The effect of chloride and nitrogen on nitrate accumulation and yield in beetroot (Beta vulgaris var. conditiva) TapioSalo, Liisa Pietola and Raili Jokinen Salo, T., Pietola, L. & Jokinen, R. 1992. The effect of chloride and nitrogen on nitrate accumulation and yield in beetroot {Beta vulgaris var. conditiva). Agric. Sei. Finl. 1: 351-360. (Agric. Res. Centre of Finland, Inst. Crop and Soil Sei., SF- -31600 Jokioinen, Finland.) A pot and a field experiment were conducted to evaluate the effects of different nitro- gen and chloride fertilizer levels on the nitrate content ofbeetroot. The yield and dry matter content were also determined. Sulphate fertilization was used as a control to chloride fertilization. There was a considerable decrease in the nitrate content of beetroots during the growing season. High nitrogen fertilization caused nitrate accumulation in both experiments. Chloride had a significant decreasing effect on the nitrate accumulation towards the middle of the growing period in the pot experiment. In the field experiment, chloride also decreased nitrate accumulation towards the middle of the growing period, soon after additional application of ammonium nitrate limestone (13.8 % NH4-N; 13.7 % NOj-N). Chloride tends to decrease nitrate accumulation only at an early stage of root development when nitrate is not the only source of nitrogen in the soil. The yield was higheron high nitrogen supply, in the pot experiment also on chloride application. Nitrogen decreased the dry matter content, but chloride had this effect only in the field experiment. Key words: ammonium nitrate, fertilization, vegetables, dry matter Introduction High nitrate levels in human food are undesirable, because nitrate may be converted into nitrite which causes methemoglobinemia or is converted into carcinogenic nitrosoamines. Vegetables are the main source of nitrate in theFinnish diet (Penttilä et al. 1990). Chloride in the soil is antagonistic to nitrate uptake (James et al. 1970). According to Hähndel and Wehrmann (1986 b), reduction of the nitrogen supply and addition ofchloride decreases consider- ably the nitrate contents of spinach and lettuce. Van der Boon et al. (1988) reported that a high level of chloride decreases the nitrate content oflettuce and suggested that, in the presence ofammonium nitro- gen, chloride may replace nitrate as a vacuolar osmoticum. Chloride may also replace nitrate as a counter-anion ofcations (Allen and Smith 1986). The experiments reported here were conducted to find out, whether chloride has the same effect on the nitrate content in beetroot as in lettuce or spinach. The pot experiment was carried out during the growing season of 1989 on an organic soil and the field experiment during the growing season of 1990 on a clay loam soil. 351 Agric. Sei. Fin!. 1 (1992) https://www.c-info.fi/info/?token=4nfpnBpBknLe6MD_.pa-AlxxhhnnpkTBtmp1oDg.WSqs5cCUCkzeTAmJtNAmJAnjxeiPHYWNSPAu5NT0JnZz86iI4CPgxYXbA2cKbSVeZcnhXyzi7SnbKjs-8EFCgMBz_6oxq4vKB58h9dUJKxnya_rjmPZ5vaCPP2KRH0e5DzINnY1dTcg0DzSZYwOAXmEBbqE10KZ1fFytOWSZtYjnVvYDmUcYloMJ5ltLcuWERwckMCq5E6C_V6zUX9yD_nCBYohjMLXpu4l0FJhkZS6_77-NpFwOcR_vrNgdnWaEzbrqpRjiWlT4XAIWzp0d09Q6SG08EdY1b4lqmTm3ucYpTg Material and methods The experiments were carried out in Jokioinen (60°49’N; 23°28’E). The experimental soils were analyzed for potassium, phosphorus, calcium and magnesium extractable in acid (pH 4.65) ammo- nium acetate (Vuorinen and Mäkinen 1955, Kurki et al. 1965), as well as pH and electrical con- ductivity (EC) in water suspension. The soil EC was determined also after the growing season. The boron content was determined by the azomethine- H method (Sippola and Erviö 1977), the