Economics of Using an Adjuvant with Foliar Potassium Nitrate (KNO₃) on Cotton

Foliar potassium nitrate (KNO₃) applications can correct late season K deficiencies. Adjuvants may promote absorption of foliar-applied nutrients, reducing nutrient loss and enhancing yield. The objective was to determine if applying an adjuvant with foliar KNO₃ on medium-to-high-K soils is economically beneficial to cotton producers. Experiments were conducted between 1992 and 1995 on no-tillage cotton produced on a high-K Collins silt loam soil at Jackson, TN, and in 1993 and 1994 on conventional- and no-tillage cotton produced on a medium-K Loring silt loam soil at Milan, TN. Treatments were non-foliar check, foliar KNO₃, and foliar KNO₃ plus adjuvant. Foliar treatments were applied four times at 4.1 kg K ha^-1 (11.2 kg KNO₃ ha^-1) in 94 L H₂O starting at flowering to 14 d after flowering on a 9-to-14-d interval. The adjuvant was added to the foliar solutions at 1.25% (v/v). Partial budgeting was used to estimate net revenue differences ($ ha^-1) among the treatments. Cost of KNO₃ was $27.33 ha^-1, the adjuvant, $17.34 ha^-1, and machinery and labor costs for foliar application summed to $22.95 ha^-1. Yields did not increase sufficiently to cover the higher cost of the foliar KNO₃ treatment compared with the check. The foliar KNO₃ plus adjuvant treatment, compared with the check, increased yields 70 kg ha^-1 for Jackson, 52 kg ha^-1 for the conventional-tillage at Milan, and 112 kg ha^-1 for the no-tillage treatments at Milan, causing net revenues to increase $35.98 ha^-1 at Jackson, $9.34 ha^-1 for conventional till at Milan, and $98.14 ha^-1 for no-till at Milan. Results indicated that no-tillage cotton producers who farm medium-to-high-K soils could increase net revenue by applying foliar KNO₃, but only if the adjuvant is applied with it. Results were less convincing for conventional-tillage cotton.