Wednesday, November 15, 2006

Effect of Suppy-Limited Deficit Irrigation on Cotton Growth and Yield.

Robert Van Pelt, USDA-ARS-NPA-SPNRU, USDA-ARS, 302 W I-20, Big Spring, TX 79720

Sub-surface drip irrigation (SDI) is increasingly used to supplement rainfall in areas with poor or diminished well capacity.  Little is known concerning the effects of severe deficit irrigation on cotton and the yield increase necessary to justify the cost of SDI installation.  We initiated this study to investigate the contributions of small supplemental water volumes on growth and yield of cotton in the semi-arid Southern High Plains of Texas.  We constructed a SDI system with 12 individually controlled plots 0.1 ha in size.  We applied water in volumes that could be achieved in 120 hours per week with well capacities of 20, 10, 5, and 2.5 l/min/ha.  These well capacities allowed weekly application depths of 21.2, 10.6, 5.3, and 2.7 mm and freeze-free season depths of 832, 416, 208, and 104 mm, respectively.  Mean lint yields in 2004, a year with record rainfall but a 60day period without rainfall in July and August, were 1132, 1096, 1050, and 889 kg/ha for the 20, 10, 5, and 2.5 l/min/ha treatments, respectively.  Although there were no adjacent dryland check plots in 2004, the yield of the 2.5 l/min/ha treatment was almost 300 kg/ha greater than the farm dryland average.  Mean lint yields in 2005, a year with normal rainfall, were 1324, 930, 813, 713, and 632 kg/ha for the four irrigation treatments and the adjacent dryland check plots, respectively.