). At the second sampling (50 dap), the differences in plant N concentration due to method were re- versed. Placement application produced clearly Table 21. Effect of N rate and application method on the total N concentration in cabbage tops, leaves or heads (g kg-1 DM) on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors Dap Sample 0 80 120 160 (Method) N rate Method Interact. 29 Tops 0 vs. N Broadcast 59.6 0.001 63.3 63.8 64.8 63.9 ns 0.007 ns Placement 0.083 60.7 61.6 62.8 61.7 Mean (N rate) 62.0 62.7 63.8 50 Tops Broadcast 33.1 0.001 42.4 46.3 46.1 44.9 0.049 0.001 ns Placement 0.001 50.0 52.3 51.5 51.3 Mean (N rate) 46.2b 49.3a 48.8a 70 Leaves Broadcast 25.9 0.001 31.8 36.6 38.9 35.8 0.006 0.006 ns Placement 0.001 37.6 39.8 39.3 38.9 Mean (N rate) 34.7b 38.2a 39.1a Heads Broadcast 29.3 0.002 30.9 33.3 35.1 33.1 ns 0.021 ns Placement 0.004 36.5 35.7 35.4 35.9 Mean (N rate) 33.7 34.5 35.2 99 Leaves Broadcast 18.7 0.001 23.9 27.5 27.3 26.2 ns 0.006 ns Placement 0.001 27.1 29.4 28.0 28.2 Mean (N rate) 25.5 28.4 27.7 Heads Broadcast 16.0 0.001 19.7 22.9 23.2 21.9 0.015 ns ns Placement 0.001 21.6 24.1 22.7 22.8 Mean (N rate) 20.7b 23.5a 22.9a ns = not significant; P > 0.10. Means of N rates 80–160 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 80–160 kg ha-1. 200 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion higher N concentrations than broadcast applica- tion. At this sampling, high N rate also resulted in slightly higher N concentrations. In the sepa- rate head and leaf N concentrations of the third sampling (70 dap) and harvest, placement again produced higher N concentrations than broad- casting, excluding head N concentration at har- vest. High N rate resulted in higher leaf N con- centrations at the third sampling (70 dap) and head N concentrations at harvest. At the first sampling (33 dap) in 1995, the leaf N concen- tration in the placed treatment was 6.0 g kg-1 DM higher than the N concentration in the broadcast treatment (P < 0.001). Carrot Shoot N concentration decreased from over 40 Table 22. Effect of N rate and application method on the total N concentration (g kg-1 DM) of carrot roots and shoots on different days after sowing (das) in 1993. N rate (kg ha -1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Das Shoot N concentration 0 vs. N 78 Broadcast 38.6 ns 39.7 40.7 38.4 39.6 ns ns ns Placement ns 39.7 43.7 39.3 40.9 Mean (N rate) 39.7 42.2 38.9 106 Broadcast 24.5 ns 24.8 27.2 27.0 26.3 ns ns ns Placement 0.041 26.9 26.7 27.6 27.1 Mean (N rate) 25.8 27.0 27.3 150 Broadcast 17.3 0.098 17.9 18.7 19.4 18.7 ns ns ns Placement ns 17.8 19.1 18.2 18.3 Mean (N rate) 17.8 18.9 18.8 Root N concentration 78 Broadcast 17.2 ns 18.2 19.0 18.2 18.5 ns ns ns Placement 0.100 17.9 20.5 18.8 19.1 Mean (N rate) 18.1 19.7 18.5 106 Broadcast 11.2 0.019 12.0 13.4 12.7 12.7 ns ns ns Placement 0.030 12.4 13.0 12.3 12.6 Mean (N rate) 12.2 13.2 12.5 150 Broadcast 7.8 0.095 7.6 8.7 8.9 8.4 0.050 ns 0.097 Placement 0.034 8.3 8.8 8.4 8.7 Mean (N rate) 8.0b 8.7a 8.6a ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P<0.05) according to the contrast test. Das = days after sowing 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 201 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. g kg-1 DM at the first sampling (69–78 das) to about 20 g kg-1 DM at harvest (Tables 22 and 23). Nitrogen concentration of the carrot stor- age roots decreased from about 20 g kg-1 DM at the first sampling to nearly 10 g kg-1 DM at har- vest. Nitrogen fertilizer led to higher storage root and shoot N concentrations at the second sam- pling (106 das) in 1993, compared to N concen- trations in non-fertilized plants (Table 22). Fur- thermore at harvest N rates of 70 kg ha-1 and 100 kg ha-1 led to higher storage root N concentra- tions than the N rate of 30 kg ha-1 when N was broadcast (Table 22). In 1994, N concentrations in shoots and storage roots increased with N fer- tilizer at the second sampling (88 das) and at har- vest (Table 23). In 1995, storage root N concen- tration increased by 1.2 g kg-1 DM at the first sampling (84 das, P = 0.012) with N fertilizer. Onion Foliage N concentration decreased clearly dur- ing the growing period (Tables 24 and 25). For example in 1995, foliage N concentration de- creased from 44 g kg-1 DM to 23 g kg-1 DM in the N fertilized treatment. Bulb N concentration decreased until the third sampling (70–83 dap) but increased towards harvest in all three years. Both foliage and bulb N concentration were low- er without N fertilizer than with N fertilizer in all years. The N rate of 30 kg ha-1 resulted in lower foliage N concentrations at the second (34 dap) and third samplings (57 dap) in 1993 than the N rates of 70 kg ha-1 and 100 kg ha-1 (Table 24). When N fertilizer was placed, foliage N concen- tration was higher in all samplings in 1993 com- pared to broadcast N (Table 24). At harvest, placed high rates of N led to higher foliage N concentrations than broadcast high rates of N. In 1994, the N rate of 30 kg ha-1 resulted in low- er foliage N concentrations than N rates of 70 kg ha-1 and 100 kg ha-1 (Table 25). Placement caused lower N concentration in foliage than broadcast application at the second sampling (55 dap) in 1994 (Table 25). In 1993, excluding the sampling at harvest, the N rate of 30 kg ha-1 resulted in lower bulb N concentrations than N rates of 70 kg ha-1 and 100 kg ha-1 (Table 24). In addition, band placement resulted in higher bulb N concentrations than broadcasting in all samplings in 1993 (Table 24). In 1994, the N rate of 30 kg ha-1 resulted in low- er bulb N concentrations than N rates of 70 kg ha-1 and 100 kg ha-1 (Table 25). At the second sampling (55 dap) in 1994, broadcasting led to higher bulb N concentrations than placement. 3.3.2 Plant nitrogen uptake Cabbage Plant N uptake in the non-fertilized treatments was 90, 159 and 117 kg ha-1 in 1993, 1994 and 1995, respectively. The highest N uptakes var- ied between years, being 311, 339 and 288 kg ha-1 in 1993, 1994 and 1995, respectively. Table 23. Effect of N rate on the total N concentration (g kg-1 DM) of carrot roots and shoots on different days after sowing (das) in 1994. N rate (kg ha-1) Days after sowing 69 88 147 Shoots 0 46.9 29.2b 19.7b 30 46.2 30.8b 21.1ab 70 45.1 32.8a 22.2a 100 43.4 34.2a 22.7a Probability* ns 0.001 0.061 Roots 0 18.0 11.2c 8.6b 30 19.7 12.8ab 10.3a 70 19.0 12.5b 10.2a 100 18.5 13.8a 11.4a Probability* ns 0.009 0.011 ns = not significant; P > 0.10. *Significance of difference between N rates on each sam- pling date. Means of N rates followed by no letter or a com- mon letter do not differ significantly (P < 0.05) according to the contrast test. 202 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Table 24. Effect of N rate and application method on total N concentrations (g kg-1 DM) in onion foliage and bulbs on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage N concentration 0 vs. N 34 Broadcast 37.4 0.028 38.4 40.7 40.5 39.9 ns 0.010 ns Placement 0.001 43.0 41.9 41.6 42.2 Mean (N rate) 40.7 41.3 41.1 57 Broadcast 20.9 0.001 25.1 29.7 29.2 28.0 0.005 0.001 0.072 Placement 0.001 29.3 30.9 32.6 30.9 Mean (N rate) 27.2b 30.3a 30.8a 83 Broadcast 18.2 0.008 21.5 23.1 23.6 22.7 0.007 0.001 ns Placement 0.001 24.0 25.7 26.2 25.3 Mean (N rate) 22.7b 24.4a 24.9a 98 Broadcast 15.9 0.150 17.9 19.1 19.0 18.7 0.053 0.001 0.040 Placement 0.011 19.2 21.0 22.3 20.8 Mean (N rate) 18.5 20.1 20.6 Bulb N concentration 34 Broadcast 15.4 0.034 16.3 19.6 20.2 18.7 0.045 0.001 ns Placement 0.001 21.9 22.6 23.9 22.8 Mean (N rate) 19.1b 21.1ab 22.0a 57 Broadcast 9.3 0.001 13.2 16.9 18.3 16.1 0.009 0.002 ns Placement 0.001 17.5 19.8 20.9 19.4 Mean (N rate) 15.4b 18.4a 19.6a 83 Broadcast 6.6 0.002 8.4 9.8 10.8 9.7 0.001 0.001 ns Placement 0.001 9.8 12.7 13.5 11.9 Mean (N rate) 9.1b 11.1a 12.1a 98 Broadcast 7.7 0.001 10.7 11.2 10.8 10.9 ns 0.001 0.085 Placement 0.001 11.9 14.5 14.4 13.6 Mean (N rate) 11.3 12.8 12.6 ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 203 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Table 25. Effect of N rate and application method on total N concentrations (g kg-1 DM) in onion foliage and bulbs on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage N concentration 0 vs. N 35 Broadcast 43.6 0.007 47.2 51.2 52.3 50.2 0.001 ns ns Placement 0.001 48.2 54.7 50.9 51.3 Mean (N rate) 47.7b 53.0a 51.6a 55 Broadcast 31.8 0.001 37.8 39.7 40.1 39.2 0.036 0.002 ns Placement 0.001 36.0 38.1 37.6 37.3 Mean (N rate) 36.9b 38.9a 38.9a 78 Broadcast 26.6 0.003 26.7 29.6 30.7 29.0 0.001 ns ns Placement 0.006 27.4 29.4 31.0 Mean (N rate) 27.1c 29.5b 30.8a 105 Broadcast 27.4 0.063 28.0 29.4 29.9 29.1 0.006 ns ns Placement 0.025 27.8 29.4 31.0 29.3 Mean (N rate) 27.9b 29.8a 29.9a Bulb N concentration 35 Broadcast 18.3 0.001 20.7 23.2 22.2 22.1 ns 0.078 0.023 Placement 0.015 20.6 20.3 22.7 21.2 Mean (N rate) 20.7 21.8 22.5 55 Broadcast 15.7 0.001 21.1 23.0 25.5 23.2 0.004 0.031 ns Placement 0.001 19.9 22.2 22.5 21.5 Mean (N rate) 20.5b 22.6a 24.0a 78 Broadcast 10.2 0.001 11.3 13.5 14.8 13.2 0.001 ns ns Placement 0.001 11.0 13.9 14.4 13.1 Mean (N rate) 11.1b 13.7a 14.6a 105 Broadcast 12.3 0.040 11.9 14.0 15.6 13.8 0.007 ns ns Placement 0.030 12.4 14.2 15.5 14.0 Mean (N rate) 12.1b 14.1a 15.6a ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 204 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Nitrogen uptake was low until the first sam- pling (28–33 dap), followed by a rapid increase until the second sampling (47–55 dap) in 1993 and 1995 or until the third sampling (70 dap) in 1994 (Fig. 11). Towards harvest N uptake con- tinued at a slightly lower rate. Nitrogen uptake was less in the non-fertilized plots than in the fertilized treatments, excluding the placed treat- ments at the first sampling (28 dap) in 1994. In 1993, broadcast application produced higher N uptake at the first sampling (28 dap) than placement application (Table 26). At the second sampling (55 dap), higher N rates led to higher N uptake. At the third sampling (78 dap), total N uptake was greater with high N rate in broadcast applications, but not in placement ap- plications (interaction P = 0.008, data not shown). Distribution of N in plant showed that broadcast application produced more N alloca- tion to the cabbage head than placement appli- cation. In addition, the N rate had an increasing effect on N uptake in the cabbage heads in the broadcast treatments. At harvest, the N rate had a clear effect on total above ground N uptake (P = 0.002, data not shown) as well as on the N uptake of leaves and heads. There was a slight interaction in total above ground plant N uptake, because N uptake was greater with high N rate in broadcast applications than in placement ap- plications (interaction P = 0.033). This trend was also clear in the allocation of N to the heads. After the third sampling, there was practically no N uptake in non-fertilized and 125 kg ha-1 fertilized treatments. The amount of N in the crop residues increased with N rate from an average 90 kg ha-1 to 134 kg ha-1. In 1994, N uptake was greater with broad- cast application at the first (29 dap) and second sampling (50 dap) than with placement applica- tion (Table 27). After that the differences be- tween fertilized treatments were equalised. At harvest there was a slight interaction with high- er N rates leading to higher head N uptake after broadcasting but not after placement of N. The Fig. 11. N uptake rate for cabbage in 1993–1995. Fig. 12. N uptake rate for carrot in 1993–1995. 