Agricultural and Food Science in Finland 423 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. 8 (1999): 423–440. © Agricultural and Food Science in Finland Manuscript received August 1999 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. 8 (1999): 423–440. Paavo Elonen – In Memoriam Responses of yield and N use of spring sown crops to N fertilization, with special reference to the use of plant growth regulators Liisa Pietola Department of Applied Chemistry and Microbiology, PO Box 27, FIN-00014 University of Helsinki, Finland, e-mail: liisa.pietola@helsinki.fi Risto Tanni and Paavo Elonen † Agricultural Research Centre of Finland, Plant Production Research, Crops and Soil, FIN-31600 Jokioinen, Finland (†deceased) The role of plant growth regulators (PGR) in nitrogen (N) fertilization of spring wheat and oats (CCC), fodder barley (etephon/mepiquat) and oilseed rape (etephone) in crop rotation was studied in 1993–1996 on loamy clay soil. Carry over effect of the N fertilization rates (0–180 kg ha-1) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120–150 kg ha-1) was not affected by PGRs. The seed and N yields of oilseed rape were improved most frequently by recommended use of PGR. The yields of oats were increased in 1995–96. Even though PGR effectively shortened the plant height of spring wheat, the grain yield increased only in 1995. N yield of wheat grains was not increased. Response of fodder barley to PGR was insignificant or even negative in 1995. The data suggest that PGRs may decrease some N leaching at high N rates by improving N uptake by grain/seeds, if the yield is improved. The carryover study showed that in soils with no N fertiliza- tion, as well as in soils of high N rates, N uptake was higher than in soils with moderate N fertiliza- tion (60–90 kg ha-1), independent of PGRs. According to soil mineral N contents, N leaching risk is significant (15–35 kg ha-1) only after dry and warm late seasons. After a favourable season of high yields, the N rates did not significantly affect soil mineral N contents. Key words: barley, chlormequat, cereals, etephon, grain quality, mepiquat, oats, oilseed rape, yield, wheat Introduction High nitrogen (N) fertilization inputs and use of plant growth regulators (PGR) could increase yield and N use efficiency of spring sown crops in Scandinavia, where short growing seasons and varied weather conditions are the norm. Ferti- lizer N applied at rates up to 90–100 kg ha-1 on spring cereals appears to increase nitrate leach- mailto:liisa.pietola@helsinki.fi 424 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization ing very little as compared with no N fertiliza- tion (e.g. Bergström and Brink 1986). However, if severe lodging occurs in humid soil conditions, the efficiency of fertilizer N to produce high yield is reduced and the risk of nitrate leaching may increase. Under dry soil conditions nitro- gen uptake is also reduced (Kaila and Elonen 1970). PGR-like chlormequat chloride (CCC ) prevents lodging (Tolbert 1960) and may also decrease drought sensitivity by increasing the root system, as has been shown for wheat on clay soil (Teittinen 1975, Sten and Wünsche 1990). Thus, CCC may increase fertilizer N use under various weather conditions. By increasing yield components of barley (Waddington and Cart- wright 1986, Moes and Stobbe 1991) such PGRs as mepiquat chloride and etephon may also pro- mote nutrient uptake, suggesting higher optimum of N fertilizer rate than without PGR use. PGRs could, thus, minimize the risks of high N appli- cations, which is important because of the envi- ronmental effects of the leaching of excess ni- trate and also for economic reasons. The goal of this paper is to evaluate the joint effects of PGR and N fertilization and how these possibly can be utilized for improving yields and N use efficiency. The main questions addressed are: Does the use of PGRs change the optimum N fertilization rates and N uptake on spring ce- reals and oilseed rape. Even if the crop response to PGRs has been the subject of much research, information on the response of oilseed rape and spring cereals at high N rates is still needed. To achieve optimum N rate for yields, application rates of fertilizer N varying between zero and 180 kg/ha N and PGRs were used according to the recommendations for the best effect for crop yield. To evaluate the environmental effects of N fertilizer use, soil mineral nitrogen was ana- lysed before sowing and after harvest. Finally, we focused on the year-to-year carryover effect of N fertilization and PGRs to predict the long- term effects of different N rates on soil fertility. Material and methods Site and weather conditions of the experimental field The data was collected from a field experiment (82.5 m x 115 m), established at the Agricultur- al Research Centre of Finland in Jokioinen (60° 49’N; 23° 28’E) on loamy clay soil in 1993– 1997. The weather conditions in Jokioinen are given in Table 1. Table 1. Weather conditions at Jokioinen in 1993–1997 and the 30-year average. Number of rainy days (>0.1mm) in parenthesis. Data provided by the Finnish Meteorological Institute. mean air temperature, C° 1993 1994 1995 1996 1997 1961–90 May 13.6 7.8 8.7 8.8 7.7 9.4 June 11.4 12.1 16.7 13.1 16.1 14.3 July 15.6 19.0 15.3 13.9 17.8 15.8 August 12.9 15.1 15.1 17.0 17.8 14.2 September 5.7 10.0 10.3 8.3 10.0 9.4 precipitation, mm (number of rainy days) 1993 1994 1995 1996 1997 1961–90 May 1 (4) 34 (13) 87 (22) 65 (15) 16 35 June 56 (18) 66 (19) 121 (15) 52 (16) 101 47 July 107 (14) 1 (1) 53 (15) 136 (23) 141 80 August 136 (20) 54 (12) 65 (10) 14 (9) 44 83 September 13 (11) 105 (19) 45 (19) 20 (11) 78 65 425 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. 