HIGH-FREQUENCY BASIN IRRIGATION DESIGN FOR UPLAND CROPS IN RICE LANDS

Rice soils are generally characterized by heavy textures, poor structures, low porosities and permeabilities, shallow traffic pans, and slow rates of drainage. Crop growth and yields of upland (i.e., nonrice) crops in these soils are adversely affected because of restricted root aeration and development. Under these conditions, irrigation of nonrice crops poses serious problems because of thc low air porosity and thc tendency of the soil to waterlog. A high-frequency basin irrigation method for nonrice crops in rice soils is developed. It is based on a computer solution of the Lewis and Milne surface irrigation volume balance equation by numerically inverting thc Laplace transform of the equation. Thc method provides an optimum design for thc alleviation of the soil-related adverse effects while enabling a high application efficiency and uniformity. The method is field-tested in three different fields, in which 0.330, 0.326, and 0.374 m of water are applied in 8, 7. and 10 low-volume irrigations. respectively. Overall application efficiencies of 90.9%, 92.3%, and 93.6% are achieved, routinely exceeding the