205 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Table 26. Effect of N rate and application method on the cabbage N uptake (kg ha-1) on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors Dap Sample 0 125 188 250 (Method) N rate Method Interact. 28 Tops 0 vs. N Broadcast 9 0.002 20 17 21 19 ns 0.003 ns Placement 0.018 12 13 14 13 Mean (N rate) 16 15 17 55 Tops Broadcast 47 0.001 136 148 170 151 0.022 ns ns Placement 0.001 136 141 168 148 Mean (N rate) 136b 145b 169a 78 Leaves Broadcast 42 0.001 87 150 127 121 0.055 ns 0.071 Placement 0.001 113 115 148 125 Mean (N rate) 100 132 137 Heads Broadcast 33 0.001 58 104 90 84 0.062 0.022 0.002 Placement 0.001 76 68 72 72 Mean (N rate) 67 86 81 105 Leaves Broadcast 50 0.001 86 110 138 111 0.001 ns 0.090 Placement 0.001 94 109 130 111 Mean (N rate) 90c 110b 134a Heads Broadcast 40 0.001 93 127 173 131 0.004 ns 0.042 Placement 0.001 100 132 157 129 Mean (N rate) 97c 130b 165a ns = not significant; P > 0.10. Means of N rates 125–250 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 125–250 kg ha-1. N content in the crop residues of the fertilized plots averaged 153 kg ha-1 (Table 27). In 1995, N uptake was not affected by the method of application (data not shown). Nitro- gen uptake of the N fertilized treatments aver- aged 276 kg ha-1, from which an average 135 kg ha-1 was in crop residues. Carrot Plant uptake of N varied from 135 to 170 kg ha-1 and from 142 to 178 kg ha-1 in 1993 and 1994, respectively. In 1995, the average uptake of N was 166 kg ha-1. The amount of N in the storage roots increased rapidly from the middle of July 206 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion until harvest (Fig. 12). Nitrogen uptake in shoots was about 20 kg ha-1 towards the end of June. The content of N in shoots increased up to 40 kg ha-1 during July, but then N uptake started to slow down in August. In 1994, nitrogen uptake at the second sampling was lower in non-fertilized than in fertilized plots (P = 0.043, data not shown). At harvest, the shoots contained 35–39%, 32– 34% and 32–33% of the total plant N in 1993, 1994 and 1995, respectively. Table 27. Effect of N rate and application method on the cabbage N uptake (kg ha-1) on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors Dap Sample 0 80 120 160 (Method) N rate Method Interact. 29 Tops 0 vs. N Broadcast 2 0.002 6 7 7 7 ns 0.001 ns Placement 0.094 2 3 3 3 Mean (N rate) 4 5 5 50 Tops Broadcast 35 0.001 100 126 114 113 ns 0.045 ns Placement 0.001 94 101 97 97 Mean (N rate) 97 113 105 70 Leaves Broadcast 87 0.001 129 153 176 153 ns ns ns Placement 0.001 151 155 159 155 Mean (N rate) 140 154 168 Heads Broadcast 38 0.004 60 70 79 69 ns ns ns Placement 0.005 62 66 65 64 Mean (N rate) 61 68 72 99 Leaves Broadcast 74 0.001 127 164 159 150 ns ns ns Placement 0.001 147 160 161 156 Mean (N rate) 137 162 160 Heads Broadcast 85 0.001 136 170 180 162 0.059 ns 0.078 Placement 0.001 181 160 165 Mean (N rate) 145 175 170 ns = not significant; P > 0.10. Means of N rates 80–160 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 80–160 kg ha-1. 207 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Onion Plant N uptake in the non-fertilized treatments was 48, 81 and 26 kg ha-1 in 1993, 1994 and 1995, respectively. The highest plant N uptakes in each year were 140, 128 and 60 kg ha-1 in 1993, 1994 and 1995, respectively (Fig. 13). Nitrogen up- take in the bulb increased exponentially during the growing season (Tables 28 and 29). Foliage N decreased after the third sampling (70–83 dap). At harvest the foliage contained 24–28% of to- tal plant N uptake in 1993, 26–37% in 1994 and 22–25% in 1995. In each year, N uptake was low- er without N than with N fertilizer. In 1993, N uptake increased at the third sam- pling (83 dap) and at harvest with increasing N rates. At the first (35 dap), third (78 dap) and fourth sampling (105 dap) in 1993, N uptake was higher when fertilizer was placed compared to broadcasting (Table 28). In 1994, the N rate and application method had little effect on N uptake (Table 29). At the third and fourth sampling, N uptake in the bulbs was less with the N rate of 30 kg ha-1 than with higher N rates. In addition, there was an interaction at harvest in 1994, when N uptake in the foliage increased by high N rates in the broadcast application but not in the place- ment application. 3.3.3 Apparent recovery of fertilizer nitrogen Cabbage The apparent recoveries of fertilizer N in cab- bage plants varied from 0.71 to 0.88 in 1993, from 1.01 to 1.79 in 1994 (Table 30) and from 0.82 to 1.39 in 1995 (data not shown). There were no statistically significant differences be- tween treatments. Carrot In 1993, as a result of high N uptakes from non- fertilized plots apparent recovery values were often not applicable (value less than zero). The N uptake without N fertilizer was commonly higher than with N fertilizer. In 1994, the appar- ent recovery of N varied from 0.27 to 0.85, but in this year too, 25% of the plots gave negative N recovery values. In 1994, there were no dif- ferences in apparent recovery values between N rates (data not shown). In 1995, two out of four apparent recovery values were also below zero. Onion The apparent recovery of N was clearly higher with band placement in 1993 (Table 31). The apparent recovery of N decreased from 1.05 to 0.59 in the broadcast treatments and from 1.78 to 0.92 in the placement treatments when the N Fig. 13. N uptake rate for onion in 1993–1995. 208 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Table 28. Effect of N rate and application method on the onion N uptake (kg ha-1) on different days after planting (dap) in 1993. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage N uptake 0 vs. N 34 Broadcast 6 0.077 6 7 8 7 ns 0.002 ns Placement 0.006 9 10 9 9 Mean (N rate) 57 Broadcast 20 0.004 31 34 37 34 ns ns ns Placement 0.001 38 37 31 35 Mean (N rate) 34 36 34 83 Broadcast 35 0.006 39 51 54 48 0.002 0.001 ns Placement 0.001 53 57 68 59 Mean (N rate) 46c 54b 61a 98 Broadcast 13 0.028 20 25 29 25 0.001 0.001 ns Placement 0.010 26 33 39 33 Mean (N rate) 23c 29b 34a Bulb N uptake 34 Broadcast 2 ns 2 2 2 2 0.066 0.001 0.084 Placement 0.002 2 3 3 3 Mean (N rate) 2 3 3 57 Broadcast 6 0.015 7 9 10 9 ns 0.047 ns Placement 0.001 10 12 10 10 Mean (N rate) 8 11 10 83 Broadcast 22 0.001 28 33 37 33 0.001 0.001 ns Placement 0.001 37 44 49 44 Mean (N rate) 33c 39b 43a 98 Broadcast 35 0.001 60 68 78 68 0.004 0.001 ns Placement 0.001 76 98 101 91 Mean (N rate) 68b 83a 89a ns = not significant; P > 0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 209 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Table 29. Effect of N rate and application method on the onion N uptake (kg ha-1) on different days after planting (dap) in 1994. N rate (kg ha-1) Mean Significance (P) of factors 0 30 70 100 (Method) N rate Method Interact. Dap Foliage N uptake 0 vs. N 35 Broadcast 4 0.048 4 4 5 5 ns ns ns Placement 0.017 5 5 6 5 Mean (N rate) 5 5 6 55 Broadcast 15 0.001 19 19 22 20 ns ns ns Placement 0.005 21 19 20 20 Mean (N rate) 20 19 21 78 Broadcast 35 ns 39 42 45 42 ns ns ns Placement 0.092 43 46 38 42 Mean (N rate) 41 44 42 105 Broadcast 24 0.048 27 28 37 30 ns ns 0.038 Placement 0.038 37 31 33 34 Mean (N rate) 32 29 35 Bulb N uptake 35 Broadcast 2 ns 2 2 2 2 ns ns ns Placement ns 2 2 3 2 Mean (N rate) 2 2 3 55 Broadcast 3 0.001 4 4 5 5 ns ns ns Placement 0.001 5 5 5 5 Mean (N rate) 5 5 5 78 Broadcast 25 0.012 28 31 36 32 0.010 ns ns Placement 0.008 28 34 32 31 Mean (N rate) 28b 33a 34a 105 Broadcast 57 0.032 58 80 90 76 0.050 ns ns Placement 0.052 64 73 75 71 Mean (N rate) 61b 76ab 83a ns = not significant; P>0.10. Means of N rates 30–100 kg ha-1 followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. Dap = days after planting 0 vs. N = significance of difference between 0 kg ha-1 and broadcast or placed 30–100 kg ha-1. 210 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion rate was increased from 30 kg ha-1 to 100 kg ha-1. Apparent recovery of N decreased with high N rates in both application methods. In 1994, soil mineralisation was so high that N uptake from some of the non-fertilized plots was even higher than from the 30 kg ha-1 fertilized plots. Place- ment of 30 kg ha-1 N caused higher apparent re- covery of N than broadcasting of 30 kg ha-1 N (Table 31). In 1995, the apparent recovery of N was low, on average 0.33, due to the low growth. 3.4 Interaction between nitrogen uptake and sample yield When fresh sample yield increased, N uptake increased with all crops studied (Figs. 14–16). However, the variation of N uptake at the same yield level was considerable. When a linear equa- tion through the origin was fitted to the fresh yield data, the following equations were ob- tained: Table 30. Effect of N rate and application method on the apparent recovery of fertilizer nitrogen for cabbage in 1993– 1994. Application method Year N rate (kg ha-1) Broadcast Placement Mean (N rate) 1993 125 0.71 0.83 0.77 188 0.78 0.80 0.79 250 0.88 0.79 0.84 Mean (Method) 0.79 0.81 Probability* N rate ns Method ns Interaction 0.100 1994 N rate (kg ha-1) Broadcast Placement Mean (N rate) 80 1.30 1.79 1.55 120 1.46 1.51 1.49 160 1.12 1.01 1.07 Mean (Method) 1.30 1.44 Probability* N rate ns Method ns Interaction ns ns = not significant, (P > 0.10). *Significance of difference between N rates and applica- tion methods. Table 31. Effect of N rate and application method on the apparent recovery of fertilizer nitrogen for onion in 1993– 1994. Application method Year N rate (kg ha-1) Broadcast Placement Mean (N rate) 1993 30 1.05 1.78 1.41a 70 0.64 1.18 0.91b 100 0.59 0.92 0.76c Mean (Method) 0.76 1.29 Probability* N rate 0.001 Method 0.001 Interaction ns 1994 N rate (kg ha-1) Broadcast Placement Mean (N rate) 30 0.32 0.73 0.53 70 0.38 0.33 0.35 100 0.46 0.29 0.37 Mean (Method) 0.39 0.45 Probability* N rate ns Method ns Interaction 0.066 ns = not significant, (P > 0.10). *Significance of difference between N rates and applica- tion methods. Means of N rates followed by no letter or a common letter do not differ significantly (P < 0.05) according to the contrast test. 211 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Cabbage: N uptake (kg ha-1) = 3.8 x Yield (t ha-1); (R2 = 0.764, n= 68) Carrot: N uptake (kg ha-1) = 1.6 x Yield (t ha-1); (R2 = 0.170, n= 42) Onion: N uptake (kg ha-1) = 2.5 x Yield (t ha-1); (R2 = 0.485, n= 64) When the sampled dry matter yield was com- pared to the N uptake, the following linear equa- tions were obtained: Cabbage: N uptake (kg ha-1) = 0.022 x Dry matter (kg ha-1); (R2 = 0.685, n= 68) Carrot: N uptake (kg ha-1) = 0.011 x Dry matter (kg ha-1); (R2 = 0.293, n= 42) Onion: N uptake (kg ha-1) = 0.015 x Dry matter (kg ha-1); (R2 = 0.670, n= 64) Fig. 14. Cabbage head yield vs. N uptake at harvest in 1993– 1995. Fig. 15. Carrot root yield vs. N uptake at harvest in 1993– 1995. Fig. 16. Onion bulb yield vs. N uptake at harvest in 1993– 1995. 