Soil compaction in cropping systems: A review of the nature, causes and possible solutions

Soil compaction is one of the major problems facing modern agriculture. Overuse of machinery, intensive cropping, short crop rotations, intensive grazing and inappropriate soil management leads to compaction. Soil compaction occurs in a wide range of soils and climates. It is exacerbated by low soil organic matter content and use of tillage or grazing at high soil moisture content. Soil compaction increases soil strength and decreases soil physical fertility through decreasing storage and supply of water and nutrients, which leads to additional fertiliser requirement and increasing production cost. A detrimental sequence then occurs of reduced plant growth leading to lower inputs of fresh organic matter to the soil, reduced nutrient recycling and mineralisation, reduced activities of micro-organisms, and increased wear and tear on cultivation machinery. This paper reviews the work related to soil compaction, concentrating on research that has been published in the last 15 years. We discuss the nature and causes of soil compaction and the possible solutions suggested in the literature. Several approaches have been suggested to address the soil compaction problem, which should be applied according to the soil, environment and farming system.

The following practical techniques have emerged on how to avoid, delay or prevent soil compaction: (a) reducing pressure on soil either by decreasing axle load and/or increasing the contact area of wheels with the soil; (b) working soil and allowing grazing at optimal soil moisture; (c) reducing the number of passes by farm machinery and the intensity and frequency of grazing; (d) confining traffic to certain areas of the field (controlled traffic); (e) increasing soil organic matter through retention of crop and pasture residues; (f) removing soil compaction by deep ripping in the presence of an aggregating agent; (g) crop rotations that include plants with deep, strong taproots; (h) maintenance of an appropriate base saturation ratio and complete nutrition to meet crop requirements to help the soil/crop system to resist harmful external stresses.     

不同放牧强度对滩羊生产性能影响的研究

五种不同放牧强度，历期154d的滩羊放牧试验结果表明：滩羊的采食量随着放牧强度的加重而降低，同一放牧强度下，随着放牧时间的推移，采食量先是逐渐增大，尔后又下降；不同放牧强度下，滩羊的体重随着时间的推移总体上都呈增加的趋势，但放牧强度轻的处理日增重峰值较高，持续时间较长：滩羊个体增重与放牧强度之间存在着强的负相关，单位草地面积(1hm^2)增重与放牧强度之间呈强的正相关：随着放牧强度的加重，饲料报酬先增大后减小，在同一放牧强度下，饲料报酬随着时间的推移先升高后降低；当放牧强度超过0．750只／hm^2以后，滩羊出现了空怀、产羔率降低和推迟怀孕的现象。综合考虑各研究指标，本类草地放牧强度以不超过0．750只／hm^2为宜。     

中国牧草育种工作研究进展

在综述中国牧草育种工作进展的同时,分析了牧草育种工作中存在的问题,主要包括育成的牧草品种少,良种推广和覆盖面积较小以及牧草育种理论基础薄弱等,并针对性地提出应从改进牧草育种的方法和途径、培育具有地方特色的独特牧草品种、加强种质资源的保护与利用、加快良种向现实生产力的转化以及通过各部门协作攻关等方面解决这些问题。     

大型溞对栅藻摄食行为及影响因素的研究

了解浮游动物与周围浮游植物的相互关系,对探讨富营养化的生态调控机制,促进水域生态环境的改善具有理论上的指导意义。为此,利用显微镜直接计数法研究了大型溞对栅藻的摄食率及一些影响因素?峁砻鳎?在全暗条件下,大型溞的摄食率要高于全光照条件。不同时刻,大型溞的摄食率也不同,在最初的4h内,大型溞对栅藻的摄食率和滤水速度明显较高,随后的时间内摄食率和滤水速度将显著降低并趋于稳定。随栅藻藻液密度增大,大型溞摄食率增大,但滤水速度减慢。盐度对大型溞的摄食率有一定的影响,在水体盐度为0.1%～0.2%时,大型溞摄食率增加,盐度进一步增大,则对大型溞的摄食产生抑制作用。     

草甸草原牧草贮藏养分积累与消耗规律的研究

１９９２年４～９月在内蒙古呼伦贝尔盟草甸草原上，选择１５种牧草进行了牧草贮藏养分积累与消耗规律的研究。采用３．５－二硝基水杨酸比色法对野外采集的样品进行贮藏碳水化合物的定量分析。试验结果表明，双子叶植物贮藏碳水化合物含量的季节变化呈Ｕ型曲线，而禾本科植物的一般为双峰或多峰型曲线。根据试验结果，作者指出了该草地类型放牧利用的适宜时期。     

