Muriate of potash (KC1) was broadcast before planting at 0, 30, 60, 120 lb/acre K20 to both conventional and no-till cotton plots at the Ames Plantation Experiment Station in the spring of 1992. The cultivar Deltapine 50 was planted in a split plot design with the main plot as soil applied K₂O rates and foliar applied potassium nitrate (KNO₃) as sub-plots. Foliar plots were sprayed with 10 lb/acre KNO₃ four times on a two week interval starting at the blooming stage. The plot area tested low in extractable K the previous year. Significantly less fungal leaf spots (mainly Alternaria spp.) were noted as K₂O rates were increased. Leaf defoliation followed a similar pattern as the leaf disease. Typical foliar K deficiency symptoms were also noted along with leaf spot symptoms as K₂O rates declined. Yields also declined significantly as K₂O rates declined.

A slight trend toward less disease and defoliation was noted in no-till plots when compared to conventional plots. A significant reduction inleaf spot and defoliation ratings were observed with foliar applications of potassium nitrate in conventionally-tilled cotton but not in no-till cotton. However, yields were significantly increased with the foliar applications of KNO₃ in both conventional and no=till plots.

It appears that increased levels of soil applied potash on a low testing soil can reduce the late-season, leaf-spot-disease complex as well as increase yields. Foliar application also showed promise.