8 (1999): 423–440. Experimental design and treatments The experiment used a split-plot design with four replicates. The effects of PGR were studied in the main plots, which were divided into seven subplots (2.5 m x 12.5 m) according to N fertili- zation rates of 0, 30, 60, 90, 120, 150 and 180 kg ha-1(= N 0 – N 180 ). A similar design was ap- plied to four crops separately on the same field area side by side. The annual cropping sequence in the first cropping block was spring sown wheat (cv. Satu), oats (cv. Yty), barley (cv. Loviisa), and oil seed rape (cv. Kulta). The second adja- cent cropping block was planted first with oil seed rape, the third block with oats, and the fourth one with barley. All plant species were sown once in each block in 1993–1996. Crop stands were treated by PGRs as recommended as follows: Chlormequat chloride (CCC ) was sprayed at the 3–4 leaf stage at the beginning of stem elongation for wheat (375 g ha-1, water vol- ume 200 dm3 ha-1) in 1995 twice because of heavy rain right after the first treatment, and for oats (1125 g ha-1). Cerone (ethephon 480 g dm-3) was sprayed for oil seed rape at the beginning of flowering (240 g ha-1) and Terpal (mepiquat/ ethephon for barley at the 2-node stage (305/155 g ha-1). Rain delayed the treatments in 1995. In 1997, all cropping blocks were sown with bar- ley at fertilizer N rate of 30 kg/ha to control for year-to-year carryover effect. No PGRs were used in 1997. The results were studied statistically by em- ploying ANOVA and Tukey’s tests HSD (Hon- estly Significant Difference) to the significant (P=0.05) differences between group means. Soil For analyses of soil texture (Elonen 1971), or- ganic carbon (Sippola 1982), pH and extracta- ble nutrients (Vuorinen and Mäkitie 1955) of the experimental field, the soil was sampled in Sep- tember 1994 at depths of 0–25 cm and 25–60 cm from N 90 subplots of each replicate and crop- ping block (i.e., 32 samples). Ten subsamples were taken from the topsoil and three subsam- ples from the deeper layers. The experimental field can be characterized as loamy clay soil, low in organic carbon (2–3% at 0–25 cm and below 1% in subsoil) and high in phosphorus content (30–40 mg dm-1) to the soil depth of 25 cm. Oth- er nutrient contents were adequate in subsoil as well, according to the common classification used in Finland. Soil pH varied 6.1–6.5 between blocks in 0–25 cm, 6.6–6.9 in subsoil. Field operations and observations Before sowing, autumn-ploughed soil was tilled by a rotary harrow and fertilized with 250 kg ha-1 of PK fertilizer (30 kg ha-1 P, 35 kg ha-1 K). In 1993–1994, the PK fertilizer contained also 3% N, which was added to the N rates. PK fertilizer was drilled parallel to the sowing direction across the plots. Different N rates were applied in NH 4 NO 3 fertilizer at sowing by combine drilling to a soil depth of 8 cm. Herbicides for spring cereals (tribenuron-methyl 7.5 g ha-1 with water volume 200 dm3 ha-1 in 1993–1994, 1996) and insecti- cides for oilseed rape (deltamethrin 2.5 g ha-1 in 1993 and 7.5 g ha-1 in 1994, lambda-cyhalothrin 3.75 g ha-1 in 1995 and 5.0 g ha-1 in 1996) were used in accordance with general recommenda- tions. In 1995, however, cereals were sprayed with mecoprop/MCPA/clopyralid 800/400/43 g ha-1 on the same day as PGR application. The plant height was measured in the beginning of August at three locations per subplot (1995– 1996), and lodging was observed on each sub- plot before harvesting. At harvest, straw was left in each plot. Yield analyses Grain and seed yields were recorded by harvest- ing 10 m x 2.1 m per subplot. Grain/seed mois- ture was determined gravimetrically from a sub- sample (40 g). The remainder of the subsample (1 kg) was dried and non-grain residues were sort- ed out to determine the purity of yield and other quality components. Pure grain yields were cal- culated by using grain moisture of 15%. For rape, seed moisture of 9% was used. Total N in grains 426 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization and seeds was analysed according to the near-IR reflectance technique (McGuire 1986). The total N was multiplied by 6.25, or for wheat by 5.7 for the protein content. The oil content of rape seeds was measured by the near-IR reflectance tech- nique. The Hagberg falling number was deter- mined by a falling number apparatus (ICC stand- ard 107, ICC 1968). The volume weight of the grain was determined according to the official method of the State Seed Testing Station of Fin- land by weighing