JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND 99 Maataloustieteellinen Aikakauskirja Vol. 61: 99—HI, 1989 Effects of different fertilization practices on the N03-N, N, P, K, Ca, Mg, ash and dietary fibre contents of carrot AINO-MAIJA EVERS Kemira Oy, Espoo Research Centre, Luoteisrinne 2 SF-02270 Espoo, Finland Abstract. The effects of different fertilization practices on the N03 -N, N, P, K, Ca, Mg, ash and dietary fibrecontents of carrots were studied in field experiments in southern Finland. Unirrigated and irrigated placement and broadcast fertilization, NPK fertirrigations without basic fertilization, NPK fertirrigations with NPK basic fertilization and PK placement with N fertirrigations were compared. Further, single application was compared with split applica- tions. The results of 1986 were analysed by contrast analysis. Fertilization practices affected the NO s-N content in carrot, and irrigation increased the NO,-N content. Highest NOrN contents were observed with NPK fertirrigations treatments. Fertilization increased the N content of roots, and nitrogen content was higher with PK place- ment with N fertirrigations as compared to NPK fertirrigations without basic fertilization, or to NPK fertirrigations. Placement fertilization increased P content as compared to broadcast fertilization, NPK fertirrigations without basic fertilization, NPK fertirrigations or split appli- cation. Irrigation decreased P content. Fertilization increased the K contents of carrot roots as compared to unfertilized treat- ments, but there were no significant differences between fertilization practices. Fertilization had no effect on the Ca or Mg contents of carrot roots. Fertilization increased the ash content. Placement fertilization, single application and unirrigated single application yielded higher ash contents than did split application, NPK fertirrigations or PK placement with N fertirriga- tions. Fertilization and irrigation increased the dietary fibre content as compared to unferti- lized and unirrigated treatments, respectively. Irrigated single application increased dietary fibre content as compared to split application and PK placement with N fertirrigations. Besides the fertilization experiment, samples from two organically cultivated fields were collected in order to obtain data concerning organically cultivated carrots. Index words: fertilization practices, carrot, quality, nutrients, nitrate, ash, dietary fibre, organic culture Introduction The aim of modern vegetable cultivation is an even and high-quality yield. At harvest each plant should be similar in size and at the same developmental stage. Thus all cultivation https://www.c-info.fi/en/info/?token=Agkos1aI2A7WHGmb.64Io5gIRIHt_jukVjeBkXA.1AIS-7jemQ9SBupIhF8hoPnOk3R4b5i8jvd-OX5R-Qe6_LoU5A6uealPZzOcJRy4NYr7yC73MxgSFT_OnuLKaBc5cDX3E4-CgtgoNflHhH-boVGH7NZi3NFE2wzA0bsRyJQc-NqAqce1fBBpWW2EBuUUajjlmXbZGQMDGSYT 100 practices should promote even germination, sprouting and growth. The most common fertilization practice in vegetable cultivation is broadcast fertilization. With the present distribution methods, how- ever, it is difficult to accomplish an even dis- tribution, quaranteeing that every single plant gets the same amounts of nutrients at each growing stage. Fertilizer efficiency, too, can be intensified by developing even distribution systems and by dividing fertilizer applications according to the growth process of the plant being cultivated. Fertilizer placement has been shown in cereals to increase the uptake of nitrogen, in particular, but also the uptake of phosphorus and potassium (Aura 1967, Kai- la & Elonen 1970). Fertilizer placement in- creases the yield of barley and spring wheat, particularly at low fertilizer levels, but it has not increased the mineral content of grains (Esala & Larpes 1986 a, b). Only a few reports have been published con- cerning fertilizer placement in the cultivation of carrots. Ekeberg (1986) reported that fer- tilizer placement increased carrot yield, but decreased the dry matter content of carrots on peaty soil. The mineral contents of carrots were not determined in his experiment. Celius (1970) stated that the placement of phosphorus could be a profitable alternative in carrot growing. Carrot has a great need for phosphorus in the beginning of the growing season (Balvoll 1978). On the contrary, as the germinating carrot seeds are sensitive to a high salt concentration in the soil (Balvoll 1978), one could expect the placement of phosphorus and other nutrients below and be- side the seed row to be beneficial. In Holland, Baker et al. (1984) compared broadcast fertilization with fertirrigation on lettuce. They found that the yield was very even with fertirrigation, but that the nitrate content was higher than with broadcast fer- tilization. High levels of nitrate in vegetables are undesirable, because N02 may be harm- ful to human health (Corre & Breimer 1979). The objective of this study was to determine how placement and broadcast fertilization, fertirrigation and their combinations affect the nitrate, nitrogen, phosphorus, potassium, calcium, magnesium, ash and dietary fibre contents of carrots. Simultaneously with the field experiments in 1986, material from two organically cultivated fields were collected in order to get some data of the mineral, ash and dietary fibre contents of organically cultivated carrots. Materials and methods The field experiments were carried out on the Kotkaniemi Experimental Farm of Kemira Oy. in Vihti during the growing seasons of 1985 and 1986. Carrot cv. Nantes Duke Nota- bene 370 Sv was grown as reported elsewhere (Evers 1988). The trials were set up accord- ing to the method of completely randomized blocks, four blocks and ten treatments (Ta- ble 1). Each plot was 25 m 2. The sample size was in 1985 20 carrots per treatment, in 1986 80 carrots per treatment for NOj-N and 20 carrots per treatment for minerals, ash and dietary fibre. The blocks were determined separately. In 1985, some preliminary carrot root and shoot samples for the N0 3-N, N, P, K, Ca and Mg determinations were collected three times during the growing season (1. = August 20, 1985, 75 days from sowing; 2. = September 10, 1985, 96 days from sowing; 3. = September 30, 1985, 116 days from sowing at harvest). Figure 2 was compiled according to the results of these sample determinations, and shows the development of macronutrient contents in car- rot shoots and roots. The results of 1985 were not studied statistically. In 1986, carrot root and shoot samples for the N, P, K, Ca, Mg, ash and dietary fibre determinations were collected at harvest, for the NOj-N determinations three times during the growing period (1. = August 12, 1986, 66 days from sowing; 2. = September 3, 1986, 88 days from sowing; 3. = October 6, 1986, 121 days from sowing at harvest). The dietary fibre determinations were made only from roots. The results of 1986were studied statisti- Table 1. The fertilization treatments. Treatment Number and time of fertilizer applications mm NPK No fertilization No irrigation 0 0 0 0 0 Irrigation 0 0 0 0 3xlo NPK placement No irrigation 1 before sowing 80 35 133 0 Irrigation 1 before sowing 80 35 133 3x 10 NPK broadcast No irrigation I before sowing 80 35 133 0 Irrigation I before sowing 80 35 133 3x 10 NPK fertirrigations Without basic fertilization 3 during season 80 29 160 3xlo Half the basic NPK fertilization 1 1 before sowing and 80 32 142 3x 10 3 during season PK placement 2 3N-fertirrigalions 1 before sowing and 81 56 133 3x 10 3 during season 4N-fertirrigations 1 before sowing and 155 56 133 4x 10 