Cotton and Soil Responses to Annual Potassium Fertilization Rate

Abstract

The objective of this study was to evaluate the effect of potassium (K) fertilization rate (0, 27.9, 56.4, 84.7, 112.9, and 141.1 kg K/ha) and cotton ( Gossy pium hirsutumn L.) cultivars of slightly differing maturity on seedcotton yield and Mehlich-3 soil-test K concentrations. The cotton cultivars “Stoneville 4892” and “Stoneville 5599” represented long-season cultivars while “Paymaster 1218” and “Deltapine 444” represented early-season cultivars. The same K fertilizer treatments were applied to the same plots during the three years of the study. Higher order interactions of cropping year, cotton cultivar and K-fertilization rates were not significant ( P ≥ 0.50), indicating the two cultivars of slightly different maturity respond similarly to K-fertilization. Cropping year and K-fertilizer application rates significantly affected seedcotton yield ( P < 0.0001). Potassium fertilization did not significantly influence seedcotton yield in the first year but significantly increased seedcotton yield in second and third year ( P ≤ 0.0074), as well as 3-year average, and total seedcotton yields ( P ≤ 0.0006). Seedcotton yields ranged from 3418 to 4127 kg·ha -1 and 2980 to 3487 kg·ha -1 in the second and third year respectively while 3-year average and total seedcotton yields were 2943 to 3443 and 8832 to 10,330 kg·ha -1 . The relation between annual, 3-year average, and total K application rates and seedcotton yield was linear (R 2 ≥ 0.82, P ≤ 0.0125). Potassium fertilization significantly increased post-harvest (fall) Mehlich-3 extractable soil K in all three years ( P ≤ 0.0002). This study indicated that, in a representative Mississippi River Delta silt loam soil, when Mehlich-3 extractable K was <98 mg·kg -1 , K fertilization was needed to increase seedcotton yield and prevent soil K depletion. This supports the current University of Arkansas fertilizer recommendations for irrigated cotton production, where application of 56 kg of K ha -1 is recommended to optimize seedcotton yield and prevent soil K reserve depletion when Mehlich-3 extractable soil test K is medium (91 - 130 mg/kg).