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1.
施用预处理稻秆的土壤供氮特征及对冬小麦氮吸收的影响   总被引：8，自引：2，他引：8  
采用盆栽试验方法,研究了经过预处理的水稻秸秆(预处理稻秆)施入土壤后对土壤的供氮特征及小麦氮营养的影响。研究结果表明,稻秆经过预处理后,纤维素、半纤维素以及二氧化硅比原始稻秆都有所降低,而可溶性物质增加;施用时配施无机氮肥,小麦全生育期内土壤微生物量N和矿质态N平均分别比对照(纯土壤)提高232.3%和66.0%,小麦干物重和吸收总氮量分别比对照高56.3%和124.3%,并优于未经处理的原始秸秆及单施尿素处理。可见处理秸秆配施尿素能够显著改善土壤的供氮状况,促进小麦对氮素的吸收,增加小麦产量,提高化学肥料氮的利用率。  相似文献   

2.
In organic farming systems, it has been demonstrated that grain pulses such as peas often do not enhance soil N supply to the following crops. This may be due to large N removals via harvested grains as well as N‐leaching losses during winter. In two field‐trial series, the effects of legume (common vetch, hairy vetch, peas) and nonlegume (oil radish) cover crops (CC), and mixtures of both, sown after peas, on soil nitrate content, N uptake, and yield of following potatoes or winter wheat were studied. The overall objective of these experiments was to obtain detailed information on how to influence N availability after main‐crop peas by adapting cover‐cropping strategies. Cover crops accumulated 56 to 108 kg N ha–1 in aboveground biomass, and legume CC fixed 30–70 kg N ha–1 by N2 fixation, depending on the soil N supply and the length of the growing period of the CC. Nitrogen concentration in the aboveground biomass of legume CC was much higher and the C : N ratio much lower than in the nonlegume oil radish CC. At the time of CC incorporation (wheat series) as well as at the end of the growing season (potato series), soil nitrate content did not differ between the nonlegume CC species and mixtures, whereas pure stands of legume CC showed slightly increased soil nitrate content. When the CC were incorporated in autumn (beginning of October) nitrate leaching increased, especially from leguminous CC. However, most of the N leached only into soil layers down to 1.50 m and was recovered more or less by the following winter wheat. When CC were incorporated in late winter (February) no increase in nitrate leaching was observed. In spring, N availability for winter wheat or potatoes was much greater after legumes and, after mixtures containing legumes, resulting in significantly higher N uptake and yields in both crops. In conclusion, autumn‐incorporated CC mixtures of legumes and nonlegumes accomplished both: reduced nitrate leaching and larger N availability to the succeeding crop. When the CC were incorporated in winter and a spring‐sown main crop followed even pure stands of legume CC were able to achieve both goals.  相似文献   

3.
The plant‐available soil water, amount and distribution of rainfall or irrigation are primary factors that may affect yield and quality of winter wheat in heterogeneous fields. The objective of this 2‐y study was to vary N application and water supply in order to achieve a more mechanistic insight into the effects of underlying differences in the site‐specific productivity on heterogeneous fields. Two N fertilizer rates (120 and 180 kg N ha–1) and three different water supply treatments (rain sheltering, irrigation, rain‐fed) were compared on field sites with lower or higher plant available soil water capacities. On the whole, the site, rather than rainfall or N fertilisation, was the primary factor that accounted for variability in grain yield. Rainfall distribution during the growing season affected the overall yield level in a given year. The sites characterised by lower plant available water capacity did not show higher grain yield and improved quality with the increased N rate. This suggests that the reduced N rate should be recommended on these sites to take into account the environmental sustainability of N fertilisation. With respect to the higher N application at sites of high plant available soil water capacity, although the already high yield levels were not increased further, the protein quality was significantly improved in the first season within all treatments and in the second season in the irrigated treatments. Therefore, a higher N‐rate proved to be advantageous, especially considering that the residual nitrate levels after harvest were low. The study demonstrated that the response of winter wheat to water shortage or abundance and N fertilisation is site‐specific and dependent on the availability of soil water.  相似文献   

