Legume–barley intercropping stimulates soil N supply and crop yield in the succeeding durum wheat in a rotation under rainfed conditions

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.     

小麦/蚕豆间作体系中的氮节约效应及产量优势

通过田间小区试验,研究了小麦/蚕豆间作条件下作物的产量优势及不同施氮水平和种植方式中土壤硝酸盐累积。研究表明,间作可以提高作物单位面积复合产量,增产幅度在6%3～3%之间,不施氮处理间作小麦产量比单作增加达84%;间作和施氮对蚕豆产量没有显著影响。不同种植方式下土壤剖面中硝酸盐累积量趋势表现为蚕豆单作>小麦、蚕豆间作>小麦单作。不施氮、施氮量为20、406、0.kg/hm2条件下,种蚕豆的土壤硝酸盐累积量分别比种小麦的土壤增加了25.4、63.5、50.9、93.4.kg/hm2,间作降低了土壤中硝酸盐累积。小麦、蚕豆间作体系中的产量优势主要是种间氮营养生态位发生了分化,蚕豆通过固定空气氮而减少对土壤有效氮的吸收,把土壤中的有效氮节约供给与之相伴的作物小麦利用。     

Nitrogen fixation efficiency,interspecies N transfer,and root growth in barley-field pea intercrop on a Black Chernozemic soil

Summary Barley-field pea intercrops have been shown to increase N yield when grown under cryoboreal subhumid conditions. In this study, we extended previous research by testing the hypotheses that (1) the intercropped field pea fixes a greater proportion of its shoot and root N than does sole-cropped field pea; (2) N is transferred from the annual legume to the cereal during the growing season; and (3) root production is greater under intercropped than sole-cropped conditions. Unconfined microplots seeded to barley, field peas, or a barley-field pea intercrop were fertilized with N at 10 kg ha^-1 as (NH₄)₂SO₄ (5.21 atom % ¹⁵N excess). Both the intercropped and sole-cropped barley derived more than 93% of their N from the soil. In contrast, 40% of N in the intercropped field pea was derived from soil. This study provided no evidence for transfer of N from the legume to the cereal. On average, the proportion of N derived from air by both pea intercrops was 39% higher than that derived by the sole-cropped pea. Root length determined by a grid intersection method following digitization using an image analyzer tended to be higher under intercropping than in sole crops. We conclude that even on fertile soils benefits may accrue from annual intercropping that includes a legume. The benefits arise from (1) increased N production, (2) greater N-fixation efficiency, and/or (3) more shoot and root residue-N mineralization for subsequent crops.     

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.     

Soil N dynamics and N yield of barley grown on Breton loam using N from biological fixation or fertilizer

Summary Soil N dynamics and barley yields (Hordeum vulgare L.) were compared in pot experiments using surface samples from a Gray Luvisol under three cropping systems at Breton, Alberta: (1) an agroecological 8-year rotation including cereals, forage, and fababeans (Vicia faba L.) as green manure, from wich two plots were selected, one following fababeans, and the second following 3 years of forage; (2) a continuous grain system, with fertilizer N at 90 kg ha^-1 year^-1; and (3) a classical Breton 5-year rotation [following oats (Avena sativa L.)] involving forage and cereals, without returning crop residues to the land, selecting one plot with PKS treatment and a second as control. The fertilizer N equivalent for the cropping system; A_N value and A value (analogous to A_N), but in fertilizer ¹⁵N units, soil biomass, and C and N mineralization were monitored. In the first agroecological plot (after fababeans), grain and total plant biomass production were 116% greater than from the continuous grain treatment. Barley plants in the two agroecological plots derived 48.5% and 37.8%, respectively, of their N requirement from non-labelled soil N sources not present in the continuous grain plot. At crop maturity, the recovery of ¹⁵N microbial biomass was 1.5 times higher in soil from the first agroecological plot than from the continuous grain plot. The fertilizer N equivalent was 2670 mg pot^-1 (485 kg ha^-1) for the first and 1850 mg pot^-1 for the second agroecological treatment. Fertilizer N equivalent values exceed net amounts of N mineralized by a factor of 4. Recovery by the barley crop of ¹⁵N added at 55 mg pot^-1 was more efficient in the agroecological treatments (45%–51%) than in the continuous grain or classical Breton treatments (35%–37%). It was concluded (1) that past soil history may be associated more with the ability of barley plants to compete for available N, and hence the use of N, than with net soil N mineralization; and (2) an increased supply of N to crops following the incorporation of fababean residues, manure application, and the soil N-conserving effect of growing legumes were all partly responsible for the observed differences in soil fertility.     