organic carbon content by a Leco-analyzer at 1370 °C (Sip- pola 1982) and the particle size distributionby the method of Elonen (1971). The characteristics of experimental soils are presented in Table 1. Table I. Characteristics of experimental soils Pot soil Field soil org. C, % 15.3 2.7 particle size < 2 pm, % 80.5 40.5 2-20 pm, % 10.1 25.8 > 20 pm, % 9.4 33.7 pH w , 5.4 6.7 EC, l.l 5.9 P, mg/1 soil 8.2 48.8 K, —" 403 260 Ca, —2710 3257 Mg, —294 414 B, —0.6 1.5 Pot experiment The pot experiment was set up according to the split-plot design, where the main plot was nitrogen fertilization (N Q, N25 0, N5OO, N75 0, N500+250 ) and the subplot NaCl fertilization (Cl 250, Cl 500 ) or Na,S04 fertilization (S |13, 5225).S 225). A total of twenty treatments were compared (Table 2). The experiment was made with five replicates, of which one was used for sampling 80 days after sowing. Nitrogen was added as NITNC" . Treatments with NaCl and4 3 Na,S0 4 contained equal amounts of Na. Table 2. Fertilization treatments in the pot and field experi- ments. Pot experiment A. Nitrogen application / I kg soil N 0 0 mg N250 250 N 5OO 500 m 8 N750 750 mg N500+250 500 mS + 250 m 8 *) B. Chloride application / 1 kg soil S |l3 omg (Na 163 mg, S 113 mg) 5225S 225 0 mg (Na 325 mg, S 225 mg) Cl250 250 mg (Na 163 mg) Cl500 400 mg (Na 325 mg) *) 250 mg was given 54 days after sowing Field experiment A. Nitrogen fertilization /hectare N,,» 100 kg N2M 200 kg B. Chloride fertilization/ hectare S,, 0 kg (K 100 kg, S 44 kg) S Bg 0 kg (K 200 kg, S 88 kg) Cl95 95 kg (K 100 kg) C1 190 190 kg (K 200 kg) Basic fertilization was given as powdered PK- fertilizer (P 7.0 %, K 16.6 %) 10 g per pot. Other nutrients of this fertilizer were: N 2.0 %, Ca 5.4 %, S 12.0 %, Mg 2.5 %, Na 0.5 %, Fe 0.1 %, Cl 0.7 %, B 0.15 %, Cu 0.1 %, Mn 0.7 %, Zn 0.1 %, Mo 0.01 % and Se 0.0016 %. The additional boron (10 mg per pot) was added as boric acid. The soil was limed with CaCO, at the rate of 18 g per pot because of low pH value. The liming material as well as the fertilizing powder and solutions were thoroughly mixed in the soil. Four kilograms of the fertilized soils (moisture around 55 % on bulk basis) were put into 6 1 plastic pots and compacted slightly. Twenty seeds per pot were placed on the surface and covered with a 2 cm 352 Agric. Sei. Finl. 1 (1992) layer of fertilized soil. The beetroot cultivar was ‘Little Ball SG’, which is a common beetroot culti- var in Finland. A week after emergence the plants were thinned to 12 plants per pot. The plants were watered with de-ionized water once or twice a day. The percolated water was collected and reused. The first root and shoot samples were collected 54 days after sowing when the plants in the whole experiment were thinned to 6 plants per pot. The second sampling was carried out 80 days after sow- ing by harvesting one replicate. The other four re- plicates were harvested 96 days after sowing. The shoot and root yields were measured. The roots were grated and frozen at -20 °C for labora- tory analyses. The nitrate nitrogen content was ana- lysed with a nitrate electrode (ORION 1983, Aura 1985).For the determination of dry matter content, samples were dried at 60 °C for 48 hours. The results were analysed using the analysis of variance of split-plot design, and Tukey’s FISD (Honestly Significant Difference) test was used to determine the significances (p=0.05) of differences between group means (Steel and Torrie 1981). Field experiment The field experiment was set up according to a split-plot design, where the mainplot was nitrogen fertilization (N |0|), N200) and the subplot was K2 S04 or KCI fertilization S gg, Cl95 , Cl |90). The