212 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion 3.5 Interaction between dry matter accumulation and nitrogen concentration Non-fertilized plants had lower N concentrations (P < 0.05, confidence intervals) than N fertilized plants at the same dry weight in cabbage (Fig. 17) and onion (Fig. 19), but there was no differ- ence between carrot treatments (Fig. 18). The critical N% concentration equation sug- gested for cabbage by Greenwood and Draycott (1989) and supported by Guttormsen and Riley (1996) was located between the non-fertilized and fertilized plant N concentrations (Fig. 17). Equations from experimental data produced the following coefficients with a 95% confidence interval for cabbage: Model B = 3.00 (Greenwood and Draycott 1989) N 0 kg ha-1 : B = 2.14 (1.86–2.42); n= 47 N fertilized : B = 3.80 (3.66–3.94); n= 223 Fig. 17. Cabbage dry weight vs. N concentration in 1993– 1995. Fig. 18. Carrot dry weight vs. N concentration in 1993– 1995. Fig. 19. Onion dry weight vs. N concentration in 1993– 1995. 213 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. The critical N% concentration suggested for carrot according to the N_ABLE model (Green- wood et al. 1996a) was in good agreement with the measured data (Fig. 18). Equations from experimental data produced the following coefficients for carrot: Model B= 1.26 (Greenwood et al. 1996a) N 0 kg ha-1 : B = 1.66 (1.43–1.90); n= 36 N fertilized : B = 1.87 (1.75–1.98); n= 120 The critical N% concentration for onion ac- cording to the N_ABLE model (Greenwood et al. 1996a) was clearly higher than the measured concentrations (Fig. 19). Equations from experimental data produced the following coefficients for onion: Model B= 2.42 (Greenwood et al. 1996a) N 0 kg ha-1 : B = 0.51 (0.31–0.70); n= 48 N fertilized : B = 1.29 (1.20–1.38); n= 207 4 Discussion While this study aimed to find out the effects of N rate and application method on growth and N uptake, the results strongly depend on growth conditions creating yield potential. As full yield potential can be realised only if all environmen- tal factors are optimised, environmental factors related to climate, experimental soil, micro-or- ganisms, weeds and pests must be considered (Krug 1997). This background has an effect to- gether with cultivar characteristics, plant densi- ty and crop management. When generalising the following results, we must estimate whether it was possible to reach full yield potential and whether the environmental factors correspond- ed to practical farming conditions. The experimental soil was rich in nutrients, seemed to mineralise high amounts of N and re- tained considerable soil moisture. Soils in prac- tical vegetable production tend to be of this qual- ity, although they are usually more sensitive to drought. Weather conditions varied largely, but in 1993 temperature and rainfall seemed almost optimal for growth. In July 1994, high tempera- ture and probably drought, despite irrigation, stressed growth, which was especially observed with onion. In 1995, high rainfall in May and June delayed crop management measures and establishment, consequently crops never reached the yield levels of previous years. Cabbage and carrot produced good to mod- erate yields each year, but the onion yield var- ied greatly. Cabbage and carrot cultivars could, due to their long growing periods, compensate growth quite well after stress periods. On the contrary, onion seemed unable to increase its growth after stress periods. The plant densities used for cabbage and carrot affected growth, but yield was compensated by larger individual plants when the plant density was lower. Crop management succeeded well in general, which can be seen from the ratio of actual to planned plant densities (Table 4) and the marketable yields of onion and carrot. Concerning criticism of the experimental set- up, the use of completely randomized blocks instead of a split-plot design would have ena- bled us to test all the treatments at the same time. Further, crop rotation could have been consid- ered more carefully. Although residual N left from the preceding crop was supposed to leach during autumn and spring, and the inorganic N in soil in spring was low, the experimental set- up of the previous year probably increased ex- perimental error. Crop rotation may have par- tially caused the low onion yield after cabbage in 1995, because residues of cruciferous plants contain allelopathic substances that can decrease growth of the next crop (Oleszek 1987). As fi- brous roots were sampled only once or twice in 1993 for determining root length, the dry matter accumulation and N uptake in the root system is excluded from the discussion. Determination of 214 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion carbon and N fluxes to the roots must be consid- ered more precisely in forthcoming studies. 4.1 Inorganic nitrogen in soil Amount of inorganic nitrogen in soil As can be expected from the good solubility of ammonium nitrate fertilizer (Peterson and Frye 1989), the amount of soil inorganic N was high one month after fertilizer application. However, the variation in the soil inorganic N content was considerable. Riley and Guttormsen (1993a) as- sume that the variation in soil inorganic N for three weeks after fertilizer application might be caused by incomplete dissolving of fertilizer. They used calcium nitrate, which is also easily soluble in water (Finck 1982). In my experiments a more probable cause of variation is the low number of subsamples and the high differences in inorganic N content between soil layers. Although only two to three soil inorganic N samples were taken during the growing season, the decreasing trend of inorganic N in soil, caused mainly by crop N uptake, can be ob- served. According to the precipitation data, it can be supposed that leaching was low in 1993 and 1994, and that plant N uptake corresponded to the measured decrease in soil inorganic N con- tent. Actually, mineralisation of soil N has often supplied more N to the plants than the decrease in soil inorganic N content shows. While soil inorganic N at harvest tends to increase with increasing amounts of fertilizer applied (e.g. Everaarts 1993a), the low residual soil inorganic N contents in my experiments imply that N rates did not usually exceed crop demand. For example, N fertilizer rates up to 250 kg ha-1 did not increase soil inorganic N content after cabbage in autumn 1993. Soil inorganic N after harvesting carrot was slightly increased when the highest N rate was used. However, the difference between non-fertilized and 100 kg ha-1 fertilized treatment was only about 20 kg ha-1. This can be explained by the observation of Moussa et al. (1985) that carrot N uptake result- ing from soil mineralisation decreased when fer- tilizer N rates were increased. However, varia- tion in onion yields, and thus in onion N uptake, can result in high residual N in the soil at har- vest. The non-fertilized onion plots contained 45 kg ha-1 inorganic N in the soil, whereas the broad- cast 100 kg ha-1 plots contained 80 kg ha-1 in the 0–60 cm layer in 1994. In years such as 1994, when high temperature increases mineralisation of soil N and onion growth is not good, the rec- ommended N rates can result in considerable amounts of residual N in the soil. Distribution of inorganic nitrogen in soil Band placement creates large vertical and hori- zontal differences in soil inorganic N content. Although nitrate moves easily in soil, there was more N close to the fertilizer bands 1–2 months after N application. Vertical distribution of N was also definite one month after planting in 1993 and 1994. In the cabbage field, most of the placed N was in the 10–15 cm layer and in the 5–10 cm layer in the onion field. This is in accordance with the field experiment results of Aura (1967), where still in July most of the N was found at the placement depth and most of the N was in the fertilizer bands. Everaarts et al. (1996) no- ticed a clear spatial distribution after band place- ment even at the time of harvest of cauliflower, if N rate was high. In my experiments, with all crops most of the broadcast N was in the top 0– 10 cm layer, where N had been incorporated. Nitrogen, broadcast on the soil surface, tends to remain in the top 2.5 cm for a considerable peri- od without heavy rainfall or a longer wet period (Kaila and Hänninen 1961). When N was broad- cast, there was sometimes more N between plant rows than within rows, as shown also by Ever- aarts at al. (1996). This indicates that in their experiments the root system was not able to take up N from interrow areas as the row distance of 75 cm suggests. The above mentioned results imply that placed fertilizer N remains for a considerable 215 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. time in the application depth and band. Thus it can take much time for the roots to grow into the N deposits. If the banded N dose is high, for example 160–250 kg ha-1, the osmotic potential in that soil volume is also very low, and thus the roots probably cannot approach the deposits un- til the N concentrations are diluted. This was not probably the main reason for the weak start of cabbage growth, since the dry matter produc- tion was also low after banding of 60–120 kg ha-1 N. One additional problem of steep N con- tent gradients is that plant roots might concen- trate on areas rich in N and thus have less po- tential to take up other nutrients and water from other parts of the soil volume. The existence of this phenomenon is, however, unclear as dis- cussed by Robson et al. (1992). On the other hand, if the distance between plants is long and growth period is short, roots probably do not use all the soil volume. In this case, placement of N in bands close to the plant roots should be ben- eficial. In addition, the distribution of N in the 0–10 cm layer after broadcasting can be prob- lematic in dry conditions where irrigation is not available. 