ECONOMICS OF FOLIAR-APPLIED POTASSIUM FOR CONVENTIONAL AND NO-TILL COTTON

Foliar applying low K rates as a supplement to broadcast application o n low K soils can partially correct late season K deficiencies and inc rease cotton (Gossypium hirsutum L.) lint yields, The objective of thi s study was to determine the economic effectiveness of supplementing 4 yr of soil applied K2O with foliar K for conventional and no-tillage c otton on a low K soil, Data were obtained from field experiments condu cted from 1991 to 1994 at the Ames Plantation Experiment Station of th e University of Tennessee, Conventional (CT) and no-tillage (NT) syste ms with initial extractable K levels of 90 and 80 lb/acre (low) were e valuated. Experimental design for each tillage system was a split-plot arrangement of a randomized complete block Main plots were soil appli ed KCl rates of 0, 30, 60, and 120 lb K2O/acre applied to the same plo ts each year, Split-plots were foliar KNO3, foliar Ca(NO3)(2), and a c heck (nonfoliar), The foliar KNO3 treatment received four applications of 4.4 lb K2O/acre starting at or shortly after bloom and applied on a 9-to-14-d interval. The foliar Ca(NO3)(2) treatment received four ap plications of 1.4 lb N/acre equal to the N in the KNO3 treatment, Net revenue gains per acre from foliar KNO3 were calculated using yield re sponse models estimated for each tillage system and year, For CT cotto n at the mean 1985 to 1994 cotton Lint price, net revenue gains per ac re from foliar KNO3 were positive, except in 1993 when they became neg ative for K2O rates greater than 66 lb/acre, Net revenue gains per acr e were positive for NT cotton for 1991 and 1992, but for 1993 and 1994 they became negative for K2O rates greater than 76 lb/acre, Net reven ue gains per acre for foliar Ca(NO3)(2) were mostly negative for CT co tton, suggesting the yield response to foliar KNO3 was from K rather t han N. Foliar Ca(NO3)(2) results for NT cotton indicated some response to the N in KNO3 in 1992 and 1993. Economic analysis suggests that fo liar KNO3 can be profitable on tow K soils even for high rates of soil applied K2O (120 lb/acre), but that foliar KNO3 may no longer be econ omically justified for NT cotton after 3 or 4 yr of soil applied K2O r ates greater than about 76 lb/acre per yr. This rate is lower than the 90 lb K2O/acre recommended for this soil, The results for CT cotton s uggest that foliar KNO3 may be profitable even after it yr of high soi l applied K2O rates, but that poor growing conditions may reduce its e ffectiveness.