Correlation and Calibration of Mehlich‐3 Phosphorus Recommendations for Winter Wheat Following Rice in Arkansas

Abstract

Accurate soil‐test based fertilizer recommendations depend on the correlation between nutrient concentrations extracted by routine soil tests and crop response to fertilization. In Arkansas, phosphorus (P) deficiency of soft red winter wheat (Triticum aestivum L.) grown following rice (Oryza sativa L.) is commonly observed from December through February. Data from 18 studies evaluating yield response of wheat following rice to P fertilization in Arkansas were summarized to i) correlate Mehlich‐3 P (1:7 extraction ratio, M3P1:7) with relative yield response, and ii) define the critical M3P1:7 threshold and P fertilizer rates needed to optimize wheat yields. Relative grain yield was regressed against the linear and quadratic terms of M3P1:7. The relative yield of unfertilized wheat increased nonlinearly (r2=0.54) as Mehlich‐3 P increased. The critical M3P1:7 concentration was 19 mg P kg−1 for the 95% relative yield level. The linear terms for M3P1:7 and P fertilizer rate and their interaction described a significant (P<0.001) relationship with relative wheat yield. Recommendations for P fertilizer rates can be made using the multiple regression equation where the targeted relative wheat yield is a continuous function of the soil M3P1:7 and P fertilizer rate, or several soil‐test P categories can be defined and each assigned a single P fertilizer rate that will produce near optimum yields. The M3P1:7 boundaries defining each soil‐test P level were <10 mg M3P1:7 kg−1 for “very low,” 10–14 mg M3P1:7 kg−1 for “low,” 15–19 mg M3P1:7 kg−1 for “medium,” 20–30 mg M3P1:7 kg−1 for “optimum,” and >30 for “high” with recommended P rates of 35, 30, 25, 11, and 0 kg P ha−1, respectively. Fertilization recommendations are specific for winter wheat grown on silt loam soils following rice in the rotation, and are correlated and calibrated with soil‐test P from composite soil samples collected after rice harvest.