土壤微生物量氮对小麦各生育期氮素形态的调控

[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...     

减量施氮与间作大豆对华南地区甜玉米农田氮平衡的影响

本文在广东广州华南农业大学试验中心,通过大田定位试验(2015—2016年两年4季)对比了两种施氮水平[减量施氮(300 kg·hm~(-2),N1)和常规施氮(360 kg·hm~(-2),N2)]、3种种植模式[甜玉米单作(SS)、甜玉米//大豆2∶3间作(S2B3)、甜玉米//大豆2∶4间作(S2B4)]农田生态系统的氮素输入、输出和平衡状况,旨在为减少化学氮肥投入水平,提高氮素利用效率,在华南地区发展环境友好型的玉米可持续生产模式提供科学依据。结果表明:1)减量施氮与甜玉米//大豆间作降低了系统氮素总输入量,大豆固氮和秸秆还田降低了化肥氮输入的比重,与常规施氮相比,减量施氮下SS、S2B3和S2B4的化肥氮输入占年均氮素总输入的比例分别下降3.24%、3.64%和3.77%。2)间作大豆增加了系统籽粒氮素累积量,N1和N2处理甜玉米//大豆间作的年均籽粒氮素累积量分别是单作甜玉米的2.43倍和2.18倍;减量施氮与甜玉米//大豆间作能降低甜玉米农田氮素损失,N1和N2处理甜玉米//大豆间作的年均氨挥发量分别比单作甜玉米低39.02%和27.26%;间作甜玉米的氮淋溶量比单作低13.85%。3)减量施氮与间作大豆显著降低了系统氮素盈余量,S2B3-N1、S2B3-N2和S2B4-N1、S2B4-N2年均氮素盈余量分别为71.03 kg·hm~(-2)、133.7 kg·hm~(-2)和42.87 kg·hm~(-2)、100.64 kg·hm~(-2),分别比SS处理N1和N2的平均值减少81.27%、64.75%和88.69%、73.47%。因此,减量施氮甜玉米//大豆间作模式能维持系统作物产量、减少生产成本、降低环境污染风险,具有较高的经济和生态效益。     

禾豆间距对间作豌豆“氮阻遏”减缓效应的影响

针对禾豆间作协同利用化学氮肥和豆科固氮潜力调控依据薄弱问题,以河西走廊区主导间作模式玉米/豌豆间作系统为研究对象,研究了禾豆间作间距为15 cm、30 cm和45 cm空间结构对间作豌豆氮阻遏减缓效应的影响,以期为禾豆间作种植模式优化空间结构、减缓氮阻遏、提高氮素利用效率提供理论依据。2013和2014两年研究结果表明,与单作相比,间作豌豆有效根瘤个数和根瘤重均有显著提高,根瘤数提高幅度达0~500%,其中间距为30 cm时,豌豆的根瘤数和瘤重达最大。以根瘤数和根瘤重计算的氮阻遏消减效应(Ca)均为正值,施氮条件下,玉米与豌豆间距为30 cm处理的氮阻遏消减效应显著高于15 cm和45 cm间距处理,2013年和2014年以根瘤数计算的Ca值分别达78.70%和161.21%,说明间作相对于单作都具有减缓氮阻遏的作用。而在此期豌豆的营养竞争比率(CRpm)大于1,豌豆相对于玉米具有较强的种间竞争能力。禾豆间作可显著提高氮素利用效率,以间距为30 cm的间作处理最高,2013年和2014年两年平均较间距为15 cm和45 cm空间结构的间作模式分别提高21.90%和21.88%。说明优化空间结构可有效增加间作豌豆的结瘤数和瘤重,增强氮阻遏减缓效应,调控禾豆间作系统氮素吸收利用,提高氮素利用效率。     

