ABSTRACT

The physical environment largely determines crop water use, when the soil water supply is adequate. Plant productivity within a given physical environment and water supply differs among species and possibly within species. Plant productivity per unit available water is defined as water use efficiency. We have evaluated the yield response of numerous cotton cultivars to a wide range of water supplies within each year over the past seven years. This paper summarizes our results. Water use efficiency defined as lint yield per unit water supply (kg lint/mm water) has a very strong environmental effect varying by nearly two fold from year-to-year. There were genetic differences in WUE between pickers and strippers with the pickers having a slight advantage. No consistent response to growth habit was observed. The results of this long-term study suggest that the physical environment dictates water use efficiency of cotton. However, genetic differences do exist for WUE, although fairly small.