treat- ments are presented in Table 2. The experiment was made with four replicates. Nitrogen fertiliza- tion was applied as ammonium nitrate limestone (13.8 % NH4 -N; 13.7 % N03-N), 70 % in spring and 30 % ten weeks after sowing. In K2S04 and KCI fertilizations equal amounts ofK were given. Because of the good nutrient status of the soil (Table 1) the only basic fertilization given was 200 kg superphosphate (20 % P). Potassium chloride and potassium sulphate were applied with Tupla- Tume fertilizer drill. Superphosphate and ammo- nium nitrate limestone were broadcasted by a manually used fertilizer spreader working on the principle of an ordinary fertilizer drill. The fertil- izers were harrowed into the depth of 5 cm. The tractor drove along traffic lanes to avoid soil com- paction. The distance of the tractor wheels was 2 m, which was also the widthof the subplots. Seeds were sown 3 cm deep at a row distance of 40 cm by a Nibex sowing machine. The plants were later thinned to 25 plants/m. There were four rows in a plot, 10 m each. Phenmedipham was sprayed with weed control and dimethoate was applied three times against tarnished plant bug (Lygus rugulipennis). Topsoil (20 cm) samples were taken 11, 66, 77, 91, 111 and 146 days after sowing from two replicates. The first and the second samples were taken from between the middle and edge rows, and the other samplings from places, where beetroots were grown for plant samples. Soil mineral nitro- gen was extracted with 2 M KCI (Keeney and Nel- son 1982) and analyzed with a Skalar autoanalyzer (Krom 1980, Greenberg et al. 1980). Root samples were taken 75, 82, 89, 97, 102 and 117 days after sowing to determine the nitrate con- tent of roots. The samples were taken from the edges of the middle rows along a length of one meter. Sampling was always done between 8.00 and 10.00 a.m. because of the diurnal change in the nitrate content. Samples were prepared and nitrate contents determined like in the pot experiment. The root and shoot yields were harvested and measured 102 days after sowing along a length of 4 m from two middle rows (= 8 m). The beetroots were classified according to root diameter into three classes: <4 cm, 4-8 cm and >8 cm. There were no roots larger than 8 cm in diameter. Some beetroots were left in the edges of the plots for determinationof nitrate content later in autumn. Statistical analysis was made using multivariate analysis of variance to test differences between treatments in all six plant samplings (Littell et al. 1991). The analysis of variance and Tukey’s HSD test were used to test significances of differences between group means of samplings (Steel and Torrie 1981). 353 Agric. Sei. Fint. 1 (1992) Table 3. Effect of different fertilization treatments on soil EC, and nitrate content, yield and dry mattercontent ofbeetroot in the pot experiment. Fertilizations, Soil EC Nitrate content in Final Dry matter mg/kg soil 1 roots, ppm in FW yield in FW content Days after sowing g/ 6 plants % in root 54 96 root shoot yield NO C10 (S ||3) 6.4b 14 22 35 39 C1 0 (S2„) 8.0" 14 45 37 42 Cl250 6.2" 29 31 33 48 Cl500 8.5s 47 32 35 52 N250 Cl0 (Sm) 4.9" 78 17 235 89 16.8 C10 (S225 ) 6.8" 107 23 260 91 15.9 Cl250 4.4" 61 25 255 89 15.8 Cl500 4.9 h 124 27 305 120 17.0 N5OO Cl0 (Sm) 5.0" 951 31 396 165 15.5 C10 (S225 ) 7.2' 1220 54 379 173 15.0 Cl250 4.3" 896 26 443 205 14.6 Cl500 4.3" 1360 36 413 202 14.1 N750 Cl0 (Sm) 5.3b 2240»b 124 496 239 b 13.6 C1 0 (S225 ) 7.3* 2760* 192 495 247*b 12.2 Cl 250 3.9C 2320»b 98 535 249"b 13.4 Cl 500 3.7C 1880b 144 573 294' 13.6 N500+250 Cl 0 (S m) 4.8" 196* 519 243 13.3 C10 (S225 ) 6.1" 168* 528 248 13.8 Cl250 3.6' 66"b 583 224 13.8 3.B' 40" 579 259 13.3 N levels N 0 7.3' 26e * 32 35 d 45 d N250 5.2b 93c 23 264= 97c 16.4* N5OO 5.2b 1110b 37 408b 186b 14.8*J> N750 5.1 b 2300' 139 525' 257* 13.2b Ksmtm 4.6 b 117 552' 243' 13.5'b CI levels Cl0 (S m) 5.3b 820 78 336 155" 14.8 C1 0 (S 225 ) 7.1* 1020 96 340 160" 14.2 Cl250 4.5 C 830 49 370 163" 14.4 Cl 500 5.0* 850 56 381 186* 14.5 * 1 replicate Figures without a common superscript letter are significantly different (p<0.05). Figures without superscript letters have no significant differences. 