不同种植模式粮田土壤氮素淋失的研究进展

氮素淋失既是农田养分氮损失的主要方式,也是农业生产污染水体环境的重要途径。单作、间作和轮作是常见的农业种植模式,由于水肥和耕作管理、作物氮素吸收和土壤氮素转化等方面的差异,不同种植模式下的氮淋失特征各异。通过分析文献,综述了粮食作物玉米、小麦和水稻单作的氮淋失特征及其影响因素,分析了豆科禾本科间作在降低氮淋失方面的优势及其机理;同时对常见农作物轮作种植的氮淋失特征进行了归纳总结,并就填闲作物控制氮淋失的研究进行了讨论,以期为今后开展不同种植模式氮淋失研究提供参考。     

蚕豆/玉米间作系统经济生态施氮量及对氮素环境承受力(简报)

通过河西走廊灌区田问试验,对不同施氮水平下蚕豆/玉米间作系统的生产力、氮素吸收利用率及土壤无机氮累积量进行了研究,并利用线性加平台模型探讨了间作系统的经济生态施氮量.结果表明间作系统的生产力与施氮量的线性加平台模型的相关性达到极显著水平(P＜0.001), 0～160 cm土壤无机氮累积量与施氮量间以二次曲线模型相关性最高;种间互作显著提高系统生产力和氮素吸收,增幅分别为23%和33%;间作系统生产力、养分吸收量及土壤无机氮量随着施氮量的增加而增加;高氮肥量和种间互作使作物发生氮素"奢侈吸收".如果充分考虑到生产、生态和经济效益,则间作系统适宜施氮量为186 kg/hm2,对应生产力为10.6×103kg/hm2,增产14%,节约38%氮,减少75%土壤无机氮残留.     

施氮和木薯–花生间作对作物产量和经济效益的影响

【目的】 研究分析不同木薯–花生间作与木薯净作、花生净作之间作物产量和经济效益的差异,揭示木薯–花生间作模式的间作优势和最优模式,以期为木薯–花生合理间作和氮肥高效利用提供理论依据。 【方法】 于2015和2016年,设计施氮 (180 kg/hm2)、不施氮两个水平和木薯净作、花生净作、木薯间作1行花生、木薯间作2行花生及木薯间作3行花生五种模式,研究了施氮和不同木薯–花生间作对作物产量和经济效益的影响。 【结果】 施氮显著增加净作和间作木薯的单株薯数、鲜薯产量和鲜生物产量;施氮显著提高花生净作的荚果产量和生物产量,显著降低三种间作模式的荚果产量和生物产量;施氮显著提高木薯的氮素积累总量、各时期氮素积累量以及净作花生的氮素积累总量,但降低了三种间作模式花生的氮素积累总量;施氮提高五种种植模式的总产值和经济效益。三种间作模式木薯的鲜薯产量和氮素积累总量显著低于木薯净作,花生的氮素积累总量、荚果产量和生物产量显著低于花生净作,总产值和经济效益显著高于木薯和花生净作。系统氮素积累总量从高到低的顺序为木薯间作3行花生、木薯间作2行花生、花生净作、木薯间作1行花生和木薯净作。三种间作模式的产投比大于花生净作,而小于木薯净作。随着花生行数的增加,木薯氮素积累总量随之降低,花生氮素积累总量、荚果产量和生物产量随之显著增加,间作优势和土地当量比随之显著提升,总产值和经济效益随之增加。 【结论】 与净作相比,木薯间作2行和3行花生模式间作优势明显,经济效益显著提升,系统氮素积累总量显著增加,土地利用率提高31%～62%。      

