Effects of Varying Irrigation on Yield, Quality, and Spectral Reflectance of Cotton

In the semi-arid Texas Rolling Plains, the growth and yield of cotton (Gossypium hirsutum L.) is driven by the amount of water available to the crop through irrigation and precipitation.  A field study was conducted in 2012 and 2013 at Chillicothe, TX, to investigate the growth, yield, water use efficiency (WUE), and spectral reflectance responses of cotton under different irrigation and tillage treatments. A split-split plot design with three replications was used with irrigation as the main plot (dryland, 45% evapotranspiration replacement, 90% evapotranspiration replacement, and irrigation based on a remote sensing method developed by researchers in the current study), tillage (conventional and minimum) as the sub plot, and varieties (PHY499, DP1044, PHY375, and FM9170) as the sub-sub plot. Plant height, lint yield, WUE, and fiber quality were significantly affected by irrigation and irrigation-by-variety interaction. Increasing irrigation level resulted in a linear increase in lint yield and WUE. The irrigation-by-variety interaction showed that the 90% evapotranspiration (ET) replacement treatment involving PHY375 produced the greatest lint yield and WUE. Tillage did not significantly affect lint yield, WUE, and fiber quality. Increasing irrigation resulted in a linear increase in fiber length and strength, and a linear decrease in fiber micronaire. Two vegetation indices, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) were calculated using spectral reflectance measurements in this study. During the peak growing season, NDWI performed better compared to NDVI as no saturation problems were observed. We suggest further investigation on using NDWI for irrigation management for cotton in the Texas Rolling Plains.