Spatial Variation of Soil Moisture and its Effect on Lint Yield in a Deficit Irrigated Cotton Field

As the population increases in Southwest Texas in recent years, the urban water demand is drastically increasing. Regulated deficit irrigation (RDI) is expected to be one of the potential water management practice for saving water while maintaining crop yield. A field experiment was conducted at the AgriLIFE Research center in Uvalde in summer 2008 to examine the water saving potential. Seven irrigation schemes and four varieties were assigned to the experimental field to test their effects on lint yield. As the spatial correlation of the soil moisture/ soil water content were suspected, a spatial analysis on lint yield and soil water content was conducted. The analysis results showed that: 1) The soil water contents showed spatial correlations, while the lint yield did not. 2) The relationship between lint yield and soil water content can be described by linear model better than spatial autocorrelation model. 3) The variogram fit of the soil water content showed a completed curve; the contour map generated using ordinary kriging illustrated the irrigation schemes effect well, and gradient effect was suspected. The variogram of the lint yield could not be fitted by a completed curve, which indicated that the sample field was not large enough to determine the variance function. Further study is needed to determine the slope effect on soil water content, and to improve the contour map precision of the lint yield.