Competition of wild oat with wheat in comparison to the wheat itself

In a glasshouse experiment, an increase of the number of wheat plants per pot caused the plants to became taller, have more ears and a greater grain yield per pot, while the number of tillers decreased and the straw mass did not change. The N and P contents in straw and N in grain also trended to decrease, while the translocation of these nutrients to the grain increased. The increase of wild oat plants (Avena sterilis spp.macrocarpa Mo.) per pot, produced a decrease of the growth attributes, grain yield and N accumulation in grain of wheat per pot. Wild oat competition with wheat was higher than the wheat competition with itself. Such competition affected the height, number of tillers and ears, the fertility index of the shoots, the straw and grain mass, and the total accumulation of N, P and K nutrients per wheat plant.     

Grain yield and kernel weight of two maize genotypes differing in nitrogen use efficiency at various levels of nitrogen and carbohydrate availability during flowering and grain filling

Grain yield per plant (GYP) and mean kernel weight (KW) of maize (Zea mays L.) are sensitive to changes in the environment during the lag phase of kernel growth (the time after pollination in which the potential kernel size is determined), and during the phase of linear kernel growth. The aim of this study was to assess genotypic differences in the response to environmental stresses associated with N and/or carbohydrate shortage at different phases during plant development. The rate and timing of N and carbohydrate supply were modified by application of fertilizer, shading, and varying the plant density at sowing, at silking or at 14 d after silking. The effects of these treatments on the photosynthetic capacity, grain yield and mean kernel weight were investigated in two hybrids differing in N use efficiency. The total above-ground biomass and grain yield per plant of the efficient hybrid responded little to altered environmental conditions such as suboptimal N supply, enhanced inter-plant competition, and shading for 14 d during flowering, when compared to the less efficient genotype. We conclude that grain yields in the efficient genotype are less sensitive not only to N stress, but also to carbohydrate shortage before grain filling. Shading of N deficient plants from 14 d after silking to maturity did not significantly reduce grain yield in the non-efficient genotype, indicating complete sink limitation of grain yield during grain filling. In the efficient genotype, in contrast, grain yield of N-deficient plants was significantly reduced by shading during grain filling. The rate of photosynthesis declined with decreasing foliar N content. No genotypic differences in photosynthesis were observed at high or low foliar N contents. However, at high plant density and low N supply, the leaf chlorophyll content after flowering in the efficient genotype was higher than that in the non-efficient genotype. Obviously, the higher source capacity of the efficient genotype was not due to higher photosynthetic N use efficiency but due to maintenance of high chlorophyll contents under stressful conditions. In the efficient genotype, the harvest index was not significantly affected by N fertilization, plant density, or shading before the grain filling period. In contrast, in the non-efficient genotype the harvest index was diminished by N deficiency and shading during flowering. We conclude that the high yielding ability of the efficient genotype under stressful conditions was associated with formation of a high sink capacity of the grains under conditions of low carbohydrate and N availability during flowering and with maintenance of high source strength during grain filling under conditions of high plant density and low N availability.     

Variation in nitrogen use efficiency among soft red winter wheat genotypes

Summary Nitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.The investigation reported in this paper (No. 85-3-122) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director     

The effect of inoculation with Azospirillum brasilense on growth and nitrogen utilization by wheat plants

Azospirillium brasilense is a rhizosphere bacteria that has been reported to improve yield when inoculated on wheat plants. However, the mechanisms through which this effect is induced is still unclear. In the present work, we have studied the effects of inoculating a highly efficient A. brasilense strain on wheat plant grown in 5 kg pots with soil in a greenhouse, under three N regimes (0, 3 or 16 mM NO₃ ^–, 50 ml/pot once or twice-a -week), and in disinfected or non-disinfected soil. At the booting stage, the inoculated roots in both soils showed a similar colonization by Azospirillum sp. that was not affected by N addition. The plants grown in the disinfected soil showed a higher biomass, N content and N concentration than those in the non-disinfected soil, and in both soils the inoculation stimulated plant growth, N accumulation, and N and NO₃ ^– concentration in the tissues.At maturity, the inoculated plants showed a higher biomass, grain yield and N content than the uninoculated ones in both soils, and a higher grain protein concentration than the uninoculated. It is concluded that in the present experiments, A. brasilenseincreased plant growth by stimulating nitrogen uptake by the roots.     

