Potassium fertilizer represents a non-trivial input cost in rice (Oryza sativa L.) production and its rate recommendation is often based on yield and K deficiency observations alone. However, profit-maximizing fertilizer-K rate not only hinges on the yield response to both initial available soil K and applied fertilizer K, but also the crop value and fertilizer cost. To that end, K application rate studies for rice, performed across 91 site-years from 2001 to 2018, allowed estimation of a generic yield response curve to calculate profit-maximizing K rates for producers in the mid-southern United States. To determine whether those calculation efforts are justified, we compared profit-maximizing fertilizer-K rates to those currently recommended. Using rice prices and yields, fertilizer-K cost, and a range of initial soil-test K values, as observed over the last 10 yr, we find that current fertilizer-K rate recommendations are too high. Profit-maximizing rates added from US$0.88 ha−1 at initial Mehlich-3 K availability values of 75 mg K kg−1 to $28.19 ha−1 at 105 mg K kg−1 on average. The corresponding fertilizer-K reductions were 0.35 and 56 kg K ha−1, respectively, resulting in attendant yield penalties of only 4 kg ha−1 and 105 kg ha−1. Hence, performing soil tests and using decision support software to obtain profit-maximizing fertilizer-K rates is expected to enhance producer profit at rice yield penalties that are smaller than fertilizer cost savings. While profit-maximizing rate recommendations do vary in a field with varying available soil K, using the mid-range estimate rather than variable-rate technology was deemed most feasible.
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