4.
The objective of this work was to provide evidence on the effects of faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) on the dynamics of soil N availability and yield parameters of wheat (Triticum turgidum L. var. durum) in a legume–wheat rotation in comparison with the effects of the more extensively studied common vetch (Vicia sativa L.). Soil samples were taken from field plots just before wheat sowing and incubated in the laboratory to assess N mineralization potential, soil respiration and N immobilization after incorporation of legume residues. Soil after vetch cultivation showed the highest residual N and mineralization potential (120 mg N kg?1 soil), the greatest CO2 release and the smallest N immobilization. Smaller mineral N release (80 mg N kg?1 soil) was shown by soil after faba bean cultivation, which, however, would be capable to support an average wheat production without fertilization. Soil after chickpea and wheat cultivation manifested no differences in residual N and mineralization or immobilization potential. Laboratory results were well correlated with grain yield and N uptake during the second season of rotation in the field. All legumes resulted in significant yield surpluses and provided N credit to the following unfertilized wheat.  相似文献   

5.
A laboratory study was conducted at the Indian Agricultural Research Institute, New Delhi on a sandy clay loam soil of pH 7.9 and organic C content of 0.34% to study the effect of incorporating Sesbania or Vigna legume residues or wheat straw at 15 and 30t ha?1 on temporal variation in ammoniacal and nitrate‐N in soil under submergence and well drained conditions. Under submergence most mineral N was present as ammoniacal‐N, while under well drained conditions it was present as Nitrate‐N. The content of ammoniacal N in soil was the highest after 30 days of incubation and declined thereafter under submergence. On the other hand under well drained conditions the mineral‐N (mostly nitrate) content in soil at 30 DAI was very little and showed increases only later, reaching the highest level at 90 DAI. Application of wheat straw specially at 301 ha?1 level resulted in immobilization of native soil‐N. These results show that rice which is grown under submergence can be transplanted soon after incorporation of legume residues, but for wheat or other crops which are grown under well drained condition a time interval of 30 days or more needs to be provided before sowing the crop.  相似文献   

6.
ABSTRACT

This study aimed to understand the effects of Medicago spp proportion on symbiotic and non-symbiotic nitrogen (N) utilization of plants, and subsequent forage production and soil N status in an artificial Leymus chinensis grassland. By a two-year field experiment conducted in semi-arid northern China, it was found that the corresponding biomass proportions of legume in swards were 0, 39, 63, 83 and 98% when legume seedling proportions at sowing were 0, 25, 50, 75 and 100%, respectively. Increased Medicago seedling proportion (from 25 to 100%) decreased legume N2 fixation capacity from 53 to 21%, as a consequence, this reduced total symbiotic N2 fixation and its contribution to forage production with Medicago seedling proportion increasing from 50 to 75% or more. However, as increased Medicago seedling proportion enhanced legume biomass and sward uptake to soil mineral N, higher legume stands still led to the greater biomass and N yield. The cultures with 50% seedling of legume had 4–13% greater soil N concentration than the cultures with 0, 25, 75 and 100% seedling of legume. We concluded that pure Medicago stands led to the greatest forage yield, while medium Medicago stands could lead to the greater symbiotic N fixation and soil N concentration.  相似文献   