4.2 Plant growth and final yield The highest dry matter accumulations during the experiments were 14 000 kg ha-1 , 15 000 kg ha-1 and 8000 kg ha-1 in cabbage, carrot and onion, respectively. Dry matter accumulation of the same magnitude is reported in cabbage e.g. by Welch et al. (1985a) and Guttormsen and Riley (1996), and in carrot e.g. by Greenwood et al. (1980). In European countries, onion is usually cultivated with higher plant density than in Fin- land and dry matter accumulations of 7000–13 000 kg ha-1 (Greenwood et al. 1992) and 15 000 kg ha-1 (Tei et al. 1996) have been reported with 30% higher plant populations compared to my experiment. Brewster (1990a) reports 10 000 to 12 000 kg ha-1 dry weights for spring-sown on- ion in his experiments, but considers 5000 kg ha-1 dry yield typical of practical farming. The dry matter accumulation of the plants studied usually increases with the plant population, but cabbage and carrot seem to be more effective than onion in compensating low plant density by increasing growth of individual plants. A sigmoidal (i.e. S-shaped) curve is the ba- sic pattern of limited plant growth (Krug 1997). First dry matter accumulation is low, then in- creases rapidly and starts to decrease towards the maximum dry weight. This sigmoidal growth curve has been observed e.g. for cabbage by Huett and Dettman (1989), Riley and Guttorm- sen (1993b) and Guttormsen and Riley (1996), for carrot by Evers (1989) and for onion by Dragland (1975, 1992). The short growing sea- son in Finland can sometimes cause growth ces- sation early, when the growth rate is still high. This can result in low yield quality due to im- mature plants. In my experiments all crops were usually harvested when growth still seemed to be high. The reason for the cabbage was the de- sired head weight, for carrot, a late cultivar that ceased growth due to low temperatures, and for onion due to harvesting directly after leaf fall- down. The growth rate of cabbage remained high until harvest, and was similar to the growth curve of summer cabbage in Norway (Guttormsen and Riley 1996). As in my experiments, Evers (1989) reported that the carrot shoots grew close to their maximum weight in three months, thus follow- ing the sigmoidal growth curve. Whereas the storage roots grew slowly during the first two months, growth increased considerably during the third and fourth month. As onion was har- vested soon after leaf fall-down, the growth curve also lacked sigmoidal characteristics. Con- sidering allocation between bulb and onion foli- age, the bulb dry weight started to increase rap- idly at the beginning of July and continued in an exponential fashion, whereas growth of onion foliage was depressed at the end of July. This growth curve of bulb and foliage is similar to the results obtained in Norway by Dragland (1975, 1992). The period of rapid foliage growth 216 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion was from the middle of June until the middle of July (Dragland 1975), when the foliage fresh weight was at its maximum. Towards harvest the foliage fresh weight decreased by approximate- ly 50% (Dragland 1992). The final yields include more spatial varia- bility than the growth measured by samples. Cabbage yields in my experiment, 50–80 t ha-1, were about the same magnitude as the yields re- ported by e.g. Everaarts (1993a) in the Nether- lands and Guttormsen and Riley (1996) in Nor- way. Although for cabbages the plant density was 35% lower in 1994 than in 1993, the difference in yield was only 10%. The low yield of 50 t ha-1 in 1995 was due to the aged transplants that also suffered from the moist early summer, re- sulting in 30% transplant mortality. The carrot yield levels in my experiments, 45–100 t ha-1, were usually higher than the yield levels present- ed by Dragland (1977) in Norway (50–70 t ha-1) and Evers (1989), (39–45 t ha-1) but close to the yields presented by e.g. Roll-Hansen (1976) in Norway and Greenwood et al. (1980) in Eng- land. The lowest carrot yield, 45 t ha-1 in 1995, was caused by a low plant density that was only one fifth of the densities of the previous years. With cabbage and carrot, it seems that the full yield potential can be achieved in quite varying conditions when the plant population is high enough. Considering onion, plant densities were sim- ilar each year but yields varied considerably. The large variation in onion yields, from almost 50 t ha-1 in 1993 to only 20 t ha-1 in 1995, is typical for Finnish experiments (Aura 1985, Suojala et al. 1998). Yield estimations on the farms have varied between 13 and 22 t ha-1 in 1984–1997 (Information Centre of the Ministry of Agricul- ture and Forestry 1998). As the vegetative growth and bulb development of onion are strongly de- pendent on day length and temperature (Brews- ter 1990a), it is likely that in certain seasons the onion crop is not able to produce high yields in the Finnish climate. However, further studies concerning the effects of photoperiod, tempera- ture and different stresses on onion growth and yield in Finland are required. Nitrogen rate While N is an essential compound in plant tis- sues, it especially promotes leaf area index and duration (Marschner 1995). High and long-last- ing leaf area increases photosynthesis and dry matter accumulation. The crops studied had var- iable responses to enhanced N fertilization. Cab- bage benefited from N application every year, onion two years out of three, but carrot yielded well without N fertilizer. The application of a fixed rate of N before planting seemed to secure good yield levels in years like 1993 and 1994. However, a lower N rate than recommended was sufficient for sev- eral crops due to high mineralisation of soil N. While the soil inorganic N in spring was gener- ally 30–40 kg ha-1, this alone cannot explain the high plant N uptakes after small N rates. Thus the balance sheet method, which estimates soil N mineralisation during summer, looks a prom- ising method to adjust N rates. Top dressings can be given according to the balance sheet calcula- tions or more complicated simulation models. The benefit of simulation models can be tested in further studies considering also the year 1995, when part of the fertilizer N must have been leached. Growth of cabbage increased every year by N fertilizer, but in 1994 the low N rate of 80 kg ha-1 was sufficient for the highest yield level achieved. Mostly cabbage has been found to re- spond strongly to fertilizer N and, for example, N min target values for summer cabbage yields of 40 000 kg ha-1 and winter cabbage yields of 80 000 kg ha-1 in Germany are 250 and 350 kg ha-1, respectively (Scharpf and Weier 1996). Nitro- gen uptake of this magnitude was also recorded in my experiments. The prevailing N recommen- dation for cabbage in Finland, 180–200 kg ha-1 for 50 000 kg ha-1 yield, is rather modest when compared to recommendations of other Europe- an countries (Table 1). However, Finnish soils are often high in organic matter and growing seasons with excessive rainfall causing leaching are rare, and thus both soil N supply and the ef- ficiency of fertilizer N should be good. 217 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. The fact that N rate had no effect on carrot growth or yield in my experiments is in agree- ment with several experiments where carrot has produced high yields with a modest N rate. Roll- Hansen (1974, 1976) recommended an N rate of 78 kg ha-1 for peat soils and 80 kg ha-1 for sandy soils in Norway. An N rate of 80 kg ha-1 was suf- ficient to produce 55 000 kg ha-1 yields also in Finland (Aura 1985), but 80 kg ha-1 was the low- est N rate applied. Dragland (1977) obtained the highest yield after application of 40 kg ha-1 N and the yield then averaged 61 000 kg ha-1. Eke- berg (1986) obtained 43 000 kg ha-1 yield with N rates of 52 or 104 kg ha-1. Even in the experi- ments of Greenwood et al. (1980) where the soil had been cultivated without N fertilizer for sev- eral years to diminish soil N reserves, the opti- mum level of N fertilizer for carrot was 84 kg ha-1. In Denmark, Sørensen (1993) studied N supply from soil inorganic N in spring and from N fertilizers, and recommended 60 kg ha-1 for this total N supply when the yield was 85 000 kg ha-1. In Germany, the N min value for a carrot yield of 60 000 kg ha-1 is 100 kg ha-1 (Scharpf and Weier 1996). In the experiments mentioned above the var- iation of yield levels from 43 000 to 85 000 kg ha-1 with an optimum N rate is, however, con- siderable. Moussa et al. (1986) concluded that varied climate, water supply and soil status have a great effect on optimum N rates. The carrot yield variation in my experiments was mainly due to the weak plant establishment in 1995. Carrot growth has often been good even without N fertilizer (Table 32). In the experiments of Ekeberg (1986) and Evers (1989), yields of non- fertilized treatments were as high as 80–95% of the maximum yields obtained. Table 32. N uptakes and harvested yields of cabbage, carrot and onion cultivated without N fertilizer. Crop Preceding crop P and K Fresh yield N uptake Reference t ha-1 kg ha-1 Cabbage 3 year grass + *43 117 Peck (1981) ? + 29 56 Welch et al. (1985a) ? (sandy soil) + 19 33 Riley and Guttormsen (1993a) ? (loamy soil) + 43 69 Riley and Guttormsen (1993a) Cereals + *24 *58 Greenwood et al. (1980) Barley + 19 70 Dragland (1982) Barley + 23 90 1993, present study Carrot + 51 159 1994 Carrot + 27 117 1995 Carrot Potato + *64 103 Dragland (1977) Cereals + 85 *114 Greenwood et al. (1980) Carrot – 46 *69 Evers (1989) Barley + 71 110 1993, present study Onion + 97 142 1994 Onion + 85 163 1995 Onion Wheat + 34–43 56–66 Brown et al. (1988) ? ? 