Potassium Fertilization of Cotton Produced on a Low K Soil with Contrasting Tillage Systems

Abstract

Correcting K deficiency in fast-fruiting cotton (Gossypium hirsutum L.) cultivars requires information on growth response to available soil K, soil K 2 O rates, and supplemental foliar K. Field research was initiated in 1991 on a Memphis silt loam soil (fine-silty, mixed, active, thermic Typic Hapludalf), low in Mehlich I extractable K, to evaluate cotton responses to soil- and foliar-applied K for conventional-tillage (CT) and no-tillage (NT) production systems in Tennessee. Potassium rates of 0, 30, 60, and 120 lb K 2 O/acre were soil-applied to the same plots each year. Foliar treatments included: no-foliar K, KNO 3 , and Ca(NO 3 ) 2 . KNO 3 was applied four times per year to supply 4.4 lb K 2 O/acre per application. Ca(NO 3 ) 2 was applied at 1.4 lb N/acre per application, equalling the N applied in the KNO 3 foliar applications. Petiole K concentrations were evaluated for each foliar application. Soil samples (0-6 in.) were collected after harvest from the no-foliar K treatments of each main plot to evaluate Mehlich I extractable soil K. Lint yields were determined by mechanically picking the two center plot rows twice each year. Extractable soil K increased linearly with increased soil K 2 O rates each year for both tillage systems. Yields in both tillage systems were increased by soil- and foliar-applied K. Regression equations expressing yield as a function of K 2 O rate were developed for KN03 and no-foliar K treatments each year for both tillage systems. In 1991 and 1992, the foliar KNO 3 treatment increased yields at all soil K 2 O rates. In 1993, foliar KNO 3 increased yields at soil K 2 O rates up to 94 lb K 2 O/acre in CT and up to 103 lb K 2 O/acre in NT. In addition, foliar KNO 3 increased yields at soil K 2 O rates up to 108 lb K 2 O/acre for the 1994 NT cotton. Relationships found between Mehlich I soil extractable K and soil K 2 O rates were used to calculate the critical soil extractable K levels for predicting yield response to foliar K. These values ranged from 158 to 161 lb K/acre and correspond to the 160 lb K/acre value used to distinguish between medium and high testing soils in Tennessee. For this soil, foliar K supplemented soil K 2 O rates and increased yields when extractable K was medium or lower. Moreover, petiole K concentrations indicated plant K was deficient in 1991 and 1992 at all K 2 O rates and was deficient in 1993 for K 2 O rates of 60 lb/acre or less.