Nitrogen Fixation by Hybrids of White Clover (Trifolium repens L.) and Trifolium nigrescens

Development of hybrids between white clover ( Trifolium repens L.) and Trifolium nigrescens provides a novel route for genetically improving the reproductive capacity of white clover, provided the hybrids are agronomically viable, particularly with respect to N₂ fixation. A comparative study of growth and rates of N₂ fixation over 21 days was conducted with the parental species, F ₁ hybrids and backcross hybrids, in flowing solution culture, without a supply of mineral N to the plants. T. nigrescens was unable to fix N₂ in association with the strains of Rhizobium leguminosarum biovar. trifolii selected for inoculation. Rates of N₂ fixation per plant increased in the order T. nigrescens < F ₁ hybrid < T. repens < backcross 1. Specific rates of N₂ fixation (days 0–21) increased in the order T. nigrescens < F ₁ hybrid < backcross 1 <  T. repens . Dry matter production and nodule biomass per plant increased at a higher rate in backcross 1 hybrids than in T. repens. The results suggest that the potential for N₂ fixation by backcross 1 hybrids is at least as great as that by T. repens .     

Einfluß des Lichtangebotes auf das Wachstum und die biologische Stickstoff-Fixierung von Weißklee (Trifolium repens L.)

Influence of light quantity on growth and biological nitrogen fixation of white clover ( Trifolium repens L.)
The influence of photon irradiance (E_p; 100 to 500 μmol m⁻² s⁻¹) and of the photoperiod (16 or 11 h) on growth and nitrogenase activity of nodulated white clover plants was studied in growth chambers at two nitrate levels (1.0 and 7.5 mM NO₃⁻).
Total dry mass production, the root proportion and nitrogenase activity increased with increasing E_p and photoperiod. Nitrogenase activity generally increased proportionally to root mass. Only at low E_p (100 μmol m⁻² s⁻¹) and under a short photoperiod (11 h) was the specific nitrogenase activity per unit root mass reduced. An abrupt change in E_p led to a rapid and parallel change in nitrogenase activity and relative growth rate.
A higher NO₃⁻ concentration in the nutrient solution (7.5 mM) led to a marked decrease in specific nitrogenase activity, but increased growth between 200 and 500 μmol m⁻² s⁻¹ during early development only. At 100 μmol m⁻² s⁻¹, there was no growth response to nitrate, although its effect on nitrogenase activity was more marked than at a higher E_p.
The results show that with changing light quantity, biological nitrogen fixation of white clover adapts to the existing demand for nitrogen and does not limit growth except during early development, even when light supply is low.     

Physiological Investigation of the Impact of Nitrogen and Sulphur Application on Seed and Oil Yield of Rapeseed (Brassica campestris L.) and Mustard (Brassica juncea L. Czern. and Coss.) Genotypes

Field experiments were conducted to determine the physiological basis of the effects of N and S interactions on seed and oil yield of Brassica species. Five combinations of N and S (in kg ha⁻¹) 0S+100N (T₁), 40S+60N (T₂), 40S+100N (T₃), 60S+100N (T₄) and 60S+150N (T₅), were used for this purpose. Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various growth stages, as the two enzymes catalyse rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these enzymes were strongly correlated with seed and oil yield. The highest nitrate reductase activity, ATP-sulphurylase activity and yield were achieved with the combination T₃ in both species. Any variation from this combination decreased the activity of these enzymes, resulting in a reduction of the seed and oil yield of Brassica species. The higher seed and oil yield achieved in these species at T₃ could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by N and S assimilation.     

Nitrogen Fixation, Growth and Yield of Intercropped Mungbean (yigna radiata L.) and Groundnut (Aracbis bypogaea L.) as Affected by the Genotype

