Cotton yields have remained static for the past 25 years on the Texas High Plains at an average of 310 for dryland and 436 pounds/acre for irrigated production. Water stress due to inadequate precipitation and excessive evaporative demand is considered the primary cause of the relatively low yields. However, analyses of precipitation versus dryland yields does not result in a strong positive correlation between total annual nor growing season rainfall and yield. Additionally irrigated yields parallel dryland yields in most years with a yield advantage of only 150 to 200 pounds/acre. Although yields are not directly affected by total water supply, we do believe intermittent periods of rather intense plant water stress is the major contributor to the relatively low yields of this vast production area.

Our research program has had a primary goal of increasing productivity and water use efficiency within the constraints of this difficult environment. Analyses of yield components reveals that the boll number component (boll m^-2) accounts for nearly 90% of the yield variability across years, water supplies, and plant populations. The bollsplant^-1 component has a greater influence on bolls m^-2 than does plant m^-2. We have conducted population density experiments using two different soil textures and five different water supplies over a period of three years. The purpose was to determine the interaction between plants m^-2 and bolls plant^-1 and to determine the water supply plant^-1 required to maximize bolls plant^-1. The results obtained indicated that as plant density exceeded 10 plants m^-2 the bolls plant^-1 component declined rapidly resulting in a reduction in bolls m^-2 and corresponding lint yield. Reducing the between row spacing from 1.0 m (40 in) to 0.75 m (30 in) resulted in appreciable yield advantage due to more plants acre^-1, greater light interception plant^-1 and a reduction in evaporative loss of water from the bare ground between rows. Similarly, frequent irrigation (6 days intervals) with volume equivalent to 75% ET resulted in the greatest yields compared to longer intervals or more or less volumes per application.