Greenhouse Gas Emissions from Nitrogen- Vs Phosphorus-Based Manure and Compost Management of Grain Corn.

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), methane (CH₄), and carbon dioxide (CO₂) emissions. A field study was initiated in 2001 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. The field was rotated to alfalfa in 2006 (no further nutrient addition) and back to corn in 2010 when the manure, compost and inorganic N treatments were continued. Greenhouse gas emissions were initiated in 2014 and continued in 2015. In 2014, highest dry matter (DM) yields were obtained with N-based manure and optimum N rate (112 kg N ha^-1) applications (8.5 Mg 100% DM ha^-1). Shifting from N-based to P-based management resulted in 5 and 3% yield decrease in manure and compost treatments, respectively. Shifting from N- to P-based compost increased CH₄ uptake by 53% whereas methane uptake remained unchanged with a shift from N- to P-based manure. A shift from N- to P-based compost did not impact soil nitrate levels. However, shifting from N- to P-based manure with tillage incorporation increased soil nitrate levels at planting and harvesting by 17 and 45%, respectively. Nitrous oxide emissions ranged from 216 g N₂O ha^-1 growing season^-1 (zero N control) to 964 g N₂O ha^-1 growing season^-1 (112 kg N ha^-1). A shift from N-based to P-based manure and compost resulted in 29 and 43% lower N₂O emissions, respectively. However, across all treatments, corn grain yield and N₂O emissions were positively and linearly related (r²= 0.94; P≤0.001) reflecting a 400 g N₂O ha^-1 growing season^-1 emission per Mg DM yield. These results suggest that a shift from N- to P-based management reduces N₂O emissions and grain yield at the same time. If these results reflect N limitations to growth in the P-based treatments, additional fertilizer N could be needed for P-based management, increasing not only the yield but also N₂O emissions. Research is ongoing (2015 growing season) to evaluate if additional N in the P-based treatments can enhance yield.