Urea as an organic nitrogen source for hydroponically grown tomatoes in comparison with inorganic nitrogen sources

Tomato (Lycopersicon esculentum Mill., cv. Momotaro) plants were grown in nutrient solutions with several levels of urea, nitrate, and ammonium alone or in combination to evaluate the role of urea as an organic nitrogen source compared with that of nitrate and/or ammonium as inorganic nitrogen sources. Nitrogen deficiency and excess symptoms were detected in the urea-fed plants at lower (28 mg N L^-1) and higher nitrogen levels (336, 504 mg N L^-1), respectively. The effect of urea on plant growth and leaf elemental composition was intermediate between that of nitrate and ammonium. Solution pH under urea nutrition slightly increased or remained stable. When plants were cultured with the solution containing 168 mg N L^-1, the total dry weight of the plants which received urea+nitrate was significantly higher than that of the plant which received urea and was almost equal to that of the plants which received nitrate or nitrate+ammonium. Both absorption and utilization of nitrogen in the plants fed with urea decreased compared with those of the plants fed with nitrate or ammonium. The insufficient absorption and utilization of nitrogen were estimated to be the main factors associated with the growth reduction of tomato plants under urea nutrition. However, combined application of urea and nitrate is useful for adequate plant growth without a reduction of the cation absorption in tomato while maintaining a stable solution pH.     

Effects of atmospheric nitrogen dioxide on uptake and assimilation of ammonium in soybean plants

Twelve‐day‐old soybean plants were supplied with 1 mM ammonium chloride (NH₄C1) to roots and exposed to 0.2–0.25 μL.L^‐1 nitrogen dioxide (NO₂) for seven days. Amount and rate of ammonium uptake were decreased by NO₂ exposure. However, the ammonium concentration in leaves and leaf pH of exposed plants were increased by NO₂ exposure. These results suggest that the decrease in ammonium uptake may be due to the decline in hydrogen (H⁺) ion concentration in exposed plants which resulted from the reduction of the nitrate and nitrite from NO₂ absorption. They also suggest that the decrease in ammonium uptake and the competition for energy between nitrate reduction and ammonium assimilation may limit ammonium assimilation to organic nitrogen (N) which would further inhibit acidity increase in exposed plants and ammonium uptake by roots.     

Absorption and translocation of foliar applied triazone‐n as compared to other nitrogen sources in tomato

Absorption and translocation of foliar applied ¹⁵N labeled S‐tetrahydrotriazone (triazone), as compared to other N forms, was evaluated in tomato plants. Triazone‐N was taken up into leaf tissue in quantities similar to urea, ammonium, and nitrate‐N when applied at a N concentration of 0.35% w/v. Although >40% of the ¹⁵N label was exported from the treated leaf after 7 days, nearly 50% of the translocated triazone ¹⁵N label accumulated in non‐treated leaf tissue as compared to only 10% or less for the other N sources. The largest percentage of the translocated urea‐, ammonium‐, and nitrate‐¹⁵N label accumulated within developing fruit tissue. Multiple (3) foliar applications of triazone and urea at concentrations of 0.94% or higher and 1.0% N (w/v), respectively, enhanced both leaf and fruit tissue N concentrations. No growth responses to foliar applied N were observed.     

Significance of Nickel Supply for Growth and Chlorophyll Content of Wheat Supplied with Urea or Ammonium Nitrate

ABSTRACT

Nickel (Ni) is an essential element for activation of urease in higher plants. The effects of Ni as an essential micronutrient on growth and chlorophyll content of wheat plants grew in nutrient solutions supplied either with ammonium nitrate or urea as two different nitrogen (N) sources were investigated. Plants were allowed to grow for six weeks, then leaf chlorophyll content, shoot and root fresh and dry weights, and Ni concentration in shoots and roots were determined. Shoot and root Ni concentration in both urea and ammonium nitrate-fed plants increased significantly with the increase in Ni concentration. Growth and chlorophyll content in leaves of the urea-fed plants increased when Ni concentration in the solution was as high as 0.05 mg L^?1 and decreased at 0.1 mg Ni L^?1. In ammonium nitrate-fed plants, these parameters increased up to 0.01 mg Ni L^?1 and started to decrease with further increase in Ni concentration. Plants that grew in nutrient solutions containing urea had more shoots and roots fresh and dry weight at third and fourth Ni levels (0.05 and 0.1 mg L^?1) than those that grew in media containing ammonium nitrate with similar Ni levels. Total chlorophyll content was also higher in plants supplied with urea plus Ni. The amount of Ni required for optimum wheat growth was dependent on the forms of N used. When supplied with ammonium nitrate or urea, the amount of Ni needed was 0.01 and 0.05 mgL^?1 of nutrient solutions, respectively.     

