Changes in some physical properties of a clay soil in Central Italy following the passage of rubber tracked and wheeled tractors of medium power   总被引：1，自引：0，他引：1  

M. Pagliai  A. Marsili  P. Servadio  N. Vignozzi  S. Pellegrini 《Soil & Tillage Research》2003,73(1-2):119-129

The aim of this study was to evaluate the compacting effect of rubber tracked tractors in comparison to that of the traditional wheeled tractors. Macroporosity, pore shape and size distribution, bulk density, penetration resistance and saturated hydraulic conductivity were analysed in a clay soil (Vertic Cambisol) near Rome (Italy) following one and four passes on the same track of rubber tracked and wheeled tractors of medium power. The soil structure attributes were evaluated by characterising porosity by means of image analysis of soil thin sections prepared from undisturbed samples. Macroporosity decreased in the 0–10 cm layer of compacted soil, particularly after four tractor passes, due to a large reduction in the proportion of elongated pores and in their vertical continuity. The rubber tracked tractor had a more pronounced compaction effect in the surface layer (0–10 cm) than the wheeled tractor both after one and four passes; the latter treatment producing the lowest soil porosity. The same trend was observed for hydraulic conductivity, which showed a highly significant correlation with elongated pores. In the 10–20 cm layer the porosity was significantly decreased following traffic, apart from in the soil under one pass of the rubber tracked tractor. Again in this layer, the lowest values of porosity were found in soil after four passes of the rubber tracked tractor. Single and multiple passes made by the two tractors induced different effects regarding soil penetration resistance and bulk density. Increment ratio of penetration resistance after tractor passes with respect to the control was: 12.5 and 49.9% with the wheeled and 34.4 and 39.8% with the tracked after one and four passes, respectively. Increment ratio of dry bulk density values after tractor passes with respect to the control was 7.9 and 11.7% with the wheeled and 7.5 and 8.3% with the tracked after one and four passes, respectively. The tractor passes transformed the initial subangular blocky structure into a massive structure with sometimes a platy structure in the upper few centimetres. The results indicated that soil compaction following traffic with the rubber tracked tractor was generally the more pronounced. However the compacting effect of this tractor after one pass seemed to be limited to the surface layer only.  相似文献   

Implication of relationships among suspended sediment size, water discharge and suspended sediment concentration: the Yellow River basin, China     

Jiongxin Xu 《CATENA》2002,49(4)

According to the yearly maximum suspended sediment concentrations (SSC) in the Yellow River and its tributaries, the rivers are divided into three types of more than 300, 20–300, and less than 20 kg/m³. The middle Yellow River basin is located in the transitional zone from subhumid to semiarid climates, and covered by a thick loess mantle. Neighboring on the desert areas to the northwest, the surface material of the Loess Plateau exhibits some marked areal differentiation in grain size and forms three zones covered by sandy loess, (typical) loess and clayey loess from northwest to southeast. Controlled by these physico-geographical conditions, the grain size of river-transported sediment shows some particular characteristics; at small water discharge or SSC, the grain size of suspended sediment abruptly decreases to a minimum with increasing water discharge or SSC. At water discharge of more than ca. 40 m³/s or at SSC of more than ca. 40 kg/m³, the grain size increases with water discharge or SSC.During the low-stage season, the relatively clear baseflow may scour the coarse bed materials, so the suspended sediment is relatively coarse. In the rainy season, rainstorm runoff washes out fine loess materials to the river, making suspended sediment fine. During relatively strong rainstorms, there often occur hyperconcentrated flows at SSC of more than 300 kg/m³. The relatively coarse grains could then remain suspended in the mixture of water and fine suspended sediment.  相似文献   

履带式稻(麦)联合收割机液压——机械式行走系统的研究          下载免费PDF全文

王金武  金英子  迟媛  赵匀 《农业工程学报》2003,19(1):117-120

液压行走系统因其结构简单、操纵方便、转向灵活等特点已广泛在联合收割机中采用。该文分析了液压一机械式联合收割机行走系统的工作过程，并以某联合收割机为例，对液压行走系统的配置方案、液压元件的选型、液压系统主要参数的确定、液压系统的性能验算和实测等方面进行了研究。研究结果表明，此液压行走系统的设计是合理的、可行的，完全可以满足联收机实际使用条件和较恶劣的工况。这为我国联合收割机液压行走系统的设计和配置提供重要的参考价值。  相似文献   

土地整理项目管理与决策支持系统的构建   总被引：7，自引：1，他引：7  

高向军  贾文涛  陈原  张中帆 《农业工程学报》2002,18(3):169-172

土地整理项目管理信息化是提高项目管理效率和科学化水平的重要途径。该文从土地整理和土地整理项目的基本概念入手，对项目管理进行了信息化需求分析，阐述了“土地整理项目管理与决策支持系统”研制的背景与现实意义，介绍了土地整理项目管理与决策支持系统的结构与功能，以及系统构建采用的关键技术。  相似文献   