¹⁵N-aided investigations were conducted to ascertain the Nj fixation and the nitrogen (N) contribution by mungbean ( Vigna radiata L.) and groundnut ( Aracbis hypogaea L.) when intercropped with maize ( Zea mays ). The study involved growing seven genotypes of the above legumes with maize in alternate rows in two separate experiments. A sole crop of maize was used as the reference crop to determine N2 fixation by the ¹⁵N methodology. Significant genotypic differences in pod yield and stover N content were observed in intercropped mungbean and groundnut. The percentage N derived from the atmosphere showed a genotypic variation of 31 to 45 % (7 to 10 kg N₂ fixed ha⁻¹O in mungbean and 47 to 69 % (9 to 18 kg N₂ fixed ha⁻¹) in groundnut. Harvest index for N varied from 58 to 77 % in mungbean and 55 to 75 % in groundnut. In groundnut, the uptake of soil N was significantly affected by the genotype. Assuming that the N contribution to the soil by the helow-ground plant parts was negligible, the removal of seeds at maturity resulted in a negative N balance in the soil in all the genotypes of mungbean. In groundnut, some genotypes produced a positive N balance in the soil. Owing to high N₂ fixation capacity and low harvest index for N, groundnut showed a greater N supplementing ability than mungbean.     

Soybean Genotypic Variation for Nitrogen Fixation

Eighteen soybean ( Glycine max [L.] Merr) cultivars from maturity groups V and VI were screened with two Bradyrhizobium japonicum strains (USDA 110 and TAL 378) in the greenhouse to determine N₂ fixation (C₂H_2: reduction) rates. Antibiotic resistant markers were used for observing nodule occupancy. Cultivars L.-76-0132, PI 159319, Hoberland, Lee, PI 22173 and Centennial showed high nitrogenase activity of 6.25, 5.54, 17.43, 4.73, 6.94, and 4.81 μM C₂H₄/Pl/hr, respectively. Cultivars PI417419, PI 230978, Ogden , and FC 31665 showed low nitrogenase activity of 1.51, 0.80, 0.62 and 0.94 μM C₂H₄/Pl/hr, respectively. The data from this screening experiment suggest that the N₂ fixation varied among genotypes and all the nodules were occupied by the inoculated strains only. Rhizobial strain effect was observed among soybean cultivars (MGVI).     

Seasonal Changes in the Photosynthetic Capacity of Winter Rape Plants under Different Nitrogen Regimes Measured in the Field

Winter rape (cv.'Falcon') grown under different nitrogen regimes (N₀, N₁₂₀; 0 and 120 kg.ha⁻¹, respectively) in northern Germany was investigated over the 1996 spring–summer season. Using a CO₂, H₂O diffusion porometer, diurnal courses or net photosynthesis and respiration were measured in situ and were related to microclimatic conditions and leaf water relations. Photosynthesis was modelled and daily CO₂ gain was calculated. In contrast to the N₁₂₀ plants, plants of the low nitrogen plot (N₀) grew less densely and their leaves behaved more like sun leaves. Increased nitrogen supply had little influence on photosynthetic capacity but it increased productivity through higher leaf area index and an extended period of photosynthetic activity. N₁₂₀ plants also appeared to be better acclimated to hot, summer conditions. Higher nitrogen supply substantially increased seed production with the yield of the N₁₂₀ plants being 16% of the N₀ plants.     

Estimation and Partitioning of Nitrogen Fixed by Soybean in Mediterranean Climates

A field study was conducted to estimate the nitrogen fixation by soybean [ Glycine max (L.) Merr.], using the A-value and the N-difference methods, and to examine the N partitioning within the plant. The cultivar Clark and its non-nodulating isoline (as reference crop) were grown in a silty clay (Typic Xerothent) soil, in 1991 and 1992. ₁₅N-Labelled fertilizer was surface applied in solution, at rates of 20 and 100 kg N ha⁻¹ to the nodulating and non-nodulating soybean, respectively. Plant samples were taken at full bloom (R2), beginning of seed growth (R5) and physiological maturity (R7). There was little nitrogen fixation at the early growth stages but it increased rapidly during the seed filling period. At R7 nitrogen fixed was estimated by the A-value method as 155 kg N ha_-1 in 1991 and as 240 kg N ha⁻¹ in 1992. The corresponding estimates by the N-difference method were significantly smaller. The seeds had a higher, and the vegetative parts smaller, proportion of fixed nitrogen compared to the whole plant. During the seed filling period, the translocation efficiency for fixed nitrogen was greater (93 % in 1991 and 85 % in 1992) compared to the N derived from soil (75 and 56 %, respectively). It was estimated that, after the harvest of pods, the soil was depleted by a net amount of 121 kg N ha⁻¹ in 1991 and 90 kg N ha⁻¹ in 1992.     

