Corn yield response to phosphorus and potassium fertilization in Arkansas

Phosphorus and potassium are key nutrients for plant physiological processes and are required in large amounts for adequate corn (Zea mays L.) production. Corn is a major row crop, and up-to-date soil test-based fertilizer recommendations are required to enhance production and profitability. The results from 32 P and 42 K field trials evaluating irrigated corn response to fertilizer P and K rates were used to (i) correlate corn's relative yield response to Mehlich-3 soil test P and K, (ii) determine the frequency and magnitude of the yield response to fertilization, and (iii) calibrate fertilizer P and K rates to soil test P and K. The quadratic and linear models identified 36 parts per million (ppm) P (r(2) = .68, P < .0001) and 110 ppm K (r(2) = .36, P < .0001) as the Mehlich-3 soil test P and K values needed to produce 95% of maximum yield without fertilization. Additional research is needed on soils with P 35 ppm and K 120 ppm to enhance the scope of data in the analyses and improve our understanding of corn's response to P and K fertilization. The current thresholds defining soil test K levels perform well in interpreting soil K availability and corn's response to K fertilization. Mehlich-3 soil test P level definitions should be modified to improve the accuracy of soil test-based decisions for irrigated corn. The calibration results suggest the recommended P2O5 and K2O rates are greater than needed to maximize yield.