The response of pearl millet to changes in nitrogen concentration or form during grain fill

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a potentially productive, high‐yielding grain crop in the southeastern USA. A lack of response in pearl millet grain yield to fertilizer N in field studies indicates pearl millet may be able to remobilize N from vegetative to reproductive tissue. The N remobilization capabilities of a plant can be affected by the form of N supplemented. The objectives of this study were to evaluate the effects of N‐form ratio (NH₄ ⁺ : NO₃ ^‐) on the N remobilization capabilities of pearl millet when N is removed from the nutrient solution at the boot stage and to evaluate the effects of changing N‐form ratios at the boot stage on the seed yield and N content of pearl millet. Pearl millet was grown in solution culture under greenhouse conditions. There were 10 treatments: an initial NH₄ ⁺ : NO₃ ^‐ ratio of 3:1 followed by a change at the boot stage to either all NO₃ ^‐, no N, or a continuation of the initial ratio; an initial NH₄ ⁺ : NO₃ ^‐ ratio of 1:1 followed by a change at the boot stage to either all NO₃ ^‐, all NH₄ ⁺ no N, or a continuation of the initial ratio; and an initial NH₄ ⁺ : NO₃ ^‐ ratio of 1:3 followed by a change at the boot stage to either all NH₄ ⁺ no N, or a continuation of the initial ratio. Pearl millet dry matter accumulation was insensitive to changes in N‐form ratio or N removal at the boot stage. The lack of seed yield response to removal of N was a result of pearl millet utilizing N present in culms and leaves for seed production. Applications of N after the boot stage did not increase seed yield, but led to luxury consumption of N.     

Effects of solution pH,temperature, nitrate/ammonium ratios,and inhibitors on ammonium and nitrate uptake by Arabica coffee in short‐term solution culture

Solution pH, temperature, nitrate (NO₃ ^‐)/yammonium (NH₄ ⁺) ratios, and inhibitors effects on the NO₃ ^‐ and NH₄ ⁺ uptake rates of coffee (Coffea arabica L.) roots were investigated in short‐term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH₄ ⁺ and NO₃ ^‐ uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 μmol g^‐1 FWh^‐1 between 4 and 16°C, and increased three‐fold between 16 to 22°C. Between 4 to 22°C, NH₄ ⁺ uptake rate increased more gradually from 1.00 to 3.25 μmol g^‐1 FW h^‐1. In the 22–40°C temperature range, NH₄ ⁺ and NO₃ ^‐ uptake rates were similar (averaging 3.65 and 3.56 umol g^‐1 FW h^‐1, respectively). At concentrations ranging from 0.5 to 3 mM, NO₃ ^‐ did not influence NH₄ ⁺ uptake rate. However, NO₃ ^‐ uptake was significantly reduced when NH₄ ⁺ was present at 3 mM concentration. Most importantly, total uptake (NO₃ ^‐+NH₄ ⁺) at any NO₃ ^‐/NH₄ ⁺ ratio was higher than that of plants fed solely with either NH₄ ⁺ or NO₄ ^‐. Anaerobic conditions reduced NO₃ ^‐ and NH₄ ⁺ uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH₄ ⁺ and NO₃ ^‐ uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH₄ ⁺ and NO₃ ^‐ uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.     

Nutrient uptake and yield of sweet pepper as affected by stage of development and N form

Uptake of NO₃ ^‐, NH₄ ⁺, P, K⁺⁺, Ca⁺⁺ and Mg⁺⁺, as influenced by the stage of plant development and three NO₃ ^‐: NH₄ ⁺ ratios (1: 0, 1: 1, and 0: 1), was determined for sweet pepper (Capsicum annuum L. cv. ‘California Wonder'). Uptake was highest during fruit development and immediately after fruit harvest, indicating that fruit removal promotes nutrient uptake. When NO₃ ^‐ and NH₄ ⁺ were supplied in equal concentrations, NO₃ ^‐ was absorbed more readily. Each increment in NH₄ ⁺ decreased the uptake of K⁺, Ca⁺⁺, and Mg⁺⁺ by fruit tissue, while no significant effect on the N and P content of the fruit was observed. Ammonium nutrition reduced plant dry weight and fruit yield in comparison to NO₃ ^‐. Results from this study suggest that NO₃ ^‐ is the preferred N form, and that fertilizer application should be scheduled according to specific physiological stages to maximize nutrient uptake. Nutrient content of vegetative tissue was not indicative of potential yield.     

