Effect of Preplant‐Only Irrigation on Cotton Yields 1

Irrigation practices for cotton ( Gossypium hirsutum L.) are changing on the Texas High Plains because the irrigation water supply is declining. The objectives of this study were to calculate yield probabilities for cotton planted on both early and late dates and grown with only a preplant irrigation, and then to compare these yield probabilities with those previously calculated for dryland conditions. Yields from early and late plantings that had received only a preplant irrigation for the period 1960 through 1971 were used for calculating probabilities for various yield levels. The expected average yields (50% probability) of the early and late plantings of preplant‐irrigated cotton are 530 and 503 kg/ha, respectively; and about 70% of the time the respective yields will differ by less than 50 kg/ ha. Thus, the yield potential of preplant‐irrigated cotton was not greatly affected by a wide range of planting dates. Also, 50% of the time preplant‐irrigated land can be expected to yield about twice as much as comparable dryland and to vary much less in year‐to‐year yields.