7.
Legume–cereal intercropping is increasingly being appreciated in dryland areas, where severe climatic conditions and intensive agricultural practices, generally dominated by continuous cereal cultivation, determine depletion of soil nutrient resources and decline of soil fertility. This research aimed to assess whether and to what extent a newly introduced legume-based intercropping system is able to ameliorate the biological fertility status of an arable soil in a way that is still noticeable during the succeeding durum wheat cropping season in terms of changes in bacterial community structure, soil C and N pools, and crop yield. A field experiment was carried out under rainfed conditions in Southern Italy on a sandy clay loam soil cultivated with durum wheat following in the rotation a recently established grain legume (pea, faba bean)–barley intercropping. Soil chemical, biochemical and eco-physiological variables together with compositional shifts in the bacterial community structure by LH-PCR fingerprinting were determined at four sampling times during the durum wheat cropping season. Soil fertility was estimated by using a revised version of the biological fertility index. Results showed that even though the microbial biomass was significantly altered, the preceding legume intercrops stimulated C-related functional variables thus leading to an increased release of mineral N, which was larger in crop treatments succeeding pea-based than faba bean-based intercropping. The increased N made available in soil enabled the succeeding durum wheat to achieve an adequate grain yield with a reduced N-fertilizer use. Soil type and environmental conditions rather than crop treatments were major determinants of bacterial community structure. The biological fertility status was not varied, suggesting that in intensively managed rainfed areas long-term crop rotations with intercropped legumes are needed to consistently ameliorate it.  相似文献   

8.
在高肥力土壤条件下,研究了施氮量对土壤无机氮分布和微生物量氮含量及小麦产量的影响。结果表明,小麦生长期间,施氮处理0100.cm土层硝态氮积累量显著大于不施氮处理;当施氮量大于150.kg/hm2时,随施氮量增加,0100.cm土层硝态氮积累量显著增加;随小麦生育进程推进,施氮处理上层土壤硝态氮下移趋势明显,至小麦成熟时,施氮1952～85.kg/hm2处理60100.cm土层硝态氮含量显著大于其它处理。小麦生长期间,0100.cm土层铵态氮积累量较为稳定,施氮处理间亦无显著差异。与不施氮肥相比,施氮提高小麦生长期间040.cm土层土壤微生物量氮含量;当施氮量小于240.kg/hm2时,随施氮量增加,土壤微生物量氮含量增加。小麦的氮肥利用率随施氮量增加而降低;施氮1051～95.kg/hm2,收获时小麦植株吸氮量、生物产量、子粒产量和子粒蛋白质含量提高;而施氮量大于240.kg/hm2时,小麦生育后期的氮素积累量降低,收获时植株吸氮量、生物产量和子粒蛋白质含量降低。说明本试验条件下,施氮1051～50.kg/hm2可满足当季小麦氮素吸收利用,获得较高的子粒产量和蛋白质含量。继续增加施氮量,土壤微生物量氮含量增加,但土壤中残留大量硝态氮,易淋溶损失。  相似文献   

9.
Legumes have been shown to increase P uptake of the following cereal, but the underlying mechanisms are unclear. The aim of this study was to compare the effect of legume pre-crops and their residues on the growth, P uptake and size of soil P pools in the rhizosphere of the following wheat. Three grain legumes (faba bean, chickpea and white lupin) were grown until maturity in loamy sand soil with low P availability to which 80?mg P kg?1 was supplied. This pre-crop soil was then amended with legume residues or left un-amended and planted with wheat. The growth, P uptake and concentrations of P pools in the rhizosphere of the following wheat were measured 6?weeks after sowing. In a separate experiment, residue decomposition was measured over 42?days by determining soil CO2 release as well as available N and P. Decomposition rates were highest for chickpea residues and lowest for wheat residues. P release was greatest from white lupin residues and N release was greatest from faba bean residues, while wheat residues resulted in net N and P immobilisation. The growth of the following wheat was greater in legume pre-crop soil without residue than in soils with residue addition, while the reverse was true for plant P concentration. Among the legumes, faba bean had the strongest effect on growth, P uptake and concentrations of the rhizosphere P pools of the following wheat. Regardless of the pre-crop and residue treatment, wheat depleted the less labile pools residual P as well as NaOH-Pi and Po, with a stronger depletion of the organic pool. We conclude that although P in the added residues may become available during decomposition, the presence of the residues in the soil had a negative effect on the growth of the following wheat. Further, pre-crops or their residues had little effect on the size of P pools in the rhizosphere of wheat.  相似文献   

