Impact of Nitrogen Vs Phosphorus-Based Manure and Compost Management on Corn Yield and Nitrous Oxide Emissions.

Shifting from N-based to P-based manure (liquid and composted) management can reduce P and K accumulation in the soil over time but also impact crop yield. Our objective was to evaluate the impact of a change from N-based applications without incorporation to a P- based (crop-removal) management system with immediate incorporation of manure on (i) corn grain yield and soil nitrate, and (ii) soil nitrous oxide (N₂O) emissions. A 2-yr field study was conducted in 2014 and 2015 with annual spring applications of two rates of composted dairy manure (34 and 90 Mg ha^-1), two rates of liquid dairy manure (93 and 160 kL ha^-1), and two inorganic N fertilizer rates (0 and 112 kg ha^-1) to corn. In 2015, the manure treatments were split with half of the plots receiving 168 kg N ha^-1 applied at sidedress time, to assess N limitation in P-based treatments. In 2014, the highest corn grain yields were obtained with N-based manure and optimum N rate (112 kg N ha^-1) applications (8.5 Mg DM ha^-1). Shifting from N-based to P-based management resulted in 5 and 3% yield decrease in manure and compost treatments, respectively. Corn grain yields ranged from 2.8 Mg DM ha^-1 in P-based compost to 6.1 Mg DM ha^-1 in optimum N rate. Low yields in P-based manure and compost treatments and significant yield increase with sidedress N addition suggested over-estimation of N availability from compost and ammonia conservation by immediate tillage-incorporation. Shifting from N- to P-based manure with tillage incorporation increased soil nitrate levels at planting and sidedressing in 2014 but not in 2015. 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 249 g N₂O ha^-1 yr^-1 (P-based compost) to 776 g N₂O ha^-1 yr^-1 (112 kg N ha^-1). In both years, soil N₂O emissions increased with corn grain yield reflecting yield increase with N addition. Our results suggest additional fertilizer N is needed to overcome N limitation in P-based management which will increase N₂O emissions as well.