Abstract:
In situations where increasing irrigation demand for growing high yielding varieties of crops is to be met, deficit irrigation might be a better option to cover more areas and thus extend benefits to more farmers with increase of overall yield and return at some sacrifice of unit yield. Optimal area under two major crops using deficit irrigation is determined in a groundwater based tubewell irrigation system in the High Barind Tract, a drought prone area in the northwestern Bangladesh. Study area comprises four thanas having an irrigable area of 90,660 ha and 1463 deep tubewells, each of capacity 56.6 I/s. Yield and the yield response factors for deficit irrigation determined from experimental plots at the farm of Bangladesh Agricultural Research Institute, Shyampur, Rajshahi for Boro rice and wheat repeating the experiment in two cropping seasons of the year 2001-2002 and 2002-2003 (Islam, 2004). Using the experimentally determined yields and yield response factors, yield and net return for farmer's field condition under deficit irrigation were estimated. Then optimal areas under each crop determine by a liner optimization model which demonstrates that practicing deficit irrigation with limits on area under Boro rice and wheat to maintain the present area under respective crops as farmer's preference, the total coverage of irrigated area can only be increased if the pumps operate at full capacity, the amount of increase being 50, 60 and 80%, respectively in dry, average and wet years from present coverage of 39%. Growing wheat seems more profitable because Boro rice is consumes more water. At 80% pump capacity, only the minimum areas specified under crops could be irrigated, and operating pumps at 60% capacity no irrigation could be provided satisfying the minimum area limits. Eighty percent dependable rainfall is generally used for irrigation design and as such additional tubewells need to be installed to increase irrigated agriculture.