4 during season Half of the nutrients were given by basic placement fertilization and half by NPK fertirrigations. Phosphorus and potassium were given by basic placement fertilization and nitrogen in fertirrigations. ' The nutrient amounts were 30 % higher in 1985 than in 1986. cally by contrast analysis (Steel & Torrie 1980). The plant analyses were done by Vilja- vuuspalvelu Oy, Helsinki, a commercial laboratory. For the N03-N determinations the samples were ground, extracted in water and NOj-N was determined by ion chro- matography (IC) according to Hunt & Sey- mour (1985). Total N was determined accord- ing to the Kjeldahl method (Anon. 1984). For the P, K, Ca and Mg determinations the dried samples were ashed, extracted in HCI, and de- termined by plasmaemissiospectrometry (ICP- AES) (Anon. 1984). The dietary fibre deter- mination was done according to the method described by Prosky et al. (1985). In Results, Figure 2, representing macronutrient contents during the season, is based on determinations in 1985, and the effects of different fertiliza- tion practices discussed in the text are based on determinations and statistical analyses made in 1986. Results and discussion Nitrate-N Macronutrient Irrigation water amounts in 19863 amounts in kg/ha 1985 and 1986 Nitrate-N is undesirable in vegetables, be- cause N0 2 is dangerous to health, especially in babies (Maynard et al. 1976, Corre & Breimer 1979). Nitrate-N accumulation in plants is attributed mainly to genotype, light intensity, day length, temperature, soil mois- ture content and nitrogen fertilization. Wide fluctuation has been observed also during a 24-hour period (Maynard et al. 1976, Corr£ & Breimer 1979). Carrot is not typically a species that concentrates NOrN, but as the consumption of carrots is considerable, the N0 3-N concentration in carrots is interesting. According to the literature, in fertilizer ex- periments the NOj-N contents have increased markedly with increasing amounts of nitrogen fertilization. Lehtinen (1984) reported an NO,-N content in carrot roots of 2.08—3.53 g/kg dry matter (DM) (level of fertilizer N 101 g Table 2. The effect of different fertilization practices on the NO,-N, N, P, K, Ca and Mg contents of carrot roots and shoots at harvest in 1985 and 1986. % in dry matter Treatment NO,-N N P K Ca Mg Roots Shoots Roots Shoots Roots Shoots Roots Shoots Roots Shoots Roots Shoots 1985 Unfertilized 0.01 0.02 0.88 2.25 0.20 0.23 2.90 5.47 0.23 1.61 0.10 0.28 Placement fertilized 0.01 0.01 0.85 1.84 0.19 0.21 2.79 5.65 0.22 1.39 0.10 0.26 Broadcast fertilized 0.03 0.05 1.00 2.16 0.22 0.19 3.13 5.25 0.23 1.38 0.11 0.22 NPK fertirrigations, no basic fertilization 0.04 0.23 1.18 2.56 0.23 0.21 2.93 6.37 0.21 1.64 0.10 0.30 NPK fertirrigations, half the basic fertilization 0.01 0.04 0.91 1.99 0.22 0.19 3.15 5.25 0.24 1.42 0.10 0.24 PK placement with 3N fertirrigations 0.03 0.03 1.00 2.55 0.22 0.20 3.16 6.30 0.23 1.57 0.09 0.26 PK placement with 4N fertirrigations 0.03 0.04 1.06 2.16 0.22 0.19 3.45 6.05 0.21 1.35 0.12 0.30 1986 Unfertilized 0.10 0.14 0.94 1.62 0.22 0.17 2.71 4.07 0.30 1.90 0.10 0.26 Unfertilized and irrigated 0.14 0.13 0.78 1.56 0.21 0.18 2.52 3.77 0.29 2.17 0.10 0.27 Placement fertilized 0.12 0.13 1.15 1.82 0.25 0.18 3.11 4.01 0.30 1.82 0.11 0.29 Placement fertilized and irrigated 0.15 0.15 1.02 2.05 0.23 0.20 3.26 5.18 0.29 1.58 0.10 0.26 Broadcast fertilized 0.13 0.14 1.19 2.05 0.22 0.20 3.07 4.49 0.30 1.65 0.10 0.31 Broadcast fertilized and irrigated 0.14 0.14 1.06 2.00 0.21 0.18 3.12 4.46 0.30 1.67 0.10 0.28 NPK fertirrigations, no basic fertilization 0.16 0.15 1.03 2.19 0.20 0.19 2.88 4.31 0.29 1.58 0.10 0.32 NPK fertirrigations, half the basic fertilization 0.16 0.13 0.96 1.75 0.23 0.19 3.20 4.68 0.30 1.86 0.09 0.25 PK placement with 3N fertirrigations 