Dairy farmers often surface apply phosphorus (P)-based liquid manure to corn (Zea mays L.) for silage, supplementing with N fertilizers to reach optimum corn nitrogen (N). This optimizes crop production while decreasing P loss to the environment. However, injecting manure may further conserve losses and reduce the need for synthetic N fertilizer. An experiment was conducted on a dairy farm located in Breese, IL from May 2019 to April 2022 with two main treatments including (i) surface application of manure at P-based rate supplemented with 123 kg ha-1 synthetic N and (ii) manure injection at P-based rate supplemented with 17 kg ha-1 of synthetic N fertilizer. Both treatments delivered a total of 201 kg N ha-1 to meet corn N need based on current extension guidelines. Our results indicated that yield and quality of silage corn and cereal rye were similar in both treatments. This suggests that injection can limit losses of the ammonium-N fraction of the manure and decrease the need for supplemental N fertilizer by 106 kg ha-1, which translates into up to $150 ha-1, while not affecting the quality and quantity of yields. Moreover, the effect of manure injection on soil test P (STP) was similar to that of surface application and did not increase STP over a three-year period. Elevated STP in high P-supplying soils can be an environmental concern for using manure, but our results show that neither treatment increased STP. Future research should focus on quantifying N loss through denitrification and leaching when manure is injected versus surface applied to provide a more holistic overview of the soil and environmental impact of each system.
