Effect of NO3:NH4 ratio and light intensity on nitrogen partitioning in pepper plants

Pepper plants were hydroponically grown in a growth chamber with two levels of light intensity (300 and 240 w/m²) and two NO₃:NH₄ ratios (100:0 and 80:20). Plants grown with both N forms (80:20) under high light regime displayed greater concentrations of free NH₄, organic soluble N and insoluble N than NO₃, treated plants, this effect was more pronounced for stem, petioles and root. By contrast, nitrate‐ammonium fed plants with light reduced over 25% presented similar concentrations of organic N (soluble and insoluble) as compared to plants supplied with NO₃ as sole source of N, however, the amount of free NH₄ in stem and root was increased. Results indicat that NH₄ supplied at low concentration was more deletereous for pepper plants grown under high light conditions, when light was reduced, plants presented an alleviation of toxic effect of NH₄ supply. Finally, nitrogen use efficiency is related to form of N nutrition and the light supplied to crop.     

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.     

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.     

Influence of Ammonium and Nitrate Nutrition on Plant Growth and Zinc Accumulation by Indian Mustard

ABSTRACT

The source of nitrogen (N) used in soil fertility practices affects plant growth, nutrient absorption, and the availability of nutrients. Consequently, the potential of plants to extract zinc (Zn) from soils may be increased by controlling the ratio of NH₄ ⁺ to NO₃ ^? to maximize growth and Zn accumulation. The objectives of this research were to determine the effects of Zn supply and different molar ratios of NH₄ ⁺ to NO₃ ^? on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.). In a factorial experiment with solution culture, Indian mustard (accession 182921) was supplied with two concentrations of Zn (0.05 and 4.0 mg L^?1) in combination with six N treatments with different molar percentage ratios of NH₄ ⁺ to NO₃ ^? (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for three weeks. Zinc supplied at 0.05 mg Zn L^?1 represented a common concentration of Zn in solution culture, whereas 4.0 mg Zn L^?1 was excessive for plant nutrition. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, which became severe if plants were supplied with 80% of N as NO₃ ^?. Supplying high proportions of NO₃ ^? in the nutrient medium stimulated Zn accumulation, whereas increasing proportions of NH₄ ⁺ (up to 50% of the total N) enhanced shoot growth. The pH of nutrient solutions generally decreased with increasing proportion of NH₄ ⁺ in solutions and with increased Zn supply. The Zn phytoextraction potential of Indian mustard was maximized, at about 15 mg Zn plant^?1, if plants received 10% of the total N as NH₄ ⁺ and 90% as NO₃ ^?.     

Growth,Nitrate Accumulation,and Macronutrient Concentration of Pakchoi as Affected By External Nitrate-N: Amino Acid-N Ratio

ABSTRACT

A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO₃ ^?) accumulation, and macronutrient concentrations of pakchoi (Brassica chinensis L.) in hydroponics. Plants were supplied with NO₃ ^? and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO₃ ^?-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO₃ ^?-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO₃ ^?-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO₃ ^?-N/AA-N ratios reduced NO₃ ^? concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO₃ ^?-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO₃ ^? concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields.     

Time of availability influences mixed‐nitrogen‐induced increases in growth and yield of wheat 1