354 Agric. Sei. Finl. 1 (1992) Results Pot experiment On average, the nitrate contents remained low in the pot experiment (Table 3). Towards the middle of the growing period, 54 days after sowing, the ni- trate contents were about ten times higher than at harvest time, the nitrate values increasing with increasing nitrogen levels. The effect of chloride application on the nitrate contents was not so clear as the effect of nitrogen. Towards the middle of the growing period, chloride decreased the nitrate accumulation significantly (p=0.05) only in the treatment of maximum nitro- gen and chloride levels. In these samples, the nitrate contents were 2200-2800 ppm in FW below the highest chloride level, but 1900 ppm at the highest chloride level. Two weeks before harvesting and at harvest the nitrate contents were very low. Consequently, the nitrate content was not significantly dependent even on the nitrogen fertilization. However, in the treatment of additional nitrogen fertilization 54 days after sowing, chloride application still decreased the nitrate concentrations. The differ- ences were significant (p=0.05) between the groups of highest chloride level and lowest sulphate level. Towards the middle of the growing period, at nitrogen levels of 200 and 400 mg/kg soil, more nitrate was accumulated at the highest sodium level. The effect of Na2S04 can be explained by an increase in soil EC (Table 3) caused by this treatment. Even though the seedlings emerged slowly in the pots given high rates of NaCl, both root and shoot yields were the highest on the highest chloride supply. In shoot yield the difference between low Na2 S04 and high NaCl levels was significant (p=0.05). Nitrogen application decreased the dry matter content of roots significantly (p=0.05), but chloride had no effect on the dry matter content. Fig, I. Soil mineral nitrogen contents in a field experiment during the growing season of 1990. 355 Agric. Sei. Fint. 1 (1992) Field experiment Nitrate nitrogen in soil decreased continuously during the growing season (Fig. 1). The difference in soil nitrate contents between two nitrogen treat- ments was almost double until October. The soil ammonium nitrogen level was low 66 days after sowing. Nitrogen application 67 days after sowing doubled the amount of soil ammonium after two weeks. Then it dropped to a constant low level in two weeks. The nitrate contents of roots decreased signific- antly (p=0.01) during the period between 75 and 117 days after sowing. At the nitrogen level of 200 kg/ha, the fresh roots had on average 900 ppm high- er nitrate contents than in the nitrogen treatment of 100 kg/ha (Fig. 2). The difference was statistically significant (p=0.01). There was no significant difference in nitrate accumulation between KCI and applications according to the multivariate analysis of variance (Fig. 3). When every sampling was compared sepa- rately using the analysis of variance, there was a significant difference in the first sampling, 75 days after sowing. The fertilization of S04-S 88 kg/ha caused about 400 ppm higher nitrate content in fresh roots than the chloride treatments. As compared with the nitrogen fertilization