four volumes of 250 ml. The weight of 1000 seeds was calculated from the average weight of four counted lots of 100 seeds. Soil mineral N analyses The soil was sampled in each replicate and at five fertilization rates of 0, 90, 120, 150 and 180 kg ha-1 after harvest in 1994 (barley block ) and 1996 (wheat block) and from the same blocks before sowing in 1995 and 1997. The soil was very dry in September 1996. Samples were taken from soil layers of 0–25 cm and 25–60 cm (i.e. 40 samples per sampling time). Twenty subsamples per whole plot were taken from the top layer and ten sub- samples from the deeper layer. The subsamples were bulked and the soil was homogenized. One subsample per plot was taken and stored frozen (–18°C) in plastic bags until analysis. The extract- able ammonium and nitrate N content was ana- lysed from thawed soil samples (100 g) by ex- tracting in 250 ml 2 M KCl for two hours (Esala 1995) and analysing the extract by Skalar Auto- Analyser (Krom 1980, Greenberg et al. 1980). The dry matter content of the soil was determined by drying 40 g moist soil overnight at 105°C. Results and discussion Crop response Lodging, stem shortening and response of crop yield varied among plant species and were highly dependent on weather conditions (Tables 2a–d). Generally, PGRs improved the grain yield at moderate and high N fertilizer rates (Tables 3a– d). Optimum N rate for yields was not, howev- er, changed by using the regulators. For spring wheat and barley, the highest yields and protein content were recorded at N rates of 150 or 180 kg ha-1, in agreement with Esala and Larpes (1986ab). The optimum N rate for yields of oats and oilseed rape varied more between years, and in the rainy season of 1995, the highest yields were obtained at the highest N rate. N yield was determined by dividing the pro- tein content of grain/seed by 6.25 (5.2 for wheat) and multiplying by the grain/seed yield (first cor- rected for grain or seed moisture, 15 or 9%) from Tables 3a–d. N yield was mostly increased by PGR use, if affected (P=0.05). As N yield in ears represents 65% of N uptake by cereals (Hans- son et al. 1987), differences over 10 kg ha-1 were remarkable. These effects were, however, infre- quently recorded. Wheat The yield of spring wheat was increased by CCC at N fertilisation rates over 90 kg ha-1 in 1995– 1996. In 1995 when June was very rainy the yield increase was even 1000 kg/ha, and N fertilization could be reduced by 30 kg ha-1 to achieve the same yield. No statistically significant increase was, however, found in 1993–1994, when the temper- atures in June were below average (Tables 1, 3a). In addition, severe drought damage was recorded in 1994 in both treatments. In agreement with Steen and Wünsche (1990), CCC efficiently short- ened stem (Table 2a). Lodging occurred only in 1993 after heavy rains in July (107 mm), and was effectively reduced by PGR use. Grain moisture at harvest was increased by PGR in 1995–1996, suggesting the delaying effect of CCC on matu- ration processes reported by Mukula et. al (1966). The grain quality was slightly weakened by CCC in 1995–1996, as protein content and 1000 grain weights were lowered at most N rates (Table 3a). Because of the decrease in N content of grains, N yield was significantly increased by PGRs only in 1994, at N rate of 97 kg ha-1, i.e., 11 kg ha-1. 427 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. 8 (1999): 423–440. Oats CCC increased oats yield by 400–1000 kg ha-1 at high N fertilization rates in 1995–96, but had no influence on crop yield in the dry year of 1994 (Tables 1, 3b). The yield increase was related to stem shortening (Table 2b). In 1993, CCC re- duced lodging, but yield was improved only at the N rate of 157 kg ha-1. Grain moisture at har- vest were increased, and grain weights were gen- erally decreased by PGR. Significant increases in N yield by PGR use were recorded in 1995 at N rates of 150 and 180 kg ha-1, (14 and 12 kg ha-1 , respectively) and in 1996 at N rates of 90 and 180 kg ha-1, (5 and 13 kg ha-1, respectively). Barley The effect of etephon/mepiquat on yield was in- consistent, influenced to a large extent by the weather conditions, as was reported also by e.g. Erviö et al. (1995). In 1993 the effect was insig- nificant at all N rates even if lodging occurred (Tables 2c, 3c). In the dry year of 1994 PGR in- creased yield by 300 kg/ha at high N rates, even if no lodging was recorded. After the heavy rains Table 2a. Effect of N fertilization on plant height (1995–96), lodging (no lodging in 1994–1996), and grain moisture at harvest (1993–1996) of spring wheat, without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Plant height, cm 1995: PGR- 63 80 85 90 92 95 94 86 7 PGR+ 42 49 52 57 62 66 67 57 “ HSD 0.05 2 1996 PGR- 81 88 90 91 89 88 86 88 4 PGR+ 58 67 71 74 76 75 75 71 “ HSD 0.05 2 Lodging, % 1993: PGR- 0 0 0 0 0 16 32 7 9 PGR+ 0 0 0 0 0 2 9 2 “ HSD 0.05 3 1994–1996: no lodging Grain moisture at harvest, % 1993: PGR- 29.7 24.0 24.2 26.3 28.7 30.1 31.7 27.8 2.9 PGR+ 30.7 24.4 24.2 25.5 27.4 27.4 29.0 26.9 “ HSD 0.05 n.s.2 1994 PGR- 16.0 16.7 16.8 18.4 19.3 