Effect of Split Nitrogen Application on Growth and Yield of Wheat (T. aestivum L.) Genotypes with Different N-Assimilation Potential

A field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the 'HNR' genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity ('LNR' genotypes) when an extra dose (40 kg N ha⁻¹) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both 'HNR' and 'LNR' genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha⁻¹) at the time of anthesis increased grain yield of 'HNR' genotypes by 38.5 % as compared to 'LNR' genotypes.     

减量施氮对带状套作大豆土壤通气环境及结瘤固氮的影响

为研究种植模式和施氮量对大豆土壤通气环境及结瘤固氮的影响,本研究采用二因素裂区试验设计,主区为种植模式:大豆单作(SS)、玉米/大豆带状套作(MS),副区为不同施氮量:不施氮(NN:0 kg hm^-2)、减量施氮(RN:45kghm^-2)和常量施氮(CN:60kghm^-2),监测了大豆生育期内土壤的O₂含量和土壤呼吸速率的动态变化规律,分析了各处理的土壤水稳性团聚体、容重和孔隙度差异,探讨了大豆生育期内结瘤量、固氮能力的变化特征。2年数据结果表明,与单作大豆相比,带状套作大豆可提高土壤O₂含量、>2 mm粒径团聚体的百分含量、显著增加土壤孔隙度、显著增强后期土壤呼吸的速率,显著降低<1mm粒径团聚体百分含量与土壤孔隙度;R5期根瘤干重差异不显著,但结瘤数量显著增加39.9%,固氮酶活性与固氮潜力也在此时显著高于单作大豆。各施氮量间,土壤O₂含量、0.25～1.00mm粒径的百分含量、带状套作大豆的土壤呼吸速率以RN处理最高,施氮能降低<0...     

Untersuchungen über die Wirkung von Ammonium- und Nitrat-Ernährung auf die Ertrags- und Proteinbildung bei Hafergenotypen

Investigations about the effect of ammonium- and nitrate nutrition on the formation of yield and protein of oats genotypes
The formation of yield and proteins of three different oats genotypes (cv. Gambo, Flämingskrone, Caesar ) in dependence on ammonium or nitrate nutrition was investigated in pot trials over 2 years (from 1982 to 1983). On oats the NH₄-nutrition showed in comparison to NO₃ nutrition increases in grain yield up to 20 % due to a favourable influence on the number of panicles per pot (s. Fig. 1).
Protein content and protein yield increased particularly by high fertilizing with NH₄-N (N₃- and Invariant); the best effect was ascertained by the N₄-variant increase of 4 % (D.M.). Among the protein fractions (albumins, globulins, prolamins, glutelins) the albumin- and prolamin-proteins increased after NH₄-fertilizing by 1–2 %, whereas at the same time the glutelins decreased by 1–4 %; the globulins showed no differences.     

The Performance of Pea (Pisum sativum L.) and its Role in Determining Yield Advantages in Mixed Stands of Pea and Oat (Avena sativa L.)

On a brown warp soil (Fluventic Eutrochrept) near Goettingen, Germany, conventional leafed pea ( Pisum sativum L. cvs Messire and Bohatyr) and semileafless types (cvs Profi, Juno and Azur) were grown in mixed stands together with oat ( Avena sativa cvs Alf and Lutz) in substitutively designed experiments from 1995 to 1997. Oat was the dominant component. Crowding coefficients for oat averaged 7.4. No relationship could be detected between the crowding coefficient of oat and any yield advantage from the mixture. Crowding coefficients for pea varied substantially, between 0.1002 (Juno and Alf in 1996) and 0.2979 (Bohatyr and Alf in 1996). Crowding coefficients for semileafless pea cultivars were smaller than for conventional leafed types. The yield advantage of the mixture increased as the crowding coefficient of pea increased. The maximum yield increase for the mixture was achieved when the relative yield total (RYT)=1.17 or + 11 dt grain DM ha^–1 for mixtures of the long-strawed conventional leafed cultivars Bohatyr and Alf (in 1996). The crowding coefficients of pea were positively correlated with the level of symbiotically fixed N₂ in the mixed stands. When N₂ fixation with mixed cropping was about 30 kg N ha^–1, RYT was unity. Increasing symbiotic N₂ in the mixtures resulted in increasing yield advantages in the mixture. Short-strawed pea cultivars seem unsuitable for mixing with oat. Plant height of pea appeared to be more important than plant leaf type. Accordingly, mixtures containing the long-strawed semileafless pea cultivars Profi and Alf were more successful. It is concluded that increased competitiveness of the pea component in the mixture with oat entails increasing the level of symbiotic N₂ fixation including resource complementarity and thus yield advantage in the mixed stands.     