Production of Chinese cabbage in relation to nitrogen source,rate, and leaf nutrient concentration

Abstract

Chinese cabbage (Brassica rapa L. Chinensis group) production is expanding in the U. S., and guidelines regarding its production under Western cultural practices are needed. The objectives of this study were to investigate the effects of N source and rate on Chinese cabbage yield, marketability, and wrapper leaf nutrient concentrations, and to estimate the critical wrapper leaf‐N concentration associated with maximum yield and marketability. Chinese cabbage was grown in five sequential plantings using raised‐bed, polyethylene mulch culture with subsurface irrigation on a sandy soil. Nitrogen fertilizer was applied at rates of 0, 67,112, and 157 kg/ha using the following sources: 1) ammonium nitrate. 2) calcium nitrate, 3) urea‐ammonium nitrate solution (Uram, 32% N), 4) urea, and 5) a urea‐calcium solution (18% N). Mature Chinese cabbage wrapper leaf concentrations of P, Ca, and Mg increased with increasing N rate, while leaf‐K concentration decreased. Leaf‐N concentration increased in response to N rate, but was not affected by N source or harvest date. Leaf‐P, K, Mg, and B concentrations were sufficient or high according to established standards, but leaf‐Ca was low. Leaf‐Ca and Mg concentrations were lowest with N sources containing only urea, and highest where at least part of the N was applied as NO₃ ^‐. Chinese cabbage head weight and percentage marketable heads increased as N rate increased. Yield and quality were highest with N sources which contained NO₃ ^‐, and were smallest where N was applied entirely as urea, which may have been due to plant sensitivity to NH₄ ⁺. The critical value of mature cabbage wrapper leaf‐N concentration above which yield or marketability was not limited was estimated to be 36 to 41 mg/g, which agrees well with established standards.     

Nitrogen assimilation in sunflower leaves and upward and downward transport of nitrogen

The assimilation of ammonium and nitrate nitrogen into amino acids of mature sunflower leaves and their transport to the other plant parts were investigated using nitrogen-15 as a tracer. In the leaf, to which ¹⁵N-labelled ammonium was vacuum-infiltrated, the ¹⁵N content of glutamine was always the highest of the amino acids tested and that of alanine was higher than that of glutamic acid and aspartic acid at 15 min after the infiltration. On the other hand in the leaf to which ¹⁵N-labelled nitrate was vacuum-infiltrated, the ¹⁵N content of glutamic acid and aspartic acid was superior to that of glutamine. The incorporation of ¹⁵N into serine was not active in the case of either ¹⁵N-labelled ammonium or nitrate. In the internodes above and below the treated leaf, through which photosynthates were transported into other parts, the ¹⁵N content of γ-aminobutyric acid and glutamine was markedly high when both nitrogen sources were supplied. There were no differences in the labelling patterns of amino acids between the upper and lower internodes. From these results it may be concluded that glutamine, glutamic acid, and aspartic acid play an important role in the assimilation of ammonium and nitrate nitrogen in leaves and that nitrogen is transported mainly in the forms of γ-aminobutyric acid and glutamine from the leaves to the other plant parts,     

Influence of N form on growth photosynthesis of Phaseolus vulgaris L. plants

Many plant species are characterized by pronounced sensitivity to sole ammonium supply and exhibit growth depression and particularly reduced leaf growth rates. Stress symptoms under sole ammonium supply may be related to perturbation of photosynthetic processes, e.g., low rates of net CO₂ assimilation, low quantum yield, reduced stomatal conductance, and carboxylation capacity. The results of three experiments with French bean plants supplied with an N concentration of 5 mM illustrate significantly lower dry mass and specific leaf area, reduced leaf expansion, and higher chlorophyll and N content of ammonium‐ compared to nitrate‐supplied plants. Light‐saturated rates of CO₂ assimilation (A_max) per unit leaf area were higher under ammonium compared to nitrate supply while no significant effects of N form on quantum yield and A_max per unit leaf weight and chlorophyll were found. Maximal carboxylation (V_cmax) and electron‐transport (J_Max) rates were significantly higher under ammonium supply only in one of three experiments. V_cmax was linearly related to total leaf N, the slope of the regression was similar with both N forms, the x‐axis intercept was significantly higher for ammonium‐ compared to nitrate‐supplied plants. The ratio V_cmax : J_Max was not affected by N form. It is concluded that ammonium supply had no negative effects on the operation of photosynthetic protein‐enzyme complexes.     