10.
Straw incorporation is a useful management practice in sustainable agricultural systems to improve soil fertility and to reduce air pollution from straw burning. A three-year field experiment was conducted under two rice straw managements and four nitrogen (N) application rates in Rugao, China during 2010–2013, to examine whether straw management practices integrated with fertilizer N applications affect crop yield, N balance and N use efficiency in the wheat season of rice-wheat cropping systems. The results showed that straw incorporation had positive effects on plant N uptake and grain yield. This may be attributed to the greater soil water content and lower amount of seasonal rainfall. However, straw incorporation resulted in lower soil inorganic N and more N surplus at the early growth stage. Grain yield had a significant relation with wheat N uptake from sowing to jointing and from jointing to anthesis with straw incorporation. Therefore, our results suggest that in adjusting the ratio of basal and topdressing N fertilizer, it is important for the supply of optimum N to the crop and to maintain grain production with straw incorporation.  相似文献   

11.
Legume pre-crops may increase P uptake of the following wheat, but the mechanisms behind this effect are unclear. A rotation study was carried out to assess the concentrations of rhizosphere P pools of three grain legumes and wheat (phase 1) and their effects on P uptake and P pools in the rhizosphere of the following wheat (phase 2). Faba bean, chickpea, white lupin and wheat were grown for 10 weeks in a loamy sand soil with low P availability. The following wheat was grown in the pre-crop soil with and without addition of pre-crop residues. Among the pre-crops, white lupin had the strongest effect on the P pools; it depleted the labile P pools, resin P and NaHCO3-Pi and also the less labile P pools, NaOH-Pi and residual P; whereas the concentration of NaHCO3-Po was higher than that in the rhizosphere of the other pre-crops. White lupin had a smaller biomass compared to faba bean which depleted the P pools to a lesser extent. Phosphorus uptake of the following wheat was greatest in white lupin pre-crop soil. Chickpea increased P uptake of the following wheat when residues were added. In the presence of residues, wheat after legumes depleted labile P pools to a greater extent than wheat after wheat, but this coincided with greater P uptake only in wheat after chickpea and white lupin, which may be explained by the small root biomass of wheat after faba bean. The results show that the greater P uptake of the following wheat induced by pre-crops may be due to two mechanisms: P mobilisation (white lupin) or P addition with legume residues (chickpea). This study further showed that P uptake by a crop is only partly a function of the depletion of P in the rhizosphere; another important factor is the ability to exploit a large soil volume.  相似文献   

12.
Ground 15N-labelled legume material (Medicago littoralis) was mixed with topsoils in confined microplots in the field, and allowed to decompose for 7 and 5 months in successive years (1979, 1980) before sowing wheat. The soil cropped in 1979 (and containing 15N-labelled wheat roots and legume residues) was cropped again in 1980.The results support evidence that ungrazed legume residues, incorporated in amounts commonly found in southern Australian wheat growing regions, contribute only a little to soil available N and to crop N uptake, even in the first year of their decomposition. Thus mature first crops of wheat, although varying greatly in dry matter yield (2.9-fold) and total N uptake (2.4-fold), took up only 27.8 and 20.2% of the legume N applied at 48.4 kg ha?1, these corresponding to 6.1 and 10.8% of the N of the wheat crops. The availability of N from medic residues to a second wheat crop declines to <5% of input. For both first and second wheat crops, uptake of N from legume residues was approximately proportional to legume N input over the range 24.2 to 96.8 kg ha ?1.The proportional contributions of medic N to soil inorganic N, N released in mineralization tests, and to wheat crop N, differed between seasons and soils, but for a given crop did not significantly differ between tillering, flowering and maturity. In both years, grain accounted for 52–65% of the total 15N of first crops, roots for < 5–6%. In neither year did the amounts of N or 15N in the tops change significantly between flowering and maturity, despite a gain in tops dry matter in 1979; by contrast N and 15N of roots decreased significantly during ripening in both years. Wheat plants at tillering contained about 75% of the N and 15N taken up at flowering. The amounts of legume-derived 15N in mature first wheat crops were equivalent to 82–88% of the amounts of inorganic 15N in the soil profiles at sowing. Wheat straw added at the rate of 2.5 t ha?1, 2 months before sowing, decreased the uptake of N (15%) and 15N (18%) by wheat in a nitrogen responsive season.  相似文献   