长刺对两种单细胞藻类牧食力研究

用直接计数法和叶绿素a测定法评估了长刺氵蚤对不同密度的小球藻、舟形硅藻及其混合藻液的牧食力。结果表明 :当小球藻密度在 5 .2 0 0mg/L～ 12 .688mg/L(湿重 )时 ,随藻液密度降低 ,长刺氵蚤的滤水速度逐渐升高 ,摄食速度(细胞 /氵蚤·h)则逐渐降低 ,小球藻密度为 3 .4 3 2ml/L～ 5 .2 0 0ml/L(湿重 )时 ,随藻液密度降低 ,长刺氵蚤的滤水速度及摄食速度都明显降低。当舟形硅藻密度为 7.885mg/L～ 63 .3 65mg/L(湿重 )时 ,随藻液密度降低 ,长刺氵蚤的滤水速度逐渐升高 ,摄食速度逐渐降低。长刺氵蚤的摄食使浮游植物产氧量降低。在混合藻液中 ,长刺氵蚤选择性摄食舟形硅藻 ,选择指数S =0 .0 86。长刺氵蚤对舟形硅藻、小球藻为代表的中小型藻类具有较强的牧食力 ,证实了用长刺氵蚤等大型枝角类治理水体富营养化的可行性。     

不同放牧强度荒野地区的大型土壤动物群落具有异质性

Moderate grazing by cattle increases the heterogeneity of soil and vegetation. This has been suggested as an ecologically sustainable mean of managing natural environments endangered by tree encroachment, such as heathlands. Our study was performed to test the impact of grazing intensity on soil macroinvertebrate communities in heterogeneous landscapes in a private property eligible to the Natura 2000 European Network of Special Protection Areas within the Brenne Natural Regional Park (Indre, France). We sampled macroinvertebrates along a broken line crossing 5 different land-use types, from pasture to pine forest, passing through a besom heath (Erica scoparia) heathland at 3 levels of cattle pressure. We hypothesized that: i) litter-dwelling (mostly arthropods and mollusks) and soil-dwelling macroinvertebrates (mostly earthworms) would respond in an opposite manner to various grazing intensities, and ii) intermediate cattle pressure (pastured heath) would increase soil and community heterogeneity. The results supported the first hypothesis, which was explained by land-use impacts mediated by soil properties. However, our results supported only partly the second hypothesis since maximum dissimilarity (whether in the composition of soil macroinvertebrate communities or in soil features) was observed in only one out of the two pastured heaths where cattle pressure was intermediate.     

新疆地区牧户对退牧还草政策的认知程度及其影响因素调查分析

[目的]选取新疆自治区布克赛尔县为研究的样本区,对该区牧户退牧还草政策进行调查分析,以期为该地区草原生态环境与社会经济的协调发展提供科学依据。[方法]通过问卷调查的方式对样本区150户牧民参与退牧还草工程的情况进行调查,并采用最优尺度分析法对问卷数据进行建模分析。[结果]牧户的文化程度、家庭收入水平、从退牧还草政策中的获利程度和对草场退化的认知程度对牧户参与退牧还草政策的积极性存在显著正向影响;而牧户的年龄、家庭人口规模对牧户参与退牧还草的积极性存在显著负向影响。[结论]在退牧还草政策影响下,文化程度和家庭收入水平高的、从政策中获益多的牧民更愿意调整生产结构、转变生产方式;牧户参与退牧还草积极性的高低主要取决于参与退牧还草能否能获利和是否有能力承担转变后的风险。     

Nutrient management in low input grazing–based systems of meat production

Abstract. Low input grazing-based meat production is often practised on land where alternative land use is restricted and where high biodiversity warrants specific environmental payments. Although these systems are characterized by low external nutrient inputs, significant nutrient losses may occur per unit of produce, even though losses per unit area are low. If the aim is to have animal production without further eutrophication of watercourses, these losses should be minimized,. However, if nutrient-poor grasslands characterized by high biodiversity are the aim, some losses must be accepted to balance nutrient inputs by atmospheric deposition. The impact of grazing animals on nutrient dynamics in grasslands is reviewed in this paper, and options to further improve nutrient management are discussed. It is concluded that nutrient management should largely be addressed indirectly through management of animal behaviour in relation to grazing and supplemental feeding, as well as through optimization of the seasonal distribution of livestock size. A case study indicated that N losses from a cattle farm could be reduced considerably by these means, while animal production could actually be improved. Sustainability issues and trends in legislative and social pressures on low input grazing-based systems of animal production are discussed in relation to nutrient management and practical recommendations.