20.7 20.5 18.4 2.4 PGR+ 17.3 17.7 17.1 19.4 19.7 21.8 20.9 19.1 “ HSD 0.05 n.s. 1995 PGR- 28.8 27.8 27.5 28.1 29.0 30.6 29.6 28.8 2.0 PGR+ 30.1 29.3 29.0 28.9 30.2 31.0 30.4 29.8 “ HSD 0.05 0.9 1996 PGR- 22.0 22.1 25.3 27.8 29.9 31.4 32.5 27.3 1.8 PGR+ 24.6 23.1 26.1 28.2 30.2 32.0 33.2 28.2 “ HSD 0.05 0.9 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 428 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization in early season of 1995, ethephon/mepiquat even lowered the yield, although the PGR also short- ened the stem length. In 1996, when PGR effec- tively reduced lodging at high N rates, positive response (400–500 kg/ha) occurred at N rates of 90 and 120 kg/ha. At higher N rates no yield in- crease was found, even if etephon treatments have been reported to increase barley yields when they reduce lodging (Dahnous et al. 1982). Both positive and negative grain yield respons- es to etephon were reported also earlier (Dah- nous et al. 1982, Simmons et al. 1988). Grain moisture at harvest was higher in treated plots, indicating the delaying effect. Grain quality was little affected (Tables 2c, 3c). PGR use showed negative response to N yields (3 to 12 kg ha-1) at N rates of 30–120 kg ha-1 in 1995, with the grain yield decrease. PGR use increased N yields only at the N rate of 120 kg ha-1, in 1994 (i.e., 3 kg ha-1 ) and in 1996 (i.e., 10 kg ha-1). Table 2b. Effect of N fertilization on plant height (1995–96), lodging (no lodging in 1994–1995), and grain moisture at harvest (1993–1996) of oats, without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Plant height, cm 1995: PGR- 58 70 80 90 97 108 109 87 13 PGR+ 56 70 75 84 86 97 100 81 “ HSD 0.05 5 1996 PGR- 69 106 121 128 134 133 129 117 10 PGR+ 64 93 101 108 113 116 117 102 “ SD 0.05 2 Lodging, % 1993: PGR- 0 0 2 19 46 52 65 26 22 PGR+ 0 0 2 5 20 30 42 14 “ HSD 0.05 11 1996: PGR- 0 0 0 0 0 2 14 2 n.s.1 PGR+ 0 0 0 0 0 0 0 0 “ HSD 0.05 n.s. Seed moisture at harvest, % 1993: PGR- 21.7 20.3 20.7 23.3 23.1 25.6 25.7 22.9 2.7 PGR+ 22.1 21.0 21.5 22.7 24.4 25.4 26.6 23.4 “ HSD 0.05 n.s. 1994 PGR- 25.8 20.3 19.0 19.4 20.0 20.0 20.2 20.7 2.1 PGR+ 27.0 21.9 20.7 20.9 21.2 20.9 20.8 21.9 “ HSD 0.05 1.3 1995 PGR- 25.3 22.8 20.9 20.6 19.7 19.2 18.4 21.0 3.5 PGR+ 26.5 24.3 21.7 22.4 21.3 21.0 19.4 22.4 “ HSD 0.05 0.9 1996 PGR- 28.2 22.0 19.5 18.7 17.5 16.7 17.2 20.0 1.7 PGR+ 30.0 24.8 22.2 20.7 19.1 17.6 17.1 21.7 “ HSD 0.05 0.9 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 429 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. 8 (1999): 423–440. Oilseed rape Oilseed rape yields were generally improved by ethephone in both dry and wet seasons (Tables 1, 3d). The yield increase was not related to shortened stem or prevented lodging as strongly as was observed for cereals (Table 2d), but rath- er because of increased branching. This was ob- vious in 1994, as after a rainless July the seed yield was improved 250 kg ha-1 by PGR at N rates of 120 and 150 kg ha-1. In 1993 and 1996 yield increases also reached 250 kg ha-1at higher N rates. After the wet early season of 1995 the yield response to PGR was on average only slightly less than in other years. On the other hand, clear- ly positive effects of PGR over the whole N range were shown this year. Seed weight increased in 1994–1995, but generally seed quality was very little affected by ethephone. Positive response of PGR use in N fertiliza- tion was found each year: In 1993–1994, the N Table 2c. Effect of N fertilization on plant height (1995–96), lodging, and grain moisture at harvest (1993–1996) of fodder barley, without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Plant height, cm 1995: PGR- 36 40 48 57 62 69 74 55 7 PGR+ 30 33 36 42 47 54 56 43 “ HSD 0.05 6 1996 PGR- 45 70 88 95 89 84 83 79 16 PGR+ 43 62 82 92 94 91 81 78 “ HSD 0.05 n.s.1 Lodging, % 1993: PGR- 0 0 6 10 13 23 23 11 14 PGR+ 0 0 3 5 9 13 11 6 “ HSD 0.05 2 1994–1995: no lodging 1996: PGR- 0 0 0 5 49 92 96 35 26 PGR+ 0 0 0 0 6 49 71 18 “ HSD 0.05 10 Seed moisture at harvest, % 1993: PGR- 30.8 28.7 28.0 28.5 29.3 31.7 30.0 29.5 2.8 PGR+ 33.3 30.7 29.4 30.1 30.7 31.3 30.5 30.8 “ HSD 0.05 0.8 1994 PGR- 28.3 25.5 25.2 25.5 26.0 26.7 27.2 26.3 2.0 PGR+ 29.5 28.0 28.1 28.1 28.5 28.8 30.1 28.7 “ HSD 0.05 0.4 1995 PGR- 24.3 17.0 16.0 15.9 16.6 17.0 18.5 17.9 2.8 PGR+ 25.6 18.9 21.3 20.0 19.9 18.8 19.2 20.5 “ HSD 0.05 0.9 1996 PGR- 23.5 15.8 15.2 15.6 16.5 18.8 19.9 17.9 4.5 PGR+ 23.8 17.2 16.8 16.7 18.1 20.0 21.5 19.2 “ HSD 0.05 n.s. 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 430 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization Table 2d. Effect of N fertilization on plant height (1995–96), lodging (no lodging in 1994–1995), and seed moisture at harvest (1993–1996) of oilseed rape, without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Plant height, cm 1995: PGR- 42 48 58 62 68 73 75 61 9 PGR+ 43 46 56 60 65 70 72 59 “ HSD 0.05 2 1996 PGR- 79 97 106 113 118 120 122 108 13 PGR+ 70 91 96 105 111 112 118 100 “ HSD 0.05 3 Lodging, % 1993: n.d.2 1996: PGR- 0 0 5 9 23 40 40 17 14 PGR+ 0 0 2 5 7 19 21 8 “ HSD 0.05 9 Seed moisture at harvest, % 1993: PGR- 15.2 13.3 13.9 14.4 15.0 15.1 16.9 14.8 2.3 PGR+ 14.5 14.2 13.8 15.2 16.1 16.3 16.7 15.2 “ HSD 0.05 n.s.3 1994 PGR- 14.0 14.1 14.9 15.1 15.4 15.4 16.1 15.0 2.0 PGR+ 14.2 14.7 15.2 15.3 15.6 16.1 16.3 15.4 “ HSD 0.05 0.2 1995 PGR- 14.5 13.9 13.4 13.6 13.6 14.0 14.3 13.9 1.4 PGR+ 14.7 14.1 13.5 13.6 14.0 14.5 14.9 14.2 “ HSD 0.05 0.3 1996 PGR- 9.5 9.5 10.0 10.9 12.8 14.2 15.8 11.8 2.2 PGR+ 9.9 9.6 10.1 10.9 12.6 13.7 14.6 11.6 “ HSD 0.05 n.s. 