不同管理方式对小麦氮素吸收、分配及去向的影响

【目的】随着氮肥在农业生产中的广泛应用,已有许多通过不同施氮水平调控,分析作物养分吸收,提高氮素利用率的相关研究,但是关于高产体系下作物花前花后氮素利用、转移规律的研究相对较少。本文探讨传统（CT）和优化（YH）两种栽培体系对冬小麦氮素吸收、分配及去向的影响。分析高产条件下化肥氮的作物吸收土壤残留损失的新变化,解析小麦花前花后氮素利用、转移规律,探讨肥料氮、土壤氮与作物氮之间的关系。【方法】在传统和优化两种栽培体系定位试验中设置15N 微区,采用将15N 标记的尿素表施的方法,通过测定植株、土壤样品分析氮素利用特征。新鲜土壤 NH+4-N和NO-3-N 含量采用TRACCS 2000型流动分析仪测定。15N土壤及植物全氮用美国THERMO finnigan 公司的稳定同位素质谱仪Delta plusXP 测定。【结果】在该试验条件下,优化管理小麦籽粒产量和吸氮量均显著高于传统处理,分别比传统管理高35%和34%。优化管理15N利用率比传统管理高,差异达显著水平。小麦各器官中氮素的累积量及向籽粒中的转移量均表现为来自土壤氮高于来自肥料中的氮,说明土壤氮是小麦生长的主要氮源。传统管理籽粒氮素大部分来源于花前累积,转运氮的贡献率为81.65%,优化管理为62.14%。优化管理土壤硝态氮及15N含量显著低于传统管理;开花期传统管理土壤表层硝态氮及15N大量累积;收获后4060 cm土层15N 出现累积峰,氮肥随水向下运移。两种管理方式的小麦当季化肥去向均表现为土壤残留作物吸收损失;传统管理土壤氮肥残留率高达 69.33%,优化管理较低,为39.17%。【结论】在优化栽培体系中冬小麦施氮量为139 kg/hm2 时,小麦籽粒产量达到高产且氮肥高效利用。合理调控氮素投入量以及适度的水分胁迫可以实现水氮高效前提下的作物高产。     

向日葵和马铃薯间作条件下氮素的吸收和利用

间套作不但能提高作物产量和资源利用效率,也是有效降低土壤风蚀的重要措施。明确间套作体系中氮素竞争与互补机理,提高氮素利用效率对区域农业可持续发展有着重要意义。该研究于2010年和2011年在内蒙古武川进行了大田试验,利用半微量凯氏定氮方法测定植株各器官氮素含量和氮吸收量,探讨间作中作物对氮素吸收和利用的特征。结果表明,从系统角度出发,向日葵和马铃薯间作系统的氮吸收当量比(NER)为0.95～1.02,差异不显著,这种间作模式对作物氮的吸收效率没有影响。从作物角度出发,间作没有显著提高向日葵的氮素吸收和利用效率,却降低了系统中马铃薯的氮素吸收和利用效率。间作中,向日葵氮偏吸收当量比为0.53～0.74,大于其种植比例(50%),说明间作向日葵具有显著的氮素竞争和吸收优势;而马铃薯氮偏吸收当量比为0.28～0.42,低于其在间作中所占的比例(50%),处于显著劣势。间作马铃薯产量(鲜薯质量,80%含水率)的氮素生理利用效率(NPE)为249.2g/g,略低于单作(269.8g/g),其中4行马铃薯:4行向日葵(4P:4S)间作马铃薯的NPE为238.2g/g,显著低于单作。4P:4S间作向日葵产量(籽粒质量,12%含水率)的NPE为30.1g/g,高于单作(25.9g/g)和2行马铃薯:2行向日葵(2P:2S)间作的NPE(22.8g/g)。在4P:4S间作模式中,向日葵的NPE有所提高,作为代价,降低了马铃薯的NPE。间作中马铃薯的收获指数HI(0.83)低于单作(0.87),间作向日葵的HI(0.40)高于单作的HI(0.33)。间作作物NPE的变化主要受作物收获指数HI的影响。     