The contributions of plant and bacteria genotypes in the growth and nitrogen accumulation of inoculated alfalfa

The symbiotic efficiency of each of 30 alfalfa (16 Medicago sativa and 14 M. varia) cultivars inoculated with 7 Rhizobium meliloti strains was studied in three field experiments. Two-factor analysis of variance of the obtained date demonstrated that the green mass yield and nitrogen accumulation depend on genotypes of both partners. The total contribution of plant and bacterial genotypes to the variation of green mass yield increased from 0–17% in the first year of alfalfa growth to 40–78% in the third year. The effect of the genotypic variability of the symbiotic partners was higher for N accumulation than for the green mass. There was a negative correlation between plant mass and N accumulation in the uninoculated plants with the relative (%) deviations of these parameters in the inoculated plants. In the experiments conducted in the Tashkent region the efficiency of the “alfalfa-R. meliloti” symbiosis was higher than in the experiment conducted in the Tumen region.     

Contribution of inoculation with azolla combined with nitrogen,phosphorus and zinc to rice in Nile Delta

Rice performance, in terms of plant height, productive tillering, yield and N-contents of grain and straw, harvest index (grain yield as a percentage of grain plus straw yields) and relative fertilizer N-use efficiency (kg grain yield/kg fertilizer-N) was enhanced by urea, ZnSO₄ and green manuring withAzolla caroliniana. Unlike urea fertilizer, calcium superphosphate increased the rate of azolla field colonization and promoted a thick, healthy dark-green mat of the fern. Response to ZnSO₄ was higher in the azolla-free sub-subplots. Application of ZnSO₄ corrected symptoms of Zn deficiency in rice but the addition of calcium superphosphate in the absence of Zn intensified the symptoms of Zn deficiency.     

Photosynthetic efficiency and nitrogen distribution under different nitrogen management and relationship with physiological N-use efficiency in three rice genotypes

Nitrogen fertilization strategies were widely adopted to enhance grain production and improve nitrogen utilization in rice all over the world. For fertilization timing strategy, ear fertilization was usually employed in recent years. For fertilization amount strategy, nitrogen fertilization would continually increase to meet the demands of increasing people for food. However, under heavy ear fertilization as well as great nitrogen amount (NA), physiological N-use efficiency (PE, defined as grain production per unit nitrogen uptake by plants) decreased. Under three NA and two ratios of fertilization given during ear development period to total NA (ear fertilization distribution ratio, EFDR), net photosynthetic rate (Pn), Pn to nitrogen content per unit area (photosynthetic N-use efficiency, Pn/N), nitrogen accumulation in plant tissues and PE of three rice (Oryza sativaL.) genotypes, Jinyou 253, Liangyoupeijiu and Baguixiang were screened in the first and second seasons in 2002 so as to understand the fluctuation patterns of Pn/N and nitrogen distribution in leaf blades under great NA & EFDR and relationship with PE in rice. Results showed that under greater NA & EFDR, Pn in flag leaves at heading and plant nitrogen accumulation at maturity always increased and PE & Pn/N always decreased in spite of increased grain production. Rice distributed more nitrogen in leaf blade under greater NA and EFDR. PE indicated significantly (P<0.05) positive relationship with Pn/N and negative relationship with nitrogen distribution ratio in leaf blades at heading and maturity, and no association with Pn in two growing seasons. Results suggested that low PE in rice under great NA and heavy ear fertilization is associated to more nitrogen distribution in leaf blades and decreases in photosynthetic efficiency.     