Previous studies have indicated that under hydroponic conditions, spring wheat (Triticum aestivum) plants produce higher grain yields, more tillers, and increased dry matter when continuously supplied with mixtures of NO₃ and NH₄ than when supplied with only NO₃. The objective of this study was to determine if mixed N needs to be available before or after flowering, or continuously, in order to elicit increases in growth and yield of wheat. During vegetative development, plants of the cultivar ‘Marshal’ were grown in one of two nutrient solutions containing either a 100/0 or 50/50 mixture of NO₃ to NH₄ and, after flowering, half the plants were switched to the other solution. At physiological maturity, plants were harvested, separated into leaves, stems, roots, and grain and the dry matter and N concentration of each part determined. Yield components and the number of productive tillers were also determined. Availability of mixed N at either growth stage increased grain yield over plants receiving continuous NO₃, but the increase was twice as large when the mixture was present during vegetative growth. When the N mixture was available only during vegetative growth the yield increase was similar to that obtained with continuous mixed N. The yield increases obtained with mixed N were the result of enhanced tillering and the production of more total biomass. Although plants receiving a mixed N treatment accumulated more total N than those grown solely with NO₃, the greatest increase occurred when mixed N was available during vegetative growth. Because availability of mixed N after flowering increased the N concentration over all NO₃ and pre‐flowering mixed N plants, it appears that the additional N accumulation from mixed N needs to be coupled with tiller development in order to enhance grain yields. These results confirm that mixed N nutrition increases yield of wheat and indicate that the most critical growth stage to supply the N mixture to the plant is during vegetative growth.     

Nitrate versus chloride nutrition effects in a soil‐plant system on the growth,nitrate accumulation,and nitrogen,potassium, sodium,calcium, and chloride content of carrot

The experiment was conducted to evaluate the effects of various nitrate/ chloride (NO₃/Cl) ratios on growth, nitrate accumulation, and mineral absorption in carrot, Daucus carota L., plants in a controlled environment. The experiment included two Cl sources [potassium chloride (KC1) and calcium chloride (CaCl₂)] and five NO/Clratios at 100/0, 90/10, 80/20, 70/30, and 60/40 with total‐nitrogen (N) concentration of 400 mg NO₃ kg^‐1 soil in 100/0 treatment. Fresh and dry weights of shoots and storage roots, and length and diameter of storage roots increased significantly with mixed NO₃/C1 treatments with both Cl sources as compared to single NO₃ (100/0) treatment. Growth was enhanced up to the 80/20 NO₃/C1 treatments. With Cl present in the treatments, the concentration of total‐N unchanged and NO₃ decreased in plants, and Cl and potassium (K) increased with the Cl sources. In KC1 treatments, Na absorption decreased. Calcium (Ca) content of the plants significantly differed by the treatments. It was concluded that N fertilization provided with combined Cl forms and NO₃/Cl rates can enhance production of better quality carrot and at the same time decrease of the N fertilizer input.     

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 nitrogen nutrition on salt tolerance of Pisum sativum during vegetative growth

The influence of different nitrogen (N) forms on salt tolerance of Pisum sativum L. was investigated. Plants of the pea cultivar “Resal” were subjected to 0 (control) or 90 mM NaCl and one of the following nitrogen forms: 5 mM mineral N supplied as either NO , NH , or NH₄NO₃ or N supplied by biological N₂ fixation (inoculated with Rhizobium leguminosarum bv. viciae). Root and shoot biomass were determined 15, 30, 45, and 60 d after emergence, and Na⁺, K⁺, and Cl^– concentrations were determined by capillary electrophoresis. Nitrogen sources induced significant differences in plant growth and in ion accumulation and distribution and in differentially affected salt tolerance. In the absence of salt, the largest biomass accumulation was obtained with NH₄NO₃. In the presence of NaCl, NO ‐fed plants experienced less salt toxicity than plants supplied with other N sources, as indicated by lower Na⁺ and Cl^– and higher K⁺ concentrations in the shoot. The results also suggest that it is possible to establish an effective symbiosis under saline conditions, provided that a salt‐tolerant Rhizobium isolate with good N₂‐fixing ability is used. The use of the appropriate N‐fertilizer source can enhance the growth of Pisum sativum. Hence, NH₄NO₃ may be preferably used under non‐saline and NO under moderately saline conditions.     