覆盖作物－玉米间作对土壤碳氮含量及相关酶活性的影响

  目的  针对东北地区常规农业重用轻养以及玉米连作导致土壤养分不均衡、土壤健康下降等问题,开展覆盖作物－玉米间作对土壤碳氮含量及相关酶活性的影响研究,以期为东北地区保护性利用模式的扩展提供科学依据。  方法  在覆盖作物－玉米间作种植模式下,探讨紫花苜蓿、毛苕子和黑麦草三种覆盖作物对土壤碳氮及酶活性的影响。  结果  不同种植模式和覆盖作物类型显著影响了覆盖作物－玉米间作系统的土壤氮含量及相关酶活性,土壤有机碳含量仅在不同种植模式间有显著差异。在拔节期,与玉米单作相比,紫花苜蓿－玉米间作可以显著增加土壤速效氮含量,其硝态氮和铵态氮含量分别增加了14.94 mg kg?1和2.07 mg kg?1,并且参与氮转化的亮氨酸氨基肽酶活性提高17.9 nmol g?1 h?1。与其他覆盖作物相比,单作毛苕子可以显著提高土壤乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶的活性。毛苕子间作系统的过氧化氢酶和多酚氧化酶活性显著高于黑麦草间作系统,二者分别提高了12.65%和66.94%。在成熟期,玉米单作和间作的土壤有机碳和全氮含量显著高于覆盖作物单作,土壤碳氮水解酶和氧化酶活性均无显著差异。冗余分析表明,土壤铵态氮含量是影响土壤酶活性的关键环境因子。  结论  玉米与豆科覆盖作物的种植增加了间作玉米土壤速效氮的含量,提高了氮转化相关酶的活性,增强了土壤氮素转化潜能及可利用性。研究区适宜选取紫花苜蓿和毛苕子作为覆盖作物种植。     

基于减少土壤硝态氮淋失的作物搭配种植模式研究进展

农业生产中为获得较高作物产量而投入大量的化学肥料,同时不合理的田间管理措施使硝态氮在土壤中大量累积,增加了淋溶风险。不同作物搭配生长及种植模式在协同提高作物产量、充分利用光热资源、提高集约化生产能力方面是一种有效的栽培措施,同时在高效利用土壤养分、改善生态环境、降低硝态氮污染方面具有很大潜力。本文从不同类型作物搭配生长及不同种植模式(设施蔬菜与填闲作物、粮食作物与经济作物、粮食作物与粮食作物、粮食作物与露地蔬菜、蔬菜与蔬菜)方面综述了高效利用土壤氮素、降低土壤硝态氮累积与淋失的效果,并根据不同类型作物特点进行了机理上的解释。文末以搭配作物根系为突破点对作物种植模式进行了研究展望。     

Field evaluation of nitrogen fixation and use of nitrogen fertilizer by sorghum/pigeonpea intercropping on an Alfisol in the Indian semi-arid tropics

A field experiment was conducted to obtain the N balance sheet for sole crops and intercrops of sorghum [Sorghum bicolor (L.) Moench] and pigeonpeas [Cajanus cajan (L.) Millsp.]. Intercropping gave a significant advantage over sole cropping in terms of dry matter production and grain yield, as calculated on the basis of the land equivalent ratio and area-time equivalent ratio. The N fertilizer use efficiency and atmospheric N₂ fixation by pigeonpea were estimated using ¹⁵N-labeling and natural abundance methods. The N fertilizer use efficiency of sorghum was unaltered by the cropping system, while that of the pigeonpea was greatly reduced by intercropping. Although intercropping increased the fractional contribution of fixed N to the pigeonpeas, no significant difference was observed between the cropping systems in total symbiotically fixed N. There was no evidence of a significant transfer of N from the pigeonpea to the sorghum. This study showed that use of soil N and fertilizer N by pigeonpeas was almost the same as that by sorghum in sole cropping, indicating the potential competence of pigeonpeas to exploit soil N. However, when N was exhausted by a companion crop in intercropping, the pigeonpea crop increased its dependency on atmospheric N₂ fixation. We conclude that knowledge of how N from different sources is shared by companion crops is a prerequisite to establishing strategies to increase N use, and consequently land productivity, in intercropping systems.     

Effects of NPK fertilizer combinations on yield and nitrogen balance in sorghum or pigeonpea on a vertisol in the semi-arid tropics

