Potentially significant amounts of sulfate‐S found in phosphorus fertilizers

Abstract

The occurrence of S deficiency in Midwest crops in the past 20 years is likely a result of the consistent decline of atmospheric S deposition during this time period. In the absence of intentional S fertilization, crops utilize SO4‐S mineralized from soil organic matter and potentially also the incidental application of S in non‐S fertilizers. Based on the analysis of hundreds of P fertilizer samples in 2021 and 2022 we found monoammonium phosphate (MAP), diammonium phosphate (DAP), triple superphosphate (TSP), and ammonium polyphosphate (APP) had SO4‐S concentrations of 1.88 ± 0.35, 1.80 ± 0.30, 1.66 ± 0.27, and 0.61 ± 0.18% SO4‐S (mean ± standard deviation). If MAP, DAP, and TSP are applied to replace P removal of average yielding corn (Zea mays L.) and soybean (Glycine max L.) crops grown in rotation, SO4‐S applied by MAP, DAP, and TSP at median and 3rd quartile values would be 4.0 to 4.6 lb SO4‐S acre−1, approximately equivalent to ∼42 to 52% of the S removed in the grain of a single crop. If used as a starter fertilizer (5 gal acre−1) APP would apply <0.4 lb acre‐1, <4% of grain S removal. The crop availability of SO4‐S in P fertilizers is conditional on the timing of their application relative to crop need, soil properties, and rainfall in addition to the amount of S applied. The contribution of P fertilizers to S cycling in environmental studies should also be considered.This article is protected by copyright. All rights reserved