下辽河平原农业生态系统不同施肥制度的土壤养分收支

本试验是在潮棕壤上进行了10年的定位试验,研究了在养分循环再利用的基础上采取不同施肥制度下作物养分移出量,并结合施肥量计算出土壤中N,P,K养分收支。结果表明,在保持农业系统养分循环再利用的基础上,根据养分供给力设计化肥施用量,不仅可实现作物主产,而且可平衡土壤养分收支,避免土壤中肥料养分过剩（主要是N）进入环境,并揭示了我国我国在20世纪70年代以前大面积农田土壤缺P和80年代农田土壤大面积缺K的原因。     

Short–rotation woody crops: A prospective method for phytoremediation of agricultural land at risk of salinisation in southern Australia?

Growing short–rotation woody crops (SRWC) in rotation with conventional agriculture (phase farming with trees) is a prospective method for ameliorating degraded soils, particularly those at risk from salinisation. This work details changes in soil water storage and crop and pasture growth in the first 2 years after harvesting SRWCs at two sites in Western Australia between 2002 and 2004.This trial has demonstrated that where the roots of SRWCs can penetrate deeply into the subsoil, it is possible to develop soil water deficits large enough to subsequently allow several decades of conventional agriculture before groundwater recharge is resumed. At one site, Eucalyptus polybractea dried the soil to 10 m, creating a soil water deficit of 1350 mm within 6 years of planting. It is estimated that annual crops and pasture could be grown at this site for 68 years before the soil again reaches field capacity. Further work is required to determine where in the landscape SRWCs can develop these large soil water deficits.Reduced soil fertility limited crop and pasture growth in the first year after the SRWC at one site, while reduced plant–available water limited crop and pasture growth for 2 years after the SRWC at the other. Monitoring is continuing to determine longer-term changes in soil water content and crop and pasture productivity.     

Soil tillage reduces arthropod biodiversity and has lag effects within organic and conventional crop rotations

Crop rotation systems in organic and conventional farming systems differ in crop types, management and duration. However, changes in arthropod communities over the entire rotation system are poorly understood, as many studies have surveyed only single years or have not covered the entire rotation period. Here, we describe changes in arthropods in two contrasting systems at a split organic‐conventional farm: an 8‐year organically managed rotation with five crops and a 5‐year conventionally managed rotation with three crops. Arthropods were classified into three functional groups, representing epigeal predators, foliar predators/parasitoids and herbivores/pollinators. Epigeal predators were particularly reduced by soil tillage which occurred annually in the conventional rotation, but was intermittent in the organic. Arthropods were most abundant on the conventional rotation, but most taxonomically diverse on the organic. In the conventional system, all functional groups showed a cyclical change in their taxonomic composition that closely matched the crop rotation sequence, whereas in the organic rotation, the cycle was less clear. Whilst the current year's crop type was the major determinant of arthropod community composition, there was a significant “lag effect” for many taxa from the preceding year's crop. Our results suggest that both the amounts of soil tillage (e.g., in no‐till systems) and crop rotation order have major impacts on arthropods in agroecosystems. Rotations with excessive soil tillage are likely to reduce the abundance of some groups of beneficial arthropods, especially epigeal predators.     

辽西褐土施肥及养分循环再利用中长期试验Ⅳ.土壤肥力变化

经12年田间试验,各施肥处理耕层土壤的肥力变化表明,在保持农业系统养分循环再利用基础上,施用适量化肥以平衡土壤养分收支,不仅可实现作物高产,减少过剩养分进入环境,并可改善土壤肥力,表现为明显提高了耕层的有机C,N浓度,不过,在本例中欲保持较高的土壤有效P水平,恐需在平均土壤P收支基础上适当增加P肥施用量。     

Landscape effects of transgenic cotton on non-target ants and beetles

Transgenic crops producing toxins from Bacillus thuringiensis (Bt) can be planted in the same field for many years, and many insects exploiting such crops must disperse to other habitats to persist. Accordingly, effects of transgenic crop farming could accumulate through time and affect insect populations across agricultural landscapes. We monitored the population density of seven ant genera and beetle families and of rare ants and beetles in 84 non-cultivated sites abutting agricultural fields in Central Arizona. We assessed the short-term (during planting year) and long-term (over 5–6 years) landscape effect of farming Cry1Ac cotton on ant and beetle density in non-cultivated sites, in addition to several local and regional variables. Landscape variables (e.g., sequence of crops planted in neighbouring fields, crop diversity, and abundance) were more frequently associated with insect density than local variables (e.g., plant productivity and diversity in non-cultivated sites). In the short-term, use of Bt relative to non-Bt cotton in neighbouring fields was positively associated with density of one ant and two beetle groups in non-cultivated sites. However, acreage of Bt cotton located within 1 km from non-cultivated sites had more negative effects than acreage of non-Bt cotton on density of one ant and one beetle group. In the long-term, the proportion of years that Bt cotton was planted in neighbouring fields was positively associated with ant density but not beetle density. Results suggest that the farming of Bt cotton in neighbouring fields frequently resulted in positive short- and long-term landscape effects on ants and beetles in non-cultivated sites, while Bt cotton planted farther away had less frequent negative short-term impacts.     