45 65 Dragland (1992) Barley + *45 66 Henriksen (1984) Cereals + *31 *47 Greenwood et al. (1980) Barley + 29 48 1993, present study Barley + 31 81 1994 Cabbage + 13 26 1995 * N uptake or fresh yield is calculated using other values in the article. + = P and K fertilization – = no P and K fertilization ? = not mentioned in the article 218 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion Nitrogen promoted onion growth and yield in 1993 and 1995, but in 1994 the non-fertilized plots grew as well as the N fertilized. This is in accordance with the large variation of optimum N rates for onion, from 20 to 350 kg ha-1, as re- ported by De Visser et al. (1995) from the Neth- erlands. In Denmark the total N supply from soil and fertilizer that gave the best yield was 135 kg ha-1 (Sørensen 1996). In Germany, Lang (1988) advised fertilization for onions with 15– 20 kg ha-1 per 10 000 kg ha-1 bulb yield, but there are also higher recommendations such as 160 kg ha-1 for a 60 000 kg ha-1 yield (Scharpf and Wei- er 1996). All these recommendations and exper- iments are for sown onion, which benefits from the mineralisation of soil N during its long grow- ing period. Although onion has a sparse and shal- low root system, it can sometimes maintain good yields without N fertilizers (Table 32). Maximum increases with N fertilizer have varied from 23 to 90% (Greenwood et al. 1992). Nitrogen tends to promote leaf growth while delaying development of reproductive or stor- age tissues (Marschner 1995). With cabbage, this was not observed. On the contrary, the leaf to head ratio decreased with increasing N in 1993. The proportion of shoot dry weight to total dry weight for carrot has been slightly higher with higher N rates (Greenwood et al. 1980), but this was not observed in my experiments. In 1993, high N rates led to increased onion foliage dry weights towards harvest, but there was not a sta- tistically significant increase in bulb dry weights. The trend that high N rates led to higher onion foliage growth than bulb growth has been ob- served by Dragland (1992). Method of application Application methods seemed to affect dry mat- ter accumulation in a more complicated way than expected. The common hypothesis, that band placement results in a better availability of the fertilizer N and thus a higher yield or lower N fertilizer demand, was not unambiguously real- ised. The growth rate of cabbage was lower with band placement than with broadcasting in two years out of three, and the final yield was also lower in one year. On the contrary, the growth rate and final yield of onion was increased in one year out of two, whereas carrot growth was not influenced by the application method. The location of the fertilizer band seems to need care- ful consideration, as the main reason for higher cabbage growth in broadcast treatments was that N was easily available to the small transplants. It can be problematic to find common solutions for different crop management techniques. The positive effects of band placement were usually related to low N rates, thus indicating that band placement may be a more effective application method in low N supply conditions. This was probably due to weak growth which caused roots to occupy only a small soil volume, and thus part of the N between rows was unavailable, where- as with good N supply plant yields were usually insensitive to the application method. Early growth of cabbage benefited from the even distribution of soil inorganic N created by broadcast fertilization. Later the differences were minimised as the plant roots in placement plots grew into the N deposits and presumably the plants also created a full-grown root system to utilize water and nutrients from the interrow area. From the root samples it was observed that there were cabbage roots also between rows 63 days after planting in 1993 in both placement and broadcast treatments. This is in accordance with the measurements of Portas (1973), who observed that cabbage roots had developed hor- izontally about 20 cm at the start of heading. Nitrogen placement experiments with cab- bage or related species have given positive or no effects. Cauliflower responded well to placement probably due to a shorter growing period than onion and leeks (Sørensen 1996). Everaarts and de Moel (1995 and 1998) got only a few positive effects from band placement and concluded that band placement is not a relevant strategy to in- crease yields or reduce N application in cabbage or cauliflower production. Banded N application did not affect cabbage growth either compared to broadcasting according to Wiedenfeld (1986). Considering placement of all main nutrients, 219 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Smith et al. (1990) found higher yields in cab- bage with band placement of NPK fertilizer when NPK fertilizer was placed in double bands 10 cm on each side of the transplant and 10 cm deep. If the immediate nutrient demand of cabbage is supplied by a starter solution, then placement of N will probably be a more certain method than broadcasting. Nitrogen placement would most likely be beneficial, where irrigation is not possi- ble and in soils where water evaporates rapidly. If the growing period of the cabbage cultivar is short, fertilizer bands can be close to the plant row, but if the growing period of the cultivar is long, ferti- lizer bands should cover also the interrow area. This enables development of an even root system and prevents formation of high salt concentrations that are especially harmful in dry soil conditions. The early growth of carrot is slow, and dif- ferences in distribution of soil inorganic N will probably decrease before rapid N uptake starts. However, Hole and Scaife (1993) stated that the nutrient reserves of carrot seed are used within 15 days or less and then the seedling should be able to take up nutrients from soil solution. At this stage, localized variation in nutrient availa- bility can cause nutrient deficiency. Probably in field conditions there is enough N in soil solu- tion for seedling uptake of N. In addition, if the growth of the young seedling is restricted, it can be compensated later during the growing season. For these reasons, carrot seems to be insensitive to the placement of N. Experiments related to nutrient placement with carrots are rare, and data were found only from Norway and Finland. In Norway, placement of NPK fertilizer resulted in 2–12% higher car- rot yields than broadcasting of NPK fertilizer in dry years and had no effect in a rainy year (Eke- berg 1986). As placement of PK fertilizers re- sulted in a yield increase of the same magnitude as placement of NPK fertilizers, Evers (1989) assumed that the yield increase was mainly due to the placement of phosphorus and potassium. Onion is reported to be vulnerable to osmot- ic stress, and even broadcast N rates between 100–150 kg ha-1 have decreased early growth by 20% and the plant population density of onions produced from sets by 15% (Greenwood et al. 1992). However, in my experiments high soil inorganic N concentration usually had a positive effect on growth. The only negative trend in growth, although not statistically significant, can be seen in the foliage growth of the placed 100 kg ha-1 treatment, 57 days after planting in 1993. In addition, root growth was weak at the loca- tion of fertilizer band one month after planting in 1993. One reason to suppose that onion could benefit from band placement is that onion roots can occupy only a small soil volume. The depth of rooting did not increase with an increasing total root length throughout the growing period, and the 20 cm top layer contained 90% of onion roots (Greenwood et al. 1982). Also Portas (1973) noted that onion had a shallow root sys- tem with a depth of 15–21 cm. The dry matter accumulation of onion was slightly increased by band placement in 1993, and finally there was a clear increase in bulb fresh yield. Placement of N was clearly benefi- cial at the two lower N rates. It seems that place- ment was a more effective application method in 1993 and it supplied enough N for good growth even at low application rates. This agrees with the work of Sørensen (1996) where place- ment of low amounts of N fertilizer showed high- er yield compared to broadcasting of N. The dry matter accumulation followed a similar pattern at the four-leaf stage and 3–4 weeks later. How- ever, bulb yields were not statistically signifi- cantly influenced by the method of application (Sørensen 1996). Variation between years can be observed from the study of Wiedenfeld (1986) in Texas, USA, where banding of N increased onion yield by 12% in only one year out of three. In 1994, when the soil inorganic N supply was high even without N fertilizer, placement of N did not affect growth. The onion growth rate was low in 1994, probably because of low tempera- tures in May and high temperatures in July. Thus it seems that placement of N may be beneficial for onion growth only if the soil N supply is low and the onion growth rate is high. Most of the nutrient placement experiments with onion have been made with NP or NPK fer- 220 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion tilizers. Placement of NPK fertilizers has result- ed in 12% (Cooke et al. 1956) or 9% (Dragland 1992) higher onion yields when compared to broadcasting of NPK fertilizer. Estimating the influence of N and P on growth can be done from the experiments of Henriksen (1987) where placement of monoammoniumphosphate to on- ion sets gave the best yield, placement of super- phosphate some yield increase and placement of ammoniumsulphate did not affect yield com- pared to broadcasting of nutrients. NP placement increased growth by 60% at the four-leaf stage, by 20% 3–4 weeks later and by only 5% in yield (Sørensen 1996). The trend, showing that yield differences equalise towards harvest, has also been noticed in liquid starter fertilizer experiments in England. Rowse et al. (1988) determined 50–60% higher seedling weights when injecting starter NPK so- lution below the onion seeds. However, later in the growing season this benefit was lost (Costi- gan 1988). Injection of starter ammoniumphos- phate increased P and N concentrations in seed- lings and later in the growing season shoot dry weights (Brewster et al. 1991). However, bulb yields were not significantly increased with starter fertilizers. The reason for the disappearance of yield differences was a shortened growing peri- od obtained after using starter fertilizers. Brews- ter et al. (1991) concluded that starter fertilizer responses frequently result from enhanced P up- take by seedlings, but enhanced N uptake may also be important. There are also results where higher yield was obtained with starter fertilizers. Rahn et al. (1996b) measured higher early growth of onions when placing NP starter solution 3 cm under the drilled onion seed. Dry matter was dou- bled 10 weeks after drilling and there was still a yield increase of 4.5 t ha-1 until harvest. 