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.d.= not determined 3 n.s.= not significant Table 3a. Effect of N fertilization on grain yield and quality of spring wheat (1993–96), without and with the use of plant growth regulators (PGR-/PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Grain yield, kg ha-1 1993: PGR- 2250 3170 3860 4240 4650 4900 5000 4010 740 PGR+ 2070 3040 3880 4320 4650 4540 5200 4000 “ HSD 0.05 n.s.2 Table 3a. continues 431 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. 8 (1999): 423–440. N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 1994 PGR- 2710 3550 3730 3730 3760 4100 3980 3650 980 PGR+ 2820 3780 3810 4130 3960 4210 4120 3830 “ HSD 0.05 n.s. 1995 PGR- 2190 3150 3840 4390 5050 5740 5180 4220 1160 PGR+ 2470 3460 4230 4800 5910 6400 6190 4780 “ HSD 0.05 530 1996 PGR- 2480 3510 4300 4930 5280 5690 5880 4580 520 PGR+ 2450 3500 4470 5210 5620 6050 6110 4770 “ HSD 0.05 70 Protein content, % 1993: PGR- 11.1 11.1 12.1 13.3 14.9 15.7 16.2 13.5 1.1 PGR+ 11.1 10.7 11.4 13.0 14.4 15.4 16.0 13.1 “ HSD 0.05 n.s. 1994 PGR- 11.2 12.1 14.1 15.8 17.3 17.9 18.6 15.3 2.3 PGR+ 10.9 12.0 13.8 15.6 17.4 17.5 18.3 15.0 “ HSD 0.05 n.s. 1995 PGR- 10.9 10.8 11.2 11.8 13.0 14.6 15.5 12.6 0.9 PGR+ 9.7 9.6 10.0 10.4 11.6 12.8 13.9 11.2 “ HSD 0.05 0.3 1996 PGR- 10.0 9.8 10.6 11.4 12.0 12.5 13.3 11.4 0.8 PGR+ 9.7 9.6 10.1 10.6 11.3 12.2 12.9 10.9 “ HSD 0.05 0.1 Falling number 1993: PGR- 235 245 228 235 224 220 215 229 n.s. PGR+ 246 237 234 238 243 232 230 237 “ HSD 0.05 n.s. 1994 PGR- 261 244 247 243 236 231 228 241 27 PGR+ 265 258 259 251 230 223 229 245 “ HSD 0.05 n.s. 1995 PGR- 210 232 249 267 290 262 309 260 55 PGR+ 215 202 218 206 236 263 309 235 “ HSD 0.05 23 1996 PGR- 320 293 291 292 295 298 297 298 24 PGR+ 300 293 285 300 300 304 301 298 “ HSD 0.05 n.s. 1000 grain weight, g 1993: PGR- 31.2 32.9 33.7 34.0 34.7 34.9 35.1 34.7 1.6 PGR+ 29.2 30.4 31.0 32.3 33.3 34.2 34.1 32.1 “ HSD 0.05 0.6 1994 PGR- 32.4 33.6 31.8 32.4 31.1 31.8 31.7 32.1 2.2 PGR+ 32.2 32.8 31.2 31.4 31.2 32.4 31.2 31.8 “ HSD 0.05 n.s. 1995 PGR- 33.7 36.5 36.5 36.4 37.1 37.5 35.9 36.2 2.2 PGR+ 31.7 33.5 34.2 34.2 35.2 35.5 34.6 34.1 “ HSD 0.05 1.0 1996 PGR- 33.0 34.3 35.0 35.2 35.4 35.1 34.9 34.7 1.6 PGR+ 31.1 32.0 32.7 32.9 32.6 32.0 31.4 32.1 “ HSD 0.05 n.s. 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 432 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization yield increase was 5–8 kg ha-1 at N rates of 90– 150 kg ha-1. In 1995, the increase was found at N rates of 60, 90, and 180 kg ha-1 (4, 6 and 11 kg ha-1, respectively ). In 1996, the increase was statis- tically significant only at N rate of 150 kg ha-1, being 7 kg ha-1. Table 3b. Effect of N fertilization on grain yield and quality of oats (1993–96), without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Yield, kg ha-1 1993: PGR- 2940 4420 5410 5880 6150 6120 6390 5330 640 PGR+ 2950 4320 5430 5900 6320 6550 6460 5420 “ HSD 0.05 n.s.2 1994 PGR- 2850 3950 4470 4710 4870 4890 4830 4370 510 PGR+ 2800 3890 4450 4780 4850 4890 4960 4380 “ HSD 0.05 n.s. 1995 PGR- 2230 3300 3950 4810 5550 6300 6670 4690 1140 PGR+ 2580 3740 4380 5320 6050 6910 7320 5190 “ HSD 0.05 n.s. 1996 PGR- 2510 3900 4720 5040 5190 5110 4420 4410 570 PGR+ 2600 4030 5030 5600 5710 5540 5500 4860 “ HSD 0.05 430 Protein content, % 1993: PGR- 9.3 9.3 10.3 11.2 12.2 12.9 13.3 11.2 0.9 PGR+ 9.3 9.3 10.3 11.1 12.1 12.6 13.2 11.1 “ HSD 0.05 n.s. 1994 PGR- 9.2 10.2 11.6 13.4 15.4 15.8 16.5 13.2 1.5 PGR+ 9.6 9.9 11.7 13.4 14.8 15.6 16.5 13.1 “ HSD 0.05 n.s. 1995 PGR- 9.4 8.9 9.0 9.2 10.4 11.7 12.9 10.2 1.7 PGR+ 9.3 8.8 8.8 9.6 10.7 12.2 13.0 10.3 “ HSD 0.05 n.s. 1996 PGR- 9.1 9.1 9.5 10.5 11.3 12.4 12.7 10.6 0.8 PGR+ 9.1 9.0 9.4 10.0 10.3 11.5 11.9 10.2 “ HSD 0.05 0.3 1000 grain weight, g 1993: PGR- 33.2 32.5 33.3 32.8 33.4 33.6 32.5 33.0 1.6. PGR+ 31.8 31.3 31.9 32.3 33.0 32.8 33.0 32.3 “ HSD 0.05 0.4 1994 PGR- 27.1 26.0 26.2 26.6 27.8 28.3 29.2 27.3 2.0 PGR+ 25.9 24.9 24.6 24.9 26.6 26.6 27.6 25.9 “ HSD 0.05 0.7 1995 PGR- 31.0 31.7 31.7 32.6 32.7 34.4 34.2 32.6 2.1 PGR+ 30.6 31.6 31.0 32.7 32.7 33.1 33.4 32.1 “ HSD 0.05 n.s. 1996 PGR- 32.8 32.9 34.2 33.9 33.2 32.8 32.2 33.2 1.9 PGR+ 32.1 33.6 33.5 34.0 32.8 31.0 30.4 32.5 “ HSD 0.05 0.6 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 433 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. 