Assessing Organic Phosphorus Contributions for Predicting Soybean Response to Fertilization

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Core Ideas The contribution of P indices that include organic P to predict soybean P fertilization response was evaluated. Bioavailable P and MA‐P indices correlated with soybean relative yield. MA‐P index correlated with labile organic P fractions. MA‐P index improved the accuracy to predict soybean yield response to applied P. The use of organic P fraction in soil test P for soybean [ Glycine max (L.) Merr.] under no‐till could improve the accuracy to predict crops response to P fertilization. The research objectives were to assess the contribution and accuracy of P indices that include organic‐P fractions to predict soybean yield response to P fertilization in comparison with Bray soil test P (BP). The study included P fertilization experiments conducted in the Pampas Region of Argentina during three growing seasons. We selected sites considering Cate and Nelson quadrants (I, II, III), established by a critical BP concentration of 9 mg P kg −1 and a relative soybean yield (RY) of 85%. Bray P, bioavailable (BioP), particulate (POM‐P), and mineral‐associated (MA‐P) soil P fractions were determined in soil samples from the 0‐ to 5‐cm and 0‐ to 20‐cm depths. Bray P varied from 4.8 to 31 mg P kg −1 and BioP from 8 to 29 mg P kg −1 at the 0‐ to 20‐cm depth. Phosphorus content in POM ranged from 19 to 171 mg P kg −1 , and MA‐P ranged from 208 to 446 mg P kg −1 . Bioavailable P and MA‐P correlated with RY, whereas POM‐P did not. Bioavailable P performed similarly to BP test to predict soybean yield response to P fertilization. Phosphorus content in MA fraction reduced Cate–Nelson classification errors, improving the accuracy to predict soybean yield response to applied P in comparison with BP test. Sampling at the 0‐ to 5‐cm depth did not improve soil test P performance compared with the 0‐ to 20‐cm depth.