玉米/大豆和玉米/甘薯模式下玉米干物质积累与分配差异及氮肥的调控效应

【目的】西南山地玉米区是我国第三大玉米主产区,但单产比全国低近750 kg/hm2。由于该区特殊的气候条件,玉米以多熟间套种植为主,如何利用多熟种植中各作物的间套优势和茬口特性,寻求提高本区玉米产量的新途径,是农业科技工作者研究的热点。本文在四川的两个玉米主产区,通过四年的田间小区试验,对比研究了西南玉米主要的两种套作模式—玉米/大豆和玉米/甘薯模式下玉米干物质积累分配、转运差异及施氮量对其的调控效应,以探讨种植模式和氮肥管理的增产效应。【方法】2008年设置玉米/大豆和玉米/甘薯两个套种田间试验,分析比较两种模式玉米干物质积累、分配和转运的差异;2009 2010年在前一年的基础上分带轮作,即玉米分别种在大豆或甘薯茬上,分析套作和轮作效应对玉米干物质积累的影响;2011年,在前三年的基础上,采用小区套微区的方式,研究两种模式下不同施氮水平(N0、N90、N180、N270、N360)对玉米干物质积累和转运的调控。【结果】1)在玉米/大豆模式下,玉米干物质积累量从蜡熟期开始显著高于玉米/甘薯模式,茎鞘输出率也显著高于玉米/甘薯模式,最终产量增加2.4%3.2%,但差异未达显著水平;2)分带轮作后,从拔节期开始,玉米/大豆模式下玉米干物质积累量就显著高于玉米/甘薯模式,到成熟期两套种模式下玉米单株干物质积累两试验点平均相差达26.8 g,茎秆向籽粒的输出率和贡献率也显著高于玉米/甘薯模式,收获指数玉米/大豆模式平均较玉米/甘薯模式提高3.9%,最终玉米/大豆模式下玉米产量较玉米/甘薯模式增幅加大,两年两个试验点分别增加了7.4%和14.4%;3)氮肥对两种模式下玉米干物质积累分配和产量的调控效应显著,玉米/大豆模式下,玉米以施氮180kg/hm2处理,而玉米/甘薯模式下270 kg/hm2处理与同一模式下其他氮素水平相比,增加了光合产物的积累,提高了干物质增长速率,延长了灌浆持续天数,有利于茎鞘和叶片的干物质向籽粒转移,显著提高收获指数,进而提高玉米的增产潜能,玉米/大豆模式下低氮处理(0 180 kg/hm2)对玉米的增产效应比较明显,在高施氮水平(270360 kg/hm2)下两种模式间玉米产量差异不显著。【结论】西南丘陵旱地应选择玉米与大豆套作,采用分带轮作种植方式,既有利于提高玉米产量,又可避免大豆的连作障碍;且氮肥管理措施应因种植模式不同而有所差异,在中高等肥力条件下,与大豆套作玉米施氮180 kg/hm2,与甘薯套作施氮应提高至270 kg/hm2。     

