Agro-Environmental Consequences of Shifting from Nitrogen- to Phosphorus-Based Manure Management of Corn

The relationships among corn (Zea mays L.) grain yield, N supply, and N2O emissions as influenced by a change from N-based surface applications of manure (no incorporation) to a P-based (crop removal) management system with immediate incorporation of manure were studied in 2014 and 2015. Treatments were annual spring applications of separated dairy solids (34 and 90 Mg ha(-1)), liquid dairy manure (93 and 159 kL ha(-1)), and two inorganic N fertilizer rates (0 and 112 kg ha(-1)). In 2015, half of each manure-amended plot received 168 kg N ha(-1) at sidedressing time to assess if yields were N-limited. Shifting from N-to P-based management resulted in 5 and 3% yield decreases in the manure and solids treatments, respectively. Corn yields and N uptake increased with N sidedressing in 2015, reflecting an N limitation in those treatments. Shifting from N-to P-based manure with tillage incorporation increased soil NO3-N levels at planting and sidedressing in 2014 but not in 2015, consistent with weather differences. Nitrous oxide emissions ranged from 216 g N2O ha(-1) yr(-1) (zero-N control) to 964 g N2O ha(-1) yr(-1) (112 kg N ha(-1)) in 2014 and from 249 g N2O ha(-1) yr(-1) (P-based solids) to 776 g N2O ha(-1) yr(-1) (112 kg N ha(-1)). In both years, soil N2O emissions increased linearly with N availability and, therefore, corn grain yield. Our results suggest that N2O emissions increase with yield when N is yield-limiting, independent of N sources.