A long-term experiment was carried out on a Vertisol from 1986 to 1992 to examine the combined effects of NPK fertilizers on yield using sorghum (Sorghum bicolor L. Moench cv. CSH 5) and short-duration pigeonpea (Cajanus cajan L. Millsp. cv. ICPL 87). The fertilizer treatments were as follows: 0 (no fertilization), N (150 kg N ha^-1 ), P (65.5 kg P₂O₅ ha^-1), K (124.5 kg K₂O ha^-1), and all possible combinations (NP, NK, PK, and NPK). In this study we continued this experiment during the period 1993 to 1994 and analyzed the crop yield response to fertilizers and the N balance. The amount of N derived from the atmosphere and fertilizer was estimated by the ¹⁵N natural abundance method and ^l5N isotope dilution method, respectively. A combined application of Nand P fertilizers gave the highest grain yield for the two crops under the 8th and 9th continuous croppings, unlike the application of K fertilizer. The values of total N for the two crops were significantly higher in the NP and NPK plots. These crops took up N mainly from soil. There was a significant positive relationship between the uptake of N_dff and N_dfs by each crop. Pigeonpea or sorghum took up more N from the soil in the N fertilizer plots than in the plots without N, suggesting that soil N fertility was enhanced and the amount of N supplied from soil increased in the plots with consecutive application of N fertilizer for 7 y. Even pigeonpea, which fixes atmospheric N inherently, needed N fertilizer to achieve high grain yield, suggesting that N fixation by the nodules was not always sufficient to meet the N requirements of the crop under these conditions. Although fertilizer N exerted a beneficial effect on plant growth and yield in the two crops, the values of fertilizer N recovery (FNR) by the two crops were considerably low. Therefore, it is suggested that the development of N fertilizer management which could maximize FNR of each crop should be promoted.     

Assessment of slow release fertilizers and nitrification inhibitors in flooded rice

This work evaluates the effect of different slow-release fertilizers and nitrification inhibitors (NI) on N-use efficiency, grain yield and N₂ fixation in rice fields of Valencia (Spain) during three consecutive crop seasons (1998–2000). Eight N sources [ammonium sulphate, urea, polymer-coated urea (PCU 32% and 40% N), sulphur coated urea, isobutylidene diurea (IBDU), ammonium sulphate nitrate (ASN) plus dicyandiamide and ASN plus dimethyl pyrazole phosphate, were applied at 120 kg N ha^–1 and at 2 or 15 days before flooding (DBF) during 1998. Another experiment was based on the use of urea blended with PCU (40% N) at four ratios (1:0, 3:1, 1:1, 1:3) and applied at 15 DBF and at four rates (70, 95, 120 and 145 kg N ha-1) during 1999 and at only one rate (120 kg N ha^–1) during 2000. Both experiments also included a control (no N). The results showed that, when applied shortly before flooding, PCU (32% and 40% N) and IBDU application improved biological N₂ fixation compared to the conventional fertilizer application, with or without NI, reaching similar values to those observed in the absence of N fertilizer. Slow release fertilizers, particularly PCU 40% N applied basally before flooding, were the best N source for grain yield and improved recovery efficiency. Differences among N sources were only significant when the flooding was delayed for 15 days after fertilizer application.     

Green Manuring in Crop Production

ABSTRACT

The positive role of green manuring in crop production has been known since ancient time. Importance of this soil ameliorating practice is increasing in recent years because of high cost of chemical fertilizers, increased risk of environmental pollution, and need of sustainable cropping systems. Green manuring can improve soil physical, chemical, and biological properties and consequently crop yields. Furthermore, potential benefits of green manuring are reduced nitrate (NO₃ ^?) leaching risk and lower fertilizer N requirements for succeeding crops. However, its influence may vary from soil to soil, crop to crop, environmental variables, type of green manure crop used, and its management. Beneficial effects of green manuring in crop production should not be evaluated in isolation; however, in integration with chemical fertilizers. The objective of this article is to review recent advances in green manuring practice, in the context of potential benefits and drawbacks in use of this practice for annual crop production and sustain soil health and fertility.     