Growth,photosynthesis and protein content in cucumber plants as affected by supplied nitrogen form

Cucumber plants were grown hydroponically in three different nutrient solutions to determine the effect of NO₃ ^‐/NH₄ ⁺ ratio on several parameters. Top and root growth, CO₂ fixation, and ion content (K⁺, Ca⁺², NO₃ ^‐) were always lower when urea and ammonium nitrate were the major N source as compared with a Hoagland solution in which nitrate was the major N source. No significant differences were found in total N and protein content among the three nutrient solution treatments.     

Effect of Nitrogen Fertilizer Forms on Growth,Photosynthesis, and Yield of Rice Under Cadmium Stress

ABSTRACT

A pot experiment was conducted to study the influence of four nitrogen (N) fertilizer forms [Urea; calcium nitrate, Ca(NO₃)₂; ammonium sulfate, (NH₄)₂SO₄; and organic N] on growth, photosynthesis, and yield of rice under two cadmium (Cd) levels (0 and 100 mg Cd kg^?1 soil). Cadmium addition significantly reduced photosynthetic rate, and the reduction varied with N fertilizer form, with ammonium (NH₄ ⁺)-N and urea treated plants having more reduction. Nitrogen form had a distinct effect on SPAD value, and the effect was also dependent on Cd level and growth stage. Cadmium-stress significantly reduced flag leaf area, but for the second leaf, only the plants supplied with organic N showed the reduction. There was a significant difference in plant height among four N forms, with NH₄ ⁺- and nitrate (NO₃ ^?)-treated plants having the highest and lowest height, respectively. Cadmium stress caused significant reduction in grains per panicle and total plant weight, and the reduction varied with N form, with organic N treatment showing more reduction. There were significant differences among N forms in N and Cd concentrations of the plants subjected to Cd stress, with NH₄ ⁺-N treated plants having highest N and lowest Cd concentrations and NO₃ ^?-treated plants having lowest N and highest Cd uptake. The results showed that the inhibition of Cd stress on growth and yield formation of rice is closely related to N fertilizer form.     

Growth attributes,xylem sap composition,and photosynthesis in common bean as affected by nitrogen and phosphorus deficiency

The effects of nitrogen (N‐) and phosphorus (P‐) deficiency, isolatedly or in combination, on growth, nitrogenous fraction, and inorganic phosphate in xylem exudade, and photosynthesis of common bean (Phaseolus vulgaris L. cv. Negrito) were investigated. Plants were grown in nutrient solution adjusted daily to pH 5.5 and aerated continuously. Ten days after emergence mineral deficiency was imposed. Plants were then supplied with high N (7.5 mol m^‐3) or low N (0.5 mol m^‐3), and also with high P (0.5 mol m^‐3) or low P (0.005 mol m^‐3). All sampling and measurements were made 28 days after emergence. N‐ or P‐deprivation brought about large decreases in total leaf area by inhibiting the emergence of new leaves and primarily the expansion of the leaves. The specific leaf area did not change under N‐ but decreased under P‐limitation. The decreased shoot to root ratio in all deficiency treatments was a consequence of a lowering mass of above‐ground organs, especially of leaves.

The content of chlorophylls declined significantly only under N‐deficiency alone; carotenoids declined under both N‐ and combined N‐ and P‐limitation. No alteration in amino acid concentration in xylem exudate occurred in plants experiencing N‐starvation, while ureides increased by 79%, and nitrate and inorganic phosphate decreased greatly. Under P‐deprivation, amino acids and nitrate in xylem sap dropped by about half; ureides were held relatively constant, and phosphate was severely depressed. Total upward translocation of N through xylem was estimated to be about 16% higher in N‐deficient plants than in plants without mineral limitation, but leaf N levels in the former were lower as compared to control plants. The net carbon (C) assimilation decreased similarly regardless of the imposed deficiency treatment. Such a decrease was mainly determined by non‐stomatal factors. In general, no additive effect between N‐ and P‐limitation on any of measured parameters was observed.     