Partitioning of nitrogen from biological fixation and fertilizer in Phaseolus vulgaris

Nitrogen uptake, distribution and remobilization in the vegetative and reproductive parts of the plant were studied in bean (Phaseolus vulgaris L.) cultivars Negro Argel and Rio Tibagi inoculated with either Rhizobium strain C05 or 127 K-17. Greenhouse grown plants were supplied with 2.5 mg N (plant)⁻¹ day⁻¹ as KNO₃ or K¹⁵NO₃ and the relative contribution to total plant nitrogen of mineral and symbiotically fixed nitrogen was determined. Control plants included those entirely dependent on fixed nitrogen as well as uninoculated plants supplied with 10 mg N (plant)⁻¹ day⁻¹. No differences were observed between inoculated treatments in total nitrate reductase activity and in the amount of mineral nitrogen absorbed, but there were considerable differences in the contribution of fixed nitrogen. Nitrogen fixation supplied from 58 to 72% of the total nitrogen assimilated during the bean growth cycle and the symbiotic combinations fixed most of their nitrogen (66 to 78% of total nitrogen) after flowering. Maximum uptake of mineral nitrogen was in the 15-day-period between flowering and mid-podfill (47 to 58% of total mineral nitrogen). Nitrogen partitioning varied with Rhizobium strains, and inoculation with strain C05 increased the nitrogen harvest index of both cultivars. Applied mineral nitrogen had a variable effect and in cv. Negro Argel was more beneficial to vegetative growth, resulting in smaller nitrogen harvest indices. Seed yield was not increased by heavy nitrogen fertilization. In contrast, cv. Rio Tibagi always benefited from nitrogen applications. Among the various nitrogen sources supplying the grain, the most important one was the fixed nitrogen translocated directly from nodules or after a rapid transfer through leaves, representing from 60 to 64% of the total nitrogen incorporated into the seeds.     

The effect of copper and nitrogen on the amino acid composition of oat straw

Summary The effect of fertilization with nitrogen and copper on the amino acid composition of oat straw has been studied.The plants (Avena sativa cv Yielder) were grown in peat with a very low copper content and supplied with two levels of nitrogen (NH₄ or NO₃) and three levels of copper sulphate.The higher level of nitrogen stimulated growth only when copper was added, whereas, without copper, it had an adverse effect on growth and prevented grain formation altogether. The higher level of nitrogen increased the nitrogen content of the straw at all levels of copper, but particularly in plants receiving no copper.Total amino acids in the straw hydrolysate of copper sufficient oats accounted for about 50% of the total N and was about 20% higher in copper-deficient tissues. The addition of copper caused a decrease in the amounts of all amino acids. The relative proportions of most of the amino acids to glycine remained fairly constant. Threonine, serine, alanine, iso-leucine, histidine and arginine showed small significant differences with copper treatment, whereas valine, tyrosine, phenylalanine, proline, lysine and cysteic acid (derived from cysteine and cystine) showed no differences. The proportion of aspartic acid relative to glycine in the straw hydrolysate was greatly increased in copper deficient plants supplied with the higher level of nitrogen, particularly as ammonium. The proportion of glutamic acid was also increased by the higher level of nitrogen, but showed no effect of added copper. Most of the difference in aspartic acid could be accounted for as free asparagine. The possible reasons for higher proportions of asparagine are discussed in relation to the metabolism of the oat plant.     

Application of photochemical parameters and several indices based on phenotypical traits to assess intraspecific variation of oat (<Emphasis Type="Italic">Avena sativa</Emphasis> L.) tolerance to drought