Soil mercury accumulation and transference to different crop grains

Mercury contamination in agro-ecosystems is one of the most important environmental issues. Farmland soil mercury accumulation and transference to crops in Changshu City, eastern China, were investigated to identify mercury migration capacity from soil to crops. The mean content of mercury for soil samples slightly increased year after year. The mercury accumulation capacity of rice grown (bioaccumulation factor (BAF) 0.028) in submerged soils under reductive conditions was stronger than that of wheat (BAF 0.0073) in dried soils under oxidative conditions. There were clear relationships between soil mercury with organic matter (OM), cation exchange capacity (CEC), and CaCO₃ of soil samples, while apparent negative relationships between Hg in rice grain with OM, CEC, and CaCO₃ of soil existed. No clear association for Hg between crops and soil was found, indicating that mercury in crop grains is mostly affected by other factors besides soil mercury. Also, soil properties and farming patterns affected mercury transference from soil to crop grains and mercury enrichment capacity in crop grains. The results suggested that appropriate selection of crop species and water management are two major possible ways to reduce total mercury accumulation in crop grains grown in mercury-contaminated regions.     

Consistent plant residue removal causes decrease in minimum soil water content in a Mediterranean environment

Residue retention and no-till farming have been widely adopted to reduce erosion risk, but residue retention in particular is becoming less common due to issues with weed control, and competing markets for residue such as bioenergy production. For this reason, the impact of residue removal on soil water contents in a sandy soil in a Mediterranean-type environment was evaluated. Crop residues were removed by burning or conventional tillage annually in autumn (April or May) from 2008 until 2011. Surface residue cover and soil water contents were measured in summer (February-March) every year from 2008 until 2012, at the time of minimum soil water content (approaching air-dry). After three years of residue removal, average ground cover in the subsequent summers (2011 and 2012) decreased from 78% to 51%, and surface soil water contents decreased from 5.1% to 3.1%. Tillage also significantly decreased ground cover (from 72% to 58%) and soil water (from 4.2% to 3.9%) during the same time period. Changes in surface cover and soil water content indicate that residue removal will have implications for soil health and sustainable crop production.     

Long‐term farming systems and last crop sown shape the species and functional composition of the arable weed seed bank

Questions: The assembly of arable weed communities is the result of local filtering by agricultural management and crop competition. Therefore, soil seed banks can reflect the effects of long‐term cumulative field management and crop sequences on weed communities. Moreover, soil seed banks provide strong estimates of future weed problems but also of potential arable plant diversity and associated ecological functions. For this, we evaluated the effects of different long‐term farming systems under the same crop rotation sequence on the abundance, diversity and community assembly of weed seed bank, as well as on the functional diversity and composition. Location: DOK (biodynamic [D], bioorganic [O], conventional [K]) long‐term trial, Therwil, Switzerland. Methods: The effects of long‐term contrasted farming systems (i.e., biodynamic, organic, conventional, mineral and unfertilised systems) and last crop sown (i.e., wheat and maize) were evaluated on different indicators of species and functional diversity and composition of the weed soil seed bank. Results: The results showed significant influences of 40 years of contrasted farming systems on the diversity and composition of the seed bank, with higher diversities being found in unfertilised and organic farming systems, but also higher abundances than those found under conventional systems. Organic farming also allowed higher functional richness, dispersion and redundancy. Different farming systems triggered shifts in species and functional assemblies. Conclusions: The results highlight the importance of organic management for the maintenance of a diverse arable plant community and its functions. However, such results emphasise the need for appropriate yearly management to reduce the abundance of settled weediness and prevent affecting crop production. The farm management filtered community composition based on functional traits. Although the soil seed bank buffers the long‐term farming and crop sequence, the last crop sown and, thus, the yearly management were important determinants of seed bank composition.     

黄土高原半干旱区苜蓿草地土壤干燥化特征与粮草轮作土壤水分恢复效应

实地测定了黄土高原半干旱区固原不同生长年限苜蓿草地和连作8a苜蓿草地翻耕轮作不同年限粮食作物后深层土壤水分特征,分析了苜蓿草地土壤干燥化特征和粮草轮作对土壤水分的恢复效应.结果表明:(1)苜蓿连作1a、5a、8a和12a等4类苜蓿草地0～1000cm土层平均土壤湿度值为6.6%,平均土壤水分过耗量702.8mm,平均土壤干燥化速率147.1mm/a,达到强烈干燥化程度,苜蓿连作5a土壤干层深度超过1000cm,苜蓿连作8a土壤干层深度超过1360cm,苜蓿草地合理利用年限为7a.(2)连作8a苜蓿草地翻耕并轮作4～7a和25a粮食作物等5类粮田0～1000cm土层土壤湿度介于6.74%～11.95%,土壤贮水量恢复值介于210.6～887.3mm,平均土壤水分恢复速率为80.8mm/a.轮作6a后粮田土壤干层轻度恢复程度以上深度达到1000cm.通过粮草轮作使苜蓿草地土壤湿度恢复到当地土壤稳定湿度需要13a以上.黄土高原半干旱区适宜的粮草轮作模式为:7a苜蓿→13a粮食作物.     

填闲种植及其在黄土高原旱作农业区的可行性分析

在主要粮食作物系统休闲期间种植填闲作物可兼顾环境与经济效益。综述了填闲种植对农田土壤水分、养分和后续粮食作物生产力形成等生态过程的影响及其具有的固碳减排、减少淋溶、控制侵蚀等环境与经济效益,并在此基础上从土壤水分限制、养分提高和产量经济效益等角度探讨了填闲种植在黄土高原旱作农业区的可行性,指出今后应重点加强填闲种植系统的水肥生产力形成机制、关键环境效益的形成机理、填闲作物与管理措施选择、生态经济效益评价以及气候变化背景下的填闲种植系统综合效益评估等方面展开定位观测与模型模拟研究,为填闲种植在黄土高原旱作农业区的推广提供科学依据。