Rhizosphere effects of maize hybrids and N forms on Cd bioavailability in a limed soil

Replacing new corn genotypes in agricultural practices requires adequate information on the reaction of the selected hybrids to Cd uptake in Cd-polluted soil and an understanding of interactions with N fertilizers. A 2 × 2 × 3 factorial pot experiment with limed soil (pH 8), two maize (Zea mays) hybrids (Pioneer cultivar yellow and Pioneer cultivar white), two N fertilization forms (NH₄ ⁺ and NO₃ ^?) and three Cd exposures (0, 2 and 5 mg kg^?1 soil) was conducted under greenhouse conditions. Shoot dry mass increased significantly with NH₄ ⁺ nutrition compared with NO₃ ^? nutrition in both maize hybrids, with greater negative influence of Cd application combined with NH₄ ⁺ nutrition. The yellow cultivar had significantly greater shoot dry mass and lower Cd uptake than the white cultivar. Both hybrids exhibited similar N uptake in shoots and roots, with the exception of yellow cultivar with NH₄ ⁺ nutrition without Cd application. NO₃ ^? nutrition always decreased Cd uptake in both cultivars compared with NH₄ ⁺ nutrition. The N balance (mean across cultivars and Cd supply) after harvest showed most N uptake with NH₄ ⁺ nutrition (63.4%) and N_min remains in the soil with NO₃ ^? nutrition (48.7%). Soil pH decreased more with NH₄ ⁺ (?0.95 pH units) than NO₃ ^? nutrition (?0.21).     

Short-term competition between crop plants and soil microbes for inorganic N fertilizer

Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH₄⁺), nitrate (NO₃⁻) or a combination thereof are expected to differ in soil N transformation rates and fates of NH₄⁺ and NO₃⁻. Using ¹⁵N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH₄⁺, NO₃⁻ or NH₄NO₃. Within each fertilizer treatment traces of ¹⁵NH₄⁺ and ¹⁵NO₃⁻ were added separately. During 8 days of fertilization the fate of fertilizer ¹⁵N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied ¹⁵N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO₃⁻ than NH₄⁺ independent of initially applied N form. Surprisingly, no inhibitory effect of NH₄⁺ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH₄⁺ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH₄⁺ in both soils. The rapid conversion of NH₄⁺ to NO₃⁻ and preferential use of NO₃⁻ by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high concentrations of NO₃⁻ and shift towards enhanced reliance on NO₃⁻ for their N supply.     

Effects of Nitrogen Levels and Nitrate/Ammonium Ratios on Oxalate Concentrations of Different Forms in Edible Parts of Spinach

Two hydroponic experiments were carried out to investigate the effects of nitrogen (N) levels and forms on the oxalate concentrations of different form in edible parts of spinach. Nitrogen was supplied at five levels (4, 8, 12, 16, 20 mM) in Experiment 1 and five ratios of nitrate (NO₃ ^?) to ammonium (NH₄ ⁺) (100/0, 75/25, 50/50, 25/75, 0/100) at a total N of 8 mM in Experiment 2. Biomass of spinach increased markedly from 4 mM to 8 mM N and reached the flat with further increase in N. The total oxalate and soluble oxalate in leaves and shoots (edible parts) increased significantly with increasing N levels from 4 to 12 mM, while the total oxalate and insoluble oxalate decreased markedly when N level was further increased from 12 to 20 mM. Oxalates of different forms in petioles increased first and then decreased and elevated again with increasing nitrogen levels. In the second experiment, decreasing NO₃ ^?/NH₄ ⁺ ratios markedly increased at first and then significantly decreased the biomass of spinach plants and the maximum biomass was recorded in the treatment of the NO₃ ^?/NH₄ ⁺ ratio of 50:50. The oxalate concentrations of different form in leaves and shoots were all decreased obviously as the ratio of NO₃ ^?/NH₄ ⁺ decreased from 100:0 to 0:100. Concentrations of total oxalate and soluble oxalate in petioles could be reduced by increasing ammonium proportion and were the lowest as the ratio of NO₃ ^?/NH₄ ⁺ was 50:50 and insoluble oxalate decreased as nitrate/ammonium ratio decreased. The concentrations of oxalate forms in leaves were all higher than those in petioles and soluble oxalate was predominant form of oxalates in both trials. It is evident that high biomass of spinach can be achieved and oxalate concentrations of different forms can be reduced by modulating N levels and NO₃ ^?/NH₄ ⁺ ratio, so this will benefit for human health especially for those people with a history of calcium oxalate kidney stones.     