Functionality of the photosynthetic system under water stress is of major importance in drought tolerance. Oat (Avena sativa L.) doubled haploid (DH) lines obtained by pollination of F ₁ oat crosses with maize were used to assess the differences in plant genotypic response to soil drought. The investigations were based on the measurements of gas exchange and chlorophyll a fluorescence kinetics. Drought was applied to 17-day-old seedlings by withholding water for 14 days and subsequent plant recovery. Non-stressed optimally watered plants served as controls. Yield components were determined when plants reached full maturity. It was shown differences among the oat lines with respect to drought stress susceptibility (SI) and stress tolerance index mean productivity and drought susceptibility index. Sensitivity to drought of individual DH lines was significantly different, as demonstrated by the correlation between drought susceptibility index and yield components, such as dry weight (GW) or grain number (GN) of the harvested plants. GW and GN were lower in drought-sensitive genotypes exposed to drought stress compared to those resistant to drought. The principal component analysis allow to separate three groups of lines differing in their sensitivity to drought stress and indicated that tolerance to drought in oat has a common genetic background.     

Fungal response from oat (Avena sativa) plants and surface residue in relation to soil aggregation and organic carbon

Abstract

The influence of soil fungi on soil organic carbon (OC) from surface residue was tested in outdoor plots in southern Ontario, Canada, 2004. Fungal hyphal length, soil aggregation, OC and light and heavy fractions of organic matter were compared with factors of plant growth (with or without oat [Avena sativa]) and surface residue (no residue, oat straw (low C:N) or corn (Zea mays) stalks (high C:N)) in a factorial arrangement. Significant increases were observed in soil OC from the oat plants, and from corn stalks compared to straw residue, in the growing season with very moist, high OC, sandy soil. In treatments with corn stalk residue, fungal hyphal length was increased with interaction from the oat plants and residue and was positively correlated with the heavy fraction organic matter along with soil OC. Fungal hyphae, plant roots and high C:N residue were all factors in soil OC increases.     

Improving grain yield in backcross populations from Avena sativa × A. sterilis matings by using independent culling for harvest index and vegetative growth index or unit straw weight

Summary Grain yield was selected in Avena sativa X A. sterilis populations of segregates by applying independent culling for harvest index and either vegetative growth index or unit straw weight. Samples of lines intensively selected for harvest index had high harvest index but low grain yield because they had low vigor. Populations intensively selected for growth rate index or unit straw weight had high biological yield but low harvest index. Intensive selection for grain yield per se resulted in samples with high grain yield, but they were late and tall. Samples selected for harvest index at a 25% selection intensity first and subsequently selected for vegetative growth index or unit straw weight had grain yield as high as the samples selected for grain yield per se and vegetative growth index, and they had acceptable heading date and plant height. Backcrosses three and four were best, among the various BC generations, for selecting oat lines with high grain yield and suitable agronomic traits. CI 7463 was superior to CI 8044 as a recurrent parent, and B 445 was inferior to other A. sterilis accessions as a donor parent.Journal Paper No. J-12287 of the Iowa Agric, and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447. This research was supported in part by a grant from the World Food Institute, Iowa State University, Ames, IA, USA     

Association of two measures of vegetative growth rate with other traits in inter and intraspecific matings of oats

Summary F₂-derived oat lines from inter (Avena sativa L. x A. sterilis L.) and intraspecific (among A. sativa cultivars) matings were evaluated in the F₃, F₄, and F₅ generations for heading date, grain and straw yields, biomass, vegetative dry weight at anthesis, vegetative growth rates until anthesis (GRA) and until maturity (GRM), and harvest index. The associations of GRA and GRM with harvest index ranged from zero to slightly negative. The positive correlations of GRA and GRM with grain yield were stronger in inter than in intraspecific matings. Grain yield was positively associated with harvest index in both inter and intraspecific matings. The results suggest the use of A. sterilis x A. sativa matings to improve vegetative growth rate, grain yield, and, to a certain extent, harvest index simultaneously without affecting the growth duration of the crop.Journal Paper No. J 12130 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011, USA. Project No. 2447. Part of a study conducted by the senior author while he was a visiting scientist at Iowa State University     

Root nodulation and nitrogen accumulation and partitioning in legume crops as affected by soil solarization

