Optimizing cotton irrigation frequency for deficit irrigation

Previous work in Arizona attempted to explain why subsurface drip irrigation (SDI) improved cotton yield compared to furrow irrigation when the same amount of water was applied. They observed a longer period of profuse flowering and delayed cutout in daily SDI compared to furrow irrigation. In similar fashion, some other studies have concluded that shorter irrigation frequency resulted in higher yields. The area of St. Lawrence, Texas has the largest concentration of SDI systems irrigated with limited water supplies. It is also common to irrigate using 10 to 15 day irrigation cycle with these SDI systems. The objective of the study was to identify if frequency levels affect cotton lint yield when grown under deficit irrigation. The experiment utilized a previously installed SDI system in the St. Lawrence, Texas region of the southern High Plains. Two frequency levels were studied: irrigate every 4 days and irrigate every 16 days. Electric valves and a controller were adapted to the subsurface drip irrigation system. The same total amount of water was applied for these two frequencies. Each treatment was replicated four times. The area is underlain by deep silty clay loam soils with high water retention. It was concluded that the short frequency resulted in 8.2% higher yield than the long irrigation frequency treatment, When cotton quality was considered in the analysis there was no difference on return between the two irrigation frequencies.