of 100 kg/ha, the nitrogen level of 200 kg/ha had a significant (p=0.01) positive influence on the root and shoot yield. The application ofKCI caused high- er shoot yield but no higher root yield compared with K2S04 fertilization (Table 4). According to the multivariate analysis of vari- ance, the nitrogen fertilization of 200 kg/ha had a significant (p=0.01) decreasing influence on the dry matter content ofroots (Table 5). The fertiliza- tion of KCI decreased the dry matter content of roots significantly (p=0.01) compared with K2 S04 fertilization. The dry matter contents decreased 89 days after sowing, because ofheavy rainfalls after a dry period of two weeks. Fig. 2. Nitrate contents in roots ofbeetroot during the grow- ing season of 1990at two rates ofnitrogen fertilization. Fig. 3. Nitrate contents in roots ofbeetroot during the grow- ing season of 1990at different rates ofchloride and sulphate fertilization. 356 Agric. Sei. Finl. 1 (1992) Table 4. Effect of different fertilizing treatments on root and shoot yield ofbeetroot in the field experiment. Shoot yield Root yield Fertilizations, kg/ha Size distribution <4 cm 4-8 cm sum tn/ha FWtn/haFW Nitrogen N.» N 2o« 11.98» 19.2l h 5.33» 14.78» 20.11» 3.85 b 24.63b 28.49b Sulphate-S and chloride S, S, 5.30 17.91 23.21 4.84 19.84 24.67 4.04 21.30 25.34 4.19 19.78 23.97 13.74c 14.43bc 16.23,b 17.98» 44 HK C',s Cl Main and sub plot means without a common superscript let- ter are significantly different (p<0.05). Means without superscript letters have no significant differences. Discussion The nitrate contents decreased both in the pot and in the field experiments during the growing season. This decrease has been noticed also by Peck et al. (1974) and Kallio et al. (1980). Nitrogen fertilizers increase the nitrate content and yield of beetroot (Peck et al. 1971). This has been noticed also in Finland (Aura 1985), where the recommended nitrogen fertilization level for optimal beetroot yield has been 60-120 kg/ha (Leh- tinen 1984, Vuorinen and Takala 1987). Nitro- gen levels over 120 kg/ha impair the quality by increasing the nitrate content. In some experiments even the yield has decreased (Lehtinen 1984). However, differences between growing seasons cause a great deal of variation in beetroot yields, and it is difficult to estimate the nitrogen require- ment for optimal yield production. Table 5. Effect of different fertilization treatments on dry mattercontent ofbeetroot roots in the field experiment. Days after sowing 75 82 89 97 102 117 Fertilization, kg/ha dry matter content % NlmS„ 10.7 13.1 10.1 12.0 12.9 14.7100 44 N lOO S 8g 10.7 12.7 9.9 12.1 13.3 15.0 N IOO CI,5 10.4 12.5 9.7 10.6 12.2 14.4 N |OOC1 1W 10.3 12.1 9.4 11.0 12.9 14.7 10.2 12.5 9.5 10.8 12.3 13.6 9.9 12.4 9.7 10.6 12.2 14.6 N 2OO C1 95 9.9 11.5 9.7 10.5 11.4 13.5 N 2OO C1 |90 10.0 11.8 9.4 10.2 11.5 13.7 Nitrogen N |0() 10.5 12.6' 9.8 11.4 12.9» 14.7 N2OO 10.0 12.0b 9.3 10.5 11.8" 13.8 Sulphate-S and chloride 544S44 10.4 12.8 9.8 11.4" 12.6a 14.2* SBg 10.3 12.5 9.8 11.3» 12.8' 14.8' Cl 95 10.2 12.0 9.2 10.6b 11.8b 13.9b Cl190 10.2 12.0 9.4 10.6b 12.2'b 14.2* Main and sub plot means without a common superscript letter are significantly different (p<0.05). Means without superscript letters have no significant differences. 