Comparison of Subsurface Drip Irrigation Uniformity Designs on Cotton Production

One of the biggest obstacles to the widespread adoption of subsurface drip irrigation (SDI) on the High Plains of Texas is the high cost of initial installation. In some cases, SDI costs can be reduced if systems are designed using lower irrigation uniformity standards. The question becomes “what is the cost in terms of cotton lint yield of lowering the uniformity standards for SDI design?” A SDI system was installed in a 16-acre area with drip lines located in alternate furrows on 30-inch rows. The field was divided into four blocks with six treatment areas per block. Within each block, two treatment areas were irrigated with each 0.630-in., 0.875-in., and 0.990-in. diameter drip tape laterals. These three lateral diameters were designed to provide flow variations (FV’s) of 0.71, 0.94, and 0.85 within the respective area. Each of the three drip designs within each block was used to irrigate cotton at two levels, 60% and 100% of a base irrigation amount. The experiment was conducted from 2001 through 2004. Total cotton lint yield within a zone was not affected by water distribution designs having FV’s between 0.71 and 0.94 during the test period. Conditions other than SDI design had bigger impacts on the spatial yield variability than the design treatments. Cotton yield response tended to follow the trends established by variations in emitter flow rate along the length of a drip tape lateral. Generally higher yields occurred at locations of higher drip emitter discharge, however, the magnitude of the yield change over the length of the lateral did not correspond the magnitude of the emitter flow rate change over the test period. Unusual conditions during the test period may have masked expected differences in SDI design, however, in some instances, SDI installation costs may be reduced by relaxing design specifications.