Effect of potassium application rate on cotton growth and yield under irrigated and dryland conditions

Abstract Potassium (K) deficiency in cotton (Gossypium hirsutum L.) grown on soils with adequate soil test K levels has become more prevalent. Field experiments were conducted with or without irrigation as the main plot and K fertilizer rates as subplot treatments. Granular K was applied preseason at rates of 0, 45, 90, 134, 179, and 224 kg K ha−1. Two in‐season foliar K programs applied a total of either 2.8 or 5.6 kg K ha−1 were included to compare against the check. Experiments were set up on two distinct soil mapping units (SMUs) in Starkville, MS, including a Leeper silty clay loam (LSCL; fine, smectitic, nonacid, thermic Vertic Epiaquepts) and a Marietta fine sandy loam (MFSL; fine‐loamy, siliceous, active, thermic Fluvaquentic Eutrudepts). Response variables collected include lint yield and fiber quality, leaf K concentrations, and cotton growth and development parameters. Across all years of the experiment, LSCL lint yields increased at a rate of 41 and 118 kg ha−1 per 45 kg K ha−1 under rainfed and irrigated conditions, respectively. On the MFSL, lint yield increase was not significant for either rainfed or irrigated conditions. Leaf K concentrations at first bloom and 4 weeks after first bloom responded quadratically to K rate, with peak leaf K concentrations occurring between 134 and 179 kg K ha−1. Differences in cotton growth parameters were observed; however, differences were likely physiologically insignificant. For all parameters, foliar K application programs did not differ from the untreated check. This investigation showed that foliar K application alone are insufficient, and responses to granular K and irrigation were dependent on SMUs.