8 (1999): 423–440. Residual effect Carryover effect of N fertilization rates According to barley yields harvested in 1997, the growth was better in plots with high N rates than in those with low rates (Table 4). However, the yields in N 0 -plots compared well with the growth in N 120 –N 180 plots. These data indicate that soil N reserves are not especially low after cultivation without N fertilizer. Measurements Table 3c. Effect of N fertilization on grain yield and quality of fodder barley (1993–96), without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Yield, kg ha-1 1993: PGR- 2980 4410 5280 5500 5850 6100 6040 5170 1060 PGR+ 3180 4430 5340 5580 6170 6390 6220 5330 “ HSD 0.05 n.s.1 1994 PGR- 2520 3950 5010 5540 5660 5840 5860 4910 440 PGR+ 2610 4070 5060 5600 5940 6140 6120 5080 “ HSD 0.05 180 1995 PGR- 1160 1570 2240 2770 3700 4190 4670 2900 900 PGR+ 1040 1330 1520 1980 2960 3480 4650 2420 “ HSD 0.05 n.s. 1996 PGR- 2040 3360 4310 5320 5940 6540 6920 4920 1150 PGR+ 2220 3550 4630 5860 6360 6430 6880 5130 “ HSD 0.05 n.s. Protein content, % 1993: PGR- 9.3 9.4 10.5 10.9 12.4 12.6 13.8 11.3 1.1 PGR+ 9.4 9.4 9.8 10.5 11.9 12.4 13.4 11.0 “ HSD 0.05 n.s. 1994 PGR- 8.5 8.8 9.9 11.0 12.2 13.3 14.2 11.1 0.7 PGR+ 8.3 8.5 9.5 10.9 12.0 12.8 13.6 10.8 “ HSD 0.05 0.1 1995 PGR- 10.2 9.2 8.6 8.8 9.8 10.2 11.5 9.7 1.3 PGR+ 10.1 9.1 9.0 8.8 9.5 9.8 10.7 9.6 “ HSD 0.05 n.s. 1996 PGR- 9.6 8.1 8.8 9.0 9.7 11.4 12.0 9.8 1.7 PGR+ 9.5 8.7 8.2 9.0 10.1 11.1 11.8 9.8 “ HSD 0.05 n.s. 1000 grain weight, g 1993: PGR- 32.2 33.5 33.1 33.2 33.0 32.9 33.1 33.0 n.s. PGR+ 31.8 32.5 33.8 34.0 34.4 34.3 33.5 33.5 “ HSD 0.05 n.s. 1994 PGR- 32.9 35.9 37.3 36.9 36.6 36.9 35.9 36.1 2.1 PGR+ 32.3 35.6 36.7 36.5 35.8 36.7 36.0 35.7 “ HSD 0.05 n.s. 1995 PGR- 31.7 33.2 36.0 36.9 39.4 40.1 41.3 36.9 2.0 PGR+ 30.5 31.0 32.3 34.5 37.2 37.3 39.0 34.5 “ HSD 0.05 1.9 1996 PGR- 31.3 32.4 33.4 33.9 32.6 32.5 33.0 32.7 2.8 PGR+ 31.3 33.1 33.8 33.6 32.7 31.5 32.3 32.6 “ HSD 0.05 n.s. 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 434 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization Table 3d. Effect of N fertilization on seed yield and quality of oilseed rape (1993–96), without and with plant growth regulators (=PGR- / PGR+). HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Yield, kg ha-1 1993 PGR- 1450 1740 1900 2170 2180 2220 2250 1990 540 PGR+ 1450 1910 2170 2370 2420 2420 2410 2170 “ HSD 0.05 140 1994 PGR- 970 1430 1520 1610 1760 1950 1660 1560 650 PGR+ 1040 1480 1710 1810 2020 2170 1990 1750 “ HSD 0.05 240 1995 PGR- 500 530 810 1170 1680 2180 2490 1340 370 PGR+ 560 680 990 1380 1750 2290 2750 1490 “ HSD 0.05 80 1996 PGR- 930 1310 1630 1950 2000 2060 2070 1710 340 PGR+ 1080 1370 1770 2090 2220 2310 2280 1870 “ HSD 0.05 n.s.2 Protein content, % 1993: PGR- 18.8 18.1 18.5 19.5 20.8 22.3 23.1 20.1 1.9 PGR+ 17.8 17.9 18.4 19.8 21.0 21.9 22.6 19.9 “ HSD 0.05 n.s. 1994 PGR- 18.9 19.8 22.2 23.5 25.3 25.6 27.0 23.2 2.5 PGR+ 19.1 20.3 22.5 23.1 24.2 25.6 26.4 23.0 “ HSD 0.05 n.s. 1995 PGR- 16.7 16.5 15.9 15.9 16.7 18.5 21.1 17.3 2.0 PGR+ 16.5 16.3 16.0 16.7 17.2 19.5 21.9 17.7 “ HSD 0.05 n.s. 1996 PGR- 17.5 16.5 17.4 18.2 21.3 22.3 23.4 19.5 1.3 PGR+ 17.9 16.8 16.7 17.9 20.4 22.0 23.0 19.2 “ HSD 0.05 0.3 Oil content, % 1993: PGR- 48.0 48.2 47.6 46.8 45.5 43.9 43.8 46.2 2.2 PGR+ 48.6 48.5 48.1 46.8 45.3 44.1 44.0 46.5 “ HSD 0.05 n.s. 1994 PGR- 49.2 47.9 45.6 45.8 44.5 43.8 42.4 45.6 2.2 PGR+ 48.6 48.9 46.7 46.1 45.1 43.8 42.6 46.0 “ HSD 0.05 n.s. 1995 PGR- 51.2 51.5 51.7 51.3 50.1 48.8 46.6 50.1 2.2 PGR+ 51.6 51.7 51.6 50.4 49.0 47.7 45.5 49.6 “ HSD 0.05 0.2 1996 PGR- 50.2 51.5 50.6 49.5 46.4 45.5 43.7 48.2 1.9 PGR+ 50.6 51.1 50.8 50.1 46.3 45.4 44.5 48.4 “ HSD 0.05 n.s. 1000 seed weight, g 1993: PGR- 2.28 2.24 2.18 2.19 2.16 2.20 2.20 2.21 0.10 PGR+ 2.26 2.20 2.23 2.17 2.19 2.17 2.22 2.21 “ HSD 0.05 n.s. 1994 PGR- 1.98 2.06 2.10 2.14 2.23 2.32 2.34 2.16 0.15 PGR+ 2.06 2.10 2.19 2.24 2.29 2.39 2.42 2.24 “ HSD 0.05 n.s. Table 3d. continues 435 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. 8 (1999): 423–440. N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 1995 PGR- 2.41 2.42 2.37 2.31 2.37 2.41 2.45 2.39 0.23 PGR+ 2.45 2.47 2.41 2.38 2.41 2.48 2.58 2.45 “ HSD 0.05 0.03 1996 PGR- 2.55 2.46 2.41 2.35 2.34 2.34 2.28 2.39 0.13 PGR+ 2.58 2.51 2.47 2.38 2.37 2.34 2.35 2.43 “ HSD 0.05 0.03 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant Table 4. Effect of N fertilization rates and PGR treatment of previous years (1993–1996) on the yield and grain protein of fodder barley in 1997 in each cropping block, at 30 kg/ha N rate. HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 Yield, kg ha-1 Block 1 PGR- 3550 3320 3150 3040 3290 3470 3490 3330 450 PGR+ 3410 3220 3130 3040 3200 3450 3440 3270 “ HSD 0.05 n.s.2 Block 2 PGR- 3670 3400 2980 3070 3190 3540 3610 3350 540 PGR+ 3480 3360 3040 3160 3300 3760 3860 3420 “ HSD 0.05 n.s. Block 3 PGR- 3100 2980 3040 3020 3070 3290 3700 3170 570 PGR+ 3040 2930 2930 2980 2900 3170 3720 3100 “ HSD 0.05 n.s. Block 4 PGR- 3230 3250 3130 3080 3420 4120 4200 3490 740 PGR+ 3260 3190 3080 2970 3300 3820 3930 3360 “ HSD 0.05 n.s. Protein content, % Block 1 PGR- 9.1 9.0 8.9 9.0 9.5 9.5 9.8 9.3 0.7 PGR+ 9.2 8.9 8.8 8.9 9.2 9.0 9.4 9.1 “ HSD 0.05 n.s. Block 2 PGR- 9.4 9.6 9.4 9.3 9.4 9.5 9.5 9.4 n.s. PGR+ 9.4 9.6 9.4 9.4 9.4 10.0 10.0 9.6 “ HSD 0.05 n.s. Block 3 PGR- 9.0 8.7 8.9 8.7 8.8 8.8 9.3 8.9 0.5 PGR+ 8.9 8.7 8.7 8.7 8.5 8.6 9.1 8.7 “ HSD 0.05 n.s. Block 4 PGR- 9.0 9.2 9.2 9.0 9.2 9.9 10.0 9.4 0.9 PGR+ 8.9 9.2 9.2 8.9 9.2 9.5 9.7 9.2 “ HSD 0.05 n.s. 