13.
氮肥施用对冬小麦籽粒产量和氮素表观损失的影响   总被引：16，自引：0，他引：16  
Excessive nitrogen （N） fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content （Nmin） in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels （average 212 kg N ha^-1）. The average optimum N rate was 96 kg N ha^-1 for the five sites with low initial soil Nmin （average 155 kg N ha^-1） before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha^-1, whereas the farmers＇ conventional N application rate resulted in losses of more than 100 kg N ha^-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields.  相似文献   

14.
黄土高原旱地冬小麦/夏玉米轮作体系土壤的氮素平衡   总被引：12，自引：7，他引：12  
在黄土高原南部旱地,通过田间小区试验研究了传统施肥方式下冬小麦/夏玉米轮作体系中土壤的氮素平衡。结果表明:土壤残留矿质态氮(Nmin)对作物产量和施用氮肥效果有重要影响,前季作物残留土壤Nmin可以促进后季作物生长,使氮肥增产效应不明显;冬小麦生长季节施氮240.kg/hm2可以增加产量和作物吸氮量,但其氮肥利用率只有39.7%,大部分以Nmin残留于0200cm土壤中或以其他途径损失;由于冬小麦季节残留肥料氮的后效,使夏玉米生长季节的氮肥利用率很低,施氮120和240.kg/hm2的氮肥利用率分别只有22.4%和3.9%,而在0200cm土层残留率则达到51.1%和87.2%;经过冬小麦、夏玉米一个轮作周期后,施氮量为240、360和480.kg/hm2时作物的氮肥利用率平均为52.2%4、2.2%和28.0%,而相应的土壤残留率平均为12.4%、25.3%和49.8%,表观损失率平均为35.4%、32.5%和22.2%。表明在土壤残留Nmin较高的条件下,夏玉米生长季节施氮量较低时盈余氮素以表观损失为主,施氮量高时大部分氮素残留于土壤剖面。  相似文献   

15.
Unground 15N-labelled medic material (Medicago littoralis) was mixed with topsoils at 3 field sites in South Australia, allowed to decompose for about 8 months before sowing wheat, and then for a further 7 months until crop maturity. The site locations were chosen to permit comparisons of recoveries and distribution of 15N in soils (organic N and inorganic N to 90 cm depth) and wheat (grain, straw and roots to 20 cm depth) in areas where rainfall (and wheat yields) differed greatly. Soils differed also in their texture and organic matter contents. Recoveries of applied 15N in wheat plus soil were 93.1% from a sandy loam (Caliph) and 92.3% from a sandy soil (Roseworthy) despite differences in rainfall and extent of leaching of the 15NO3? formed from the decomposing medic residues. From a heavy clay soil (Northfield), which received the highest rainfall, the 15N recovery was 87.7%. The loss of 15N at this site was not due to leaching, as judged by 15NO3? distribution in the soil profile at seeding and crop maturity.Wheat plants took up only 10.9–17.3% of the 15N added as legume material. Percentage uptakes of 15N were not related to grain yields. The proportions of wheat N derived from decomposing medic residues were 9.2% at Caliph (input medic, N, 38 kg N ha?1), 10.5% at Roseworthy (input medic N, 57 kg N ha?1), and only 4.6% at Northfield (input medic N, 57 kg N ha?1). Most (51–70%) of the 15N recovered in wheat was accounted for in the grain. Inorganic 15N in the soil profiles was depleted during the cropping phase, and at wheat harvest represented from 0.6 to 3.1% only of 15N inputs. The major 15N pool was soil organic 15N accounting for 71.9–77.7% of 15N inputs.We conclude that, in the context of N supply from decomposing medic tissues to wheat crops, the main value of the legume is long-term, i.e. in maintaining soil organic N concentrations to ensure adequate delivery of N to future cereal crops.The N of the wheat was not uniformly labelled, root N being generally of the highest atom% enrichmensts, and straw N of the lowest. Nevertheless, at the Roseworthy site, the enrichments of wheat N were similar to those of NO3? N in the profile at seeding, indicating that the proportions of 14N and 15N in the inorganic N pool did not change appreciably during the cropping period. By assuming equilibrium at this site, we calculate that during 15 months decomposition the soil plus legume delivered about 189 kg N ha?1, of which 93.2 kg ha?1 (49.3%) was taken up by the wheat, 37.2 kg ha?1 (19.7%) was immobilized or remained as fine root residues, and 17.3 kg ha?1 (9.2%) remained as inorganic N in the soil profile; 41.7 kg ha?1 (22.1%) was unaccounted for in the soil-plant system, and was probably lost via inorganic N. Thus about 6.5 kg inorganic N ha?1 was supplied by the soil plus medic residues per 100 kg dry matter ha?1 removed as wheat grain.  相似文献   

