田间土壤特性的空间相关结构分析及其分布描述     

许迪 《灌溉排水学报》1996,(4)

本文对雄县试区试验田的土壤特性空间变异性进行经典统计分析，并利用地质统计学半方差分析法定量描述土壤特性的空间相关结构，然后使用Ｋｒｉｇｉｎｇ最优内插估值法得到了田间土壤特性参数的空间分布等值图。分析结果表明，该试验田０～１００ｃｍ土壤范围内的平均含水量不仅在整个空间分布上而且在纵横曲型剖面上都呈现出弱变异性，空间相关结构显著，相关距离约６０～８０ｍ。采用上述结论和等值图不但能减少样本采样的数量和密度，还能根据田间含水量的空间分布特征合理布点采样，实施土壤墒情的科学监测。  相似文献   

地基差异沉降时管道的纵向力学性状分析   总被引：6，自引：0，他引：6  

张土乔  李洵  吴小刚 《中国农村水利水电》2003,(7):46-48

软土地基的不均匀沉降将导致管道纵向力学性状的变化，产生破坏管道的应力响应，从而引发工程事故。针对地基产生差异沉降的实际管道，通过建立较为合理的力学模型，分析其受力特性，计算管道上的最大挠度、转角、弯矩及确定出应力集中的危险受力区域。通过对该结果的研究，绘制相应关系曲线，为解决由于地基不均匀沉降引起的管道渗漏和爆管等问题提供了一定的理论依据。  相似文献   

曲轴模拟分析和测试技术的研究进展     

王韬  郝志勇  李秀山  冯捷 《农业机械学报》2003,34(3):142-145

曲轴的动力学特性对内燃机噪声、振动以及粗糙刺耳的音质的研究至关重要，因此必须尽可能准确地认识其内在机理。在曲轴模拟分析和测试技术研究领域中出现了许多成果．本文对这些成果作了简要介绍和分析。  相似文献   

农业机械用低碳正火钢的研究     

张洪哲  吴明洙 《农业机械学报》1992,23(3):72-78

按微合金化的成分设计方法冶炼了农机及汽车用低碳正火钢,研究了其显微组织及机械性能。在适当的化学成分及工艺条件下,低碳正火钢常规机械性能基本上达到了45号碳素钢调质水平。正火用钢空冷形成粒状贝氏体。粒状贝氏体由上贝氏体型铁素体和小岛组成,其形态分为两种,长条型和颗粒型。  相似文献   

基于WEB农业物料特性信息管理系统的开发     

余祖龙  郭康权  高梦祥  李星恕 《农机化研究》2004,(2):228-229

以农业物料特性的公式、线图、数据表及相关信息为对象，利用ASP技术，采用B／S架构结构，建立基于WEB农业物料特性信息管理系统。系统的建立为农业物料信息提供了有效的网络知识库平台，实现了数据的共享，符合我国农业信息化的发展方向。  相似文献   

油松木材幼龄期与株内幼龄材分布   总被引：6，自引：0，他引：6  

徐有明 《华中农业大学学报》1992,11(4):382-387

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Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment     

K. ZHANG  X. CHENG  H. DANG  C. YE  Q. ZHANG 《Soil Use and Management》2012,28(3):361-369

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.  相似文献   

Assessing the susceptibility of alpine soils to erosion using soil physical and site indicators     

S. Stanchi  M. Freppaz  D. Godone  E. Zanini 《Soil Use and Management》2013,29(4):586-596

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Basic handling characteristics of wood fuels: Angle of repose,friction against surfaces and tendency to bridge for different assortments     

《Scandinavian Journal of Forest Research》2012,27(1-4):583-597

Basic handling characteristics were measured for sawdust, fuel pellets, fuel chips, hog fuel and chunkwood. The aim was to find relations between the basic handling characteristics and easily measurable fuel properties to facilitate the design of feeding systems in heating plants. The angle of repose was 25–55° and increased with the increasing ratio of particle length to thickness and with the increasing content of hooked or long particles. The angle of static friction, 10–40°, was affected more by the kind of surface than the fuel and followed the ascending order: coated plywood, urethane rubber, particle board, stainless steel, concrete and rubber belt conveyor. The tendency to bridge varied considerably and increased with greater content of hooked or long particles, a deeper fuel bed depth over the opening and a higher moisture content. The results indicate that more attention should be paid to the particle shape.  相似文献   

Mineral Composition and Soil-Plant Relationships for Common Guava (Psidium guajava L.) and Yellow Strawberry Guava (Psidium cattleianum var. lucidum) Tree Parts and Fruits     

《Communications in Soil Science and Plant Analysis》2012,43(15):1960-1979

The mineral compositions of the fruit and tree parts of common guava, Psidium guajava L., and strawberry guava, Psidium cattleianum var. lucidum, were determined. The study occurred during three seasons at six locations in Hawaii to assess guava as feed for livestock. Guava bark contained the greatest concentrations of calcium (Ca) and ash; leaves the greatest concentrations of magnesium (Mg), sulfur (S), sodium (Na), boron (B), and manganese (Mn); and the shoots had the greatest concentrations of nitrogen (N), phosphorus (P), and potassium (K). The leaves and the shoots had the greatest concentrations of copper (Cu) and iron (Fe). Between guava and waiwi, guava had greater concentrations of most minerals except for Na in all plant parts, and Mg and ash in the leaves. Guava leaves and shoots meet the macromineral requirements for various phases of sheep, goat, and beef cattle life cycles with the exception of P and Na. Guava shoots do not meet Mn requirements for lactating cows.  相似文献