Irrigation timeliness indicators and application in smallholder irrigation systems in Zimbabwe

Timing of supply of irrigation water is an important measure of water management performance. Yet despite this widely accepted importance of timeliness, few studies have attempted to quantify this performance indicator. This paper suggests a methodology for quantifying timeliness. The indices thus generated are used to compare the performance of some types of smallholder irrigation schemes in Zimbabwe. Results indicate that applying measures of timeliness helps to assess water management practices across scheme types.The methodology given in this paper differentiates between timely irrigation deliveries which meet Crop Water Requirements (CWR) and surplus water supplies due to poor timeliness which cannot be used by the crop, hence denoting wastage. The timeliness indices provide more information regarding management practices than simple measures of total water applications over a given season.     

干旱缺水灌区节水灌溉评价标准及其分析

在分析节水灌溉定义内涵的基础上，提出了评价干旱缺水灌区农田节水灌溉的目标标准和技术标准，并对这些评价标准的运用进行了讨论。     

Simulation of drainage water quality with DRAINMOD

The design and management of drainage systems should consider impacts on drainage water quality and receiving streams, as well as on agricultural productivity. Two simulation models that are being developed to predict these impacts are briefly described. DRAINMOD-N uses hydrologic predictions by DRAINMOD, including daily soil water fluxes, in numerical solutions to the advective-dispersive-reactive (ADR) equation to describe movement and fate of NO₃-N in shallow water table soils. DRAINMOD- CREAMS links DRAINMOD hydrology with submodels in CREAMS to predict effects of drainage treatment and controlled drainage losses of sediment and agricultural chemicals via surface runoff. The models were applied to analyze effects of drainage intensity on a Portsmouth sandy loam in eastern North Carolina. Depending on surface depressional storage, agricultural production objectives could be satisfied with drain spacings of 40 m or less. Predicted effects of drainage design and management on NO₃-N losses were substantial. Increasing drain spacing from 20 m to 40 m reduced predicted NO₃-N losses by over 45% for both good and poor surface drainage. Controlled drainage further decreases NO₃-N losses. For example, predicted average annual NO₃-N losses for a 30 m spacing were reduced 50% by controlled drainage. Splitting the application of nitrogen fertilizer, so that 100 kg/ha is applied at planting and 50 kg/ha is applied 37 days later, reduced average predicted NO₃-N losses but by only 5 to 6%. This practice was more effective in years when heavy rainfall occurred directly after planting. In contrast to effects on NO₃-N losses, reducing drainage intensity by increasing drain spacing or use of controlled drainage increased predicted losses of sediment and phosphorus (P). These losses were small for relatively flat conditions (0.2% slope), but may be large for even moderate slopes. For example, predicted sediment losses for a 2% slope exceeded 8000 kg/ha for a poorly drained condition (drain spacing of 100 m), but were reduced to 2100 kg/ha for a 20 m spacing. Agricultural production and water quality goals are sometimes in conflict. Our results indicate that simulation modeling can be used to examine the benefits of alternative designs and management strategies, from both production and environmental points-of-view. The utility of this methodology places additional emphasis on the need for field experiments to test the validity of the models over a range of soil, site and climatological conditions.     

Using drainage systems for supplementary irrigation

The use of drainage systems for supplementary irrigation is widespread in The Netherlands. One of the operating policies is to raise the surface water level during the growing season in order to reduce drainage (water conservation) or to create subsurface irrigation. This type of operation is based on practical experience, which can be far from optimal.To obtain better founded operational water management rules a total soil water/surface water model was built. In a case study the effects of using the drainage system in a dual-purpose manner on the arable crop production were simulated with the model. Also, the operational rules for managing this type of dual-purpose drainage systems were derived.The average annual simulated increase in crop transpiration due to water conservation and water supply for subsurface irrigation are 6.0 and 5.4 mm.y^–1, respectively. This is equivalent with 520 × 10³ and 460 × 10³ Dfl.y^–1 for the pilot region (2 Dfl 1 US $). The corresponding investments and operational costs are 600 × 10³ Dfl and 9 × 10³ Dfl.y^–1 for water conservation and 3200 × 10³ Dfl and 128 × 10³ Dfl.y^–1 for subsurface irrigation. Hence, water conservation is economically very profitable, whereas subsurface irrigation is less attractive.Comparing the management according to the model with current practice in a water-board during 1983 and 1986 learned that benefits can increase with some 50 and 500 Dfl per ha per year, respectively.     

华北地区农业用水危机及其出路

华北地区水危机主要是由农业用水引起的。解决华北地区农业用水的根本途径是发展节水农业,节水农业的核心是提高水分利用效率,主要的方法有：水利工程节水、生物技术节水、农作物空间布局的调整、污水资源化、利用地下微成水、水资源价格和水价调节。     

精确农业支持技术在我国的应用与发展

重点讲述了精确农业的主要支持技术：“3S”技术、田间变量信息采集与处理技术、智能型处方农业机械、变量投入技术以及系统集成技术在我国的应用，并分析了我国发展精确农业技术研究的热点与应考虑的问题。     

残膜回收工艺和收膜机构

介绍了田间残膜的特性及机械化收膜工艺、残膜同收机中常用收膜机构的种类及工作特性，为残膜回收机的研究设计及主要工作部件结构的优化组合提供参考。     

高含沙水流水轮机转轮的改型与抗磨蚀研究

进行高含沙水流水轮机转轮的改型研究，关键是要从正确确定转轮设计参数和轴面流道型式入手，根据三维水力设计理论，考虑导叶与转轮匹配关系进行叶型设计，针对不同破坏机理选择强磨蚀区采用金属喷涂或非金属保护等综合措施，使水轮机在高舍沙水流中运行时出力增加、抗磨蚀能力提高。     

以提高农民收入,发展农村经济为目标推进农业机械化进程--兼与广大读者共贺新年

农业机械化在我国农业现代化建设中的重要作用使之成为农业现代化的重要内容和主要标志．还没有其它任何一项农业新技术能在农业生产所有领域中被普遍应用，并产生强效地促进作用。提高农民收入、发展农村经济成为农业机械化新时期的重要任务之一，建设现代农业对2004年农业机械化上作提出了新的要求。     

以农机资本经营促进大型农机自我更新

1998年，安达市被黑龙江省财政厅确定为农机资本经营试点市。几年来，在黑龙江省财政厅的大力支持下，在省农机局的精心指导下，取得了较好的经济和社会效益。实施农机资本经营，无论对地方财政建设，还是对农机事业自我完善和更新发展，都起到了积极的推进作用。为此，以实施农机资本经营为出发点，论述了大型农机的自我完善、自我更新的发展思路。