Field‐scale evaluation of struvite phosphorus and nitrogen leaching relative to monoammonium phosphate

Abstract

Abstract Struvite (MgNH 4 PO 4 ·6H 2 O) is a wastewater‐derived phosphorus (P) fertilizer with potential to reduce P as well as nitrogen (N) losses due to its low water solubility. To test hypothesized lower P and N losses from struvite relative to monoammonium phosphate (MAP), field experiments with a randomized‐complete block design were conducted in central (Urbana) Illinois on an Endoaquoll‐Argiudoll complex and in southern (Ewing) Illinois on a Fragiudalf‐Hapludalf complex. Fertilizer was broadcast applied in the fall prior to spring planting of soybean ( Glycine max L.) at a maintenance rate of 29.5 kg P ha −1 (Urbana) and 22.0 kg P ha −1 (Ewing). In the spring, soil extractable N and Mehlich 3‐P at 0‐ to 15‐cm and 15‐ to 35‐cm depths were determined, and leached N and P were estimated using fall‐installed ion‐exchangeable resin (IER) lysimeters. At Urbana, soil extractable nitrate‐N was higher under MAP than struvite at 0‐ to 15‐cm depth. At Ewing, soil Mehlich 3‐P under struvite was lower than MAP at both depths. At Urbana, leached P was 10‐fold lower, and leached N was twofold lower under struvite than MAP. Soybean yields were similar between MAP and struvite at Urbana (4.1–4.3 Mg ha −1 ) and Ewing (3.2–3.5 Mg ha −1 ), but at Ewing yields were 23% higher under struvite compared to the P‐unfertilized control. Off‐season yield‐scaled P and N losses under struvite were lower than MAP by 51% at Urbana and by 10% at Ewing. Our results support the hypothesized potential of struvite to reduce nutrient losses while meeting crop P needs. Additionally, we identify disproportionally greater reductions in N leaching and yield‐scaled N losses by substituting struvite for MAP in fall applications, indicating that struvite can offer greater relative benefits for N loss reduction than P loss reduction.

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