Effects of Nitrate and Potassium on Ammonium Toxicity in Cucumber Plants

ABSTRACT

Interactions between nitrate (NO₃ ^?), potassium (K⁺), and ammonium (NH₄ ⁺) were investigated using hydroponically grown cucumber (Cucumis sativus L.) plants. Ammonium as the sole nitrogen (N) source at 10 mM was toxic and led to overall growth suppression, chlorosis, and necrosis of leaves. After 20 days, 50% of the plants were dead. However, when NO₃ ^? was supplied at very low concentration together with high NH₄ ⁺ (only 1% of total 10 mM N) all seedlings survived and their growth was improved. High K⁺ concentration (5 mM) also alleviated NH₄ ⁺ toxicity and increased plant growth several fold compared to intermediate concentration of K⁺ (0.6 mM). Leaf total N and ¹⁵N derived from ¹⁵N-labelled NH₄ ⁺ increased in the presence of NO₃ ^?, but decreased at high K⁺ concentration. High K⁺ supply enhanced total carbon (C) and δ ¹³C and stimulated GS and PEPCase activities in leaves and roots. Nitrate supplementation had no effect on GS or PEPCase activities. It is concluded that K⁺ may alleviate NH₄ ⁺ toxicity, partly by inhibiting NH₄ ⁺ uptake, partly by stimulating C and N assimilation in the roots.     

Yield of take‐all infested winter wheat as influenced by inhibiting nitrification with dicyandiamide

Abstract

The potential for using dicyandiamide (DCD) to enhance yield of take‐all‐infested winter wheat (Triticum aestivum L.) was evaluated in six field experiments on four acid soils (pH 5.7–6.2). Ammonium and NO₃ ^‐ concentrations and NH₄ ⁺: NO₃ ^‐ ratios in 0–10 and 10–20 cm soil depths were measured for ten weeks after spring topdressing 180 kg N/ha as urea with 0, 13, or 27 kg DCD/ha. Nitrification was strongly inhibited for 6 to 10 weeks by either 13 or 27 kg DCD/ha. Averaged over the ten‐week sampling period, NH₄ ⁺: N0₃ ^‐ ratios in the 0–10 cm depth of soil were 36: 1 for DCD‐treated plots as compared to 2: 1 for plots receiving only urea. Ratios in DCD‐treated plots were considerably wider than ratios associated with take‐all suppression (10: 1 to 3: 1) in earlier studies. Extractable NH₄ ⁺ + NO₃ ^‐ concentrations in soil were high in DCD‐treated plots after 30 to 40 days, suggested that DCD had reduced crop uptake of N because of the lower mobility of NH₄ ⁺ as compared to NO₃ ^‐. In four of the six studies, grain yields tended to be reduced by DCD. Results suggest that lower rates of DCD and/or application of some NO₃ ^‐ will be necessary if DCD is to be used as a tool for suppressing take‐all.     

The significance of plant energy status for the uptake and incorporation of NH4-nitrogen by young rice plants

Uptake and assimilation of inorganic N in young rice plants has been studied with labelled N (N-15). Depletion of the plants' carbohydrate content, obtained by a preceding dark period, resulted in a drastic reduction of NH₄ ⁺-N uptake. Plants exposed to low light intensity showed diminishing NH₄ ⁺-N uptake rates as compared with plants exposed to full light intensity, the latter showing constant NH₄ ⁺-N uptake rates during the whole experimental period. The percentage of labelled insoluble N in total labelled N was not significantly affected by a preceding dark period, whereas the low light intensity resulted in a lower proportion of insoluble N in roots and shoots. The incorporation of labelled N into the insoluble fraction (proteins, nucleic acids) was higher in plants fed with NH₄ ⁺-N than in those fed with NO₃ ^-.

The uptake of NH₄ ⁺-N was not significantly affected by NO₃ ^-, whereas the NO₃- uptake rate was considerably reduced in the presence of NH^{4 +}-N. Low energy status of plants affected the nitrate uptake more than the uptake of NH₄ ⁺-N. The results show that uptake and assimilation of inorganic N depend much on the energetic status of plants. Nitrate uptake and assimilation is more sensitive to low energy conditions than NH₄ ⁺-N.     

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.     