玉米与不同豆科作物间作对氮素的竞争与恢复效应

  【目的】  竞争和恢复是间作群体优势的重要机理。本研究分析比较玉米与不同豆科作物间作共生期对氮的竞争,单独生长期氮吸收的恢复效应,以及氮竞争和恢复效应对间作模式氮吸收间作优势的影响。  【方法】  田间试验于2018—2019年在甘肃省农业科学院张掖试验站进行。共设置玉米/豌豆间作 (maize/pea,M/P)、玉米/蚕豆间作 (maize/faba bean,M/F)、玉米/大豆间作 (maize/soybean,M/S) 3个间作体系和单作豌豆 (sole pea,SP)、单作蚕豆 (sole faba bean, SF)、单作大豆 (sole soybean,SS)、单作玉米 (sole maize,SM) 4个单作体系。测定豆科作物和玉米收获期作物的干物质量和氮浓度,计算间作体系作物的偏氮吸收当量比 (partial nitrogen uptake equivalent ratio,pNER) 和间作体系的氮吸收当量比 (nitrogen uptake equivalent ratio,NER),玉米相对于豆科的氮竞争比率(competitive ratio of maize to legume,CR_ml),豆科作物收获后玉米的氮素吸收量和吸收速率。  【结果】  M/P、M/F和M/S的NER均大于1,两年平均分别为1.33、1.26和1.38。3个间作体系中,豆科作物的pNER_l无显著差异,M/S中玉米的pNER_m显著高于M/P和M/F。间作豆科作物的氮浓度与其单作相比无显著差异,但氮吸收量显著低于单作。M/P、M/F和M/S体系中玉米植株的氮浓度无显著差异,而玉米氮吸收量分别相当于单作玉米的62.2%、51.0%和79.9%,M/S体系玉米氮吸收量较M/P和M/F分别提高了33.4%和62.6%。M/S体系CR_ml大于1,M/P和M/F的CR_ml值均小于1。各间作体系玉米恢复效应2019年高于2018年,但值均小于1。CR_ml与NER和pNER_m呈显著正相关,与pNER_l呈显著负相关。  【结论】  两年的试验结果表明,河西走廊灌区玉米/豌豆、玉米/蚕豆和玉米/大豆间作体系的氮吸收当量比均大于1,相对单作具有氮吸收间作优势。玉米/豌豆、玉米/蚕豆和玉米/大豆体系共生期存在氮竞争,豌豆和蚕豆对氮的竞争强于玉米,大豆的氮竞争弱于玉米。豆科作物收获后,各体系玉米单独生长期无氮吸收恢复效应。     

接种根瘤菌对蚕豆/玉米间作系统产量及结瘤作用的影响

通过田间试验,研究了不同施氮水平下蚕豆接种根瘤菌GS374对蚕豆/玉米间作系统产量及蚕豆结瘤作用的影响。结果表明,不施氮处理接种根瘤菌所获得的单作或间作系统产量与不接种但施N225kghm-2的相应系统产量相当,且施N225kghm-2处理接种仍能促进蚕豆的结瘤作用。统计分析表明,与不接种根瘤菌、蚕豆单作、不施氮相比,接种、蚕豆/玉米间作、施氮均极显著地提高了蚕豆生物学产量,但只有间作能显著增加其籽粒产量;施氮显著增加玉米生物量和籽粒产量。施N225kghm-2后,蚕豆接种、间作对玉米生物量无显著影响;但不施氮时蚕豆接种显著提高了与之间作的玉米籽粒和生物学产量,增幅分别为34.3%和25.6%。接种根瘤菌显著提高了不同氮处理以籽粒产量为基础计算的土地当量比和不施氮处理以生物学产量为基础计算的土地当量比。蚕豆接种根瘤菌与不接种相比,其单株根瘤数和根瘤干重均显著增加;间作与蚕豆单作相比对根瘤数的影响较小,但显著促进了蚕豆单株根瘤干重的增加。因此,本研究认为豆科作物接种合适的根瘤菌,是进一步提高豆科/禾本科作物间作系统间作优势的又一重要途径。     

