Profit‐maximizing potassium fertilizer recommendations for corn and cotton

Abstract

AbstractWhereas K fertilization is necessary to maximize corn (Zea mays L.) and cotton (Gossypium hirsutum L.) yields in soils with sub‐optimum K availability, maximizing yield is rarely profit‐maximizing. Estimating the tradeoff between yield and fertilizer cost using current soil‐building and/or yield‐maximizing rate recommendations vs. profit‐maximizing fertilizer‐K rates (KR*) provides insights for producers. Thirty‐nine and 24 fertilizer‐K rate trials were used to estimate respective corn and cotton yield response based on soil‐K availability (SK). Using a field's SK, yield potential, yield response to fertilizer‐K, crop price, and fertilizer‐K cost, KR* were calculated over the past 10 yr. Averaging over that period, using KR* at SK of 75 and 60 mg K kg–1 (a) reduced fertilizer‐K rate by 10 and 38 kg K ha–1, respectively, (b) decreased yield by 53 and 32 kg ha–1, respectively, and (c) increased profitability by US$1.75 and $34.24 ha–1, respectively, in comparison to current recommendations for corn. At SK of 75 and 110 mg K kg–1, cotton profitability at KR* vs. current recommendations rose by $11.54 to $25.95 ha–1, respectively, using 36 and 101 kg K ha–1 more fertilizer, respectively, which led to 27 and 73 kg ha–1 greater yield, respectively. As with prior studies for rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.], corn results suggest using less fertilizer than currently recommended, whereas for cotton, strong yield response to fertilizer‐K and relatively high crop price justified KR* that were above currently recommended rates. A spreadsheet‐based decision tool is online to offer this insight to producers and crop consultants.