Lint Yield and Crop Maturity Responses to Irrigation in a Short-Season Environment

Cotton (Gossypium hirsutum L.) responses to supplemental irrigation need to be reassessed in humid, short-season environments. We conducted a 4-year study on a Typic Hapludalf at Jackson TN, to measure yield and maturity responses of contemporary cultivars to supplemental irrigation; to describe boll retention and distribution patterns associated with maturity responses; and to estimate the percentage of years in which yields may respond to irrigation. Treatments consisted of three rates of supplemental drip irrigation (nominally 3.81, 2.54, and 1.27 cm wk-1, adjusted for rainfall and prior irrigation), plus a nonirrigated check. Irrigation increased lint yields significantly in 3 of 4 years, with quadratic rate responses. The average yield increase was 38% at the 2.54-cm wk-1 rate. Yields were maximized with 35 to 37 cm of total water (irrigation + rainfall) between 40 and 120 days after planting. Yields were limited more by the accumulation of heat units than water supply in 2009. Irrigation delayed crop maturity by an average of 0.56 days for every additional cm water from irrigation or rainfall. Full irrigation expanded the effective fruiting zone on the plant from about 6.6 to 8.5 sympodial branches, increasing first position boll retention, but it delayed crop maturity mainly by shifting the location of the highest harvestable boll. Response to water supply showed that a yield response to irrigation could be expected in years with < 28 cm rainfall between 40 and 120 days after planting. Assuming a planting date of 3 May, this condition occurred in 60% of years of historical rainfall data for this environment.