Effect of Nitrate/Ammonium Ratios on Growth,Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO₃^?)/ammonium (NH₄⁺) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH₄⁺ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO₃^? and NH₄⁺ compared to NO₃^? or NH₄⁺ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH₄⁺. The microelements concentrations were generally increased with more NH₄⁺ added. In addition, plants fed with higher NO₃^?/NH₄⁺ ratios resulted in more minerals accumulation.     

Effects of Fertilizer Nitrogen on Short‐Term Nitrogen Loss in Bypass Flow in a Vertisol

Bypass flow, the vertical flow of free water along the walls of macropores or preferential flow paths in the soil, can lead to movement of fertilizer nutrients beyond the reach of plants. Fertilizer type and the rate of application, as well as the amount, frequency, and intensity of rainfall, can influence the amount of fertilizer nitrogen (N) loss in leaching or bypass flow. The effect of fertilizer N form and rate of application on N recovery in bypass flow in a Kenyan Vertisol was determined. Calcium nitrate and ammonium sulfate, used to supply nitrate (NO₃ ^?)‐N and ammonium (NH₄ ⁺)‐N, respectively, were surface‐broadcast to 40‐cm‐long undisturbed soil columns at equivalent rates of 50, 100, and 200 kg N ha^?1. Using a rainfall simulator, two rainfall events (30 mm of water applied in 1 h) were applied to the soil columns, one before and the other after fertilizer application. Total N, NO₃ ^?‐N, and NH₄ ⁺‐N concentrations in the bypass flow were determined after the second rainfall event. The application of NH₄ ⁺‐N, regardless of the rate, had no effect on N recovery in the bypass flow. When nitrate N was applied, the amount of fertilizer N recovered in the bypass flow significantly increased with the rate of NO₃ ^?‐N application. Of the total N in the bypass flow, 24 to 48% was derived from the soil, the bulk of which was organic N. It is concluded that following the application of NO₃ ^?‐N, bypass flow is an important avenue of loss of both fertilizer and soil N from Vertisols.     

DEVELOPMENT OF A SOIL N TEST FOR FERTILIZER REQUIREMENTS FOR WHEAT

Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO^? ₃)- N, soil ammonium (NH ⁺ ₄)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO^? ₃-N and NH ⁺ ₄-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH ⁺ ₄-N and NO^? ₃ -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO^? ₃-N.     

Fruit Yield of Tomato Cultivated on Media with Bicarbonate and Nitrate/Ammonium as the Nitrogen Source

ABSTRACT

This article presents the effects of nitrate/ammonium (NO₃ ^?/NH₄ ⁺), applied at different proportions to the root media with or without 5 mmol bicarbonate (HCO₃ ^?), on the yield and chemical composition of tomato fruit. Tomato plants were grown hydroponically (pH 6.9) in glasshouse conditions. The yield of fruit fresh matter from four clusters obtained from plants grown on the medium with NH₄ ⁺ was about 25% lower than from the plants grown on the medium containing NO₃ ^? as the nitrogen (N) source. Supplying NO₃ ^?/NH₄ ⁺ at a ratio of 4:1 increased the fruit yield by about 20% in comparison with the value recorded for NO₃ ^??plants. The enrichment of the medium with HCO₃ ^? stimulated the bearing, while the result depended on the ratio of NO₃ ^?/NH₄ ⁺. A combined treatment of HCO₃ ^? with NO₃ ^? or NH₄ ⁺ in the medium increased yields by about 28% and 11%, respectively, in comparison to plants cultivated without HCO₃ ^?. The application of NO₃ ^?/NH₄ ⁺ at ratios of 4:1 and 1:1 with HCO₃ ^? increased the respective yields by about 16% and 10% in comparison with plants grown without HCO₃ ^?. Modifications in the composition of the media affected the accumulation of organic solutions in the fruit. The NH₄ ⁺ nutrition effected a 20% decrease in the accumulation of reducing sugars in the fruit in comparison to the fruit of plants grown in media with NO₃ ^?. In the cultivation of plants in media with various NO₃ ^?/NH₄ ⁺ proportions the intermediate values of the reduced sugar concentrations were recorded in comparison with the values obtained for NO₃ ^??plants and NH₄ ⁺?plants. The enrichment of media with HCO₃ ^? increased the concentration of sugars in fruit from about 28% (for NO₃ ^??plants) to about 10% (for NH₄ ⁺?plants).