Nitrogen uptake in organically managed spring sown lupins and residual effects on leaching and yield of a following winter cereal

Three unfertilized spring sown species of lupins (Lupinus angustifolius) and peas (Pisum sativa) were compared in terms of N fixation and subsequent leaching under a following winter barley crop in an organically managed rotation. Fallow plots were included to assess the potential weed burden and the ability of the sown crops to compete with weeds when no herbicides were applied. Although peas out-yielded lupins (5.4 t compared with 3.5 t grain respectively), the yellow lupin (Wodjil) fixed more N than peas (180 compared with 120 kg N/ha) and all three lupins had higher protein contents (>30%) than peas (22%). Winter leaching amounted to >50 kg nitrate-N/ha from winter barley, regardless of whether it followed treatments which were previously fallow or cropped with legumes. There were no significant differences in leaching between the lupin species. Leachate in the first 350 mm of drainage under winter barley, following the different legume species, exceeded the European Union limit for nitrate in drinking water in all treatments. Yields of winter barley, grown without fertilizers or herbicides following legumes, were not significantly different (mean 4 t/ha), but there were higher levels of P and K in the grain compared with the amounts made available from the previously fallow soil. At this site in SW England, the crops grew well and our results suggest that lupins could provide a useful break crop in an organic arable cropping rotation and an alternative source of home-grown, high protein feed.     

Tillage, crop residue and N fertilizer effects on crop yield, nutrient uptake, soil quality and nitrous oxide gas emissions in a second 4-yr rotation cycle

An 8-yr (1998–2005) field experiment was conducted on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada, to determine the effects of tillage (no-tillage – NT and conventional tillage – CT), straw management (straw retained – R and straw not retained – NR) and N fertilizer (0, 40, 80 and 120 kg N ha⁻¹, except no N to pea (Pisum sativum L.) phase of the rotation) on seed and straw yield, mass of N and C in crop, organic C and N, inorganic N and aggregation in soil, and nitrous oxide (N₂O) emissions for a second 4-yr rotation cycle (2002–2005). The plots were seeded to barley (Hordeum vulgare L.) in 2002, pea in 2003, wheat (Triticum aestivum L.) in 2004 and canola (Brassica napus L.) in 2005. Seed, straw and chaff yield, root mass, and mass of N and C in crop increased with increasing N rate for barley in 2002, wheat in 2004 and canola in 2005. No-till produced greater seed (by 51%), straw (23%) and chaff (13%) yield of barley than CT in 2002, but seed yield for wheat in 2004, and seed and straw yield for canola in 2005 were greater under CT than NT. Straw retention increased seed (by 62%), straw (by 43%) and chaff (by 12%) yield, and root mass (by 11%) compared to straw removal for barley in 2002, wheat in 2004, and seed and straw yield for pea in 2003. No-till resulted in greater mass of N in seed, and mass of C in seed, straw, chaff and root than CT for barley in 2002, but mass of N and C were greater under CT than NT for wheat in 2004 and for canola in 2005 in many cases. Straw retention had greater mass of N and C in seed, straw, chaff and root in most cases compared to straw removal for barley in 2002, pea in 2003 and wheat in 2004. Soil moisture content in spring was higher under NT than CT and with R than NR in the 0–15 cm depth, with the highest moisture content in the NT + R treatment in many cases. After eight crop seasons, tillage and straw management had no effect on total organic C (TOC) and N (TON) in the 0–15 cm soil, but light fraction organic C (LFOC) and N (LFON), respectively, were greater by 1.275 Mg C ha⁻¹ and 0.031 Mg N ha⁻¹ with R than NR, and also greater by 0.563 Mg C ha⁻¹ and 0.044 Mg N ha⁻¹ under NT than CT. There was no effect of tillage, straw and N fertilization on the NH₄-N in soil in most cases, but R treatment had higher NO₃-N concentration in the 0–15 cm soil than NR. The NO₃-N concentration in the 0–15, 15–30 and 30–60 cm soil layers increased (though small) with increasing N rate. The R treatment had 6.7% lower proportion of fine (<0.83 mm diameter) and 8.6% greater proportion of large (>38.0 mm) dry aggregates, and 4.5 mm larger mean weight diameter (MWD) compared to NR treatment. This suggests a lower potential for soil erosion when crop residues are retained. There was no beneficial effect of elimination of tillage on soil aggregation. The amount of N lost as N₂O was higher from N-fertilized (580 g N ha⁻¹) than from zero-N (155 g N ha⁻¹) plots, and also higher in CT (398 g N ha⁻¹) than NT (340 g N ha⁻¹) in some cases. In conclusion, retaining crop residues along with no-tillage improved some soil properties and may also be better for the environment and the sustainability of high crop production. Nitrogen fertilization improved crop production and some soil quality attributes, but also increased the potential for NO₃-N leaching and N₂O-N emissions, especially when applied in excess of crop requirements.     

