ASSESSMENT OF GENERAL PERFORMANCE INDICATORS OF IRRIGATION SUPPLY AND DEMANDS AND THEIR IMPACTS ON MAJOR CROP YIELD IN A CONTROLLED SUBSURFACE DRAINAGE AREA OF MARDAN SCARP

摘要

Two sample drainage units of different areas (40 ha and 163 ha) in Mardan SCARP, provided with sub-surface tile drainage system have been assessed. The subsurface drainage systems in these units have caused main problems of over drainage (drop in groundwater table below the design level of 1.1 m) and nourishment of termites (white insects) in the root-zone. The accelerated subsurface drainage containing dissolved fertilizers does not remain lor desired duration in the field to be beneficially utilized. In order to overcome these problems, an idea of controlled drainage has been implemented. The exits of two collectors had been closed to raise the groundwater level in their commands. The impact of the operational policies of the canals irrigating theareas had been observed on the water table of study areas in pre and during monsoon. Due to controlled drainage a water table of more than 2 m could be maintained in one drainage unit while a nearly uniform water table of approximately l m could be maintained in another one. The distribution and water level regulation effects in different parts of the study area have been shown on major crop yield and water use efficiencies. Hydraulic conductivities did not show any proper pattern in relation to the areal distribution of the study area. The drop in water table ranged from 0.3 to 0.8 m due to canal closure (Jan. 9, 1999 to Feb. 27, 1999), which during monsoon raised back to a limit ranging from 0.3 to 0.5 m in the selected units. The water use efficiency was greater in drainage unit under shallower water table than the deeper one.