Malate and citrate are the main constituents of carboxylates in tomato fruit. The form of nitrogen applied to the medium did not significantly affect the concentration of carboxylates in fruit. Significant differences in carboxylate concentrations appeared in fruit grown on media enriched with HCO₃ ^? ions. In comparison with the cultivation without HCO₃ ^?, increases in the accumulation of carboxylates varied from about 22% to 30% depending on the form of the applied nitrogen. The concentration of amino acids in the fruit of plants grown with NH₄ ⁺ exceeded that in NO₃ ^??plants by about 55%. In the plants grown on media of modified NO₃ ^?/NH₄ ⁺ proportions, the concentration of amino acids in fruits were positively correlated with the level of NH₄ ⁺ in the medium. The enrichment of media with HCO₃ ^? stimulated a further increase in amino acid concentration in fruit by about 9% in NO₃ ^? plants and about 21% in NH₄ ⁺ plants compared with the respective control (without HCO₃ ^?).     

Iron Metabolism in Tomato and Watermelon Plants: Influence of Nitrogen Source

Abstract

Tomato and watermelon plants were grown in nutrient solutions in which nitrogen (N) was supplied as NO₃ ^? (6 mM‐N) or NH₄ ⁺ (6 mM‐N). The experiments were conducted to evaluate the effect which different N sources exert on iron (Fe) uptake and accumulation, on the enzymatic activities of aconitase (Aco), chelate reductase (FeCH‐R), peroxidase (POD), catalase (CAT), and Fe‐superoxide dismutase (FeSOD), and on biomass production. For both species of plants, fertilization with NH₄ ⁺ caused the total Fe concentration to be lower, in the roots and in the leaves in relation to the concentrations recorded in plants fertilized with NO₃ ^?. The response of the enzymes related to Fe correlated with their concentration. The plants treated with N?NO₃ ^? registered the highest activities in Aco, FeCH‐R, POD, and CAT for both tomato and watermelon. On the other hand, only in the tomato plants was the superoxide dismutase (SOD) activity appreciably influenced primarily by NH₄ ⁺, due possibly to the toxic effect of this N source. Finally, in relation to biomass production, fertilization with NH₄ ⁺ drastically reduced growth in the tomato plants, while in watermelon plants, no significant alteration was detected in dry‐matter production, regardless of the N form used. It was concluded that the response of the parameters analyzed to NH₄ ⁺ fertilization, in tomato and watermelon, compared to fertilization with NO₃ ^? was similar. By contrast, tomato plants, but not watermelon plants, were negatively influenced by NH₄ ⁺.     

Role of Ammonium to Limit Nitrate Accumulation and to Increase Water Economy in Wild Swiss Chard

ABSTRACT

The present study was performed to characterize the interaction between nitrogen (N) form and availability with respect to growth, water relations, and mineral nutrition of wild swiss chard (Beta macrocarpa Guss). Plants were cultured hydroponically with two levels of N concentrations, high-N (2.5 mM) or low-N (0.5 mM), added as nitrate (NO^? ₃) or ammonium (NH⁺ ₄). At high N, growth was affected significantly by N form. If the NO^? ₃ medium was considered as control, the use of NH⁺ ₄ decreased dry matter production and leaf area by ca. 35%. Use of NH⁺ ₄ led to water economy and did not affect the nutrient content of the plant tissues. Compared to growth with high N, plants growth fell in either low- NO^? ₃ or low- NH⁺ ₄ medium. In this case, the difference between the two N sources was not significant. Our results showed that the replacement of NO^? ₃ by NH⁺ ₄ as the N source decreased the NO^? ₃ concentration in consumable leaves and increased the water use efficiency.     

Uptake,Transport, and Concentration of Chloride and Sodium in Three Citrus Rootstock Seedlings

ABSTRACT

Aspects of ammonium (NH₄ ⁺) toxicity in cucumber (Cucumis sativus L.) were investigated following growth with different N sources [nitrate (NO₃ ^?), NH₄ ⁺, or NH₄NO₃] supplied in concentrations of 1, 5, 10, or 15 mM. Plant dry weights and root: shoot ratios were lower with NH₄ ⁺-fed plants than with NO₃ ^?-fed plants. Ammonium accumulated strongly in leaves, stem, and roots when the concentration in the growth medium exceeded 1 mM. The increase in tissue NH₄ ⁺ coincided with saturation of glutamine synthetase activity and accumulation of glutamine and arginine. Low tissue levels of calcium and magnesium in the NH₄ ⁺-fed plants constituted part of the NH₄ ⁺-toxicity syndrome. Additions of small amounts of NH₄ ⁺ to NO₃ ^? -grown cucumber plants markedly increased the growth.     