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 436 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization of grain protein contents show, however, that nitrogen uptake into grains was the highest in soils with high N rates. The average N yield of grains (kg ha-1) in four cropping blocks was affected by previous N fer- tilization (Table 5). The N yields in grains indi- cate that PGRs had no significant effect on the residual mineral nitrogen. The N yields were, however, better in the non N fertilized soils than in the soils of moderate rates (N 60 and N 90 ). Ob- viously, this was a result of accumulation of re- sidual N in non-fertilized plots which had pro- duced low grain and N yields. In soils of moder- ate N fertilizer rates and better N yields, more nitrogen had been used in previous years and less N was available in 1997. At high N rates crops did not use all available N, which is shown by the high N yields in the carryover study. As a long-term effect, this suggests more N losses from fields of both non- and over-optimal N sup- ply than from fertilization at moderate N rates. Leachable soil mineral nitrogen Net mineralization during a growing season changes crucially between years, averaging 55 kg ha-1 in clay soils in southern Finland that are low in organic matter (Lindén et al. 1992a, Es- ala 1994). Also leaching of nitrate by heavy rains may be substantial after the mineraliza- tion of organic nitrogen in warm conditions (Turtola and Jaakkola 1985). Our data show the impact of weather conditions on soil mineral nitrogen after harvest (Figures 1–2). In Septem- ber 1994, after a very dry and warm July and August, soil NO 3 - and NH 4 - N reserves were much higher in plots of high N fertilization rates than in plots of low N fertilization. This obvi- ously indicates the inefficient use of fertilizer N in July. Based on measurement in early spring 1995, much more N (10–20 kg ha-1) may have been leached during autumn rains and winter, or immobilized, from plots with N fertilization over 120 kg ha-1. At lower N rates, increasing N fertilization increased leaching risk very lit- tle, as was found also by Jaakkola (1984) and Lindén et al. (1992b). The N data in mg kg-1 can be estimated N kg ha-1 in plough layer (0– 25 cm) by multiplying the values by 2.3 (as- suming that the dry bulk density of soil is 1.1). Some of the possibly leached nitrogen (5 kg ha-1) was found from the subsoil in May 1995, but was no longer useful for early plant growth (Esala and Leppänen 1998). After the rainy and productive season of 1996 not much mineral ni- trogen was found (Fig. 2). The risk of N leach- ing during winter 1996–1997 did not remarka- bly differ between N fertilizer rates, as soil min- eral N content in May 1997 was rather similar between plots, in agreement with Sippola and Yläranta (1985). These data show that after a favourable growing season with high yields, the N leaching risk is low even at very high N fer- tilizer rates. However, after a dry and warm July and August, and a rainy September the N leach- ing risk is obvious (10–35 kg ha-1) at N fertiliz- er rates of over 100 kg ha-1. Table 5. Effect of N fertilization rates and PGR treatment of previous years (1993–1996) on the N yield of fodder barley in 1997, at 30 kg ha-1N rate. HSD 0.05 indicates Tukey’s honestly significant difference (P=0.05). N rate1, kg ha-1 0 30 60 90 120 150 180 mean HSD 0.05 N yield, kg ha-1 PGR- 46.1 44.0 41.8 41.5 44.1 49.1 51.0 45.4 4.6 PGR+ 44.9 43.2 41.4 41.3 43.1 48.2 50.8 44.7 “ HSD 0.05 n.s.1 1 In 1993–1994, the PK fertilizer contained also 3% N, adding 7 kg ha-1 to the N rates 2 n.s.= not significant 437 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. 8 (1999): 423–440. Fig. 1. Response of soil mineral nitrogen to N fertilization after harvest of barley (above) and be- fore the following growing season (below). HSD 0.05 for NO 3 -N in September in top layer 2.2 and in sublayer 1.1, in May 0.5 and 1.4, respectively. HSD 0.05 for NH 4 -N in September in top layer 0.5 and in sublayer not significant (n.s.), in May 0.3 and n.s., respectively. Conclusions Use of PGRs did not change the optimum N fer- tilization rate for yield formation, even if the use of PGRs improved the crop and N yield in rainy seasons in particular. Application of PGR result- ed in higher seed and N yield of oilseed rape even in dry years. Grain quality was slightly weakened by PGRs, if affected at all. The data suggest that PGRs, if applied as recommened, increase N uptake and for decrease the leaching risk for oilseed rape, and for oats in rainy summers. N use by wheat and barley were significantly decreased by delayed PGR use after the rainy early season of 1995. Use of high nitrogen fertilization rates leads to a risk of soil mineral N leaching after har- vest, but only after a dry and warm July–August. To minimize the N leaching risk, N fertilization 438 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 Pietola, L. et al. Responses of yield and N use of crops to N fertilization Fig. 2. Response of soil mineral