Double-Crop Soybean Response to Potassium on Mid-Atlantic Coastal Plain and Piedmont Soils

Potassium fertilization research on soybean [Glycine max (L.) Merr.] double cropped with winter wheat (Triticum aestivum L.) is lacking. We characterized double-crop soybean response to fertilizer K across 22 Coastal Plain and Piedmont sites with and/ or without wheat straw removal during 2013 to 2015. Mehlich-1 soil-K concentrations at 0-to 15-and 0to 30-cm depths were better in explaining relative yield variability (r(2) = 0.80), defi ning critical soil-K concentrations that ranged from 40 to 75 mg K kg(-1) for 0-to 15-cm and 36 to 66 mg K kg-1 for 0-to 30-cm depths, and identifying K-defi cient sites (100% accurate) than soil-K concentration at 0-to 60-cm depth (r(2) = 0.48; 56% accurate). Critical soil-K concentration at 0-to 30-cm depth did not change with wheat straw management, but slightly increased at 0-to 15-cm depth when straw was removed. Th e R2 leaf-K concentration with a critical range of 20 to 23 g K kg(-1) was better (75% accurate) in diagnosing K defi ciency than V5 plant-K concentration (50% accurate) with a critical range of 17 to 23 g K kg(-1). Double-crop soybean required 33 to 119% more fertilizer K than Virginia Cooperative Extension recommendations for = 50 mg soil-K kg(-1) at 0-to 15-cm depth, but 6 to 55% less fertilizer K for similar soil K concentration at 0-to 30-cm depth. Wheat straw management should not be an issue of concern for fertilizer-K recommendations based on soil-K concentration at 0-to 30-cm depth for double-crop soybean production on Coastal Plain and Piedmont soils.