Influence of ammonium,nitrate, and chloride on solution pH and ion uptake by ageratum and salvia in hydroponic culture

The influence of nitrogen (N) forms and chloride (Cl) on solution pH and ion uptake in the hydroponic culture of Ageratum houstonianum [ammonium (NH₄ ⁺)‐tolerant] and Salvia splendens (NH₄ ⁺‐sensitive) for a period of 216 hours was investigated. The pH of the hydroponic solution (initially 6.50) containing either NH₄ ⁺ or NH₄ ⁺+nitrate (NO₃ ^‐) was drastically lowered (3.08), whereas that of the same solution containing NO₃ ^‐ was raised (7.74). Solution pH changed more by ageratum than by salvia. The solution Cl^‐ concentration did not influence pH significantly. However, addition of Cl^‐ in the solution lowered transpiration rate in both NH₄ ⁺ and NO₃ ^‐ treatments. Total N uptake was the greatest in the NH₄ ⁺ + NO₃ ^‐ treatment and the lowest in the NO₃ ^‐treatment. In the NH₄ ⁺ + NO₃ ^‐ treatment, NO₃ ^‐ uptake was suppressed by NH₄ ⁺ (to about 50%), while NH₄ ⁺ uptake was not affected by NO₃ ^‐. The rate of Cl^‐ uptake was the lowest in the NH₄ ⁺ treatment, but was similar in the NH₄ ⁺ + NO₃ ^‐ and NO₃ ^‐ treatments. Uptake of potassium (K⁺), dihydrogen phosphate (H₂PO₄ ^‐), sulfate (SO₄ ^‐2), manganese (Mn⁺²), and zinc (Zn⁺²) was significantly enhanced in the NH₄ ⁺ treatment. The uptake rate of calcium (Ca⁺²) and magnesium (Mg⁺²) was the highest in the NO₃ ^‐ treatment. Absorption of copper (Cu⁺²) and boron (B) was not affected by N source. Ion uptake was more stable in the solution containing both NH₄ ⁺ and NO₃ ^‐ than in the solution containing either NH₄ ⁺ or NO₃ ^‐. The uptake rate of total N, NH₄ ⁺, NO₃ ^‐, Mn⁺², Cu⁺², and Zn⁺² was higher, whereas that of Cl^‐ and molybdenum (Mo) was lower in ageratum than in salvia. Amounts of total anion (TA) and total cation (TC) absorbed, the sum of TC and TA, and the difference between TC and TA (TC‐TA) were affected by N source, Cl^‐ level, and their interactions. The NO₃ treatment, as compared to the NH₄ ⁺ or the NH₄ ⁺ + NO₃ ^‐treatment, reduced total cation and anion uptake while increasing TC‐TA, especially in the absence of Cl^‐. Plant tissue ion contents were also affected by N source and Cl^‐ level.     

Influence of nitrate‐nitrogen and ammonium‐nitrogen on calcium (45Ca2+) absorption in sorghum root tips

Abstract

Root‐tip, 1‐cm of Sorghum bicolor (L.) Moench cv SC283, SC574, GP‐10, and Funk G522DR were exposed to calcium (⁴⁵Ca²⁺) at pH 5.5 for 2‐hr in the presence of nitrate‐nitrogen (NO3^?‐N) or ammonium‐nitrogen (NH4+‐N). Nitrate (0.1 mM) induced significantly increased ⁴⁵Ca uptake in Funk G522DR, SC283, and GP‐10 while 0.01 mM NO₃ ^?‐N induced significantly increased ⁴⁵Ca'uptake in SC574, but ⁴⁵Ca absorption was significantly decreased at 1 mM NO₃—N. In the presence of the NH4⁺ ion, ⁴⁵Ca uptake was increased up to 8X that of the NH₄ ⁺‐N untreated roots. When ammonium chloride (NH₄CI) was used, the Cl^? tended to induce an increased ⁴⁵Ca uptake. Cultivar variation was present.     

Root morphology of maize under homogeneous or spatially separated supply of ammonium and nitrate at three concentration ratios

Maize (Zea mays L. cv. Anjou 256) seedlings were grown hydroponically for 10 d in a split‐root system (3mM N; pH 5.5) under either a homogeneous supply (HS) or a simultaneous, but spatially separated supply (SS) of NH₄ ⁺ andNO₃ ^‐. Treatments comprised three NH₄ ⁺:NO₃ ^‐ ratios (1:4, 1:1, 4:1). Shoot dry matter and various root traits (dry matter, number of laterals, length of main axes, total root length and total root surface area) were determined. For all NH₄ ⁺:NO₃ ^‐ ratios, shoot dry matter, root dry matter, total root length, and root surface area, were greater under HS than under SS. Under both SS and HS, increasing NH₄ ⁺:NO₃ ^‐ ratios resulted in decreased shoot and root dry matter production, but did not alter the shoot:root dry matter ratio. Under SS, root dry matter, root length, and root surface area was greater on the NO₃ ^‐‐fertilized side than on the NH₄ ⁺ ‐fertilized side. The allocation of root dry matter, root length, and root surface area to the NH₄ ⁺ or NO₃ ^‐ compartments was unaffected by changes in the NH₄ ⁺:NO₃ ^‐ ratio. Enhanced NH₄ ⁺ nutrition has detrimental effects on top growth, but roots are apparently unable to avoid excessive NH₄ ⁺ uptake by proliferating in zones where NO₃ ^‐ is the only form of N.     