不同肥料结构对红壤稻田氮素迁移的影响

不同肥料结构对红壤稻田淹水层、不同深度渗漏水、外排水和土壤剖面中氮素的含量、形态及其动态变化的影响研究结果表明 ,各处理淹水层、外排水和渗漏水中NH4+-N含量明显高于NO3--N。淹水层中N的含量 ,水稻生育前期以单施化肥的高 ,约相当于配施有机肥的 1.18～ 1.20倍 ,而水稻生育后期 ,后者为前者的 1.11～ 1.2 1倍。各处理外排水中N素的输出量均以苗期最高 ,单施化肥明显大于配施有机肥。土壤剖面中NH4+-N向下迁移比碱解N更为明显 ,且配施有机肥的远高于单施化肥的 ,而NO3--N则相反。不同深度渗漏水中NO3--N的比例 ,上层 (30cm)低于下层 (50cm) ,随水逸出的N量各处理渗漏水均小于外排水 ;随水输入的N量远低于随水输出的N量 ,且以单施化肥的N亏损最大。水稻未利用的N量也以单施化肥的最大 ,约为配施有机肥的 1.0 9倍。     

Nitrate reduction to ammonium and organic nitrogen in an estuarine sediment

Nitrate reduction to NH₄⁺ and incorporation into organic matter was investigated in sediment-water systems composed of a 2.4-cm layer of estuarine sediment covered by 2 cm of water. Between 15 and 28% of the ¹⁵N-labelled NO₃^? added to the sediment or floodwater of the systems was recovered as NH₄⁺ and organic N. The results indicated that NO₃^? was reduced to NH₄⁺ by a dissimilatory mechanism. A separate experiment examined the influence of redox potential (+300, 0 and ?200 mV) on NO₃^? reduction in sediment suspensions maintained at pH 7.5. Conversion of NO₃^? to NH₄⁺ and organic N increased markedly with decreasing redox potential. The results suggested that although the reaction accounted for 35–42% of the NO₃^? reduced under intensely-reduced conditions (?200 mV), the significance of the reaction in nature was dependent upon NO₃^? movement into zones sufficiently reduced for reduction of NO₃^? to NH₄⁺ instead of denitrification. Under conditions in which NO₃^? moved downward through a sediment-water column into a reduced sediment zone approximately 15% of the NO₃^? was reduced to NH₄⁺ and recycled in the sediment.     

The influence of the form of nitrogen nutrition on uptake and distribution of cadmium in lettuce varieties

Four lettuce (Lactuca saliva L.) varieties ('Benita’, ‘Wendy’, ‘Mirena’, and ‘Jacky') were grown for 43 days in a pH‐controlled complete nutrient solution without cadmium (Cd) or with either 0.01 or 0.03 mg Cd/1 and with NH₄ or NO₃ as the form of nitrogen nutrition. Cadmium did not affect dry matter yield. ‘Wendy’ had a significantly higher total dry matter production when grown on NO₃ compared to NH₄, whereas growth of ‘Mirena’ was best on NH₄ (P<0.05). Dry weights of ‘Benita’ and ‘Jacky’ were not affected by the N source. Cadmium concentrations in shoots (and roots) of plants grown on NH₄ were significantly higher than in plants grown on NO₃. The Zn concentrations in the shoots were also enhanced. The distribution of Cd in the lettuce varieties was independent of the form of N nutrition. It is concluded that the N source directly affects the amount of Cd taken up, without influencing the Cd distribution.     

Nitrogen fertilization inhibits soil microbial respiration regardless of the form of nitrogen applied

We tested how amendments of different forms of nitrogen (N) affect microbial respiration rates by adding six different forms of N (NH₄NO₃, (NH₂)₂CO (urea), KNO₃, NH₄Cl, (NH₄)₂SO₄, Ca(NO₃)₂) to three distinct soils. All inorganic N forms led to a net reduction in microbial respiration, and the magnitude of the observed response (up to 60 % reduction) was consistent across all soils and negatively correlated with N concentration. Urea also reduced respiration rates in nearly all cases, but the effect was attenuated by the associated input of labile organic carbon. We observed decreases in respiration regardless of soil type, the specific N counter ion, N added as NH₄⁺ or NO₃⁻, or the effects of N form on soil pH, suggesting that decreases in respiration rates were mainly a direct result of the increase in soil N availability, rather than indirect effects caused by the form of N added.     

