Field-scale evaluation of struvite phosphorus and nitrogen leaching potential relative to monoammonium phosphate.

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 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 at two locations, on a Endoaquoll-Argiudoll complex (Urbana, IL) and a Fragiudalf-Hapludalf complex (Ewing, IL). 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 0-15 and 15-35 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 the 0-15 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 2-fold 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 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 may offer greater relative benefits for N loss reductions than P loss reductions. This article is protected by copyright. All rights reserved.