16.
过量施氮对旱地土壤碳、氮及供氮能力的影响   总被引：14，自引：8，他引：6  
【目的】过量施氮会影响土壤有机碳、氮的组成与数量,进而改变土壤供氮能力,但关于西北旱地长期过量施用氮肥后土壤有机碳、氮及土壤供氮能力变化的研究尚缺乏。本文在长期定位试验的基础上,通过分析不同氮肥水平特别是过量施氮条件下土壤硝态氮,有机碳、氮和微生物量碳、氮的变化,探讨长期过量施氮对土壤有机碳、氮及供氮能力的影响。【方法】长期定位试验位于陕西杨凌西北农林科技大学农作一站。在施磷(P2O5)100kg/hm2的基础上,设5个氮水平,施氮量分别为N 0、80、160、240、320 kg/hm2。重复4次,小区面积40 m2,完全随机区组排列。种植冬小麦品种为小堰22。本文选取其中3处理,以不施氮为对照(N0)、施氮量N 160 kg/hm2为正常施氮(N160),施氮量N 320 kg/hm2为过量施氮(N320),分别于2012年6月小麦收获后和10月下季小麦播前采集土壤样品,进行测定分析。【结果】过量施氮导致下季小麦播前0—300 cm各土层硝态氮含量显著增加,平均由对照的2.8 mg/kg增加到15.5 mg/kg;同时,0—60 cm和0—300 cm土层的硝态氮累积量分别由对照的47.2和108.9 kg/hm2增加到76.5和727.7 kg/hm2。过量施氮也增加了夏闲期间0—300 cm土层土壤有机氮矿化量,由对照的72.4 kg/hm2增加到130.7 kg/hm2。但过量施氮未显著增加土壤的有机碳含量,却显著增加了土壤有机氮含量,过量施氮0—20、20—40 cm土层土壤有机碳分别为9.24和5.39 g/kg,有机氮分别为1.05和0.71 g/kg,较对照增加52.2%和54.3%。同样,过量施氮未显著影响0—20、20—40 cm土层土壤微生物量碳含量,其平均含量分别为253和205 mg/kg,却显著提高了0—20、20—40 cm土层土壤微生物量氮含量,由对照的24.1和7.5 mg/kg提高到43.6和16.1 mg/kg。【结论】过量施氮可以显著增加旱地土壤剖面中的硝态氮累积量、夏闲期氮素矿化量、小麦播前土壤氮素供应量和土壤微生物量氮含量,但对土壤有机碳和微生物量碳没有显著性影响,同时过量施氮增加了土壤硝态氮淋溶风险,故在有机质含量低的黄土高原南部旱地冬小麦种植中不宜施用高量氮肥,以减少土壤氮素残留和农业投入,达到保护环境和培肥土壤的目的。  相似文献   

