Optimization of Subsurface Drip Irrigation Schedule of Alfalfa in Northwest China

Determination of an optimum irrigation amount and buried depth of subsurface drip irrigation laterals is significantly important in improving crop yield and irrigation water using efficiency in arid regions. In this study, the effects of three irrigation volumes (15.0, 22.5 and 30.0 mm) and three burial depths (10, 20 and 30 cm) of drip laterals on water consumption, yield and water productivity of alfalfa were investigated in a field trial. The water balance equation and FAO-56 crop coefficient methods were applied to determine the evapotranspiration of alfalfa. The results showed that the alfalfa evapotranspiration estimated by the dual crop coefficient method was closer to the actual measured values. The alfalfa water consumption, yield and water productivity increased significantly (p < 0.01) with the increase in irrigation amount, but the increasing trend turned to decrease (p < 0.05) with the increase of the buried depth of the drip irrigation laterals. During the whole growing period of alfalfa, the total water consumption ranged from 400 to 500 mm, the total yield ranged from 7500 to 12,000 kg/hm2 and the water productivity was 1.80 to 2.50 kg/m3. An optimized irrigation amount of 22.5 to 30.0 mm for an irrigation event with a frequency of 5 to 7 days using buried drip irrigation with an irrigation lateral depth of 20 cm was recommended for alfalfa in the study area.