Nitrogen concentrations and proportions of ammonium and nitrate in the nutrition and growth of yellow passion fruit seedlings

Abstract

Despite the importance of nitrogen (N) supply to plants, there are still doubts concerning the optimal relations of ammonium and nitrate in the nutrition of yellow passion fruit seedlings. This study aims to evaluate the interaction between nitrogen concentrations and ammonium and nitrate proportions in the nutrition, growth, and dry matter production of passion fruit seedlings grown in a substrate with a nutrient solution. The experiment was conducted in a greenhouse in randomized complete block design with three replications in a 4 × 5 factorial design, consisting of four N concentrations (2.5, 5.0, 10.0 and 20.0?mmol L^?1) and five ammonium proportions (0, 25, 50, 75 and 100% in relation to the total N supply). At 60?days after transplanting, green color index; accumulation of N, potassium, calcium, and magnesium in roots and shoots; stem diameter; leaf area; root length; nitrogen use efficiency (NUE); and dry matter of roots and shoots were evaluated. For the formation of seedlings of yellow passion fruit, the nutrient solution should have 13?mmol L^?1 of N, with 40% of this nutrient in the form of ammonium. The passion fruit is a plant tolerant to ammonium. However, a critical concentration above 5.7?mmol L^?1 of NH₄⁺ in the nutrient solution decreases absorption of cations, NUE, and production of dry matter.     

Effects of Molybdenum,Nickel, and Nitrogen Sources on the Mineral Nutrition and Growth of Rice Plants

Upland rice plants, cultivar ‘IAC 202,’ were grown in nutrient solution until full tillering. Treatments consisted of ammonium nitrate (AN) or urea (UR) as nitrogen (N) source plus molybdenum (Mo) and/or nickel (Ni): AN + Mo + Ni, AN + Mo ? Ni, AN ? Mo + Ni, UR + Mo + Ni, UR + Mo ? Ni, and UR ? Mo + Ni. The experiment was carried out to better understand the effect of these treatments on dry‐matter yield, chlorophyll, net photosynthesis rate, nitrate (NO₃ ^?‐N), total N, in vitro activities of urease and nitrate reductase (NR), and Mo and Ni concentrations. In UR‐grown plants, Mo and Ni addition increased yield of dry matter. Regardless of the N source, chlorophyll concentration and net photosynthesis rate were reduced when Mo or Ni were omitted, although not always significantly. The omission of either Mo or Ni led to a decrease in urease activity, independent of N source. Nitrate reductase activity increased in nutrient solutions without Mo, although NO₃ ^?‐N increased. There was not a consistent variation in total N concentration. Molybdenum and Ni concentration in roots and shoots were influenced by their supply in the nutrient solution. Molybdenum concentration was not influenced by N sources, whereas Ni content in both root and shoots was greater in ammonium nitrate–grown plants. In conclusion, it can be hypothesized that there is a relationship between Mo and Ni acting on photosynthesis, although is an indirect one. This is the first evidence for a beneficial effect of Mo and Ni interaction on plant growth.     

氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响

采用田间试验研究了氮素形态、用量及施用时期对小青菜产量和硝酸盐含量的影响。结果表明,等氮量施肥下,产量最高的是硝酸钙,尿素+微量元素处理;尿素,有机无机复混肥和碳酸氢铵处理间无显著差异,DMPP处理产量最低;追施微量元素能提高小青菜的产量。硝酸盐含量随着收获时期的延后而降低,有机无机复混肥处理则略有升高,但未达到显著水平;收获期取样时,不同氮肥对硝酸盐的积累是:硝酸钙＞DMPP＞尿素＞有机无机复混肥＞尿素+微量元素＞碳酸氢铵。配施微量元素及氮磷钾的协同吸收均能降低硝酸盐含量。综合考虑产量和品质指标,以有机无机复混肥处理效果较好。小青菜产量和Vc含量随着施氮量的提高而提高,但硝酸盐含量也随之提高;小青菜产量和Vc含量随着施氮时期的延后而降低,硝酸盐含量高峰出现在追肥后20d左右。     

Behavior of soil boron and boron uptake by M.26 apple rootstock as affected by application of different forms and nitrogen rates

