Soybean Response to Potassium Chloride and Strobilurin Fungicides.

Applying potassium chloride (KCl) pre-plant or as a foliar spray combined with fungicides to soybean [Glycine max (L.) Merr.] may allow farmers to increase yields when soil potassium (K) availability is reduced and/or when disease pressure is present. Interactions between fertilizer and fungicide management have not been examined extensively in soybean cropping systems in the central United States. The objective of this field experiment was to evaluate the effect of soil- and foliar-applied KCl alone or in combination with strobilurin fungicide applications on soybean response and severity of disease. This experiment was conducted in northeastern (Novelty) and southeastern (Qulin) Missouri in 2006 and 2007 on soils with low to medium available soil K. Leaf K concentrations increased significantly with preplant KCl compared to non-treated or a foliar application. Leaf Cl concentrations increased with preplant KCl at Qulin and an R4 foliar application of KCl at Qulin and Novelty. Preplant KCl application reduced the severity of Septoria brown spot, frogeye leaf spot, and increased yield 340 kg ha^-1, while foliar-applied KCl increased yield 110 kg ha^-1 at Novelty. An R4 application of strobilurin fungicides increased yields 230 to 360 kg ha^-1 at Novelty. At Qulin, soybean yield increased up to 390 kg ha^-1 with preplant application of KCl while there were variable effects of fungicides on the severity of disease and no yield response due to fungicides or foliar KCl at this location. Yield results indicated that foliar applications of KCl were no substitute for soil applied KCl in this research.