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.     

两个品种水稻中硝酸盐吸收和利用率对氮素饥饿的响应特征

Ammonium（NH＋4） is the main nitrogen（N） form for rice crops, while NH＋4near the root surface can be oxidized to nitrate（NO-3）by NH＋4-oxidizing bacteria. Nitrate can be accumulated within rice tissues and reused when N supply is insufficient. We compared the remobilization of NO-3stored in the tissue and vacuolar between two rice（Oryza sativa L.） cultivars, Yangdao 6（YD6, indica）with a high N use efficiency（NUE） and Wuyujing 3（WYJ3, japonica） with a low NUE and measured the uptake of NO-3, expression of nitrate reductase（NR）, NO-3transporter genes（NRTs）, and NR activity after 4 d of N starvation following 7-d cultivation in a solution containing 2.86 mmol L-1NO-3. The results showed that both tissue NO-3concentration and vacuolar NO-3activity were higher in YD6 than WYJ3 under N starvation. YD6 showed a 2- to 3-fold higher expression of OsNRT2.1 in roots on the 1st and 4th day of N starvation and had significantly higher values of NO-3uptake（maximum uptake velocity, Vmax） than the cultivar WYJ3.Furthermore, YD6 had significantly higher leaf and root maximum NR activity（NRAmax） and actual NR activity（NRAact） as well as stronger root expression of the two NR genes after the 1st day of N starvation. There were no significant differences in NRAmax and NRAact between the two rice cultivars on the 4th day of N starvation. The results suggested that YD6 had stronger NRA under N starvation, which might result in better NO-3re-utilization from the vacuole, and higher capacity for NO-3uptake and use, potentially explaining the higher NUE of YD6 compared with WYJ3.     

Poinsettia growth,tissue nutrient concentration,and nutrient uptake as influenced by nitrogen form and stage of growth

Growth, development, and uptake of essential nutrients as influenced by nitrogen (N) form and growth stage was evaluated for ‘Freedom’ poinsettias (Euphorbia pulcherrima Willd. Ex Klotz.). Treatments consisted of five nitrate (NH₄ ⁺):ammonium (NO₃ ^‐) ratios (% NH₄ ⁺:% NO₃ ^‐) of 100:0, 75:25, 50:50, 25:75, and 0:100 with a total N concentration of 150 mg L^‐1. Plants were grown in solution culture for ten weeks under greenhouse conditions. Nutrient uptake data was combined into three physiological growth stages. Growth stage I (GSI) included early vegetative growth (long days). Growth stage II (GSII) began at floral induction and leaf and bract expansion (short days). Growth stage III (GSIII) was from visible bud through anthesis and harvest. Dry weights for all plant parts and height increased as the ratio of NO₃ ^‐ increased. Leaf area and bract area were maximized with 25:75 and 50:50 N treatments, respectively. Nitrogen treatments significantly affected foliar nutrient concentrations with calcium (Ca⁺⁺) and magnesium (Mg⁺⁺) being highest when NO₃ ^‐ was the predominant N form. Uptake of each macronutrient was averaged across all treatments and divided into physiological growth stages (GS) to identify peak demand periods during the growth cycle. The greatest uptake of NH₄ ⁺ and NO₃ ^‐ was from the early vegetative stage to floral induction (GSI). Phosphorus (P), potassium (K⁺), and Mg⁺⁺ uptake were greatest from floral induction to visible bud (GSII) and Ca⁺⁺ uptake remained relatively unchanged through GSI and GSII. Uptake was lowest for all nutrients from visible bud to anthesis (GSIII). Results from this study clearly indicate that peak demand periods for macronutrient uptake existed during the growth cycle of poinsettia.     