357 Agric. Sei. Finl. 1 (1992) Nitrogen decreased the dry matter contents from 0.5 to 1.0 percentage units, which is in agreement with the results of Aura (1985). Chloride decreased the dry matter contents only in the field experiment. In the pot experiment, high levels of both nitro- gen and chloride were needed in order to decrease nitrate accumulation. In the final yield no differ- ences were observed as the beetroots used all nitro- gen because of good growing conditions. In the field experiment, chloride decreased the nitrate content only in the first sampling, 75 days after sowing, which was 8 days after additional application of ammonium nitrate limestone. Thus, it may be assumed that chloride needs ammonium- nitrogen in order to decrease the nitrate accumula- tion in beetroot. A similar conclusion was drawn by van derBoon et al. (1988) concerning lettuce. They used nutrient solutions, where it is easy to control the ion concentrations. In field conditions it is very difficult to maintain sufficiently high ammonium levels in soil because of nitrification. Nitrification inhibitors together with ammonium and urea fertilizers tend to decrease the nitrate accumulation, but high rates ofnitrogen application involve a risk of ammonium toxicity (Goh and Vit- yakon 1983, Hähndel and Wehrmann 1986 a). Kallio et al. (1980) found that nitrapyrin caused a 30 % reduction of nitrate content. In their field experiment, no differences were found in the nitrate content of yield between KCI and K,S0 4 applications, when the amount of potassium was 150 kg/ha. According to Cantliffe and Goodwin (1974), chloride containing fertilizers reduced the nitrate concentration at harvest time in the beetroot petioles, but not in the roots or the blades. Potassium chloride caused higher root yields in the pot experiment and higher shoot yields in both experiments than potassium sulphate. This suggests that chloride may promote the growth of beet- root more than sulphate. Goh and Vityakon (1983) obtained higher yields with NH4CI than with (NH4 ) 2 S0 4 in a pot experiment. There are also indications of chloride being an important micro- nutrient for beet species (Johnson et al. 1957). In the present experiments chloride seemed to decrease nitrate accumulation only at the early developmental stage of beetroot and on sufficient supply of ammonium-nitrogen. This effect of chlor- ide may be useful in the production of fresh veget- ables for early marketing in summer. However, the exact effect of the developmental stage of beetroot, the form of nitrogen and chloride fertilizers on the accumulation of nitrate in beetroot should be deter- mined in controlled conditions, e.g. growing beet- roots in recirculating nutrient solutions. Contributions ofauthors Salo, T. Final manuscript and field experiment. Pietola, L. Pot experiment. Jokinen, R. The original idea of the present study and planning of the pot experiment with L .Pietola. References Allen, S. & Smith, J.A.C. 1986. Ammonium nutrition in Ricinis communis: Its effects on plant growth and the chemical composition of the whole plant, xylem and phloem saps. J. Exp. Bot, 37: 1599-1610. Aura, E. 1985. Avomaan vihannesten veden ja typen tarve. Nitrogen and water requirements for carrot, beetroot, onion and cabbage. Maatalouden tutkimuskeskus, Tie- dote 7/85. 61 p. Boon, J. van der, Steenhuizen, J.W. & Steingröver, E. 1988. Effect ofEC, and Cl and NH 4concentration ofnut- rient solutions on nitrate accumulation in lettuce. Acta Hortic. 222: 35-43. Cantliffe, D.J. & Goodwin, P R. 1974.Effects ofnitrogen rate, source, and various anions and cations on N0 3 accu- mulation and nutrient constituents of table beets. Agron. J. 66: 779-783. Elonen, P. 1971. Particle-size analysis of soil. Acta Agric. Fenn. 122: 1-122. Goh, K.M. & Vityakon, P. 1983. Effects of fertilisers on vegetable production. 1. Yield ofspinach and beetroot as affected by rates and forms of nitrogenous fertilisers. N. Z. J. Agric. Res. 26: 349-356. 358 Agric. Sei. Fint. 1 (1992) Greenberg,A., Connors, J. & Jenkins, D. 1980. Nitrogen (Nitrate), Standard methods; For the examination of water and wastewater, p. 391-404. 