Nitrate Leaching and Nitrous Oxide Emissions from Fall Applied Manure and Phosphorous Fertilizers in Southern Illinois

Illinois nutrient loss reduction strategy is questing to reduce nitrate-N (NO₃-N) and phosphorus (P) loss by 25 and 15% by 2025. Fall applied ammonium-based P fertilizers could result in both NO₃-N and phosphate loss during the fallow period. Two ways to minimize these losses are by utilizing nitrification inhibitors and also assessing other sources of P including triple superphosphate (TSP) and dissolved air flotation (DAF) that separates solids from liquid manure. A four-times replicated experiment was initiated in fall 2023 with Randomized Complete Block Design and five treatments in Agronomy Research Center, Carbondale, IL. Treatments were fertilizers [Control, TSP, DAF (Dissolved Air Flotation), MAP, & MAPI (MAP + urease and nitrification Inhibitor)], timing (fall & spring) and application type (surface & tilled). Data on nitrous oxide emissions, moisture, temperature, NO₃-N leaching, and soil N were recorded during fall and spring prior to planting of corn (Zea mays L.) and agronomic observations (plant height, LAI & NDVI) were recorded on corn in fall. Soil N₂O-N emissions were higher in MAPI and DAF during early February and late April dates, which can be explained by N availability along with high moisture and high temperatures, respectively during those sampling dates. Over winter and spring, MAPI had consistently higher NO₃-N, NH₄-N and total N especially in the late sampling dates and leaching losses were less under DAF (23% and 34%, respectively) and TSP (56% and 63%, respectively) compared to MAP or MAPI, suggesting that nitrification inhibitor did not reduce leaching from MAP source when applied in fall. Corn growth was slightly higher under DAF compared to other fertility treatments indicating it can be a potential replacement to the synthetic P fertilizers.