Economics of Foliar‐Applied Potassium for Conventional and No‐Till Cotton

Abstract

Foliar applying low K rates as a supplement to broadcast application on low K soils can partially correct late season K deficiencies and increase cotton (Gossypium hirsutum L.) lint yields. The objective of this study was to determine the economic effectiveness of supplementing 4yr of soil applied K 2 O with foliar K for conventional and no-tillage cotton on a low K soil. Data were obtained from field experiments conducted from 1991 to 1994 at the Ames Plantation Experiment Station of the University of Tennessee. Conventional (CT) and no-tillage (NT) systems with initial extractable K levels of 90 and 80 lb/acre (low) were evaluated. Experimental design for each tillage system was a split-plot arrangement of a randomized complete block Main plots were soil applied KCI rates of 0, 30, 60, and 120 lb K 2 O/acre applied to the same plots each year. Split-plots were foliar KNO 3 , foliar Ca(NO 3 ) 2 , and a check (nonfoliar). The foliar KNO 3 treatment received four applications of 4.4 lb K 2 O/acre starting at or shortly after bloom and applied on a 9-to-14-d interval. The foliar Ca(NO 3 ) 2 treatment received four applications of 1.4 lb N/acre equal to the N in the KNO 3 treatment. Net revenue gains per acre from foliar KNO 3 were calculated using yield response models estimated for each tillage system and year. For CT cotton at the mean 1985 to 1994 cotton lint price, net revenue gains per acre from foliar KNO 3 were positive, except in 1993 when they became negative for K 2 O rates greater than 66 lb/acre. Net revenue gains per acre were positive for NT cotton for 1991 and 1992, but for 1993 and 1994 they became negative for K 2 O rates greater than 76 lb/acre. Net revenue gains per acre for foliar Ca(NO 3 )2 were mostly negative for CT cotton, suggesting the yield response to foliar KNO 3 was from K rather than N. Foliar Ca(NO 3 ) 2 results for NT cotton indicated some response to the N in KNO 3 in 1992 and 1993. Economic analysis suggests that foliar KNO 3 can be profitable on low K soils even for high rates of soil applied K 2 O (120 lb/acre), but that foliar KNO 3 may no longer be economically justified for NT cotton after 3 or 4 yr of soil applied K 2 O rates greater than about 76 lb/acre per yr. This rate is lower than the 90 lb K 2 O/acre recommended for this soil. The results for CT cotton suggest that foliar KNO 3 may be profitable even after 4 yr of high soil applied K 2 O rates, but that poor growing conditions may reduce its effectiveness.