nitrogen to N fertilization after harvest of spring wheat (above) and before the following growing season (below). HSD 0.05 for NO 3 - N in September in top layer 0.7 and in sublayer 0.3, in May 0.3 and 0.3, respectively. HSD 0.05 for NH 4 - N not significant. over 90–100 kg ha-1 should be avoided for spring cereals, at least in the conditions described here. This agrees with the agro-environmental pro- gram of Ministry of Agriculture and Forestry in Finland. However, the data also indicate that soil N reserves are not especially low after cultiva- tion without N fertilizer that has caused low yield levels. Acknowledgements. The authors wish to thank Kerttu Hämäläinen, Pekka Kivistö and Leena Mäkäräinen for plant and soil analyses and Drs. Martti Esala and Tapio Salo for valuable suggestions and constructive criticism on the man- uscript. Contributions of authors: Pietola, L. Data analysis and manuscript, Tanni, R. Field experiments and data record- ing, Elonen P. 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Responses of yield and N use of crops to N fertilization SELOSTUS Typpilannoituksen ja kasvunsääteiden vaikutukset kevätviljojen ja rypsin satoon sekä typen käyttöön Liisa Pietola, Risto Tanni ja Paavo Elonen Helsingin yliopisto ja Maatalouden tutkimuskeskus Voidaanko typpilannoituksen hyötyä parantaa kasvun- sääteiden avulla vai lisäävätkö kasvunsääteet typen käyttöä tuottamatta lisää satoa? Näitä kysymyksiä sekä typpilannoituksen jälkivaikutuksia tutkittiin edesmen- neen professori Paavo Elosen hietasavimaalle perus- tamassa kenttäkokeessa vuosina 1993–1997. Koekas- veja viljeltiin neljässä vierekkäisessä lohkossa vilje- lykierrossa, seitsemällä eri typpitasolla (0–180 kg/ha). Suurin sato saatiin typpilannoituksen tasolla 120– 150 kg/ha. Vuoden 1993 suositusten mukaiset kas- vunsäädekäsittelyt, jotka vuonna 1995 tosin viiväs- tyivät sateiden vuoksi, eivät vaikuttaneet tähän opti- mitasoon. Kasvunsääteet kuitenkin saattoivat lisätä jyvä- ja typpisatoja varsinkin suurilla typpilannoitus- määrillä, tehostaen siten typen ottoa. Lisäystä ei kui- tenkaan havaittu kaikilla viljelykasveilla. Ainoastaan rypsi (cv. Kulta) hyötyi kasvunsäädekäsittelystä (Ce- rone) kaikkina koevuosina, jopa kuivana kesänä 1994. Kasvunsääde (CCC) lisäsi myös kauran (cv. Yty) jyvä- ja typpisatoja, mutta vain sateisina kesi- nä, jolloin lakoutuminen selvästi väheni käsittelyn myötä. Kevätvehnällä (cv. Satu) vuosittainen vaihte- lu oli suuri, ja kasvunsääteen (CCC) edullinen vai- kutus jyväsatoon oli merkittävä vain vuonna 1995, jolloin alkukesä oli hyvin sateinen ja loppukesä kui- va. Tällöin kasvunsääde lyhensi selvästi vehnän kor- ren pituutta (30 cm). Typpisadot eivät kuitenkaan ko- honneet, koska kasvunsääde laski jyvän typpipitoi- suutta. Kasvunsääteen (Terpal) vaikutus rehuohran (cv. Loviisa) jyvä- ja typpisatoihin vaihteli suuresti eri vuosina. Typpisadot jopa laskivat merkitsevästi viivästyneen käsittelyn vaikutuksesta vuonna 1995. Kasvunsääteet lisäsivät yleensä puintikosteutta, mutta muuten jyvän laatu heikkeni vain vähän tai käsitte- lyillä ei ollut vaikusta valkuaispitoisuuksiin ja 1000 jyvän painoon, paitsi vehnällä vuonna 1995. Rypsin 1000 siemenen paino kasvoi vuosina 1994–95 kas- vunsääteen ansiosta. Typpilannoituksen ja kasvunsäädekäsittelyjen jälkivaikutusta tutkittiin vuonna 1997, jolloin koko koealueelle kylvettiin rehuohraa. Typpilannoitusta- so oli kaikissa koeruuduissa 30 kg/ha. Tulosten mu- kaan paras sato saatiin koealueilta, jotka lannoitet- tiin aiempina vuosina suurimmalla typpimäärällä. Myös typpisato oli näissä ruuduissa suurin, runsaat 50 kg/ha. Koevuosien lannoitustasoilla 60–90 kg/ha typpisato oli tätä 10 kg/ha pienempi. Ilman typpi- lannoitusta viljellyissä ruuduissa ero oli vain 5 kg/ha. Pienempi ero osoitti, että maahan kertyy typpeä, mikäli typpilannoitusta ei käytetä lainkaan. Tällöin heikoksi jäävä kasvusto ei todennäköisesti pysty tyhjentämään maan typpivaroja yhtä tehokkaasti kuin kohtuullisesti lannoitetut kasvustot. Vastaavasti korkeilla typpilannoitustasoilla (150–180 kg/ha) kasvi ei pysty hyödyntämään kaikkea käytettävissä olevaa typpeä, riippumatta kasvunsääteiden käytös- tä. Suuret typpilannoitusmäärät lisäsivät korjuun jäl- keisiä maan mineraalityppipitoisuuksia, mutta vain kuivan kesän jälkeen. Syksyllä 1994 maan nitraatti- typpipitoisuudet olivat 15–35 kg/ha suuremmat typ- pilannoitustasoilla 127–187 kg/ha verrattuna pienem- piin typpilannoitusmääriin. Keväällä 1995 mineraa- lityppeä oli eniten jankossa suuria typpimääriä saa- neilla koeruuduilla, osoittaen mahdollista huuhtoutu- mista. Vuoden 1996 suotuisan, hyviä satoja tuotta- neen kasvukauden jälkeen maan minaraalityppipitoi- suudet olivat lähes samanlaiset eri lannoitustasoilla. Typen huuhtoutumisen välttämiseksi tulokset puolta- vat typpilannoitustasoa 90–100 kg/ha. Tutkimus tu- kee näin nykyisiä ympäristötukiehtoja. Tulosten mukaan kasvunsääteet voivat parantaa typen hyväksikäyttöä, mutta tutkituilla aineilla toden- näköisimmin vain rypsin ja sateisina kesinä kauran viljelyssä. Title Introduction Material and methods Results and discussion Conclusions References SELOSTUS