15th Ed. Washington. Hähndel, R. & Wehrmann, J. 1986 a. Einfluss der N0 3 - Emährung auf Ertrag und Nitratgehalt von Spinat und Kopfsalat. Z. Pflanzenemähr, Bodenk. 149: 290-302. & Wehrmann, J, 1986 b. Einfluss der Cl-emährung auf Ertrag und Nitratgehalt von Spinat und Kopfsalat. Z. Pflanzenemähr. Bodenk. 149: 303-319. James, D.W., Kidman, D.C., Weaver, W.H. & Reeder, R.L. 1970. Factors affecting chloride uptake and impli- cations of the chloride-nitrate antagonism in sugarbeet mineral nutrition. J, Am. Soc. Sugar Technol. 15: 647- 656. Johnson, C.M., Stout, P.R., Broyer, T.C. & Carlton, A.B. 1957. Comparative chlorine requirements of diffe- rent plant species. Plant and Soil 8: 337-353. Kallio, H., Linko, R.R., Tikanmäki, E. & Puntari, 1. 1980. Effect of nitrapyrin on nitrapyrin residues and nitrate content in red beet roots fertilised with urea. J. Sci. Food Agric. 31; 701-708. Keeney, D.R. & Nelson, D.W. 1982. Nitrogen - Inorganic forms. Methods of soil analysis. Part 2. Chemical and microbiological Properties. Agronomy 9. p. 643-698. Madison, Wisconsin. Krom, M.D. 1980. Spectrophotometric determination of ammonia: A study of a modified Berthelot reaction using salicylate and dichloroisocyanurate. Analyst 105: 305- 316. Kurki, M., Lakanen, E., Mäkitie, O. & Sillanpää, M. 1965. Viljavuusanalyysien ilmoitustapa ja tulkinta. Interpration of soil testing results. Ann. Agric, Fenn. 4: 145-153. Lehtinen, S. 1984. Avomaanvihannesten lannoitus-ja kas- telukokeet 1978-1983. Maatalouden tutkimuskeskus, Tiedote 21/84. p. 1-62. Littell, R.C., Freund, R.J. & Spector, P.C. 1991. SAS- system for linear models. 329 p. 3rd ed. Cary, NC. ORION 1983. Guide to ion analysis. 45 p. 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Pubi. 63: 1-44. Vuorinen, M. & Takala, M. 1987. Porkkanan japunajuu- rikkaan sadetus, typpilannoitus ja kalkitus poutivalla hiekkamaalla. Maatalouden tutkimuskeskus. Tiedote 10/87. p. 1-30. Manuscript received November 1991 Tapio Salo Liisa Pietola Raili Jokinen Agricultural Research Centre of Finland Institute of Crop and Soil Science SF-31600 Jokioinen, Finland Raili Jokinen Present address: Tyynelä SF-03250 Ojakkala, Finland 359 Agric. Sei. Fint. 1 (1992) SELOSTUS Kloridi-ja typpilannoituksen vaikutus punajuurikkaan nitraattipitoisuuteen ja satoon Tapio Salo, Liisa Pietola ja Raili Jokinen Maatalouden tutkimuskeskus Vihannesten korkeat nitraattipitoisuudet ovat terveydelle haitallisia, koska nitraatti voi muuttua nitriitiksi aiheuttaen methemoglobinemiaa tai karsinogeenisiksi nitrosoamii- neiksi. Pinaatti, salaatit, retiisi ja punajuurikas sisältävät yleensä runsaasti nitraattia. Astia-ja kenttäkokeessa seurattiin erikloridi-ja typpilan- noitustasojen vaikutusta punajuurikkaan nitraattipitoisuu- teen, satoon ja kuiva-ainepitoisuuteen. Sulfaattilannoitusta verrattiin kloridilannoitukseen. Punajuurikkaiden nitraattipitoisuus laski huomattavasti kasvukauden aikana. Runsas typpilannoitus lisäsi satoa ja nitraatin kertymistä molemmissa kokeissa. Astiakokeessa myös kloridin lisäys kohotti satoa. Typpilannoitus laski kuiva-ainepitoisuutta kenttä- ja astiakokeessa, mutta kloridi alensi kuiva-ainepitoisuutta vain kenttäkokeessa. Kloridi vähensi merkitsevästi nitraatin kertymistä kasvu- kauden puolivälissä astiakokeessa. Kenttäkokeessa kloridi laski nitraattipitoisuutta myös kasvukauden puolivälissä, pian oulunsalpietarina annetun täydennystyppilannoituksen jälkeen. Kloridi näyttääkin vähentävän nitraatin kertymistä punajuurikkaalla vain juurikkaan aikaisessa kehitysvai- heessa, kun nitraatti ei ole ainoa typen lähde maassa. 360 Agric. Sei. Finl. 1 (1992)