A study was conducted to assess the performance of surface and subsurface drip irrigation systems using different irrigation water levels on water distribution in soil and wetting pattern and in order to establish relationship of moisture content, distance and depth relationship. The field experiment was conducted in sandy loam soil from October, 2014 to May, 2015 in the farm of University of Rwanda (UR) Nyagatare Campus. The experiment was laid out in strip plot design with three replications to study the effect of depth of placement of drip lateral and different levels of irrigation water.
The treatments are three levels of depth of laterals i.e. at surface, 10 cm depth from surface and 20 cm depth from surface. Soil moisture content at 0, 20 and 40 cm distances from emitter, and depths at 0 - 15, 15 - 30 cm depths was determined every 30 days before and 24 hours after irrigation to estimate soil profile moisture depletion. Based on wetting pattern radius, a linear equation was developed to evaluate relationship at the surface drip irrigation and subsurface drip irrigation at two considered depths (10 cm and 20 cm). For Vertical wetted depth, they were: Y (0 cm) = 0.217X + 5.2203, R2 = 0.9532 (surface drip), Y (10 cm) = 0.2996X + 5.8946, R2 = 0.9647 (subsurface drip, 10 cm depth) and Y (20 cm) = 0.2927X + 6.7402, R2 = 0.957 (subsurface drip, 20 cm depth). In case of horizontal wetted radius, the obtained equations were: Y (0 cm) = 0.217X + 5.2203, R2 = 0.9532 (surface drip), Y (10 cm) = 0.2996X + 5.8946, R2 = 0.9647 (subsurface drip, 10 cm depth) and Y (20 cm) = 0.2927X + 6.7402, R2 = 0.957 (subsurface drip, 20 cm depth). All these values of regression coefficients indicated that the variation of vertical wetting front and horizontal wetted radius was highly correlated to the time increase.