Calcium uptake and concentration in bell pepper plants as influenced by nitrogen form and stages of development

Calcium uptake by bell pepper (Capsicum annuum L. cv. ‘California Wonder') varied by stage of plant development and N form supplied (NO₃ ^‐NH₄ ⁺ ratios: 1:0, 3:1, 1:1, 1:3, and 0:1) in a hydroponic study. Uptake of Ca⁺⁺ was highest at bloom and during fruit expansion, making the fruit development stage the highest demand period. Calcium uptake declined with each increasing increment of NH₄ ⁺ relative to NO₃ ^‐ supplied, although fruit yield was not significantly reduced until the ratio of NH₄ ⁺ to NO₃ ^‐ exceeded 50%. Tissue Ca⁺⁺ levels in the blossom‐end of the fruit were reduced whenever NH₄ ⁺ was included with N supplied. Vegetative yield of plants followed the same trend as that observed for total fruit dry weights. Our results indicate that pepper yields are higher when NO₃ ^‐ is the predominant form of N. Also, these results strongly suggest that Ca⁺⁺ fertilizer applications should precede the bloom period and continue during fruit development to ensure adequate Ca⁺⁺ availability for fruit development.     

Changes in plant growth substances,contents and flower quality of rose cv. ‘Dolce Vita’ in response to nitrogen sources under soilless culture conditions

The aim of this study was to investigate the biochemical responses and vase life of rose cut flowers under different ratios of NO₃:NH₄:urea in soilless culture. In this study, urea was used as the source of nitrogen (N) in solution cultures. For this purpose, an experiment was conducted as completely randomized design with seven ratios of N forms and three replications. The rooted cuttings of rose cv Dolce Vita were supplied with seven different ratios of NO₃^?:NH₄⁺:urea (100:0:0, 70:15:15, 50:25:25, 50:0:50, 0:0:100, 50:50:0 and 0:100:0). Results showed that with the increase in urea and ammonium concentrations, the amounts of cuttings IAA, GA₃, zeatin, ABA and polyamines contents decreased significantly. Plants fertigated with nutrient solution containing NO₃^?:NH₄⁺:urea (50:25:25) had the highest concentrations of growth regulators, the highest stalk length and flower vase life. As the ammonium ratios in the nutrient solution increased, the flower vase life decreased significantly. It was concluded that using NO₃^?:NH₄⁺:urea at the ratio of 50:25:25 had the highest effects on improving the rose cut flowers quality by affecting plants growth regulators and can be recommended for cut rose production in soilless culture systems.     

Ammonium and nitrate influence on artichoke growth rate and uptake of inorganic ions

Artichoke plants (Cynara scolymus L.) were grown in a growth chamber in a modified Hoagland solution for seven weeks to determine the influence of ammonium:nitrate (NH₄:NO₃) ratio (100:0, 70:30, 30:70 and 0:100) on growth, water use, and the uptake of nitrogen (N) and inorganic anions and cations. Typical pH changes were recorded: the nutrient solution became acidified with NH₄ or NH₄:NO₃ nutrition; pH increased when NO₃ was the only N source. Ammonium‐fed plants (100:0 ratio) were stunted, with signs of marginal leaf necrosis, progressive wilting of leaves and poor root growth. After 49 days, leaf area was 77, 998, 2,415, and 1,700 cm² and dry weight was 1.0, 12.9, 38.0, and 26.0 g/plant, with NH₄:NO₃ 100:0, 70:30, 30:70, and 0:100, respectively. Leaf area ratio (LAR) was lower in plants supplied solely with NO₃ than in those with mixed NH₄‐NO₃. Increasing NO₃‐N percentage in the nutrient solution increased water use efficiency (WUE): 623, 340, and 243 mL of water were necessary to produce 1 g of dry matter in 100:0, 70:30, 30:70 or 0:100 NH₄:NO₃ ratio, respectively. Increasing NO₃ from 0 to 100% of the total N supplied in the nutrient solution, the shoot content of inorganic cations increased on an equivalent basis by 30% and organic anions (estimated by the difference between inorganic anions and inorganic cations) increased by 2.3 times. These results suggest that leaves are the most important site of NO₃ assimilation in artichoke. By increasing NH₄ percentage in the nutrient solution, the tissue content of inorganic anions was generally increased, except for NO₃, and the same figure was observed for the percentage of reduced N. Results from this study suggest that NO₃ is the N‐form preferred by artichoke.     