4.3 Nitrogen concentration The decrease in N concentrations during growth was typical for the crops studied (Scaife and Turner 1983) and for cabbage and carrot corre- sponded to the equations presented in the N_ABLE model (Greenwood et al. 1996a). The decrease in cabbage N concentration was simi- lar to the experiments of Riley and Guttormsen (1993a) where cabbage N concentrations de- creased from around mid-June onwards, start- ing from 45 g kg-1 DM and ending at 10–20 g kg-1 DM. The decrease in carrot shoot N con- centration in my experiments was about the same magnitude as the decrease from 34 g kg-1 DM (75 das) to 25 g kg-1 DM (116 das) reported by Evers (1989). The N concentration of carrot stor- age roots has often declined only slightly dur- ing the growing period (Nilsson 1987, Evers 1989). This differs from my measurements where storage root N concentration decreased clearly. Of the crops studied, only the onion N con- centration was clearly less than in the equation of the N_ABLE model presented by Greenwood et al. (1996a). If the measured N concentrations are compared to the data presented by Green- wood et al. (1992), they are, however, only slightly lower. There foliage and bulb dry mat- ter of 0.043 t ha-1 contained on average 45 g kg-1 N and dry matter of 10.75 t ha-1 on average 17 g kg-1 N. Thus the B value, 4.05, of the critical N curve given in that study seems to be too high and it has later been lowered for the N_ABLE model to 2.42 (Greenwood et al. 1996a). The concept of critical N curve seemed to work well for cabbage and onion where non-fer- tilized plants had lower plant N concentrations than fertilized plants. In carrot, growth was good also without N fertilizer with plant N concen- trations only slightly lower than in the fertilized plants. An approximated critical N curve can be drawn as a function of dry matter accumulation. Critical N concentration is considered a valua- ble tool in fertilization planning (e.g. Peterson and Frye 1989), but nitrate N analysis is often preferred as being a simpler and faster method (Marschner 1995). The slight increase in bulb N concentration towards harvest, observed in my experiments, has also been noticed in Sweden by Nilsson (1980). In his experiments, the N concentration 221 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. of the bulbs increased close to the harvest from 17.5 g kg-1 DM to 23.0 g kg-1 DM, the reason being translocation of N from foliage to bulb. Nitrogen rate A high N concentration should maintain a more efficient and long established photosynthetic system (Marschner 1995), but when comparing dry matter production to N concentrations, there were samplings without statistically significant differences in dry matter production although there could be statistically significant differences in N concentrations. Presumably crops lost their higher yield potential due to the following rea- sons: cabbage was harvested when the target head size was reached, carrot growth ceased due to low temperatures in late September and on- ion development depended on climatic factors. As in my experiments, the concentration of N in cabbage has been found to increase propor- tionally with increasing levels of N applied at planting (Riley and Guttormsen 1993a). Green- wood and Draycott (1989) measured a range of N in dry matter of harvested summer cabbage from 16 to 40 g kg-1 DM with fertilizer N levels from 0 to 504 kg ha-1. Measured ranges of N in dry matter of harvested winter cabbage were from 22 to 35 g kg-1 DM with N rates from 0 to 280 kg ha-1. Carrot N concentrations have been found to increase with increasing N rates (Hansen 1978, Greenwood et al. 1980). In my experiments this effect was seen in storage root N concentrations in 1993 and 1994, and in shoot N concentrations in 1994. Onion N concentrations were increased with high N rates, although dry matter accumulation was not increased in 1994. Nitrogen concentra- tion in bulbs at harvest increased with increas- ing N rates (Dragland 1975, Greenwood et al. 1980). Also in Finnish experiments by Suojala et al. (1998), an increase of N rate from 50 kg ha-1 to over 100 kg ha-1 increased bulb N con- centration by 5 g kg-1 DM. With onion there are observations that high N rates tend to improve foliage growth and to give a dark green colour to the foliage, but often the bulb yield is not high- er (Dragland 1992). Luxury consumption of N should not be especially high in onion. Green- wood et al. (1992) observed that high levels of fertilizer N did not increase the N concentration in total plants more than 10% compared to plants that obtained the lowest rate of fertilizer N for maximum growth. Method of application Although the shoots of transplanted cabbage are well developed, the roots are limited to a very small soil volume. However, the N demand of the small cabbage transplant is high and it should be able to get sufficient N as soon as possible. An onion set, on the contrary, has a large pool of reserves, and thus a high N demand starts only 1–2 weeks after planting. A carrot seed has re- serves for less than 15 days (Hole and Scaife 1993), but as the growth rate of the cultivar stud- ied was slow, N demand was low at the begin- ning of the growing period. If there is not enough N available to the plants in the soil, their N concentration will decrease and growth will be retarded. On the other hand, the N concentration of plants tends to decrease as the dry weight increases (e.g. Greenwood et al. 1996b). Therefore it is difficult to interpret plant N concentrations, as the N concentrations can be high because of small plant dry weight. The variation of cabbage N concentrations in 1994 may be caused by this interaction of plant growth on N concentrations. At first cabbage N concentrations were high in broadcast treat- ments, implying a slightly better soil environ- ment for N uptake in the broadcast treatments. Then cabbage growth in broadcast treatments in- creased and N concentrations were lower until harvest than in the placement treatments. In the majority of experiments, banding of N has not affected cabbage leaf N concentrations compared to broadcasting (Wiedenfeld 1986, Smith et al. 1990). Broadcasting N vs. banding and side dressings did not affect plant N con- centrations either (Peck 1981). In the experi- 222 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion ments of Cutcliffe and Munro (1976), the leaf N concentration of Brussels sprouts was higher with N placement. Onion N concentration responded well to the soil N availability. When onions were growing in soil with high N concentration after band placement, the onion N concentrations were usu- ally higher than in broadcast treatments in 1993. Although onion foliage contained more N and was more vigorous in placement treatments than in broadcast treatments in 1993, there were only a few positive effects of placement on the dry matter production. The reason for broadcasting resulting in higher plant N concentrations than placement 55 days after planting in 1994, can be explained by more advanced growth in the placement treatment. 4.4 Nitrogen uptake The N uptake of the crops studied depended mainly on the dry matter accumulation. Each year the amount of N uptake was highest with cabbage, moderate and stable with carrot, low and variable with onion. Nitrogen uptake curves were similar to the growth curve in the early and mid-season. Approaching harvest growth still continued, but because there was either a lack of N in the soil or a decrease in critical plant N concentration, the N uptake did not increase as rapidly as the dry weight. The decrease of the N uptake rate in the late period of growth agrees with the cabbage exper- iment of Peck (1981), where the rate of N up- take was low during the seedling stage, high during midseason and moderate as the plants approached harvest. Many scientists have report- ed that when cabbage is grown for storage, it is harvested as ‘matured’ and the N uptake pattern is sigmoidal (Dragland 1982, Huett and Dettman 1989, Everaarts 1993a). When cabbage is grown for the fresh market with a short growing peri- od, there is continuous uptake until harvest, and sufficient N must still be available in the soil for optimum growth (Welch et al. 1985a). With car- rot, rapid N uptake started two and a half months after sowing because of storage root N demand. At that time shoot N demand started to dimin- ish. The N uptake curve of onion was similar to the growth curve, and a similar N uptake curve has also been presented by Dragland (1992). The amount of N in the crop residues was 40–50%, 30–40% and 20–30% of total N uptake in cabbage, carrot and onion, respectively. The amount of N in the cabbage crop residues has been high, approximately 50% of total N uptake, in several experiments (e.g. review by Everaarts 1993a, Peck 1981). The N content in carrot shoots depends on the cultivar characteristics. In the experiments of Greenwood et al. (1980) the shoots contained 53 kg ha-1 and storage roots 107 kg ha-1 N, but Dragland (1977) determined a higher portion of N in the shoots, 69 kg ha-1, whereas storage roots contained 77 kg ha-1. The percentage of N in onion crop residues was clear- ly higher than presented by Suojala et al. (1998) where foliage N content was less than 7% of the total N content. The reason assumed by Suojala et al. (1998) was that the leaves in their experi- ment were already partly senesced compared to my experiments where the onion foliage was analyzed before senescence. During the senes- cence there is a translocation of N from foliage to bulbs and part of the leaves fall to the soil surface. The N content in cabbage crop residues after a good yield was considerable, from 134 to 160 kg ha-1. Nitrogen amounts of this magnitude can have a great effect on leaching but also on sup- plying N for subsequent crops, if N has been re- tained in the soil by correct management and fa- vourable weather conditions. Strategies for min- imizing N losses and thus retaining most of the N in crop residues for the next crop are essen- tial. The solutions related to the time of autumn cultivation and catch crops have been studied by e.g. Greenwood et al. (1996b) and Thorup-Kris- tensen (1994). In Finnish weather conditions, the short growing season creates specific problems for the use of catch crops, and thus research for finding proper solutions is important. 