EFFECT OF ROW PATTERN AND SPACING ON WATER USE EFFICIENCY FOR SUBSURFACE DRIP IRRIGATED COTTON

Abstract

Cotton production is an important economic base for western Texas; however, the region has erratic and limited rainfall and is dependent on limited groundwater supplies. Maximizing water use efficiency (WUE) for cotton lint yield is therefore a strategic goal in conserving limited water resources. In this study, different row spacings, planting patterns, and irrigation levels were evaluated to investigate water use efficiency for cotton under subsurface drip irrigation (SDI). An experiment with three row spacings, three planting patterns, and four water levels was conducted during three years in western Texas. The row spacing treatments were ultra–narrow (UNR), 0.76 m, and 1.02 m. The planting patterns for the 0.76–m and 1.02–m row spacings were every row planted, one planted and one skipped, and two planted and one skipped. The UNR cotton was solid–planted in 0.25–m rows in 1997 and in 0.38–m rows in 1998 and 1999. Driplines were placed beneath each planted row, except in the case of the UNR rows where the rows were planted over the 0.76–m dripline spacing. The UNR and the 0.76–m row spacings resulted in higher WUE than the 1.02–m row spacing for the highest water level in 1997, and for the lowest water level in 1998 for the every–row pattern. When the three years of data were combined for analysis, it was observed that for the lowest water treatment (0.6 mm/d in–season irrigation), the UNR spacing produced a higher WUE (0.258 kg/m3) than the 0.76–m and 1.02–m row spacings (0.198 kg/m3). The average WUE of the UNR spacing for three years of the experiment was 11.7% and 21.3% higher than the 0.76–m and 1.02–m row spacings, respectively. Although the 0.76–m and 1.02–m row spacings were not significantly different, the WUE of the 0.76–m row spacing was 10.5% higher than that of the 1.02–m row spacing. Therefore, we conclude that, under our conditions, row spacing can have a moderate impact on WUE for SDI systems. The narrower cotton spacing exhibited trends toward higher WUE. When the planting patterns were analyzed by combining three years of data, it was found that planting pattern did not have an influence on WUE for the 0.76–m and 1.02–m row spacings.