Effect of dual applied phosphorus and gypsum on wheat forage and grain yield

Winter wheat (Triticum aestivum L.) production on acid soils can be greatly affected by reduced phosphorus (P) availability. At low pH (below 5.5), iron (Fe) and aluminum (Al) react with P to form highly insoluble compounds that severely reduce the amount of plant available P. Previous research suggested that supersaturating localized P fertilizer bands with respect to Ca²⁺ could induce precipitation of applied P as dicalcium phosphate (DCP) or dicalcium phosphate dihydrate (DCPD) which would slowly become plant available with time. The objective of this study was to determine the effect of dual‐band applications of P and gypsum on winter wheat forage and grain yield. Methods of application included P and gypsum banded with the seed, P and gypsum broadcast, and P banded and gypsum broadcast at rates of 29 and 58 kg P ha^‐1 and 22 and 44 kg S as gypsum ha^‐1. Sources of P included diammonium phosphate (DAP; 18–20–0) and triple superphosphate (TSP; 0–20–0). Grain and forage yields increased when P was applied. Dual‐band applications of P and gypsum increased wheat grain and forage yields compared to P banded without gypsum, and P banded and gypsum broadcast. When DAP was the P source, the N‐P band reduced yields compared to P banded alone or the N‐P‐gypsum band. This suggests that gypsum should be included in the band for maximum benefit. Precipitation of DCPD and DCP may have taken place within the dual P‐gypsum band, reducing fertilizer P fixed as Fe or Al hydroxides thus increasing long‐term P availability for winter wheat forage and grain production on acid soils.