The Effect of Nitrogen Fertilization and Population Density of the Field Bean (Vicia faba L. minor) of Indeterminate and Determinate Growth Habit on the Symbiosis with Root Nodule Bacteria and on the Seed Yield

Field beans of indeterminate (cv. Nadwiślański) and determinate (cv. Tibo) growth habits were grown on field plots with a density of 20, 40 and 80 plants m⁻² at two levels of nitrogen fertilization: low (20 kg N ha⁻¹) and very high (150 kg N ha⁻¹). At the phase of intense pod growth the number and the dry matter weight of root nodules as well as their nitrogenase activity and some features of the plants growth were determined, and in the period of ripeness the components of seed yield were established.
It was found that increased density of sowing as well as the high level of nitrogen fertilization inhibited the growth and development of root nodules and limited their nitrogenase activity in both cultivars. Plants of both varieties were characterized by a similar potential of forming the root nodules, however, in plants of the cv. Tibo the nitrogenase activity of nodules was much lower than in the cv. Nadwiślański.
Increased population density of the plants has in both varieties given increased seed yield when calculated per m² of the soil, compensating in excess the depression of the seed yield from one plant. Such compensation did not occur in the case of the depression of nitrogen fixation under intense nitrogen fertilization.     

The Effects of Intercrop Spacing Patterns on the Silage Yield of Maize and Soybean

The effects of intercrop spacing patterns on the silage yields of both maize (lea mays L.) and soybean (Glycine max [L.] Merr.) were examined from 1985 to 1987. Dwarf maize was intercropped with nonnodulatmg or nodulating soybean in the spacing patterns, S_40same (two crops in the same row, 40 cm row width) and S_20ait or S_40ak (two crops in alternate rows, 20 cm or 40 cm row width, respectively). Tall maize was intercropped with nodulating soybean in S_40sames S_40alt and S_40pair (maize in 40 cm paired rows, soybean rows 20 cm outside each maize row and 80 cm from the next set of four rows) at 0 or 60 kg N ha⁻¹ and at population densities of 67% maize: 67% soybean or 50 % maize: 50% soybean. Maize and soybean were also intercropped and stripcropped on a farm-scale. The only difference between intercrops arranged in the same rows versus those in alternate rows was that the average soybean protein yields were higher in S_40same than in S_40alt. In 1986, the S_40alt maize-soybean intercrops produced higher maize yields, total biomass yields and Land Equivalent Ratios (LERs) than in S_40pirs, and in 1987, these responses were higher in intercrops than in stripcrops. In 1986, at 0 kg N ha⁻¹, the soybean biomass and protein yields were lower in S_40alt, than in S_40pairs and in 1987, these responses were lower in intercrops than in stripcrops.     

氮胁迫对甜菜幼苗生理以及相关NRTs基因表达的影响

为了深入研究缺氮环境下甜菜(Beta vulgaris L.)的氮利用调控机制,并为利用分子育种以及基因工程途径提高植物的氮利用率奠定基础,本研究以甜菜幼苗‘780016B/12优’为试材,通过对其施加低氮和缺氮逆境胁迫,利用表型观察、叶绿素含量的测定以及相关基因和酶活性的应答变化分析,来研究甜菜植株在生理以及分子方面的应答机制。研究结果表明,甜菜叶片由于缺氮而表现出局部变黄,并且SPAD值显示,叶绿素含量随逆境时间呈下降趋势。qPCR表明,BvNRT2.1和BvNRT3.2基因均受到低氮和缺氮胁迫的诱导,且它们在根部的表达量要高于叶中,BvNRT2.1基因对逆境的应答更为显著。同时,随着胁迫时间的增长,甜菜体内的硝酸还原酶活性逐渐下降,但叶片中该酶的活性始终要高于根中。因此可以得出结论,低氮或缺氮逆境对甜菜幼苗的光合作用、硝酸还原酶活性造成了较为严重的影响,从而导致其生长在一定程度上受到抑制。可以推断,为了适应氮胁迫环境,甜菜自身可能通过上调硝酸盐转运蛋白基因的表达等途径来直接或间接的补偿由于环境氮缺乏或低氮造成的营养缺失,以抵御逆境伤害。     