几种蔬菜对硝态氮、铵态氮的相对吸收能力

采用溶液培养方法探讨了莴笋、菠菜、小白菜和大青菜 4种蔬菜作物对硝、铵态氮的相对吸收能力以及这两种氮源对它们生长发育的影响。结果表明 ,单独供给NO3-N ,4种作物均生长发育良好 ;供给NO3--N +NH4+-N(NO3-∶NH4+=1∶1) ,生长量均有所下降 ,而单独供给NH4+-N时 ,生长量则大幅度下降。莴笋单独供给NO3--N时 ,其吸氮量显著高于供给NO3--N +NH4+-N的处理 ,大青菜、菠菜供给NO3--N +NH4+-N与单独供给NO3--N相比吸氮量大体相当 ;小白菜同时供应NO3--N +NH4+N时吸氮量最高 ,供给NO3--N时次之 ,供给NH4+-N时显著降低。供给NH4+-N时 4种作物吸氮量均比其它氮源显著降低。 4种作物对NO3--N与NH4+-N的吸收具有明显的偏向性。供给等氮量铵、硝态氮 (NO3--N +NH4+-N处理 )时 ,菠菜、小白菜吸收的NO3-N显著多于NH4+-N ,表现出喜硝性 ,莴笋则与此相反 ,表现出喜铵性 ;而大青菜对两种形态氮素的吸收量相差不多 ,表现出兼性吸收的特点。但上述偏向性具有阶段特点 ,即喜硝作物可能在某一阶段表现出喜铵性状     

Effect of nitrogen form during the flowering period on zucchini squash growth and nutrient element uptake

Zucchini squash (Cucurbita pepo L. cv. Green Magic) plants were grown hydroponically with nitrate (NO₃):ammonium (NH₄) ratio of 3:1 until the onset of flowering when the plants were assigned to four NO₃:NH₄ ratio (1:0, 1:1, 1:3, or 3:1) treatments. Changing the original nitrogen (N) form ratio significantly affected plant growth, fruit yield, nutrient element, and water uptake. Growth of plants was better when NO₃‐N (1:0) was the sole form of N than when NH₄‐N was part of the N treatment. Fruit yields for plants fertilized with 1:0 or 1:3 N‐form ratio were double those of plants grown continuously with 3:1 N ratio. The largest leaf area and plant water use were obtained with 1:0 N ratio treatment Total uptake of calcium (Ca), magnesium (Mg), and potassium (K) decreased with increasing NH₄‐N proportion in the nutrient solution which suggest NH₄‐N was competing with these cations for uptake. The results also demonstrated that growers may increase fruit yield by using a predominantly NO₃‐N source fertilizer through the vegetative growth stage and by shifting the NO₃:NH₄ ratio during the reproductive phase.     

减氮配施有机物质对麦田土壤性质和小麦产量的影响

探究氮肥减量配施有机物质的情况下对氮素利用状况及土壤肥力和小麦产量的影响,为我国华北平原区小麦生产中提高氮肥利用效率、实现节肥增效提供理论基础。通过田间试验,设置5个处理：不施氮肥(CK)、农民习惯施氮肥(FN)、减氮20%(80%FN)、减氮20%+生物有机肥(80%FN+OM)、减氮20%+生物炭(80%FN+BC),研究小麦生长关键期土壤容重、有机质、NO₃^-—N和土壤微生物多样性的变化,测定小麦产量并计算氮素利用效率。结果表明,土壤容重受施入有机物质影响显著,成熟期0—20,20—40 cm的80%FN+OM、80%FN+BC的土壤容重较80%FN分别下降3.83%～4.58%和2.96%～5.07%。成熟期0—40 cm的土壤有机质均以80%FN+OM最高,较其他施氮肥处理提高2.13%～18.81%。土壤NO₃^-—N受施氮肥影响显著,挑旗期80%FN+OM和80%FN+BC处理的0—40 cm土壤NO₃^-—N较高;灌浆期80%FN+BC处理的0...     