223 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. Nitrogen rate The crops studied showed clear relationships be- tween N uptake and either fresh yield or dry mat- ter yield. However, these relationships included considerable variation. Variation was caused ei- ther by variable leaf or shoot biomass or variable N concentrations. Excessive N uptake creates crop residues rich in N, but this N is, however, retained to the next season in crop residues more efficient- ly than in the pool of soil inorganic N. A cabbage head yield of one ton was achieved by an average 3.8 kg N in the total above-ground crop. This ratio is close or in the range calculat- ed from other experiments (Table 33). When white cabbage has a yield level of 70–90 t ha-1, N uptake has averaged 390 kg ha-1, with a range of 300 to 450 kg ha-1 (Scharpf and Weier 1996). These N uptake values are similar to the slightly over 300 kg ha-1 N uptakes in my experiments when head yield was more than 70 t ha-1. Varia- tion in the ratio between above-ground crop N uptake and head yield can be caused by differ- ent plant N concentrations and differences in the leaf growth needed for a certain head yield. In 1993, increasing N rates from 125 to 250 kg ha- 1 gave higher N uptakes, but in 1994 only the non-fertilized treatment took up less N than the other N rates. This indicates that in 1994, min- eralisation of soil N produced enough N for cab- bage even with an N rate of 80 kg ha-1. A carrot storage root yield of one ton was achieved by an average 1.6 kg N in the crop. This is in agreement with the results of Greenwood et al. (1980) who measured a total N uptake of 160 kg ha-1 with an optimum N rate and a yield of 100 t ha-1. A bulb yield of one ton was achieved by an average 2.5 kg N in the crop. In other experi- ments N uptakes with optimum N rates have varied from 83–150 kg ha-1 (Table 34). Onion N uptake was increased with high N rates and var- ied in well yielded treatments from 100 to 140 kg ha-1. Although luxury consumption of N was low in concentration level, it could result in con- siderable amounts of N taken up by the crop. As cabbage N demand is high, top dressings should be used as safety measure against leach- ing of N caused by high rainfall after planting. Top dressings should maintain a sufficient soil inorganic N content from one month after plant- ing until harvest. As the leaves of cabbage cover the soil surface almost totally towards harvest, the last top dressing must usually be given more than one month before harvest. The current rec- ommendation for applying top dressings in two portions (Soil Testing Laboratory of Finland 1997) seems reasonable as the useful time peri- od for applications lasts from one month to three months after planting. If natural rainfall is low, irrigation must be used to transport fertilizer N to the root zone. As the N demand of carrot is Table 34. N uptakes, bulb yields and relationships between N uptakes and bulb yields of onion. N uptake Bulb yield N uptake / Reference in bulb bulb yield and foliage (kg ha-1) (t ha-1) (kg t-1) 83 57 1.5 Brown et al. 1988 110 73 1.5 Dragland 1992 104* 61 1.7* Henriksen 1987 114 63 1.8 Brown et al. 1988 87 48 1.8 Suojala et al. 1998 118 51 2.3 Suojala et al. 1998 150 60 2.5 Dragland 1992 * solely in bulbs Table 33. N uptakes, head yields and relationships between N uptakes and head yields of cabbage. N uptake Head yield N uptake / Reference in above head yield ground crop (kg ha-1) (t ha-1) (kg t-1) 217 84 2.5 Peck 1981 307 103 3.0 Peck 1981 270 79 3.4 Dragland 1982 390 115 3.4 Slangen et al. 1990 136 39 3.5 Welch et al. 1985a 330 93 3.5 Dragland 1982 397 92 4.3 Slangen et al. 1990 364 65 4.7 Welch et al. 1985a 224 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion very low at first, in soils susceptible to leaching a major portion of the N fertilizer should be ap- plied as top dressing. Top dressings for onion should maintain a sufficient soil inorganic N content from 30 to 80 days after planting. As onion N demand is rather low, and growth does not necessarily increase although N uptake in- creases, one top dressing should be sufficient. When N supply was low, i.e. in the non-fer- tilized treatments, cabbage and carrot were able to take up large amounts of N. This indicates a high N mineralisation potential in the experimen- tal soils because the content of inorganic N in the soil was low in each spring. Especially in 1994, high temperatures in July increased N min- eralisation, and the total N uptake of cabbage without N fertilizer was as high as 159 kg ha-1. Experiments with Brussels sprouts and cauli- flower indicate that Brassica vegetables can have well developed root systems (Everaarts 1993a). A cabbage crop seems to take up 60–70 kg ha-1 of N from non-fertilized plots (Table 32). Nitro- gen uptake of this magnitude usually gives only low yields, but it gives an estimate of the ability of cabbage to use soil N reserves. In the present experiments the N uptake of carrot without N fertilizer was close to 150 kg ha-1 each year. As carrot often produces a good yield even without N fertilization (Table 32), it is able to take up considerable amounts of mineralised soil N. Although onion roots occupy a small soil volume, they are able to take up slightly over 50 kg ha-1 N during the growing season from soils with low N supply. Nitrogen uptake without N fertilizer in 1993 was typical compared to other studies (Table 32). In 1994, N uptake without N fertilizer was clearly higher than in 1993 and corresponded to the N uptakes of high yield lev- els. This can be explained by good conditions for soil N mineralisation as the top soil was kept at optimum moisture and the temperature was high in July 1994. Method of application Plant N uptake is a better estimator of N availa- bility from different N application methods than plant N concentration. When the availability of N in the soil is good, we should have a high dry matter accumulation and high N concentration to establish optimum growth. In this experiment, the application methods did not usually affect N uptake at harvest, but differences were observed during the growing period. At the beginning of two years out of three, there was a higher cabbage N uptake in broad- cast than in placement treatments. This implies better soil N availability from broadcast than from placement treatments for the small transplants. Towards harvest the differences were equalised, and thus N can be considered to have been equal- ly available to full-grown plants regardless of the application method. This conclusion is support- ed by the results of Everaarts et al. (1996) where band placement did not differ from broadcasting in the effect on N uptake of cauliflower. At least two possible reasons for the effec- tiveness of carrot in utilizing soil N reserves can be mentioned. Firstly, rapid uptake begins just two and a half months after sowing and thus soil N mineralisation can supply a large proportion of the carrot N demand. Secondly, the carrot root system is dense and able to grow in deep soil horizons (Pietola 1995). According to Pietola (1995) the large root system of carrot consisting mostly of fine roots in the fertile soil horizon may be the reason for the insensitivity of carrot yield to water and nitrogen in many studies. Onion N uptake was increased when fertiliz- er was placed in 1993, but not in 1994 when soil N mineralisation was high. Thus placement of N can increase N uptake when the soil N supply is low and growth is fast. 4.5 Apparent recovery of fertilizer nitrogen Apparent recovery was not the especially good indicator of the use of fertilizer N. Experimen- tal fields mineralised plenty of organic N for the 225 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. crop N uptake and thus small doses of fertilizer N increased crop N uptake more than the actual N dose. Furthermore, carrot took up as much N from non-fertilized as from fertilized plots. High N rates decreased the apparent recovery only for onion in 1993. Considering application methods, placement of N increased the apparent recovery for onion in 1993. Cabbage has a rather high variation in ap- parent recovery of N, as shown in the data col- lected by Everaarts (1993a) where the apparent recovery of N with cabbage varied from 0.37 to 1.24. If there are high amounts of available soil N, the apparent recovery of N can easily exceed 1.00, as was the case in my experiments in 1994. The apparent recoveries of N in 1993 were in the range 0.79–0.85 that is typical for summer cabbage in England (Greenwood et al. 1989, Greenwood and Draycott 1989). Apparent recov- ery of N with cabbage seems to decrease with increasing fertilizer rate (Greenwood et al. 1989, Riley and Guttormsen 1993a). Apparent recov- eries of N varied from an average 0.13 to 0.72 between two fields, two varieties, seven N ferti- lizer rates and two years (Riley and Guttormsen 1993a). Apparent recoveries of N with summer cabbage were somewhat higher than the appar- ent recoveries of N with winter cabbage, proba- bly as a result of the more rapid initial growth and N uptake of the former crop (Riley and Gut- tormsen 1993a). In the dry years of 1993 and 1994 in Norway, apparent recovery of N was approximately 0.80 and high rates of N applica- tion did not substantially decrease N recovery (Guttormsen and Riley 1996). The maximum apparent recovery of N for carrot measured by Greenwood et al. (1989) was 0.69. In their experiments the soil had been cul- tivated without N fertilizer several years to di- minish soil N reserves (Greenwood et al. 1980), and thus application of fertilizer N could not in- crease the utilisation of soil N. In my experi- ments the mineralisation of soil N was so high that fertilizer N was not required at all. Greenwood et al. (1992) presented a linear equation for the decline of apparent recovery of N when increasing N rates with onion: Apparent recovery of fertilizer N = 0.50 - 0.00086 x (fertilizer N) (4) Earlier Greenwood et al. (1989) had present- ed the apparent recovery of an infinitely small amount of N to be 0.31 for onion. In my experi- ments there was also a linear decline in the ap- parent recovery of N in 1993 with higher N rates. However, in 1994 the apparent recovery of N was high, from 0.85 to 1.40, and was not affected by the N rate. This can be caused by high mineral- isation of soil organic N. When there is soil in- organic N from sources other than N fertilizer, small amounts of fertilizer N can improve root growth and N uptake, thus producing apparent recovery values above 1.0. High apparent recov- ery of N for onion, from 1.0 to 1.8, was also re- ported by