Abstract

The changes in availability and uptake of boron (B) by M.26 apple rootstocks as affected by applications of different forms and rates of nitrogen (N) were examined. The study was carried out in a greenhouse using soil with low contents of organic matter, clay, calcium carbonate, NH₄‐oxalate soluble aluminum (Al) and iron (Fe), NH₂OH·HCl extractable manganese (Mn), poor cation exchange capacity and low pH. Soil N application was in the form of urea, calcium nitrate, ammonium sulphate, or ammonium nitrate at rates of 0, 17, 34, and 51 mg N kg^?1. After 1, 3, and 5 days of N application, soil B fractions were determined: B in soil solution, B specifically and non‐specifically adsorbed on soil surfaces, B occluded in Mn oxyhydroxides, and B occluded in crystalline Al and Fe oxides. The results showed that N as calcium nitrate and ammonium nitrate increased B both in soil solution and non‐specifically adsorbed on soil surface and decreased B concentration on Al and Fe oxides. This indicates that N‐NO₃ inhibited B sorption on Fe and Al oxides. Maximum B desorption from Fe and Al oxides was obtained within one day after N‐NO₃ was supplied. Nitrogen application as calcium nitrate and ammonium nitrate increased availability and uptake of B by plant roots. Thus, it was concluded that apple trees planted on coarse‐textured soils where risk of B deficiency is high, calcium nitrate or ammonium nitrates would be appropriately to apply to keep B more available.     

不同供氮形态下油菜幼苗对盐胁迫的响应

为比较不同供氮形态下油菜对盐胁迫的响应,通过供应铵态氮和硝态氮,探讨盐胁迫对油菜幼苗生物量、 光合作用、 离子含量等的效应。结果表明: 非盐胁迫条件下的硝态氮处理的植株生物量和叶片光合参数均显著高于其它处理; 在盐胁迫条件下,两种供氮形态处理油菜的生长和光合均受到明显抑制,其中铵态氮处理表现的抑制效应较显著,且其光合抑制主要来自气孔限制。在两种供氮条件下,盐胁迫使得植株Na+浓度均显著增加,其中铵态氮处理的叶片和叶柄中Na+浓度的增幅大于硝态氮处理,而其根中Na+浓度则小于硝态氮处理。盐胁迫导致两种供氮形态下整株和叶柄中K+浓度均显著降低,而在根中,则只造成硝态氮处理的K+浓度的显著降低。在整株水平上,盐胁迫下铵态氮处理的K+ 、 Na+的选择性比率（SK,Na）要显著低于硝态氮处理。综上,在盐胁迫条件下,硝态氮处理对K+吸收维持较高的相对选择性是其耐盐性高于铵态氮处理的重要原因。     

Ammonium increases the net rate of sodium influx and partitioning to the leaf of muskmelon

The influx and partitioning of sodium (Na) is controlled by potassium (K)/Na selectivity/exchange mechanisms. Since ammonium‐nitrogen (NH₄‐N) has been shown to inhibit K absorption and K/Na selectivity/exchange mechanisms control Na influx and partitioning, our objective was to observe if NH₄‐N affects Na influx and partitioning in muskmelon. Muskmelon (Cucumis melo L.) were grown in a pH controlled nutrient solution with 100 mM NaCl in a complete nutrient solution containing either 10 mM nitrate‐nitrogen (NO₃‐N) or NH₄‐N. With NH₄‐N, Na accumulation and partitioning to the leaf blade increased while K absorption was almost completely inhibited. A second study omitted K to simulate the inhibition of K absorption by NH₄‐N and monitored Na accumulation and partitioning as K was depleted in the plant. Sodium accumulation and partitioning to the leaf increased as K decreased in the plant, mirroring the effect of NH₄‐N. Roots appeared healthy in both studies. Our work indicates that at a given level of NaCl stress, NO₃‐N reduces the level of stress experienced by muskmelon plants through reducing the net rate of Na influx and transport to the sensitive leaf blade, not by reducing chloride (Cl) absorption, thereby permitting these plants to “avoid”; this stress.     

Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations

The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m^–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)^–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)^–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)^–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)^–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)^–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m^–1 may have a deleterious effect on maize growth.     

EFFECT OF FOLIAR APPLICATION OF UREA,MOLYBDENUM, BENZYLADENINE,SUCROSE AND SALICYLIC ACID ON YIELD,NITROGEN METABOLISM OF RADISH PLANTS AND QUALITY OF EDIBLE ROOTS

