Profit-maximizing potassium fertilizer recommendations for corn and cotton

Whereas K fertilization is necessary to maximize corn (Zea mays L.) and cotton (Gossypium hirsutum L.) yields in soils with sub-optimumKavailability, 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. Thirtynine 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.

Automated summary

K fertilization is necessary for maximizing corn and cotton yields in soils with sub-optimum K availability, but maximizing yield doesn't always equal maximizing profit. Estimating the tradeoff between yield and fertilizer cost provides insights for producers.