N form and concentration: Effects on reproductive development,growth and N content of southern peas 1

Southern peas [Vigna unguiculata, (L.) Walp.] cultured with 100% NH⁺ ₄ produced no viable flowers, while treatments in which NO^‐ ₃ composed 50% or more of the N form were not significantly different in the number of flowers formed. Flower abortion was least with 100% NO^‐ ₃ at the lower N concentration and with 75% and 100% NO^‐ ₃ at the higher N concentration. Further increments of NH⁺ ₄ resulted in greater flower abortion. The trends in flower survival were reflected in the number of pods and number of seed/plant. At the lower N concentration, the addition of NH⁺ ₄ slowed pod maturity, while at the higher N concentration pod maturity was hastened with the addition of up to 50% NH⁺ ₄. The dry weight and N content of tissues were generally greater with the higher N concentration and with N combinations containing predominantly NO^‐ ₃, but trends varied with the plant part being analyzed. Ammonium appears to adversely influence reproductive development and/or NO^‐ ₃ is essential to complete the reproductive development of southern peas. The observed differences in the response of southern peas to N form may account for previously reported discrepancies concerning the effectiveness of N fertilization on growth and yield parameters. Also, vegetative growth and vegetative N content appear to be poor indicators of final seed yields of southern peas if NH⁺ ₄ supplies a significant portion of the N form utilized by the plant.     

Mineral nutrition of chickpea plants supplied with NO3 or NH4 N

Chickpea plants (Cicer arietinum L cv. ILC 195) were grown for 24 days in water culture under two regimes of nitrogen nutrition (NO₃ or NH₄‐N) with or without Fe. For plants fed with NO₃‐N, Fe stress severely depressed fresh weight accumulation and chlorotic symptoms of Fe‐deficiency developed rapidly. Little difference in growth occurred in the NH₄‐fed plants, whether or not Fe was withheld, with no visual evidence of Fe‐deficiency indicating a beneficial effect of NH₄ in depressing the symptoms of Fe chlorosis. Typical pH changes were measured in the nutrient solution of the control plants in relation to nitrogen supply, increasing with NO₃ and decreasing with NH₄‐nutrition. With both forms of nitrogen, plants acidified the nutrient solution in response to Fe‐stress. Under NH4‐nutrition, acidification was enhanced by withholding Fe. In the NO₃‐fed plants the uptake of all nutrients was reduced by the stress but proportionally NO³‐ and K⁺ were most affected. Total anion uptake was depressed more than that of cation uptake. For the NH₄‐fed plants withholding Fe resulted in an increased uptake of all ions except NH₄ ⁺ which was depressed. Regardless of the form of N‐supply, when Fe was withheld from the nutrient solution the net H⁺ efflux calculated from the (C‐A) uptake values was closely balanced by the OH” added to the nutrient solution to compensate for the pH changes. Evidence of accumulation of organic acids in the Fe‐stressed plants was found, especially in the NO₃‐fed plants, indicating a role for these internally produced anion charges in balancing cation charge in relation to the depression of NO₃ ^‐ uptake associated with Fe‐stress.     

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.     

Effects of ammonium and inorganic carbon enrichment on growth and yield of a hydroponic tomato crop

Effects of varying the proportions of NO₃^— and NH₄⁺ in the growth medium on seedling growth and tomato fruit yield (Lycopersicon esculentum L. cv. Trust F1) were investigated in greenhouse hydroponic experiments. The presence of NH₄⁺ as the sole N source (11 mM) was toxic: it curtailed growth and decreased chlorophyll content of the leaves. However, at low concentration (10 % of total N), the presence of NH₄⁺, with or without added dissolved inorganic carbon (DIC), increased vegetative growth and fruit yield by ˜ 15 %, and enhanced taste/flavor of the fruits. In DIC‐enriched treatment, pH was maintained at 5.8 by addition of KHCO₃ or as CaCO₃. The presence of NH₄⁺, at 10 % of total N, inhibited NO₃^— uptake rates by ˜ 27 %. The rates of uptake of NO₃^— and NH₄⁺ were comparable (13.3 and 14.2 mmol plant^—1 d^—1, respectively, in the presence of DIC, and 14.7 and 14.0 mmol plant^—1 d^—1, respectively, in the absence of DIC), despite such a large difference in their concentrations in the nutrient feed solution. A higher proportion of NH₄⁺ (up to 50 % of total N) had no further significant effect upon early vegetative growth, but in a long‐term experiment resulted in a high incidence of blossom end‐rot (BER) disease, thereby severely curtailing fruit yield. The presence of even 1.1 mM NH₄⁺ reduced Ca²⁺ and Mg²⁺ accumulation in the leaves as well as in fruits.     