DOUGLAS-FIR SEEDLING RESPONSE TO A RANGE OF AMMONIUM: NITRATE RATIOS IN AEROPONIC CULTURE

The objective of the experiment was to identify the most favorable nitrogen (N) source ratio of ammonium (NH₄ ⁺) and nitrate (NO₃ ^?) for aeroponically-grown Douglas-fir when pH was maintained at pH 4.0. Seedlings were grown in controlled environments with solutions containing 0:100, 20:80, 40:60, 60:40, 80:20 or 100:0 NH₄ ⁺:NO₃ ^? ratios. Nutrient additions in the aeroponic culture units were controlled by solution conductivity set points. Seedling growth and nutrient allocation was observed for 45 days. Different NH₄ ⁺:NO₃ ^? ratios resulted in significant differences in the rate of N addition, growth, morphology, and nutrient allocation. Seedlings grown in solutions containing 60 or 80% NO₃ ^? were characterized by a combination of high growth and photosynthetic rates, high and stable internal plant N concentrations, and sufficient levels of other essential nutrients. High proportions of NH₄ ⁺ in solution resulted in low rates of N addition, stunted lateral root growth, and may have been toxic.     

Nitrate and ammonium nutrition in chicory and rocket salad plants

To evaluate chicory (Cichorium intybus L.) and rocket salad [Eruca vesicaria (L.) Cav.subsp. sativa (Mill.)] capability to use ammonium‐nitrogen (NH₄‐N) even in the absence of nitrate‐nitrogen (NO₃‐N) in the nutrient solution, and the chances they offer to reduce leaf NO₃ content, cultivated rocket and two cultivars of chicory ('Frastagliata’, whose edible parts are leaves and stems, and ‘Clio’, a leaf hybrid) were hydroponically grown in a growth chamber. Three nutrient solutions with the same nitrogen (N) level (4 mM) but a different NH₄‐N:NO₃‐N (NH₄:NO₃) ratio (100:0, 50:50, and 0:100) were used. Rocket growth was inhibited by NH₄ nutrition, while it reached the highest values with the NH₄:NO₃ ratio 50:50. Water and N‐use efficiencies increased in rocket with the increase of NO₃‐N percentage in the nutrient solution. In the best conditions of N nutrition, however, rocket accumulated NO₃ in leaves in a very high concentration (about 6,300 mg kg^‐1 fresh mass). For all the morphological and yield features analyzed, chicory resulted to be quite unresponsive to N chemical forms, despite it took more NO₃‐N than NH₄‐N when N was administered in mixed form. By increasing NO₃‐N percentage in the nutrient solution, NO₃ leaf content increased (5,466 mg kg^‐1 fresh mass with the ratio NH₄:NO₃ 0:100). On average, both chicory cultivars accumulated 213 mg NO₃ kg^‐1 fresh mass with the ratio NH₄:NO₃ 100:0 and, differently from rocket, they showed that by using NH₄ produce can be obtained very low in NO₃ content.     

Effects of different forms of nitrogen supply on the gas exchange of young pedunculate oaks (Quercus robur L.)

