Relation between soil organic matter and yield levels of nonlegume crops in organic and conventional farming systems

The aim of this study was to evaluate the interaction between yield levels of nonleguminous crops and soil organic matter (SOM) under the specific conditions of organic and conventional farming, respectively, and to identify implications for SOM management in arable farming considering the farming system (organic vs. conventional). For that purpose, correlations between yield levels of nonlegume crops and actual SOM level (C_org, N_t, C_hwe, N_hwe) as well as SOM‐level development were examined including primary data from selected treatments of seven long‐term field experiments in Germany and Switzerland. Yield levels of nonlegume crops were positively correlated with SOM levels, but the correlation was significant only under conditions of organic farming, and not with conventional farming treatments. While absolute SOM levels had a positive impact on yield levels of nonlegumes, the yield levels of nonlegumes and SOM‐level development over time correlated negatively. Due to an increased demand of N from SOM mineralization, higher yield levels of nonlegumes obviously indicate an increased demand for OM supply to maintain SOM levels. Since this observation is highly significant for farming without mineral‐N fertilization but not for farming with such fertilization, we conclude that the demand of SOM‐level maintenance or enhancement and thus adequate SOM management is highly relevant for crop production in organic farming both from an agronomical and ecological point of view. Under conventional management, the agronomic relevance of SOM with regard to nutrient supply is much lower than under organic management. However, it has to be considered that we excluded other possible benefits of SOM in our survey that may be highly relevant for conventional farming as well.     

The environmental performance of milk production on a typical Portuguese dairy farm

The activities associated with raw milk production on dairy farms require an effective evaluation of their environmental impact. The present study evaluates the global environmental impacts associated with milk production on dairy farms in Portugal and identifies the processes that have the greatest environmental impact by using life cycle assessment (LCA) methodology. The main factors involved in milk production were included, namely: the dairy farm, maize silage, ryegrass silage, straw, concentrates, diesel and electricity. The results suggest that the major source of air and water emissions in the life cycle of milk is the production of concentrates. The activities carried out on dairy farms were the major source of nitrous oxides (from fuel combustion), ammonia, and methane (from manure management and enteric fermentation). Nevertheless, dairy farm activities, which include manure management, enteric fermentation and diesel consumption, make the greatest contributions to the categories of impact considered, with the exception of the abiotic depletion category, contributing to over 70% of the total global warming potential (1021.3 kg CO₂ eq. per tonne of milk), 84% of the total photochemical oxidation potential (0.2 kg C₂H₄ eq. per tonne of milk), 70% of the total acidification potential (20.4 kg SO₂ eq. per tonne of milk), and 41% of the total eutrophication potential (7.1 kg eq. per tonne of milk). The production of concentrates and maize silage are the major contributors to the abiotic depletion category, accounting for 35% and 28%, respectively, of the overall abiotic depletion potential (1.4 Sb eq. per tonne of milk). Based on this LCA case study, we recommend further work to evaluate some possible opportunities to improve the environmental performance of Portuguese milk production, namely: (i) implementing integrated solutions for manure recovery/treatment (e.g. anaerobic digestion) before its application to the soil as organic fertiliser during maize and ryegrass production; (ii) improving manure nutrient use efficiency in order to decrease the importation of nutrients; (iii) diversifying feeding crops, as the dependence on two annual forage crops is expected to lead to excessive soil mobilisation (and related impacts) and to insignificant carbon dioxide sequestration from the atmosphere; and (iv) changing the concentrate mixtures.     

对汽车撞柱的仿真研究

由于许多汽车事故是因为车辆撞枉而造成的,根据采集得到的真实事故数据,应用LS—DYNA和MADY—MO对车辆撞柱进行仿真,时仿真结果与事故调查结果比较分析表明,该仿真结果能真实反应实际撞柱情况,仿真方法的有效性得以证实。     

基于GIS的绿色农产品基地适宜性评价

建立和完善绿色农产品基地适宜性评价方法,提高评价结果的实用性和准确性,是实现农产品安全的根本保障。研究依据基地认证者、规划者、生产者3种评价主体实际需求,分别引入污染潜在风险指标和经济状况指标,建立面向不同评价主体需求的多种主导因子评价指标体系,并借助GIS的空间分析方法进行定量评价,最后以北京大兴区为例进行了案例分析研究。结果表明,基地与工矿企业距离、与居民地距离等潜在污染风险对基地适宜性限制大,且不同评价主体下建立不同指标体系使评价更具针对性,利用GIS功能可提高效率,评价结果可视化程度好,具有很强的     