Effect of nitrate/ammonium ratio on biomass production,nitrogen accumulation,and use efficiency in sorghums of different origin

Plant nitrogen (N) uptake, growth, and N use efficiency may be affected by N form (NO₃ ^‐or NH₄ ⁺) available to the root. The objectives of this study were to determine the effect of mixed N form on dry matter production and partitioning, N uptake, and biomass N use efficiency defined as total dry matter produced per unit plant N (NUE₁) in U.S. and tropical grain sorghums [Sorghum bicolor (L.) Moench]. The U.S. derived genotype CK 60 and three tropical genotypes, Malisor‐7, M 35–1, and S 34, were evaluated in a greenhouse trial using three nutrient solutions differing in their NO₃ ^‐/NH₄ ⁺ ratio (100/0, 75/25, 50/50). Shoot and root biomass, N accumulation, and NUE, were determined at 10‐leaf and boot stages. Averaged over all genotypes, shoot and root biomass decreased when NH₄ ⁺ concentration was increased in the solution. Shoot biomass was reduced by 11% for 75/25 and 26% for 50/50 ratios, as compared to 100/0 NO₃ ^‐/NH₄ ⁺. Similarly, root biomass reduction was about 34% and 45% for the same ratios, respectively. Increasing NH₄ ⁺ concentration also altered biomass partitioning between shoot and root as indicated by decreasing root/shoot ratio. Total plant N content and NUE₁ were also reduced by mixed N source. Marked genotypic variability was found for tolerance to higher rates of NH₄ ⁺. The tropical line M 35–1 was well adapted to either NO₃ ^‐ as a sole source, or to an N source containing high amounts of NH₄ ⁺. Such a characteristic may exist in some exotic lines and may be used to improve genotypes which do not do well in excessively wet soil conditions where N uptake can be reduced.     

Influence of nitrogen forms and levels on the growth and nutrition of cacao

Ammonium and nitrate are the major forms of nitrogen (N) present in tropical soils. An experiment was conducted to assess the influence of nitrate and ammonium forms (NO₃^?, NH₄⁺, and mix of NO₃^? + NH₄⁺), and levels (1.5–12.0 mM) of N on the growth and nutrition of cacao (Theobroma cacao L). Growth parameters were significantly influenced by N forms, and nitrogen supplied as NH₄⁺ proved better for the growth of cacao compared with NO₃^? form and mixtures of these two forms. Irrespective of the forms of N, levels of N had no significant effect on plant growth parameters. Nutrient efficiency ratios (NERs) (shoot dry matter produced per unit of nutrient uptake) for macronutrients were sulfur>phosphorus>calcium>magnesium>nitrogen>potassium (S>P>Ca>Mg>N>K) and for micronutrients NERs were in the order of copper>boron>zinc>iron>manganese (Cu>B>Zn>Fe>Mn).     

Effects of plant age on nitrogen uptake and distribution by greenhouse plants

Water‐soluble nitrogen (N) fertilizer is intensively used in greenhouse crop production. Any N not used by a crop is subject to leaching as nitrate (NO₃‐N), which may pollute groundwater. A close correlation between N supply and N uptake by plants would increase the efficiency of N fertilization and minimize the possibility of NO₃‐N pollution. The objectives of this study were to measure N uptake by American marigold (Tagetes erecta L. ‘First Lady') and New Guinea Impatiens (NGI) (Impatiens hawkeri Bull. ‘Selenia') during growth, to determine the effect of plant age on N uptake, to determine if the two species have a preference for NO₃‐N or ammonium (NH₄‐N), and to determine the total N required for 70 days of growth.The plants were grown in solution culture using solutions supplying 120 mg each of NO₃‐N and NH₄‐N. At ten day intervals, six cultures were chosen at random for nutrient solution analysis and plant sampling for dry weight and tissue analysis. Nitrate‐N uptake was greater than NH₄‐N uptake throughout the experiment for both marigold and NGI. Total N uptake by marigold was greater during the first 50 days after transplanting with maximum N uptake during the period 30 to 50 days. In contrast, N uptake by NGI was greater during the period 40 to 70 days after transplanting. Maximum N uptake for NGI occurred during the period 60 to 70 days. Results of this study suggest that early N fertilization of marigold could be more important for their growth and quality than N applied later. For NGI, N fertilization later in the crop's development appears to be more important than early on. The total N absorbed by marigold during the experiment was 1.1 gm N plant^‐1; for NGI the quantity was 0.5 gm N plant‐¹.