Sørensen (1996). It seems that the ap- parent recovery of N can be higher for onion than suggested by Greenwood et al. (1992). Apparent recovery of N was higher with placed fertilizer for onion in 1993, because on- ion growth benefited from the good availability of fertilizer N. For onion in 1994, the method of application did not affect the apparent recovery of N, which was also the case in the experiments of Sørensen (1996). Apparent recoveries of N in his experiments were high suggesting high min- eralisation of soil organic N, and thus conditions were similar to 1994 in my experiments. How- ever, it seems that placement can improve the N uptake efficiency of onion in conditions where availability of soil inorganic N is low. 226 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion 5 Conclusions creased in cabbage and onion. This uptake con- tinued until harvest, i.e. mid-August for onion and early September for cabbage. Nitrogen up- take by carrot started rapidly just two months after sowing, but continued until harvest at the end of September. According to these periods of high N uptake, top dressings for cabbage and onion should be applied one month after plant- ing, and for carrot two months after sowing. As the N demand of cabbage is high, another top dressing can be applied two months after plant- ing. After harvest the soil mineral N content was generally low, i.e. below 25 kg ha-1 at a depth of 0–60 cm. Onion was an exception with poor growth in 1994, when soil mineral N after the highest N rate was 80 kg ha-1 at a depth of 0–60 cm after harvest. The apparent recovery of ferti- lizer N was generally good in all crops. The fer- tilizer rates were low enough to prevent a de- crease in apparent recovery values. The vegetables differed widely in their N re- quirement, and thus in their potential to cause losses of N. The N requirement of cabbage es- pecially was high and the crop residues contained large amounts of N. Thus cabbage requires care- ful management to keep N losses low. Band placement of N compared to broadcast- ing of N did not usually affect dry matter accu- mulation. Only onion in 1993 grew slightly bet- ter and cabbage in 1993 and 1994 slightly worse after band placement. However, we can assume that if plant roots are not able to take up N from the interrow area or if the moisture content of the top soil will be low, band placement of N will be more efficient than broadcasting of N. The apparent recovery of fertilizer N was in- creased in onion 1993, when growth was good and the soil N supply was only moderate. One t ha-1 of fresh yield required approximately 3.8 kg, 1.6 kg and 2.5 kg N in cabbage, carrot and onion crops including residues, respective- ly. Yields of 80 t ha-1 for cabbage, 90 t ha-1 for carrot and 35–40 t ha-1 for onion were obtained when the total crop N uptake was 300 kg ha-1, 150 kg ha-1 and 120 kg ha-1, respectively. The variation in yield and N uptake was highest with onion, whereas the yield and N uptake of cab- bage and carrot were fairly uniform each year. In cabbage almost 50% of total N was in crop residues, whereas in carrot 35% and in onion about 25% of the total N was in crop residues. When the results obtained in these experiments are compared to the N fertilizer recommenda- tions applied in Finland, it can be concluded that the recommendations correspond to the actual N demand. However, while carrot was very effi- cient in utilising soil N reserves, it is probable that the N recommendation for carrot could be lowered. The N uptake from non-fertilized soil varied from 29 to 160 kg ha-1, depending on the grow- ing season and the crop. Cabbage and carrot uti- lised soil N efficiently, usually taking up more than 100 kg ha-1 per year from non-fertilized soil. Onion, on the contrary, made relatively poor use of soil N, usually less than 50 kg ha-1 per year from non-fertilized soil. The plant N concentration decreased with dry matter accumulation. With cabbage and onion, a difference in N concentration between ferti- lized and non-fertilized plants was established. As carrot grew equally well with and without N fertilizer, the plant N concentrations differed only slightly. However, it is possible to suggest critical plant N concentrations for all crops as a function of dry matter accumulation. With all crops the rate of N uptake was low in early summer. After one month, N uptake in- 227 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 2 (1999): 157–232. References sue composition of Brussels sprouts. Canadian Jour- nal of Plant Science 56: 543–548. Danielson, R.E. & Sutherland, P.L. 1986. 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SELOSTUS Typen sijoittamisen ja typpilannoitustason vaikutus keräkaalin, porkkanan ja sipulin kuiva-ainetuotantoon, satoon ja typenottoon Tapio Salo Maatalouden tutkimuskeskus rusteella porkkana hyödyntää hyvin maasta vapautu- vaa typpeä, ja lannoitetypen tarve on vähäinen ver- rattuna muihin vastaavia typpimääriä tarvitseviin kas- veihin kuten esimerkiksi sipuliin. Porkkanan typpi- lannoitusta voitaisiinkin todennäköisesti vähentää multavilla hieta- ja turvemailla. Kaalikasvustossa typen sijoittaminen aiheutti kas- vukauden alussa typen puutetta ja heikentynyttä kas- vua. Kasvukauden kuluessa erot vähenivät, mutta en- simmäisenä koevuonna tuoresato jäi sijoitetuissa kä- sittelyissä 6 % pienemmäksi kuin hajalevitetyissä. Typpi sijoitettiin 7,5 cm taimen sivuun ja 7 cm syvyy- teen alapuolelle. Tämä oli ilmeisesti liian kaukana tai- mista, sillä taimien alkukehitys hidastui. Kuukauden kuluttua istutuksesta suurin osa 8 cm syvään pintaker- rokseen hajalevitetystä typestä oli 0–5 cm:n syvyydes- sä, kun taas sijoitettu typpi oli lähinnä 5–10 cm:n sy- vyydessä. Typpilannoitus lisäsi kaalien typpipitoisuuk- sia, kuiva-ainetuotantoa ja typen ottoa. Vuonna 1993 kaalin sato ja kuiva-ainetuotanto lisääntyivät aina suu- rimpaan 250 kg ha-1 typpilannoitustasoon asti. Vuon- na 1994 maan typen mineralisaatio oli niin voimakas- ta, että vain lannoittamattomien kasvustojen kuiva-ai- netuotanto ja typenotto olivat vähäisempiä kuin mui- den käsittelyjen. Kaalin sadonkorjuun jälkeen maan mineraalitypen määrä oli alle 25 kg ha -1. Typpilannoitus ei vaikuttanut porkkanan kuiva- ainetuotantoon ja sadonmuodostukseen. Porkkanan typpipitoisuus sen sijaan lisääntyi typpilannoituksen seurauksena. Suurin typpilannoitustaso lisäsi maan liukoisen typen määrää noin 20 kg ha-1 verrattuna lan- noittamattomaan käsittelyyn. Typen sijoittaminen harjun sisään ei vaikuttanut porkkanan kasvuun tai typenottoon. Ilmeisesti kasvualustan typpipitoisuudet ovat tasaantuneet, kun porkkanan voimakas kasvu alkaa noin kahden kuukauden kuluttua kylvöstä. Kos- ka lannoitusmenetelmien ja -tasojen välillä ei havaittu eroja, koetta jatkettiin vuonna 1994 vain eri lannoi- tustasoilla. Ensimmäisenä koevuonna sipuli kasvoi hyvin. Sekä typen sijoittaminen 5 cm istukkaiden sivulle ja Typpilannoituksen optimoimiseksi tarvitaan tietoa eri satotasojen vaatimista typpimääristä ja typenoton ryt- mistä kasvukauden aikana. Viljoilla typen sijoittami- nen on lähes ainoa levitystapa Suomessa, mutta ty- pen sijoittamisen vaikutusta vihannesten kasvuun ei ole juurikaan tutkittu. Tutkimuksessa verrattiin vuo- sina 1993–1994 typpilannoitustason ja typen hajale- vityksen sekä sijoittamisen vaikutusta maan mineraa- lityppipitoisuuksiin, kaalin (Castello), porkkanan (Narbonne) ja sipulin (Sturon) kuiva-ainetuotantoon, satoon ja typenottoon. Vuonna 1995 koekasvien kas- vua ja typenottoa mitattiin vain lannoittamattomasta ja optimiksi arvioidusta typpilannoitustasosta. Kaali tarvitsi runsaasti typpeä hyvän satotason saavuttamiseksi. Sekä kerät että ulkolehdet sisälsivät typpeä 150 kg ha-1 60 t ha-1 satotasolla, eli kaalikas- vusto otti tällä satotasolla yhteensä 300 kg ha-1 typ- peä. Kaali oli kuitenkin tehokas maasta vapautuvan typen hyödyntäjä, minkä osoittivat typenotot lannoit- tamattomista käsittelyistä, 90 kg ha-1 vuonna 1993 ja peräti 159 kg ha-1 vuonna 1994. Porkkanan satotaso vaihteli 75–100 t ha-1, ja maanpäällisen kasvuston ty- penotto oli 135–178 kg ha-1. Porkkanan naateissa oli noin kolmannes koko maanpäällisen kasvuston sisäl- tämästä typestä. Sipulin typentarve oli suurimmillaan 120 kg ha-1, joka saavutetaan nykyisillä 80–100 kg ha- 1 typpilannoitussuosituksilla. Sipulin ottamasta types- tä neljännes oli naateissa. Sipuli pystyi hyödyntämään maasta vapautuvaa typpeä heikosti, lukuunottamatta vuotta 1994, jolloin lannoittamattoman sipulikasvus- ton typenotto oli 81 kg ha-1. Kasvien typpipitoisuudet pienenivät kuiva-ainesa- don lisääntyessä. Kaalin ja sipulin typpipitoisuudet olivat lannoittamattomissa kasveissa pienemmät kuin lannoitetuissa, ja aineiston perusteella voidaan ar- vioida kasvulle kriittistä typpipitoisuutta. Kaalin ja si- pulin typenotto oli ensimmäisen kuukauden aikana vähäistä, mutta jatkui tämän jälkeen sadonkorjuuseen asti nopeana. Porkkanan nopea typenoton vaihe alkoi sitä vastoin vasta kahden kuukauden kuluttua kylvöstä ja jatkui sadonkorjuuseen asti. Kokeen tulosten pe- 232 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Salo, T. Effects of nitrogen fertilizer on growth of cabbage, carrot and onion 7 cm alapuolelle että runsas typpilannoitus nostivat sadon 45 t ha-1 tasolle. Toisena koevuonna sato jäi alle 35 t ha-1 tasolle, eivätkä käsittelyt vaikuttaneet kas- vuun. Typen parempi saatavuus joko typen sijoitta- misen tai runsaamman lannoituksen ansiosta lisäsi sen sijaan molempina vuosina sipulin typpipitoisuut- ta. Suurempi typpipitoisuus ei kuitenkaan välttämät- tä lisännyt kasvua. Kasvuston typenotto sen sijaan yleensä lisääntyi. Lannoitetypen näennäinen hyväksikäyttö oli koe- vuosina tehokasta. Sipulin lannoitetypen näennäinen hyväksikäyttö parantui ensimmäisenä koevuonna si- joituslannoituksen avulla ja väheni typpilannoituksen lisääntyessä. Toisena koevuonna käsittelyt eivät vai- kuttaneet lannoitetypen hyväksikäyttöön. Hyväksi- käyttö oli toisinaan yli 100 %, koska kohtuullinen lannoitus paransi maasta vapautuvan typen hyödyn- tämistä. Typen sijoittaminen tai hajalevitys eivät kokeen tulosten perusteella vaikuta ratkaisevasti kaalin, pork- kanan ja sipulin sadontuotantoon. Hajalevitys takasi kaalille riittävästi typpeä kasvun alkuvaiheessa. Si- puli sitä vastoin hyötyi sijoittamisesta, kun kasvuolo- suhteet olivat hyvät ja maan ravinnetila huono. Kaik- ki koekasvit todennäköisesti hyötyisivät typen sijoi- tuslannoituksesta kuivissa olosuhteissa, joissa kaste- lua ei ole mahdollista järjestää. Title Preface Title 1 Introduction 2 Material and methods 3 Results 4 Discussion 5 Conclusions References SELOSTUS