17.
  【目的】  土壤中氮素的有效性很大程度上影响着作物对氮的吸收。明确各形态氮素对作物吸氮量的贡献,研究调控土壤氮素形态的因素,为培育氮素高效和作物高产的土壤提供理论依据。  【方法】  试验基于河南新乡的“国家潮土土壤肥力与肥料效益监测基地”长期定位试验,以不施肥 (CK)、施NPK化肥 (NPK) 和1.5倍NPK化肥并配施有机肥 (1.5MNPK) 3个处理的土壤作为低肥力 (F1)、中肥力 (F2) 和高肥力 (F3) 土壤进行小麦盆栽试验。3个肥力土壤处理施肥方法相同,盆钵埋于土壤内,盆钵顶部露出地面5 cm。分别在小麦拔节期、孕穗期和成熟期采集土壤和植株样品,测定小麦产量、各生育期吸氮量,分析土壤有机氮、矿质氮 (铵态氮和硝态氮)、固持氮库 (微生物量氮和固定态铵) 含量差异,并通过结构方程模型 (SEM) 建立各形态氮素与小麦吸氮量的相关关系。  【结果】  3个肥力水平土壤矿质氮含量在小麦生长期内总体呈下降趋势,收获期土壤矿质氮含量在F1、F2、F3中分别比播种前显著下降了2.9、1.8和6.8 mg/kg。从拔节期到收获期,土壤微生物量氮在F1先增加后降低,在F3中持续增加,在F2中先降低后增加。土壤固定态铵含量在拔节期前和孕穗期后均无显著变化,但从拔节期到孕穗期,3个肥力土壤中固定态铵含量均显著提高。而固持氮库在不同肥力土壤间差异明显,其从播种前到拔节期在F1中增加了10.6 mg/kg,而在F2和F3中分别降低了14.3和32.2 mg/kg;从拔节期到孕穗期都显著增加;从孕穗期到收获期在F1中降低了2.4 mg/kg,而在F2和F3中分别增加8.2和8.7 mg/kg。小麦的产量和吸氮量均在F3中最高,F1中最低;氮素表观平衡在F1中最高,F3中最低。SEM分析结果表明,固持氮库可直接正向调控小麦吸氮量,有机氮库通过固持氮库和矿质氮库之间的变化而间接调控小麦吸氮量。  【结论】  包含微生物量氮和固定态铵的固持氮库可直接正向调控小麦吸氮量,有机氮库通过影响固持氮库和矿质氮库间接调控小麦吸氮量。由于固定态铵在拔节前和孕穗期后含量较为稳定,在高肥力土壤上微生物量氮随着小麦生育期的推进显著增加,可促进小麦的生长和氮素吸收,减少肥料氮的残留量,较高的微生物量氮又可作为氮库来固存易损失的矿质氮和肥料氮。  相似文献   

18.
In grain legumes, the N requirements of growing seeds are generally greater than biological nitrogen fixation (BNF) and soil N uptake during seed filling, so that the N previously accumulated in the vegetative tissues needs to be redistributed in order to provide N to the seeds. Chickpea, field bean, pea, and white lupin were harvested at flowering and maturity to compare the relative contribution of BNF, soil N uptake, and N remobilisation to seed N. From flowering to maturity, shoot dry weight increased in all crops by approximately 50%, root did not appreciably change, and nodule decreased by 18%. The amount of plant N increased in all crops, however in field bean (17?g?m?2) it was about twice that in chickpea, pea, and lupin. The increase was entirely due to seeds, whose N content at maturity was 26?g?m?2 in field bean and 16?g?m?2 in chickpea, pea, and lupin. The seed N content at maturity was higher than total N accumulation during grain filling in all crops, and endogenous N previously accumulated in vegetative parts was remobilised to fulfil the N demand of filling seeds. Nitrogen remobilisation ranged from 7?g?m?2 in chickpea to 9?g?m?2 in field bean, and was crucial in providing N to the seeds of chickpea, pea, and lupin (half of seed N content) but it was less important in field bean (one-third). All the vegetative organs of the plants underwent N remobilisation: shoots contributed to the N supply of seeds from 58% to 85%, roots from 11% to 37%, and nodules less than 8%. Improving grain legume yield requires either reduced N remobilisation or enhanced N supply, thus, a useful strategy is to select cultivars with high post-anthesis N2 fixation or add mineral N at flowering.  相似文献   