15N studies on the transfer of legume-fixed nitrogen to associated cereals in intercropping systems

Summary An attempt has been made to estimate quantitatively the amount of N fixed by legume and transferred to the cereal in association in intercropping systems of wheat (Triticum aestivum L.) — gram (Cicer arietinum L.) and maize (Zea mays L.) —cowpea (Vigna unguiculate L.) by labelling soil and fertilizer nitrogen with ¹⁵N. The intercropped legumes have been found to fix significantly higher amounts of N as compared with legumes in sole cropping if the intercropped cereal-legume received the same dose of fertilizer N as the sole cereal crop. But when half of the dose of the fertilizer N applied to sole cereal crop was received by intercropped plants, the amount of N fixed by legumes in association with cereals was significantly less than that fixed by sole legumes. Under field conditions 28% of the total N uptake by maize (21.2 kg N ha^–1) was of atmospheric origin and was obtained by transfer of fixed N by cowpea grown in association with maize. Under greenhouse conditions gram and summer and monsoon season cowpea have been found to contribute 14%–20%, 16% and 32% of the total N uptake by associated wheat and summer and monsoon maize crops, respectively. Inoculation of cowpea seeds with Rhizobium increased both the amount of N fixed by cowpea and transferred to maize in intercropping system.     

Characterization of the N benefit of a grain legume (Lupinus angustifolius L.) to a cereal (Hordeum vulgare L.) by an in situ 15N isotope dilution technique

Summary A crop of barley was grown on plots which had previously supported pure stands of lupins, canola, ryegrass, and wheat. The plots were labelled with ¹⁵N-enriched fertilizers at the time of sowing of the antecedent crops. The crop of lupins, which derived 79% of its N from symbiotic N₂ fixation at physiological maturity, conferred an N benefit to barley of 3.4 g N m^-2 when compared to barley following wheat. Lupins used less fertilizer N and less unlabelled soil N compared to the other crops, but the ratios of these sources of N in the plant tops were similar. The apparent sparing of soil+fertilizer N under lupins compared with wheat was 13.6 g N m^-2, which was much larger than the measured N benefit. Barley following lupins was less enriched in ¹⁵N compared to barley following wheat, and the measured isotope dilution was used to estimate the proportion of barley N derived from biologically fixed N in the lupin residues. This in turn enabled the N benefit to be partitioned between the uptake of spared N and the uptake of fixed N derived from the mineralization of legume residues. Spared N and fixed N contributed in approximately equal proportions to the N benefit measured in barley following lupins compared to barley following wheat.     

小麦/玉米套作条件下氮、磷配施的肥料效应研究

针对内蒙古河套灌区农业面源污染的现状,本研究以内蒙古河套灌区常规作物小麦和玉米为供试材料,采取"3414"部分实施方案,对氮、磷肥的施用效应及养分交互作用进行了研究,探讨进一步削减当地农业生产过程中的肥料用量的施肥技术。结果表明:小麦/玉米套作条件下,作物产量与氮、磷肥施用量之间满足二次型回归模型,氮肥、磷肥及氮磷交互效应对产量产生显著影响,氮磷交互作用氮磷。在施肥水平较低时,氮、磷肥表现出较好的协同促进作用,在达到产量的极限值后,则表现为无效及拮抗作用;中氮中磷处理能够较好地满足作物生长发育过程中对氮和磷的需求,提高作物对氮、磷的利用率。但随着施肥量的进一步增加,作物植株吸肥量也随之增加,施肥效益降低,肥料利用率持续下降。通过对氮、磷单因素及二因素肥料效应的分析,对施肥水平做进一步优化,得出小麦最佳施氮量为167.67~196.61 kg·hm-2,最佳施磷量为130.43~186.64 kg·hm-2;玉米最佳施氮量为222.10~299.14 kg·hm-2,最佳施磷量为156.14~188.00 kg·hm-2。这将为进一步削减氮、磷配施量,改善当地土壤养分平衡,减轻农业面源污染提供一定的指导作用。     