Effect of Gibberellic Acid Spray and Basal Nitrogen and Phosphorus on Productivity and Fatty Acid Composition of Rapeseed-Mustard

Two field experiments were conducted during] 994-95 to study the effect of spray of 10⁻⁵ M GA3 at 40 days after sowing on mustard ( Brassica juncea (L.) Czern & Coss.) cv. Varuna grown with basally applied 0, 40, 80 and 120 kg N ha⁻¹ (Expt. 1) and 0,15, 30 and 45 kg P ha⁻¹ (Expt. 2) on pod number per plant, seeds per pod, 1000 seed weight, seed yield, biological yield, harvest index and fatty acid composition of oil. No significant difference between water and GA3 spray was found when basally applied nitrogen was 0 or 40 kg N ha⁻¹. N₈₀ proved to be the best for yield characteristics. In another experiment on phosphorus, GA₃ and 30 kg P ha⁻¹ individually enhanced the yield, but interaction of GA₃ and P remained non-significant. The fatty acid composition of oil in both experiments was significantly affected only by nitrogen and phosphorus treatments for oleic acid and erucic acid. It was found that return in the form of yield was more for every kg applied fertilizer under GA, spray treatment. The response was more for N fertilizer in comparison to P. GA₃ at a low level of fertilization significantly increased the return from fertilization.     

Symbiotic Nitrogen Fixation of White Clover in a Mixed Sward is not Limited by Height of Repeated Cutting

The aim of this study was to investigate whether symbiotic nitrogen fixation in white clover nodules limits nitrogen supply and hence clover growth by repeated defoliation at two cutting heights. Other possible factors governing symbiotic nitrogen fixation in the field were also elucidated. Using ¹⁵N, a 2-year field experiment including white clover ( Trifolium repens L. cv. Ladino) and perennial ryegrass ( Loliumperenne L. cv. Bastion) in monocultures and in mixtures was conducted in Eschikon, Switzerland. The effect of two cutting heights (4 cm and 10 cm above ground level) on the performance of symbiotic nitrogen fixation of white clover in the different sward-types was investigated. After each harvest, the plots were fertilized with 3 g N m^-2(equivalent to 30 kg N ha^-1 cut^-1 or 210 kg N ha^-1 year^-1). In both years, white clover grown in a mixture with grass received a significantly higher percentage of nitrogen from symbiotic fixation compared with clover grown in monoculture. This phenomenon is attributed to the strong competitiveness of ryegrass in soil nitrogen uptake. Consequently, white clover in the clover-ryegrass mixture was more dependent on symbiotic nitrogen fixation than that grown in monoculture. The cutting height did not preferentially influence symbiotic nitrogen fixation, as opposed to the uptake of mineral nitrogen from the soil. From this finding it is suggested that symbiotic nitrogen fixation did not limit the supply of nitrogen to clover and hence its growth. It is proposed that symbiotic nitrogen fixation in white clover is regulated by the demand for nitrogen rather than by the availability of carbohydrate reserves in the stolons. Symbiotic nitrogen fixation should thus be looked upon as an integrated plant growth factor and not as an isolated phenomenon.     

Response of Soybean [Glycine max (L.) Merr.] Cultivars to Genistein-Preincubated Bradyrhizobium japonicum: Nodulation and Dry Matter Accumulation under Canadian Short-Season Conditions

