33P‐isotope labelling ammonium phosphate fertilizers reveals majority of early growth maize phosphorus is soil‐derived

Abstract

AbstractIn soils managed to have adequate to high Mehlich‐3 phosphorus (P) concentrations throughout the US Maize Belt, the majority of crop P is soil‐derived. Struvite, a low water solubility ammonium phosphate fertilizer, may be therefore substituted for relatively high water‐soluble monoammonium phosphate (MAP) without adversely impacting maize (Zea mays L.) P uptake and growth, while minimizing fertilizer P loss risk. We determined the relative contribution of struvite and MAP to maize P uptake and soil solution P in soils representative of the US Maize Belt by radiolabelling fertilizers with 33P. We found 8% (struvite) to 22% (MAP) of early‐to‐mid vegetative growth stage (V7) maize P was fertilizer‐derived, and thus, 78%–92% was soil‐derived. Despite similar aboveground P uptake and maize growth, maize P use efficiency (PUE) determined directly by 33P was <5% for MAP (4.9%) and struvite (1.9%) indicating that in soils with adequate to high crop‐available P, early season fertilizer PUE is relatively low. If prorated to harvest stage, in‐season PUE was estimated to be 8% for struvite and 20% for MAP. MAP and struvite did not differ in relative contributions to water‐extractable P, a proxy for P loss risk, potentially reflecting lag effects in struvite P dissolution and/or the relatively fine particle size of synthesized fertilizers (<0.1 mm diameter). Since maize aboveground biomass and P uptake were similar for both struvite and MAP, struvite could be an effective P fertilizer for soils with adequate to high Mehlich‐3 P concentrations common across the US Maize Belt.