Effect of nitrogen application on the A N value of soil

Pot experiments were conducted with two soils, from Rottenhaus and Seibersdorf in Austria, to ascertain whether the rate of fertilizer N application and the test crop would influence the amount of N available in the soil as assessed by the A-value method. ¹⁵N-labelled fertilizer was applied at rates of 10, 25, 40, 60, and 100 mg N kg^-1 soil, corresponding approximately to 20, 50, 80, 120 and 200 kg N ha^-1 respectively, and two crop species, barley (Hordeum vulgareL.) and non-nodulating soybean (Glycine max L.) were used to determine the soil A _N value under the various fertilizer regimes. The results showed that the Rottenhaus soil had a higher A _N value than the Seibersdorf soil, suggesting that the former was more fertile than the latter. The A _N values of both soils were significantly affected by the level of N application. When grown in the same soil, the two test crops showed significantly different fertilizer use efficiency and per cent N derived from fertilizer when the rate of N application exceeded 20 kg ha^-1. Thus, the A _N value as determined by the two test crops differed significantly for the same soil when the rate of N application was greater than 20 kg/ha. The difference was greater when the soil fertility level was high. The dependence of the A _N value on the level of N application and the species of crop seriously compromises the suitability of this method for determining plant-associated N₂ fixation. Hence, considerable caution is required when using this method to estimate plant-associated N₂ fixation.     

Assessment of nitrogen fertilization in cotton/soybean intercropping using the 15N isotope dilution method

Intercropping of cotton and legume plants offers long-term crop productivity while saving agricultural resources and improving soil health. However, the use of nitrogen (N) in cotton/legume intercropping systems requires further evaluation. In this study, three N fertilization rates (cotton/soybean: 160/20, 320/40 and 480/80 kg N ha⁻¹) incorporating three root barrier systems (complete, semi and no root barrier between the crops) under cotton/soybean intercropping systems were conducted to assess interactions between N supply and N transfer, recovery and residue using the ¹⁵N isotope dilution method. The results show that cotton was a stronger competitor for N than soybean plants. The 320/40 kg N ha⁻¹ treatment with no root barrier system inhibited the growth of soybean, while the growth, productivity and N uptake for cotton were maximized. The N fixation rate (%NDFA) in soybean and N transfer rate (%NTFS) from soybean to cotton decreased with the increasing N fertilizer application rate, whereas the intercropping system with no root barrier increased %NDFA and %NTFS. The higher N fertilization rate increased the N residue on the side of cotton, whereas the intercropping with no root barrier increased N utilization rate (%NUR) and reduced N residue rate (%NRR). The N transfer amount (NTA) was positively correlated with cotton yield, dry matter (DM) and N uptake, while NTA was negatively correlated with these indicators for soybean. Overall, cotton/soybean intercropping adapted to the 320/40 kg N ha⁻¹ condition and intercropping with no root barrier system by balancing growth, changing N uptake and regulating N fixation transfer, mitigating the issue of N residue.     

Effect of N supply on apparent recovery of fertilizer N as crop N and Nmin in soil during and after cultivation of winter cereals

Field trials were conducted over two years to investigate the effect of increasing N supply on apparent fertilizer N recovery by winter cereal crops (4 × wheat and 2 × barley) and on non‐recovered N. Apparent fertilizer N recovery was calculated by comparing N in fertilized and unfertilized crops. Non‐recovered N is defined as N which was neither found in crops nor soil mineral N (N_min = NH₄‐N + NO₃‐N). At N supply levels according to common farming practice (N_cfp = 190 to 220 kg N/ha), 60— 93% of the fertilizer N was recovered in crops at harvest, while at high N supply levels of 265 to 273 kg N/ha 58—76% of fertilizer N was recovered. There were small differences in soil N_min in 0—200 cm between N_cfp and unfertilized plots, but substantial increases in N_min occurred at the highest N supply. Amounts of non‐recovered N differed substantially between sites (maximum value of 84 kg N/ha). Non‐recovered N increased with increasing N rate on only 3 out of the 6 sites, indicating that N immobilization was not necessarily dependent on N rate. The fate of non‐recovered N was studied for a further year by growing catch crops on the sites after cereal harvest. N re‐mineralization deduced from changes in catch crop N and in N_min indicated that non‐recovered N had been immobilized in the soil. At three sites, crop N uptake was found between milk‐ripe stage and harvest (19 to 60 kg N/ha) suggesting substantial uptake of N mineralized from soil. However, grain yields were lower with N rates below N_cfp, indicating that late net soil N mineralization could not compensate for reductions in N fertilizer rate in these trials.