The effects of different forms and concentrations of N in the rooting medium on the CO₂/H₂O gas exchange of leaves of the pedunculate oak (Quercus robur L.) were investigated. Two-year-old seedlings were grown in nutrient solutions containing low (1.8 mM) or high (4.8 mM) concentrations of NH₄⁺, 3.6 mM NO₃^?, or both NH₄⁺ and NO₃^? (1.8 mM + 1.8 mM). In various sets of plants subjected to these N treatments, the following parameters were determined: biomasses of leaves and fine roots, leaf area-related net photosynthesis at light saturation (A) and leaf conductance (g), foliar concentrations of chlorophylls, N, Ca²⁺, Mg²⁺ and K⁺ and the ash alkalinity of the leaves (as a measure of the carboxylate content). In all treatments, the leaves were equally well supplied with nutrients. Oaks grown in high NH₄⁺ concentrations produced significantly smaller leaf and root biomasses. Compared to oaks cultivated with both N forms or with low NH₄⁺ concentration, oaks grown with high NH₄⁺ supply showed lower values of A and g, but no significant differences in ash alkalinity and leaf area-related chlorophyll concentrations. Oaks fed with NO₃^? as the only N form had an intermediate biomass production, but low values of A and g. The time courses of A in the different treatments closely followed the patterns of g. In all N treatments, the same linear relationship was found between A and g, indicating that, within a rather wide range, the variation in the form and amount of supplied N does not affect the instantaneous water use efficiency of young pedunculate oaks.     

Effect of nitrate addition on efficient use of ammonium sulfate fertilizer on corn under saline conditions. I. Pot experiment

Abstract

Plant growth in saline soils is regulated by the availability of nitrogen (N). High soil nitrate (NO₃)‐N can lead to poor water quality. Many workers think that NO₃‐N as a source for N can contribute to better plant growth in saline soils. The purpose of this work was to determine the necessity of NO₃‐N and the ratio of NO₃/ammonium (NH₄) in the N fertilizer which gives higher productivity of the biomass yield of corn. Corn (Zea mays L.) plants (Var. LG11) were grown under saline soil conditions (8.5 dS m^‐1), soils taken from the Euphrates valley (ACSAO Research Station) at Deir‐Ez‐Zor, east of Syria, from the surface layer of soil (0–25 cm). Five levels of N were applied in two forms, ammonium sulfate [¹⁵(NH₄)₂SO₄] with enrichment (1.5% a) as the NH₄‐N form and calcium nitrate [Ca(NO₃)₂] as the NO₃‐N form, besides fixed amounts of phosphorus (P) and potassium (K) for all N treatments. The corn plants were harvested at the flowering stage (56 days old), oven dried, weighed, and analyzed for total N and ¹⁵N recovery. The results indicated that the dry matter weight for treatments which received a combination of NH₄‐N and NO₃‐N gave higher dry matter yield than a single treatment of one source of N. But, NO₃‐N was more effective in improving yield than NH₄‐N. Nitrogen recoveries on the basis of added and absorbed N derived from fertilizer were significantly more affected by NO₃‐N than NH₄‐N.     

Study on ammonium tolerance of cucumber plants

The influence of N form on xylem exudate and the guttation fluid concentration in cucumber plants was studied under greenhouse conditions. Plants were hydroponically grown with three NO₃:NH₄ ratios (100:0, 80:20, and 60:40) at a constant pH of 6.0 in the nutrient solutions. Plants supplied with 60:40 NO₃:NH₄ ratio displayed a significant decrease of NO₃‐N, total‐N, organic‐P, and Mn concentrations in the xylem sap and an increase of H₂PO₄‐P, SO₄‐S, Cl, B, and Zn concentrations. Potassium and Ca uptake in these plants was slightly reduced, indicating that pH control was an important factor for cationic nutrition in cucumber plants fed with NH₄. The major ions present in the nutrient solutions are concentrated in the xylem sap, particularly for NO₃, K, Ca, and Na. The NO₃:NH₄ ratio had a small effect on the ionic levels of the guttation fluid. The concentrations of all nutrients in the guttation fluid were substantially reduced, except for Cl, showing that the leaf tissues of cucumber plants remove the excess of Cl ion. Finally, in this study, secondary effects of N source on ion uptake and release were minimized by controlling nutrient solution pH.