Effect of Row Pattern and Spacing on Water Use Efficiency for Subsurface Drip Irrigated Cotton
J. Enciso-Medina, B. L. Unruh, J. C. Henggeler, W. L. Multer
Cotton production is an important economic base for Far West 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 plant row patterns, row spacings and irrigation levels were evaluated to investigate water use efficiency for cotton under subsurface drip irrigation (SDI). An experiment with three row-spacings, two plant row patterns, and four water levels was conducted during three years in Far West Texas. The row spacing treatments were ultranarrow rows (UNR), 0.76 and 1.02-m rows. The row patterns for the 0.76 and 1.02 m row spacings were every row planted, one planted and one skipped, and two rows planted and one skipped. The UNR cotton was solid-planted in 0.25-m rows in 1997 and 0.38-m rows in 1998 and 1999. The drip lines were placed beneath each planted row, except in the case of the UNR rows where the rows were planted over the 0.76-m drip line spacing. The UNR and the 0.76-m row spacing resulted in higher WUE than the 1.02-m row spacing for the highest water level in 1997, and 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 inseason irrigation), the UNR spacing produced a higher WUE (0.258 kg/m3) than the 0.76 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 spacing respectively. Although, the 0.76-m and 1.02-m row spacing were not significantly different, the WUE of 0.76- m row spacing was 10.5% higher than the 1.02-m row spacing. Therefore, we conclude 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 row planting patterns were analyzed by combining three years of data, it was found that row pattern did not have an influence on WUE for the 0.76-m and 1.02-m row spacings.