基于不同重现期降水的LID措施水文调控性能研究

作为最典型的土地利用变化过程之一,城市化进程通过改变该地区的下垫面条件,改变了天然状态下的水文机制,并进而产生一系列水环境问题。低影响开发(LID)的雨洪调控措施通过在源头上消纳径流,被视为解决城市雨洪问题的新方法。通过SWMM(Storm water management model)软件建立模型,对不同重现期降水的典型LID措施截流池、入渗带、透水性路面和生物滞留池进行了模拟。模拟结果表明,各LID措施的调控性能随着降水重现期的不同而产生明显的变化;随着降水量的增大,各措施的洪峰流量消减率及入渗补给率(截流池除外)均有不同程度的下降,但洪峰流量消减量随着降水量的增大而增大,入渗量基本保持不变(截流池除外);当采用相同的表面面积设计时,滞留池的洪峰流量消减性能最好,入渗带的入渗补给性能最好;决定其调控性能最主要的因素本质上为其有效容积,即各措施所能容纳的水量。     

提高科技期刊影响力的实证研究

以《中国农学通报》为例,从历史积淀、办刊宗旨、主办单位、编辑水平、办刊理念等方面分析了提高科技期刊影响力的基础;论述了增强科技期刊影响力的途径,包括提高稿源水平、办刊质量、编审效率、加强管理与编辑队伍建设,加快与国际接轨。并从载文量、影响因子、即年指标变化、被引频次、基金资助论文率、网络影响力等方面阐述了近年来《中国农学通报》在农业领域影响力的提高情况。     

缓冲材料弹性模量对鸡蛋冲击特性的影响研究

就缓冲材料的弹性模量对鸡蛋跌落冲击特性的影响进行试验研究。通过分析试验数据,建立回归方程,并对回归方程进行曲线拟合,得出缓冲材料弹性模量与碰撞参数之间的关系。结果表明,缓冲材料的弹性模量对冲击力峰值和碰撞时间影响极显著,该结果可为鸡蛋的加工、包装和运输提供一定的参考。     

漳河灌区节水灌溉影响分析

为了解决越来越严重的水资源危机，发展节水灌溉已经成为灌区越来越重要的任务。自改革开放以来，漳河灌区灌溉用水量有了大幅度下降，而农业生产总产量却有所上升。灌区通过节水灌溉，使得灌溉水分生产率不断提高，在保证农业生产总产量稳步提高的前提下节约灌溉用水。与此同时，将所节约的农业灌溉用水转移到如发电、城镇供水、工业用水等非农业用水部门，从而大大提高了单方水利用效益。这是我国开展节水灌溉较为成功的典范。通过研究漳河灌区节水灌溉的影响，寻求大型灌区真实节水的途径，使得有限的水资源得到更加充分、合理的利用。     

基于动网格技术的双定子马达配流结构优化

为消除双定子叶片马达的配流冲击所产生的不利影响,对双定子马达的配流结构进行改进,即开设闭死压缩角与闭死膨胀角,有效实现预升压和预卸压。推导了双定子马达的闭死角数学模型,并对预升压与预卸压过程中闭死容腔内的压力变化特性进行了分析,基于动网格及其UDF（用户自定义函数）编程技术对双定子马达进行三维数值模拟计算。结果表明,与现有双定子马达相比,开设闭死角可以有效地减轻双定子马达的高压回流冲击以及压力突变的现象,使过渡区中油液压力的变化趋于平缓。     

PWM间歇喷雾变量喷施系统中的压力损失和液压冲击

在PWM间歇喷雾式变量喷施系统中,流量变化会引起喷杆各管路中的压力损失的变化,电磁阀的快速启闭会在管路中形成液压冲击,致使各喷头的实际喷雾压力发生波动,导致其喷施流量和雾化特性出现畸变。为揭示其管路压力损失的变化特性和液压冲击特性,构建了一套PWM间歇喷雾式变量喷施系统,并对其进行了流体动力学分析,确定了不同喷雾流量下的管路药液流态,建立了压力损失和液压冲击的计算模型,分析了0.3 MPa设定喷杆压力下的管路压力损失变化范围和液压冲击幅度,并进行了实际试验测试。结果表明:在0.3 MPa设定喷杆压力下,同一喷头前端管路的压力损失的变化幅度可达140 kPa,不同喷头间的实际喷雾压力差异可达25 kPa,由于电磁阀快速启闭而引起的液压冲击幅值可达170 k Pa。