Dating Termination of Cotton Irrigation from Soil Water‐Retention Characteristics1

Abstract

AbstractIn the semiarid San Joaquin Valley of California, about 90% of the evapotranspiration needs for nonstressed cotton (Gossypium hirsutum L.) are met by irrigation. Soil water‐retention characteristics determine the frequency with which irrigations must be made to replenish depleted soil water during the growing season. Comparatively little attention has been given to using this soil parameter in a predictive sense to help define the correct timing of a final irrigation which may save water and hasten maturity without reducing yield.Studies were conducted in the San Joaquin Valley, on two soils that have a broad difference in water retention ability, to determine the best irrigation termination date for cotton. A multiple‐regression model that included time of irrigation termination and water‐retention capacity of soil as independent variables was used to describe the influence of these variables on cotton production potential (R2 = 0.71”*). Prepared from the function was a graphic relation illustrating an irrigation termination time that allows a 98% relative yield on the basis of the amount of available water the soil can retain. An optimum irrigation termination time was 28 days later for the low water‐retaining soil of the study than for the high water‐retaining soil. Correct timing of a final irrigation saved water and hastened the opening of mature bolls without harm to lint yield or quality.