In 2006–2007 small radish was cultivated in a pot experiment. Foliar applications were applied twice with solutions of the following compounds: 1) control (water); 2) urea; 3) urea+molybdenum (Mo), 4) urea+Mo+benzyladenine (BA); 5) urea+Mo+BA+sucrose; 6) urea+Mo+BA+sucrose+salicylic acid (SA), 7) BA; 8) SA; and 9) sucrose. The above solutions contained following concentrations of compounds: urea 20 g dm^?3, sucrose 10 g dm^?3, Mo 1 mg dm^?3, BA 5 mg dm^?3 and SA 10 mg dm^?3. In comparison with the control, spraying plants with the solution of urea+Mo+BA+sucrose and SA only caused an increase in leaf mass of one plant. Foliar applications did not have any effect on the yield of edible roots. When compared with the control, the use of sucrose resulted in a decreased content of nitrate (V) in leaves, while the application of urea+Mo+BA+sucrose led to elevated content of nitrate (V) in roots. In case of spraying plants with solutions containing urea (combinations no. 2–6) there was a tendency to increase ammonium (NH₄ ⁺) and nitrogen (N)-total content in leaves and roots, and increase in N uptake by leaves and by the whole plant but not by the radish roots. In combinations 7–9 we noted a decline in the level of ascorbic acid, and in combinations 2–6 there was a decrease in the content of soluble sugars in roots. In comparison with the control, an increase was observed in combinations 2 and 3, while in combinations 7–9 a decrease in the content of free amino acids in roots was observed. None of the combinations with foliar application caused any significant changes in the content of assimilative pigments in radish leaves and concentration of nitrate (III), dry matter in leaves and roots, the content of phenolic compounds, content of potassium (K), magnesium (Mg), calcium (Ca) extracted with 2% acetic acid in roots as well as free radical activity of radish roots.     

Effect of nitrogen fertilizers on leaf and soil nitrogen levels in highbush blueberries

Abstract

Leaf N and soil nitrate and ammonium levels were monitored in 1986 and 1987 following N fertilization of 8–9 year old highbush blueberries. Urea was applied at 76 kg N/ha in a single application at bud break or in two applications (split) at bud break and petal fall. Controlled release fertilizers (CRF), of two different residual effects (Osmocote 3 mo., Osmocote 8 mo.) were applied at 38 kg N/ha or 76 kg N/ha at bud break. Compared to controls, N applications increased soil ammonium and nitrate levels early in the season and leaf N levels throughout the season. Urea provided a greater increase in leaf N and soil ammonium levels than CRF. Split urea applications increase leaf levels slightly over single urea treatments. Fertilizers increased soil ammonium and nitrate levels below the root zone, indicating that some leaching losses occurred.     

Supplements of Nickel Affect Yield,Quality, and Nitrogen Metabolism When Urea or Nitrate is the Sole Nitrogen Source for Cucumber

ABSTRACT

Influences of nickel (Ni) concentrations in the nutrient solution on yield, quality, and nitrogen (N) metabolism of cucumber plants (Cucumis sativus cv ‘RS189’ and ‘Vikima’) were evaluated when plants were grown either with urea or nitrate as the sole N source. The cucumber plants were treated with two N sources, urea and nitrate as sodium nitrate (NaNO₃) at 200 mg L^?1, and three concentrations of Ni as nickel sulfate (NiSO₄·6H₂O; 0, 0.5, and 1 mg L^?1). Treatments were arranged in a randomized block design with six replicates. The highest concentration of Ni in the leaves (1.2 mg kg^?1 Dwt) was observed in the urea-fed plants at 1 mg L^?1 Ni concentration. Additions of Ni up to 0.5 mg L^?1 had no effect on the fruit Ni concentration in the both urea and nitrate-fed plants. Yield significantly (p < 0.05) increased with the Ni supplements from 0 to 0.5 mg L^?1 (10 and 15% in ‘RS189’ and ‘Vikima’, respectively), but decreased when 1 mg L^?1 Ni applied to the solutions in urea-fed plants. Nitrate-fed plants had a higher percentage of total soluble solids compare to those urea-fed plants. Nitrate concentrations of the fruits in urea-fed plants in both cultivars were reduced by approximately 50% compared to those nitrate-fed plants. The reduction of nitrate concentration in the fruits became more pronounced as the Ni concentration increased in the solution. The rate of photosynthesis (Pn) increased with the increase of the Ni concentration in the solution with urea-fed plants. Both N concentration and nitrate reductase (NR) activity of young leaves were higher in urea-fed plants at 0.5 mg l^?1 Ni concentration. Ni supplements enhanced the growth and yield of urea-fed plants by increasing Pn, N concentration and NR activity. It can be concluded that Ni supplements (0.5 mg l^?1) improve yield, quality, and NR activity in urea-fed cucumber plants.