Relative effects of biological amendments and crop rotations on soil microbial communities and soilborne diseases of potato

Various biological amendments, including commercial biocontrol agents, microbial inoculants, mycorrhizae, and an aerobic compost tea (ACT), were evaluated, alone and in conjunction with different crop rotations, for their efficacy in introducing beneficial microorganisms, affecting soil microbial community characteristics (SMCC), and reducing soilborne diseases of potato in greenhouse and field trials in Maine. Most amendments successfully delivered microorganisms into the soil, altering microbial populations and activity in accordance with the particular organisms added, and significantly altering SMCC (as determined by FAME analysis) to various degrees from 2 to 24 weeks. Amendment effects were greatest early on (2 weeks after amendment), but effects associated with crop treatment became more dominant at subsequent assessments (10 and 24 weeks after amendment). In field trials, effects on microbial characteristics, soilborne diseases and tuber yield were variable, with some microbial inoculants and a biostimulant producing no significant effects, whereas arbuscular mycorrhizae, reduced stem canker and black scurf by 17–28%. When used in three different 2 yr crop rotations (barley/ryegrass, barley/clover, and potato, all followed by potato), biological amendments reduced soilborne disease and improved yield in some rotations, but not others. Soil-applied ACT and the combination of ACT with a mixture of beneficial microorganisms (Mix) reduced stem canker, black scurf, and common scab on tubers by 18–33% and increased yield 20–23% in the barley/ryegrass rotation, but not in the other rotations. Mix also reduced disease (20–32%) in the barley/clover rotation only. None of the amendments significantly reduced disease in continuous potato plots. Both crop rotation and amendment treatments significantly affected SMCC, but rotation effects were more dominant. These results indicate that certain rotations were better able to support the added beneficial organisms from amendments and enable more effective biological control, and also that favorable crop rotations may be more effective than amendments in manipulating or altering SMCC. Establishment and persistence of amendment effects may depend on many factors, but an effective and supportive crop rotation is apparently important.     

Changes in Grain Production,Mechanisms for Sale of Grain and Possible Effects on Grain Quality in Lithuania in the Period 1990-1999

The main objective was to compare the response of grain yield to fertiliser N in a winter wheat-white clover intercropping system with the response in wheat alone. Clover was undersown in spring barley and remained established in two consecutive crops of wheat in two field experiments. Clover reduced grain yield in the first crop of wheat and increased it in the second. There was more inorganic N in the soil and a higher concentration of N in the grains in the intercropping system. The grain and N yield response to fertiliser N was equal or less with intercropped than with wheat alone. The reduction of clover biomass with a herbicide increased grain yield of the first crop of wheat without reducing the clover biomass or the positive residual effect in the second wheat crop. It was concluded that in order to produce large grain yields, competition from clover needs to be kept small when wheat is at the tillering stage.     

