|عنوان فارسی مقاله:||زهکشی و استفاده مجدد از آب های آبیاری|
|عنوان انگلیسی مقاله:||Draining & Reusing Irrigation Water|
|رشته های مرتبط:||کشاورزی، آبیاری و زهکشی، مدیریت منابع آب|
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A well structured soil has spaces containing water and air—both necessary for plant survival and growth (refer to Irrigation Salinity Facts: Principles of Surface Irrigation). A soil at field capacity still contains a significant number of air-filled voids. In a waterlogged soil the spaces in between the soil particles are filled with water, so plant roots have no access to oxygen. Different plants react to this in different ways. Most agricultural plants (except rice) suffer as oxygen and nutrient uptake through the roots slows. Rushes, docks and sedges thrive and will out-compete more desirable species. In addition, beneficial soil microbes are destroyed, plant and animal diseases spread, and machinery and livestock damage the weakened soil structure. Research has shown that summer pasture growth is reduced after only six hours of water ponding, and that water regularly lying on perennial pastures (white clover and ryegrass or paspalum) for 24–48 hours will reduce growth by 25% over an irrigation season, and lower the clover content. Rice is the exception, as it is naturally an aquatic plant, so it tolerates waterlogging. Soil will remain waterlogged until the excess water is removed by plant use, evaporation or drainage. If ponded water remains on the soil surface.
Effects of waterlogging • nutrient uptake stops and the roots die • plants have no energy for growth • beneficial soil microbes die • machinery and livestock can damage soil structure • plant and animal diseases occur • water-loving weeds like rushes, dock and sedge thrive • pastures can be scalded by standing water heating up on a hot day • some nutrients (especially nitrogen) are leached down through the profile below the roots, where they are not used some will drain down through the soil profile, adding to the local watertable. This seepage can cause rising watertables and soil salinity, leading to environmental damage and production losses. Waterlogging becomes an even greater problem in areas with shallow watertables. Soils that become waterlogged following rainfall or irrigation will stay saturated for longer periods because there is less opportunity for downward seepage and flushing of salts. Rainfall is the major cause of waterlogging in the cooler months of the year, while poor irrigation is the major contributor to waterlogging in spring, summer and autumn.