Effect of Inorganic N Composition of Fertilizers on Nitrous Oxide Emission Associated with Nitrification and Denitrification

We studied the effect of repeated application (once every 2 d) of a fertilizer solution with different ratios of NH₄ ⁺ - and NO₃ ^?-N on N₂O emission from soil. After the excess fertilizer solution was drained from soil, the water content of soil was adjusted to 50% of the maximum water-holding capacity by suction at 6 × 10³ Pa. Repeated application of NH₄ ⁺- rich fertilizer solution stimulated nitrification in soil more than NO₃ ^?-rich fertilizer. Although the evolution of N₂O through nitrifier denitrification tended to increase with the repeated addition of a fertilizer solution rich in NH₄ ⁺ rather than in NO₃ ^?, the contribution of nitrifier denitrification remained at levels of 20 to 36% of the total emission regardless of the inorganic N composition. The total emission of N₂O also tended to increase with the application of NH₄ ⁺- rather than NO₃ ^?-rich fertilizer. It was suggested that the coupled process of nitrification and denitrification at micro-aerobic sites became important when fertilizer rich in NH₄ ⁺ was applied to soil under relatively aerobic conditions.     

Effect of N‐form on macronutrient and micronutrient concentration and uptake of creeping bentgrass 1

Abstract

Nitrogen‐form effect on nutrient uptake and the subsequent concentration of nutrients in turfgrass plant tissue has not been thoroughly investigated. This study evaluated the effects of clipping regime and N‐form on the tissue concentration of macronutrients and micronutrients and macronutrient uptake in ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.). Turfgrass plugs were grown under greenhouse conditions in a modified Hoagland's solution with a combination of three nutrient solutions (100% NO₃ ^?, 100% NH₄ ⁺, and 50:50 ratio of NH₄ ⁺:NO₃ ^?) and two cutting regimes (cut and uncut). Concentrations of macronutrients and micronutrients were determined for shoot, root and verdure. Nutrient uptake was determined weekly. Uncut NO₃ ^?‐treated plants accumulated higher concentrations of K, Ca, Mg, B and Cu in the shoot tissue; P, K, Ca, Mg, B, Cu, Mn and Zn in the root tissue; and P, Ca, Mg, B, Fe and Mn in the verdure compared to uncut NN₄ ⁺‐treated plants. Nitrate uptake was greater with uncut NO₃ ^?‐treated plants than was NH₄ ⁺ absorption with uncut NH₄ ⁺‐treated plants. Plants grown with the uncut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with the uncut NO₃ ^? and 50:50 treatments adsorbed higher amounts of P, K, and Ca compared to the NH₄ ⁺ treatment. The cut NO₃ ^?‐treated plants accumulated higher concentrations of K in the shoot tissue; P, Ca, Mg, B, Cu, Fe and Mn in the root tissue; and B in the verdure than did the cut NH₄ ⁺‐treated plants. Cut NO₃ ^?‐treated plants adsorbed less NO₃ ^? than did cut NH₄ ⁺‐treated plants adsorbed NH₄ ⁺. The cut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with NO₃ ^? and 50:50 treatments, under both cutting regimes, resulted in higher concentrations of most macro‐ and micronutrients and greater nutrient uptake compared to the NH₄ ⁺‐treated plants.     

Nitrogen Source and Concentration Affect Growth and Performance of Bedding-Plant Impatiens

ABSTRACT

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the United States, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. The objective was to determine the N concentration and the nitrate (NO₃ ^??N):ammonium (NH₄ ⁺?N) ratio of N source that optimized bedding-plant impatiens growth and flower development. Four N concentrations (3.5, 7, 10.5, and 14 mmol N · L^?1) were used in factorial combination with four ratios of NO₃ ^??N:NH₄ ⁺?N (4:0, 3:1, 1:1, and 1:3). Application of treatments was made for 30 d. Then for 10 d only deionized water was applied to reduce salt buildup. Substrate pH was lowest (4.9) with the NH₄ ⁺?N source and electrical conductivity (EC) highest, but never > 2.4 dS m^?1. Nitrogen concentration and N source displayed an interaction for most growth parameters. Shoot fresh and dry weights and flower bud number were maximized at the 1:3 NO₃ ^??N:NH₄ ⁺?N ratio with a N concentration of 10.5 mmol L^?1. However, plant diameter, leaf number, and leaf chlorophyll content responded quadratically to N form ratio, with the 1:1 ratio optimum at a concentration of 10.5 mmol N· L^?1.     