19.
《Applied soil ecology》2000,14(2):111-124
We determined the impact of the presence of lupin and wheat residues on decomposer fauna and measured the decomposition rate of these residues during summer and autumn in paddocks previously cropped with either wheat or lupin at East Beverley in Western Australia. Populations of various groups of decomposer soil biota and nitrogen dynamics (immobilization and mineralization) were measured using litterbags. In December 1996, litterbags with lupin residues were placed on soil after a lupin crop while litterbags with wheat residues were placed on soil that had grown wheat in the previous growing season.From January until the end of June 1997, substrate-induced respiration, protozoa, nematodes and microarthropods and mass loss and carbon and nitrogen contents of the remaining residues were measured at regular intervals. During the 6 months of incubation, 15–20% of mass loss occurred for both wheat and lupin residues. Decomposition rates for lupin and wheat were 0.0013 and 0.0011 day−1, respectively. The largest decrease in residue mass occurred after the first major rainfall, probably due to the loss of water-soluble compounds. Between days 60 and 130 (March to the beginning of May) the loss in mass of both residue types was gradual, coinciding with large numbers of microfauna. Mass loss of residues was minimal during the period between 126 and 188 days when large numbers of mesofauna were observed. A significant loss in nitrogen was only observed for the lupin residues, whereas net immobilization of nitrogen occurred with the wheat residues during this 6-month study. At the beginning of the study, substrate-induced respiration was higher for the lupin residues suggesting that microorganisms colonized the lupin more extensively than the wheat residues. In June, microbial biomass on lupin and wheat residues was similar. Higher nematode, amoebae and ciliate abundances on the lupin residues might have prevented a further increase in the microbial biomass. Measurable populations of protozoa and nematodes were observed in the first sampling date in March, whereas quantifiable numbers of microarthropods only appeared in May, 4 months after placement of the litterbags in the field. Prostigmatic mites were abundant on the wheat residues, while Collembola were the most abundant microarthropods on the lupin residues. Food quality and predatory pressures may have affected the succession of different soil biota communities on the lupin and wheat residue.  相似文献   

20.
Low organic matter, poor fertility and erosion are common features of rain‐fed Alfisols in southern India. Build‐up of organic matter is crucial to maintain sustainable production on these soils. The possibility of on‐farm generation of legume biomass [horsegram; Macrotyloma uniflorum (Lam.) Verdc.] by using off‐season rainfall was examined in two field experiments involving sorghum and sunflower from 1994 to 2003. The effects of this incorporation were assessed on crop yields and soil properties for 10 years together with fertilizer application. Horsegram biomass ranging from 3.03–4.28 t ha?1 year?1 (fresh weight) was produced and incorporated in situ under different levels of fertilizer application. Annual incorporation improved the soil properties and fertility status of the soil, which resulted in improved yields of test crops. With biomass incorporation, mean organic carbon content improved by 24% over fallow. Microbial biomass carbon improved by 28% at site I. Long‐term biomass incorporation and fertilizer application resulted in the build‐up of soil nutrients compared with the fallow plots. Application of N and P alone resulted in a negative balance of soil K. A time‐scale analysis of yields showed that incorporation together with fertilizer application maintained a stable yield trend over a 10‐year period in sorghum, whereas fertilizer application alone showed a declining trend. At the end of 10 years of incorporation, the increase in grain yield because of incorporation was 28 and 18%, respectively, in sorghum and sunflower over fallow when no fertilizers were applied to rainy season crops. The incorporation effect was even larger in plots receiving fertilizer. The growing and incorporation of a post‐rainy season legume crop is a low‐cost simple practice that even small and marginal farmers can adopt in semi‐arid regions of the country. Widespread adoption of this practice, at least in alternate years, can restore the productivity of degraded soils and improve crop yields.  相似文献   

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