Cropping sequence and nitrogen fertilizer effects on the productivity and quality of malting barley and soil fertility in the Ethiopian highlands

The productivity and quality of malting barley were evaluated using factorial combinations of four preceding crops (faba bean, field pea, rapeseed, and barley) as main plots and four nitrogen fertilizer rates (0, 18, 36, and 54 kg N ha^?1) as sub-plots with three replications at two sites on Nitisols of the Ethiopian highlands in 2010 and 2011 cropping seasons. Preceding crops other than barley and N fertilizer significantly improved yield and quality of malting barley. The highest grain yield, kernel plumpness, protein content, and sieve test were obtained for malting barley grown after faba bean, followed by rapeseed and field pea. Nitrogen fertilizer significantly increased yield, protein content, and sieve test of malting barley. All protein contents were within the acceptable range for malting quality. Inclusion of legumes in the rotation also improved soil fertility through increases in soil carbon and nitrogen content. We conclude that to maximize yield and quality of malting barley, it is critical to consider the preceding crop and soil nitrogen status. Use of appropriate break crops may substitute or reduce the amount of mineral N fertilizer required for the production of malting barley at least for one season without affecting its quality.     

Characterization of soil microbial communities under different potato cropping systems by microbial population dynamics, substrate utilization, and fatty acid profiles

The effects of 11 different 2- and 3-yr potato crop rotations on soil microbial communities were characterized over three field seasons using several techniques. Assessments included microbial populations determined by soil dilution plate counts on various general and selective culture media, microbial activity by fluorescein diacetate (FDA) hydrolysis, single carbon source substrate utilization (SU) profiles, and fatty acid methyl ester (FAME) profiles. Potato rotation crops evaluated in research plots at Newport, ME, included barley/clover, canola, green bean, millet, soybean, sweet corn, and a continuous potato control. Soil populations of culturable bacteria and overall microbial activity tended to be highest following barley, canola, and sweet corn rotations, and lowest with continuous potato. Differences among rotations were less apparent during the potato phase of the rotations. Populations of actinomycetes and fluorescent pseudomonads tended to be greater in barley rotations than in most other rotations. SU profiles derived from BIOLOG GN2 plates indicated that certain rotations, including barley, canola, and sweet corn tended to have higher overall microbial activity, and barley and sweet corn rotations averaged higher substrate richness and diversity. Soybean and potato rotations tended to have lower substrate richness and diversity. Principal component analyses of SU data revealed differences among rotation soil communities in their utilization of individual carbon sources and substrate guilds, including carbohydrates, carboxylic acids, amines/amides, and amino acids. Analyses of soil FAME profiles demonstrated distinct differences among all the rotation soils in their relative composition of fatty acids, indicating differences in their microbial community structure. Fatty acids most responsible for differentiation among rotation soils included 16:1 ω5c, 16:1 ω7c, 18:2 ω6c, 18:1 ω9c, 12:0, and 13:0 anteiso, with 16:1 ω5c being the single greatest determinant. Overall, monounsaturated fatty acids, particularly 16:1 ω5c, were most prevalent in sweet corn rotations and polyunsaturates were highest in barley and millet rotations. Straight chain saturated fatty acids comprised the greatest proportion of fatty acids in soils under continuous potato. FAME biomarkers for microorganism groups indicated barley and millet rotations had the highest ratio of fungi to bacteria, and soybean and continuous potato had the lowest ratio. This research has demonstrated that different crop rotations have distinctive effects on soil microbial communities that are detectable using a variety of techniques. Further studies will identify more specific changes associated with particular rotations and relate these changes to potential effects on disease management, crop health, and crop productivity.     