Soil solarization is a preplanting technique used in hot climates to control weeds and soilborne pathogens consisting of mulching the soil surface with polyethylene sheets. The increase in temperature associated with solarized soil could affect nitrogen availability for grain legume crops through effects on nitrogen fixing soil microorganisms or other mechanisms. To examine the effects of solarization on natural root nodulation and nitrogen accumulation and partitioning in the plant, two solarization field experiments were carried out over two planting seasons, involving genotypes of both faba bean (Vicia faba) and chickpea (Cicer arietinum). The effect of sowing date was also studied in the first season. Solarization increased the maximum soil temperature by 9–10 °C in the first, and by 13–15 °C in the second season. At 5 cm below the solarized soil surface, a temperature of over 46 °C prevailed for 146 and 280 h over the two respective seasons, while this temperature was not attained in unmulched soil. Solarization delayed the initiation of nodulation and consistently reduced the nodule number per host plant, but generated an approximate doubling of mean nodule weight. The total nodule mass per plant was not affected by the treatment in the first season, but was reduced in the second season. Solarization significantly increased the concentrations of NO₃^– -N, Na⁺, Zn²⁺, Ca²⁺ and K⁺ in the soil extract, and the total nitrogen accumulated in the whole plant. This latter increase was due to both higher plant growth and a greater plant nitrogen concentration. The increased nitrogen level in the plant was not uniform with respect to plant component, varying from 57% in the roots to 198% in the pods and seeds. The plants grown in non-solarized soil accumulated about 31% of their total N content in the shoots of the parasitic weed Orobanche crenata. Solarization dramatically improved grain yield by 300–900% in both seasons and in all genotypes studied, due to increased N availability in soil, N accumulation in plants, improved plant growth, and complete control of the parasite weed O. crenata. On the basis of these beneficial effects, soil solarization, which avoids site contamination and is suited to organic farming, should be a good opportunity in Mediterranean areas where the level and stability of grain yields are low, and the infestation of O. crenata is high.     

Nitrogen and phosphorus harvest indices of common bean cultivars: Implications for yield quantity and quality

Breeding for yield in common bean (Phaseolus vulgaris L.) should consider the efficiency of biomass and nutrient partitioning to grains. In field experiments, 9 and 18 bean cultivars were cultivated in 1998 and 1999, respectively, to identify the genotypic variability of harvest index (HI) and N and P harvest indices (NHI and PHI), and to evaluate the relationships between these indices and grain yield. Cultivars differed for grain yield, HI, NHI and PHI in both years, but these indices varied less than grain yield. Growth habit markedly influenced HI, with prostrate cultivars possessing higher HI, NHI and PHI than erect cultivars; hence selection for HI should be performed within each phenological group. Grain yield was strongly associated with grain N and P contents, and positively but weakly correlated to HI, NHI and PHI; the indices were highly correlated among themselves. Multiple-regression analysis showed that most genotypic variation of grain yield was associated with the amount of N and P accumulated by the crop at maturity, and some yield variation was associated with seed nutrient concentration, particularly P concentration, whereas NHI and PHI had a minor role. Combined analysis of both experiments showed that grain yield diminished by 57% from 1998 to 1999, whereas HI remained almost stable and NHI and PHI decreased slightly, but the significant year × cultivar interaction revealed different degrees of phenotypic plasticity of biomass partitioning among cultivars. Selection solely for increased HI would scarcely result in improved grain yield, raising concomitantly NHI and PHI and probably reducing grain P concentration.     

不同小麦品种吸收利用氮素效率的差异及有关机理研究 Ⅰ.吸收和利用效率对产量的影响

用盆栽试验研究了１２个冬小麦品种（ＴｒｉｔｉｃｕｍａｅｓｔｉｖｕｍＬ．）在低、高氮条件下的籽粒产量差异,及吸收和利用氮素的效率对其影响。结果证明在低氮处理中吸收效率和利用效率（ＵｔＥＧ）的共同影响导致了产量差异,但利用效率的影响更大;高氮处理则主要是吸收效率的影响,利用效率的影响较小。研究还发现能高效吸收或利用氮素的品种多为矮秆品种,因此高产品种多为矮秆。在低氮处理中的高产品种具有高效吸收或高效利用的特点;高氮处理中的高产品种主要具有高效吸收的特点,利用效率并不高。在所有品种中,只有低氮条件下的太核５０２５兼具高效吸收和高效利用的优点,说明多数品种的吸收、利用效率有待提高,以充分发挥氮肥的增产效果,达到少施氮肥多增产和保护环境的目的     