Tomato growth and mineral composition as influenced by nitrogen form and light intensity

Abstract

Tomato plants were grown in sand culture with NH⁺ ₄, and NO^? ₃, forms of N and three levels of light. Plants supplied with NH⁺ ₄, nutrition under high light intensity had symptoms of stunting, leaf roll, wilting, interveinal chlorosis of the older leaves, and one third the dry weight of N0₃‐fed plants. In contrast, growth of plants receiving NH⁺ ₄, nutrition under shade appeared normal although dry weight was reduced. NH₄‐N nutrition suppressed K, Ca and Mg accumulation in tissues and increased P contents as compared to NO₃‐N nutrition.     

Comparative Study of the Leachates from Syngonium podophyllum using Different Fertilization Techniques and Nitrogen Forms

The objectives of this article were to analyze the evolution of the nutrient parameters of the leachates collected from Syngonium podophyllum var. Silver plants cultivated for 20 weeks in a buried greenhouse with four methods of fertilization. The treatments were T₁, standard liquid feeding (SLF) [7.0 mmol L^?1 nitrate (NO₃ ^?) nitrogen (N), 0.3 mmol L^?1 phosphorus (P), and 3.5 mmol L^?1 potassium (K)] after transplanting; T₂, liquid feeding soluble fertilizer (LFSF) [6.9% NO₃ ^? N, 11.1% ammonium (NH₄ ⁺) N stabilized by 3,4-dimethylpyrazole phosphate, 8.0% P₂O₅, and 14.0% K₂O] after transplanting; T₃, controlled release fertilizer (CRF I) (7.4% NO₃ ^? N, 8.6% NH₄ ⁺ N, 8.0% P₂O₅, and 12.0% K₂O) applied before planting and half concentration of SLF from 45 days after transplanting; and T₄, controlled release fertilizer (CRF II) (8.5% NO₃ ^? N, 7.5% NH₄ ⁺ N, 8.0% P₂O₅, and 12.0% K₂O) applied before planting and half concentration of SLF from 45 days after transplanting. Solution pH, electrical conductivity (EC), NO₃ ^? N, NH₄ ⁺ N, K, and P concentrations in the leachate were analyzed weekly. Plant quality was assessed at the end of the trial through objective and subjective parameters. Significant differences among the different fertilization methods were observed. CRF treatments resulted in the greatest nutrient leachate concentration during the first 6 weeks of the study, and afterward it decreased gradually until the end of the cultivation. CRF I showed greater leachate concentrations of N, P, and K than the others during the first half of the study. The concentrations of NO₃ ^? N and P from all the fertilizer types were often above the permissible levels cited in the federal Clean Water Act. The best-quality plants were obtained with CRF II, whereas the greatest height and Aerial Dry Weight (ADW) were obtained with CRF treatments and the greatest Root Dry Weight (RDW) was obtained with the NH₄ ⁺ N treatments.     

Organic farming promotes selective uptake of glycine over nitrate uptake by pakchoi

ABSTRACT

Understanding how plants use of various nitrogen (N) sources is important for improving plant N use efficiency in organic farming systems. This study investigated the effects of farming management practices (organic and conventional) on pakchoi short-term uptake of glycine (Gly), nitrate (NO₃ ^?) and ammonium (NH₄ ⁺) under two N level conditions. Results showed that plant N uptake rates and N contributions from the three N forms in the low N (0.15 μg N g^?1 dry soil) treatment did not significantly differ between the organic and conventional soils, except the significantly greater Gly contribution in organic soil at 24 h after tracer addition. Under high N (15 μg N g^?1 dry soil) conditions, the N uptake rates, uptake efficiencies, and N contributions of Gly and NH₄ ⁺-N were significantly greater in pakchoi cultivated in the organic soil compared to conventional soil, whereas the N uptake rates and N contributions from NO₃ ^–-N decreased in pakchoi cultivated in the organic soil. The greater Gly-N uptake in plants grown in high-N treated organic soil may be related to the greater gross N transformation, Gly turnover rate and the increased expression of an amino acid transporter gene BcLHT1. Intact Gly contributed at most 6% to Gly-derived N at 24 h after tracer additions, which accounting for about 1.24% of the total N uptake in organic soil. Our study suggested that Gly-N and other organic source N might serve as a more important compensatory N source for plants in organic farming.