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。     

施用乙烯利和磷肥对玉米//花生间作氮吸收分配及间作优势的影响

【目的】在玉米//花生间作体系中,喷施乙烯利明显降低玉米株高,提高花生和间作体系的产量,研究施用乙烯利和磷肥对玉米花生间作氮吸收分配和间作优势的影响,明确其调控机理,对实现玉米、花生间作高产高效具有重要指导意义。【方法】本试验于2012~2013年在河南科技大学农场进行,设玉米单作、花生单作、玉米//花生间作和玉米//花生间作+喷施乙烯利4种种植方式,分别施磷和不施磷,共8个处理,分析了不同处理玉米、花生不同器官氮含量及氮积累量,讨论了喷施乙烯利和施磷对间作体系氮吸收间作优势的影响。【结果】与单作相比,玉米花生间作显著提高了玉米茎、叶、籽粒的氮含量和氮积累量,促进了氮向籽粒的分配;提高了花生茎、叶、果仁的氮含量,但明显降低了花生氮积累量,不利于氮向果仁分配;与单作体系相比,间作体系的氮吸收间作优势为N 26.88~42.21 kg/hm2。喷施乙烯利减少了玉米对花生的氮竞争比率,降低了间作玉米茎、叶、籽粒的氮含量和氮积累量,促进氮向籽粒的分配,并且还提高了间作花生茎、叶、果仁的氮含量和氮积累量,促进氮向果仁的分配,间作花生的氮吸收量提高23.67%~49.54%（P < 0.05）,间作体系氮吸收间作优势提高4.95%~54.65%。与不施磷相比,施磷提高了喷施乙烯利间作体系中玉米和花生吸氮量,分别提高19.49%~27.71%和34.26%~43.24%（P < 0.05）,氮吸收间作优势提高69.97%~162.57%（P < 0.05）。【结论】施用磷肥可进一步提升喷施乙烯利在降低玉米对花生的氮竞争比率,促进玉米花生间作体系氮吸收及氮向籽粒中分配,提高氮吸收间作优势的作用,促进氮素的高效利用。     

长期水稻-大麦轮作体系土壤供氮能力与作物需氮量研究

通过18年稻麦轮作,7个施肥处理,研究了水稻-大麦轮作系统中土壤生产力、氮素自然供应能力、作物氮素内部利用率及氮肥表观利用率。结果表明,在水旱轮作下,土壤对大麦产量的地力贡献率平均为69%,水稻为75%～81%; 肥料的增产贡献率分别为31%和19%～25%,可维持每年生产大麦2.3 t/hm2、稻谷6～7 t/hm2。土壤氮素自然供给力在大麦上平均为75.9%,比水稻的低3.3%～7.2%。在一年三熟水旱轮作制中,土壤和环境年供氮118～299 kg/hm2; 在一年二熟轮作制中为86～199 kg/hm2。施氮肥条件下,大麦的氮素内部利用率为31.0～56.3 kg/kg; 水稻在23.6～50.2 kg/kg之间变动; 大麦的氮肥利用率变幅在27.5%～41.2%,水稻为14.6%～41.2%。在稻麦轮作系统中,如果想获得作物产量12 t/hm2（4 t大麦和8 t 单季稻）,需要每年施氮肥 N 226～337 kg/hm2。为获得更高的作物产量,在氮肥推荐时不但要考虑作物的目标产量,作物对氮素的需要量,还要充分考虑土壤和环境氮素供应能力。     

不同施氮水平对稻麦轮作农田氧化亚氮排放的影响

利用江苏常熟田间随机区组试验,以密闭箱法采集气样,气相色谱分析N2O浓度,对稻麦轮作制下不同施氮水平的土壤N2O排放进行了观测,探讨了不同施氮水平对稻麦轮作农田氧化亚氮排放的影响。结果表明,土壤N2O排放量受施氮量的影响,稻季和麦季N2O排放量都随旌氮量的增加而增加;稻季N2O排放量最大峰值出现在烤田复水期间,其排放量大小主要受基肥和分蘖肥施用量的影响,并随施氮量的增加而增大;麦季最大峰值出现在气温回暖的第二次追肥后,排放量的最大峰值也随施氮量的增加而增大;稻麦轮作土壤N2O排放以麦季的排放为主,麦季N2O累积排放量在轮作周期中占三分之二。     