Conservation of urea-N by immobilization-remobilization in a rice-Azolla intercrop

Nitrogen losses are notoriously high in flooded rice fertilized with urea. An Azolla intercrop can reduce such losses by immobilizing urea-N during periods of potentially high N-loss. The reduction in N loss linked with the absorption and remobilization of urea-N by Azolla, was studied in two greenhouse experiments conducted in Goettingen (Germany). Grain yield and N recovery were positively influenced by Azolla more than doubling grain yield and N uptake as compared to the split application of 300 mg N pot^–1 alone (Exp. 1). In the second experiment, the yield increase was 78.3% with single applications of 97.5 and 68.4% after a split-application of a total of 195 mg N pot^–1. In both years the effect of urea and Azolla combined exceeded that of the sum of the factors alone, a clear positive synergistic effect on yield and N uptake by rice. Azolla effectively competed with the young rice plants for applied urea, capturing nearly twice the urea-N than the rice plants up to tillering in experiment 1. In the second experiment, 64.6 mg N of the 97.5 mg applied early in the season was immobilized by Azolla within 2 weeks. This represented 63.1% of the total N accumulated in the Azolla. The fraction of Azolla-N derived from urea sank to 36.4 mg within 4 weeks and only 27.2 mg at maximum tillering as a result of Azolla senescence and N-release. Of this 64.6 mg urea N immobilized 28.7% is eventually taken up by the standing rice plant, representing 43.1% of the remineralized, urea-derived Azolla N. Following the second urea application, only 17.9 mg N were immobilized in the Azolla biomass during the 2 weeks, of which 6.9 mg pot^–1 were still retained in the Azolla at maturity. At this stage, rice is the more effective competitor for applied N. As much as 42.1% of this immobilized N finds its way into the rice by maturity. Thus, Azolla contributed to the conservation of N in the system, particularly of the urea applied early in the season. Loss of N from the system amounted to no more than 15%. Although the early-applied N directly recovered by the rice plant was low (20%), 2/3 of the N captured by Azolla following this first urea application was released to the system by the time of rice harvest, over 40% of which was available to the rice plant. Azolla thus appears to act as a slow release fertilizer.     

Comparative response of wheat and oilseed rape to nitrogen supply: absorption and utilisation efficiency of radiation and nitrogen during the reproductive stages determining yield

We investigated the response of spring wheat and oilseed rape to nitrogen (N) supply, focusing on the critical period for grain number definition and grain filling. Crops were grown in containers under a shelter and treated with five combinations of applied N. Wheat and oilseed rape produced comparable amounts of biomass and yield when corrected for the costs of biomass synthesis (SC). From the responses of biomass and yield to late N applications and the apparent contribution of mobilised biomass to yield, it seems that the yield of oilseed rape was more source-limited during grain filling than that of wheat, particularly at the medium and high N levels. Both species recovered equal amounts of N from the total available N in the soil and had similar N use efficiencies, expressed as yield per unit of N absorbed. However, oilseed rape had higher efficiency to convert absorbed N in biomass, but lower harvest index of N than wheat. Oilseed rape had similar or lower root biomass than wheat, depending on N level, but higher root length per unit soil volume and specific root length. The specific uptake rate of N per unit root dry weight during the critical period for grain number determination was higher in oilseed rape than in wheat. In wheat, N limitation affected growth through a similar or lower reduction in radiation use efficiency corrected for synthesis costs (RUE_SC) than in the cumulative amount of intercepted photosynthetically active radiation (IPARc). In oilseed rape, lower growth due to N shortage was associated more with RUE_SC than IPARc, during flowering while during grain filling both components contributed similarly to decreased growth. RUE_SC and the concentration of N in leaves and inflorescence (LIN%) decreased from flowering to maturity and were curvilinearly related. Oilseed rape tended to have higher RUE_SC than wheat at high N supply during the critical period for grain number determination, and generally lower during grain filling. The reasons for these differences and possibilities to increase yield potential are discussed in terms of the photosynthetic efficiency of the different organs and changes in source–sink ratio during reproductive stages. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fate and effects on yield components of extra applications of nitrogen on spring wheat (Triticum aestivum L.) grown in solution culture