0.11 0.13 1.19 1.94 0.23 0.18 2.97 4.18 0.30 1.59 0.11 0.25 PK placement with 4N fertirrigations 0.12 0.16 1.24 2.07 0.22 0.19 3.14 4.32 0.29 1.32 0.10 0.26 Organically cultivated carrots Location 1 0.14 0.13 0.09 1.71 0.26 0.25 2.42 5.53 0.23 1.05 0.11 0.25 Location 2 0.11 0.15 0.10 1.63 0.33 0.39 3.05 6.65 0.28 2.20 0.13 0.31 4 60 kg/ha), 4.42—6.59 g/kg DM (level of fer- tilizer N 120 kg/ha) and 4.95—7.07 g/kg DM ( wel of fertilizer N 180 kg/ha). The variation at each fertilizer level is caused by differences between growing seasons. Dragland (1978) published root N0 3-N contents of 1.8—5.3 g/kg DM (0 —160 kg N/ha), and Nilsson (1979) reported contents of 0.5—1.2 g/kg DM (50—100 kg N/ha mineral fertilizer) and 0.5 0.9 g/kg DM (50—100 kg N/ha organic fer- tilizer) in roots. In the present study, at the first sampling date the N0 3 -N content in shoots was high (Fig. 1). It decreased clearly during the grow- ing period. The NO a-N content in roots decreased slightly during the season and at harvest the NO s-N contents were on the same level in shoots and roots, theaverage content for 1985 and 1986 in roots being 0.8 g/kg DM (Fig. 1). The concentration is similar to Nils- son’s (1979) results but lower than those reported by Lehtinen (1984) and Dragland (1978). There was a clear difference between years in the N0 3-N contents of roots (Table 2). In 1985, the N03-N content was lower than in 1986 at all sampling dates (Fig. 1), a result probably caused by weather conditions. In August, September and October the mean day temperature and the number of sunshine hours were higher in 1985 than in 1986 (Evers 1988). This is in agreement with the literature. Maynard et al. (1976) and Corre & Breimer (1979) reported that, among other things, low temperature and low light inten- sity increase the N03-N content of plants. In unfertilized treatment the N03 -N con- tent was low both in shoots and roots at all sampling dates (Fig. 2a, 2b). At harvest, a low NO s-N content was also measured in unir- rigated placement fertilized treatment, but there were no great differences between treat- ments (Table 2). The highest NOr N con- tent, in both shoots and roots, was with NPK fertirrigations without basic fertilization (Fig. 2a, 2b). In the study of Barker et al. (1984) with lettuce, the results clearly indicated that nitrogen fertirrigations led to a comparatively high level of N03 in the crop. They also found a relatively high N recovery percentage by the fertirrigated crop, especially at a lower level of N fertilization. The proportion of N0 3-N in the total N content was higher in the fertirrigated crop as compared to broad- cast fertilization. In 1986 at harvest, the fertilization did not cause a significant increase in the root NOr N content as compared to unfertilized treat- ments, but irrigation increased the root N03- N content significantly as compared to unir- rigated treatments (Table 3). High N0 3-N content in roots was a result of NPK fertirri- gations as compared to placement fertiliza- tion, broadcast fertilization, single applica- tion, unirrigated single application or PK placement with N fertirrigations (Table 3). High N03-N content in roots was also a result of NPK fertirrigations without basic fer- tilization as compared to unirrigated single ap- plication or PK placement with N fertirriga- tions (Table 3). The N03-N content of organically cultivat- ed carrots at three succeeding sampling dates Fig. I. The development of the NO,-N content of roots ( • 1985, O 1986) and of shoots ( A 1985, A 1986) as the average of treatments. 103 Fig. 2. The effect of different fertilization practices on the development of the NOj-N, N, P, K, Ca and Mg con tents of carrot shoots and roots (1985). 104 105 106 Table 3. Contrasts and the significance of differences (* p<0.05, ** p