Effect of surface drainage methods on root-zone water balance and water yield on an Ethiopian vertisol

Vertisols, representing over 10percent of the total landmass of Ethiopia, are one of the high potential soils. However, their productivity is constrained by their characteristic shrink-swell properties, including severe waterlogging and moisture deficit during the main rainy season (July to August) and the dry season (December to May), respectively. To partly bridge the gap, a surface drainage method, broad bed and furrow (BBF), was recently introduced, although the basic technology has been in use traditionally since antiquity. The BBF system improves yields over the traditional methods of ridges and furrows (RF) and flat (FL ). Yet little is known of the impact of the improved technology and that of the traditional methods on runoff and root-zone soil water balance. To this end, a field experiment was undertaken at Ginchi on a pellic Vertisol in 1996 to evaluate the three surface drainage methods (BBF, RF and FL) using durum wheat (Triticum durum) as the test crop. The water yield (runoff) per unit area relative to measured rainfall was determined using runoff plots. Soil moisture content was determined gravimetrically while the F AO CROPW A T model was used to calculate the Penman-Monteith reference evapotranspiration (ETo) and crop consumptive use of water expressed as crop evapotranspiration (ETc). Of the total seasonal rainfall of 387 mm, BBF and RF resulted in substantial increases in surface drainage thus transforming 53 and 44percent of incident rainfall into runoff, respectively. The advancement of the sowing date due to the use of surface drainage practices resulted in reduced water requirement although the availability of water was increased. The finding could help in developing technologies to mitigate inefficient water use. In addition, it would enhance water utilization for prospective dry season cultivation for double cropping, thereby increasing land use efficiency. Furthermore, it would promote crop-livestock productivity, as a consequence of increasing the availability of water for human and livestock use.