The addition of genistein, a plant-to-bacteria signal molecule, to Bradyrhizobium japonicum cells prior to use as inocula has been shown to increase nodule number and promote soybean N₂ fixation at low root zone temperatures. Previous greenhouse and field experiments involving only two cultivars have indicated that soybean [ Glycine max (L.) Merr.] cultivars can vary in their response to genistein application. The objective of this study was to evaluate a range of soybean cultivars for response to genistein application under short-season cool-spring Canadian conditions. A 2-year field study was conducted in 1997 and 1998 with a range of soybean cultivars recommended for Quebec. The 11 cultivars tested represented a range of yield potentials and maturity groups. They were inoculated with genistein-preincubated B. japonicum inocula or regular inocula, applied into the furrow at the time of planting. The results of these experiments indicated that neither maturity nor yield was correlated with increases in nodulation, biomass, and plant total nitrogen content resulting from genistein treatment and that all maturity groups responded to genistein application in essentially the same way. Thus, response of soybean cultivars to genistein addition is regulated by genotype characteristics other than maturity or yield level.     

烟苗生长发育对不同氮源形态的响应

为探讨不同形态氮源对烟苗素质和生长发育的影响，以烤烟新品系HN2146为参试材料，采用水培试验研究硝酸铵、硝酸钙、硫酸铵和尿素4种不同形态氮源对烟苗生长发育特性的影响。结果表明，烟苗最大叶面积以硝酸钙处理最大，为100.4cm2；烟苗叶和根系蛋白质含量以硫酸铵处理最高，分别为151.452和79.367μg/g FW；硝酸还原酶活性表现为硝酸钙>硝酸铵>硫酸铵>尿素处理；烟苗对氮的吸收能力表现为硝酸铵>硫酸铵>硝酸钙>尿素处理。通过对不同处理烟苗相关农艺性状和生理特性指标的主成分分析，其综合得分表现为硝酸钙>硝酸铵>硫酸铵>尿素处理。可见以硝态氮和铵态氮作为唯一氮源对烟苗生长发育的效果较好，而以尿素作为唯一氮源的效果最差，本研究结果为不同氮源在烤烟育苗培育上的应用提供了理论依据。     

减量施氮对玉米-大豆套作系统土壤氮素氨化、硝化及固氮作用的影响

土壤氮素氨化、硝化及固氮作用是影响作物氮素吸收及氮肥损失的主要因素, 为揭示氮肥减量下玉米-大豆套作系统的土壤氮素转化特性及排放规律, 利用大田定位试验研究了3种模式(玉米单作MM、大豆单作MS、玉米-大豆套作IMS)和3种施氮水平(不施氮NN: 0; 减量施氮RN: 180 kg hm ^-2; 常量施氮CN: 240 kg hm ^-2)对土壤硝化作用、氨化作用、固氮作用及氨挥发、N₂O排放、NO₃ ^--N累积的影响。结果表明, IMS较相应单作提高了土壤硝化和氨化作用, IMS的氨挥发损失率和N₂O损失率较MM降低21.6%和29.7%; IMS下玉米土壤的NO₃ ^--N积累量显著高于MM, 而大豆土壤的NO₃ ^--N积累量显著低于MS。各施氮处理间, RN较CN降低了玉米土壤的氨化与硝化作用, 增加了大豆土壤的硝化和固氮作用。IMS下RN的玉米、大豆全生育期固氮作用较CN增加29.7%和32.0%, 年均氨挥发总量和N₂O排放量较CN降低37.2%和41.0%。玉米-大豆套作系统在减量施氮下通过提高土壤氮素氨化、硝化与固氮作用, 减少氮素排放损失, 增强耕层土壤NO₃ ^--N积累, 为作物氮素吸收提供了充足氮源。     

Seasonal Changes in Nitrate Reductase Activity and Nitrogen Contents of Upland Rice at Low and Optimum N Fertility

A field experiment was conducted at the Livestock Research Centre of G. B. Pant University of Agriculture and Technology, Pantnagar, India during the wet season (June—October) of 1980 with the objectives of characterizing the seasonal changes in in vivo nitrate reductase activity (NRA) and N contents of upland rice cultivars grown under rainfed condition at low (0 kg N/ha) and optimum (80 kg N/ha) N fertility.
In vivo NRA increased initially up to panicle initiation stage (50 days after sowing) and declined, thereafter, until 90 days. Leaf NO₃-N content paralleled with in vivo NRA throughout crop season. Total N content of leaves and stem declined with advance in crop age, whereas panicle N content increased with the crop development. Optimum N fertility (80 kg N/ha) always resulted in higher NRA, NO⁻₃ and total N contents of rice plants.