中国水土保持公务管理信息系统设计     

许峰  郭索彦等 《水土保持学报》2002,16(2):41-44

中国水土保持公务管理系统是中国水土保持管理信息系统先行开发的子系统 ,开发目的是为水土保持管理工作中目前亟待解决的公务管理现代化任务 ,提供在网络化、GIS应用迅速普及的背景下的支持。系统设计以“信息共享、办公自动化、灵活定制”三大目标为核心 ,采用先进的计算机网络技术、数据库技术和办公自动化技术 ,以期实现较好的网络应用功能 ,并具有良好的系统安全、稳定性与灵活性  相似文献   

干旱半干旱地区植被生态用水计算   总被引：51，自引：5，他引：51  

左其亭 《水土保持学报》2002,16(3):114-117

干旱半干旱地区是生态环境比较脆弱的地区 ,特别是人类不合理开发 ,使生态环境受到严重威胁。为了挽救中国西部干旱半干旱地区已遭破坏的生态环境 ,我国政府提出了“退耕还林”的号召。针对干旱半干旱地区 ,植被生态系统实际用水量以及达到某一目标要求的生态用水量如何计算或合理确定 ,对流域规划、生态建设以及水资源合理配置都有重要意义。先从生态系统的一般意义上来介绍生态用水的概念 ,进而介绍植被生态用水的计算方法 ,并针对“退耕还林”和“植被生态改善与恢复”情况下的生态用水计算问题进行专门介绍。  相似文献   

植物篱枝叶有机碳分解研究   总被引：7，自引：0，他引：7  

孙辉  唐亚  赵其国  张炎周 《土壤学报》2002,39(3):361-367

研究植物篱枝叶的分解和养分矿化过程对该模式下养分的有效利用具有重要意义。在金沙江干热河谷坡耕地上利用分解袋法对新银合欢、山蚂蝗等 6个植物篱树种枝叶的分解进行了研究 ,结果显示山蚂蝗和新银合欢分解最快 ,前 2个星期有机碳分解了48 6 %和 5 0 0 % ;山毛豆和云南合欢次之 ,前 4星期有机碳累积分解量为 5 1 5 %和 45 6 % ;圣诞树和黑荆树分解最慢 ;将枝叶埋入土壤中比覆盖地表分解快。有机碳的分解规律可以用单指数模型Ct=C0 (1 e kt)和双指数模型Ct=C0 1 (1 e k1t) C0 2 (1 e k2 t)拟合 (式中 ,Ct 为有机碳累积分解量占全碳百分数 ,C0 、C0 1 和C0 2 分别为易分解有机碳和难分解有机碳百分数 ,k和k1分别为易分解有机碳分解常数 ,k2 为难分解有机碳分解常数 ) ,双指数模型更具合理性。研究表明有机碳的累积分解量与枝叶初始C/N比呈负相关 ,枝叶分解速度可用有机碳 (或易分解有机碳 )半减期来衡量。  相似文献   

塑棚蔬菜气象信息服务系统   总被引：3，自引：5，他引：3  

葛徽衍  张永红 《中国农业气象》2002,23(4):26-29

分析了木地塑棚蔬菜的气候背景，品种选择，温度指标，生产管理，无公害蔬菜生产等方面的状况。研究了大风，强降温，大雪，连阴天等灾害天气对塑棚蔬菜生产造成的影响以及相应的预报方法，据此开发了塑棚蔬菜气象信息服务系统，包括气象信息，灾害天气预报以及防御对策等。  相似文献   

河龙区间坝系水资源开发前景分析     

左仲国  姚党生 《中国水土保持》2002,(11):23-24

据研究 ,黄河中游在暴雨 (2 4h)频率设计标准为 1%～ 0 5 %的条件下 ,坝地总面积达到坝控流域面积的 1/ 2 0～1/ 10时可达到坝系相对稳定。河龙区间在坝系达到相对稳定后 ,通过坝系拦蓄作用 ,每年可提供 16亿～ 2 9亿m3 的农业用水 ;有 42 4%的年份年径流大部分可被拦蓄利用 ;有 5 7 6%的年份坝系土壤水分补充量可达 5 2亿m3 以上  相似文献   

应用~(15)N研究小麦花生两熟制氮肥分配方式对小麦、花生产量及N肥利用率的影响   总被引：7，自引：1，他引：7  

王才斌  成波  孙秀山  郑亚萍  陈殿绪 《核农学报》2002,16(2):98-102

在小麦花生两熟制条件下 ,全年氮肥两作 3次施用 (小麦基肥、追肥和花生基肥 )氮素利用率为 3 2 52 % ,一作两次施用 (小麦基肥和追肥 )氮素利用率为 3 7 0 1 % ,但前者土壤残留多 ,损失少 ,氮肥回收率为 69 2 4% ,较后者高 1 2 0 3个百分点。且前者有利于小麦、花生产量的形成 ,是小麦花生两熟制适宜的施肥方式。小麦当茬氮肥利用率为 1 6 80 %～ 3 5 63 %。夏直播花生当茬及前茬小麦基肥和追肥 (拔节期 )的氮肥利用率分别为 2 3 70 %、6 57%～ 7 70 %和 1 0 0 3 %～ 1 2 73 % ;施肥时间和施肥量对氮肥利用率影响较大  相似文献