Tillage, nitrogen and crop residue effects on crop yield, nutrient uptake, soil quality, and greenhouse gas emissions

Management practices that simultaneously improve soil properties and yield are crucial to sustain high crop production and minimize detrimental impact on the environment. The objective of this study was to determine the influence of tillage and crop residue management on crop yield, N uptake and C removal in crop, soil organic C and N, inorganic N and aggregation, and nitrous oxide (N₂O) emissions on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada. The 4-year (1998–2001) field experiment was conducted with two tillage systems: no tillage (NT), and conventional tillage (CT); two levels of straw: straw retained (S), and straw removed (NS); and four rates of fertilizer N: 0, 40, 80, and 120 kg N ha⁻¹, except no N to pea phase of the rotation. The plots were seeded to barley (Hordeum vulgare L.) in 1998, pea (Pisum sativum L.) in 1999, wheat (Triticum aestivum L.) in 2000 and canola (Brassica napus L.) in 2001. Tillage and straw treatments generally had no effect on crop yield during the first three years. But in 2001, NT produced 55, 32, and 20% greater canola seed, straw and chaff than CT, respectively, whereas straw retention increased seed and straw yield by 33 and 19% compared to straw removal. Seed, straw and chaff yield of canola increased with N rate up to 40 kg N ha⁻¹, and root mass (0–15 cm depth) with N rate to 80 kg N ha⁻¹. Amount of N uptake and C removed in wheat and canola generally increased with N rate, but tillage and straw management had no consistent effect. After four crop seasons, total organic C (TOC) and N (TN), light fraction organic matter (LFOM), C (LFC), and N (LFN) were generally greater with S than NS treatments. Tillage did not affect TOC and TN in soil, but LFOM, LFC, and LFN were greater or tended to be greater under NT than CT. There was no effect of tillage, straw and N fertilization on NH₄-N in soil, but CT and S tended to have higher NO₃-N concentration in 0–15 cm soil than NT and NS, respectively. Concentration of NO₃-N increased substantially with N rate ≥80 kg ha⁻¹. The NT + S treatment had the lowest proportion (34%) of wind-erodible (<0.83 mm diameter) aggregates and greatest proportion (37%) of larger (>12.7 mm) dry aggregates, compared to highest (50%) and lowest (18%) proportion of corresponding aggregates in CT + NS, indicating less potential for soil erosion when tillage was omitted and crop residues were retained. Amount of N lost as N₂O was higher from N-fertilized than from zero-N plots, and it was substantially higher from N-applied CT plots than from N-applied NT plots. Retaining crop residues along with no-tillage improved soil properties and may also be better for the environment.     

Responses of microbial biomass and respiration of soil to topography,burning, and nitrogen fertilization in a temperate steppe

Temporal dynamics of microbial biomass and respiration of soil and their responses to topography, burning, N fertilization, and their interactions were determined in a temperate steppe in northern China. Soil microbial indices showed strong temporal variability over the growing season. Soil microbial biomass C (MBC) and N (MBN) were 14.8 and 11.5% greater in the lower than upper slope, respectively. However, the percentage of organic C present as MBC and the percentage of total N present as MBN were 16.9 and 26.2% higher in the upper than lower slope, respectively. Neither microbial respiration (MR) nor metabolic quotient (qCO₂) was affected by topography. Both MBC and MBN were increased by burning, on average, by 29.8 and 14.2% over the growing season, and MR and qCO₂ tended to reduce depending on the sampling date, especially in August. Burning stimulated the percentage of organic C present as MBC and the percentage of total N present as MBN in the upper slope, but did not change these two parameters in the lower slope. No effects of N fertilization on soil microbial indices were observed in the first growing season after the treatment. Further research is needed to study the long-term relationships between changes in soil microbial diversity and activity and plant community in response to burning and N fertilization.