Spring wheat (Triticum aestivum L.) was grown with daily additions of nitrate-N. The relative addition rate of nitrate-N was decreased stepwise, and after 125 days of growth, 58 mg N plant^-1 had been introduced. The fate and effect of an extra addition of nitrate (20 mg N plant^-1) at six different times during the ontogeny (37, 54, 66, 79, 94 and 108 days from sowing) on grain yield and grain protein concentration was investigated. The plants absorbed all or most of the extra nitrate at all stages of development evaluated. Dry matter production of both aerial vegetative parts and grains, but not roots, generally increased as a result of the extra nitrate addition. The increase in grain dry matter was mainly an effect of an increased number of grains per plant. Extra nitrate applications had large effects on grain nitrogen content at all stages, but the effect on main shoot and tiller ears varied depending on the time of application. Early applications, i.e. before anthesis, mainly led to increased yield with unchanged protein concentration whereas late applications also led to increased grain protein concentration. The largest effect on grain nitrogen concentration (25–30% increase) was obtained when the extra nitrate was applied late after sowing, i.e. less than four weeks before final harvest. As the extra dose of nitrate was labelled with ¹⁵N, it was possible to follow the movement of the extra nitrogen addition within the plant. Samples were taken at one and five days after ¹⁵N-addition and at final harvest. There were differences in the movement of ¹⁵N depending on when it was introduced. Generally, net movement of the ¹⁵N-labelled N into the grain increased with age at application until 94 days after sowing when a maximum of 90% of the added ¹⁵N ended up in the grain.Abbreviations RN Relative increase in nitrogen content - RA Relative nitrogen addition rate - RG Relative growth rate - N nitrogen     

不同小麦品种(系)吸收利用氮素效率的差异及有关机理研究 Ⅲ.影响利用效率的因素分析

用盆栽试验研究了12个冬小麦品种（系）在成熟期以生物学产量为基础的利用效率（UtEB=生物学产量／吸氮量）、收获系数、氮素收获系数和籽粒氮浓度对以籽粒产量为基础的利用效率（UtEG=籽粒产量／吸氮量）的影响。相关分析证明,这4个因子对UtEG的影响各不相同。无论是低氮还是高氮处理,UtEG与UtEB和收获指数呈正相关,而与籽粒氮浓度呈负相关,与氮素收获指数的相关性较差。从相关系数的高低判断,在这名个因子中,籽粒氮浓度对UtEG的影响最大,其次是UtEB和收获指数。虽然氮素收获指数与UtEG的相关性较差,但它在高氮处理的水平较低,致使利用效率（UtEG）降低。此外还分析了开花期单株顶3叶叶绿素含量与利用效率（UtEG和UtEB）的关系。开花期单株顶3叶叶绿素含量与吸氮量的比值（UtEC）因品种（系）而异,且大多数品种（系）的UtEC受供氮水平的影响小,推测该性状可能受遗传控制。相关分析表明,在低氮处理中,UtEC分别与UtEG和UtEB呈显著或极显著正相关,说明UtEC可能是导致品种间利用效率差异的内在因素之一。在高氮处理中,由于叶绿素含量不是光合作用的限制因素,UtEC与UtEG、UtEB相关性较差,对其原因的深入研究,可为采取措施提高高肥条件下的利用效率提供理论依据。