Key points to review Nitrous oxide – produced naturally in soils through both nitrification and denitrification Nitrification – aerobic conditions Denitrification –anaerobic conditions Biologically driven system Direct nitrous oxide emissions can be summarized by 3 factors: N inputs (ie, fertilizer and crop residues (both below and above ground)) N from organic matter decomposition (ie, carbon loss) N from manure deposited on grazed soils

In-field Direct Emissions - Fertilizers Organic (manure, legume) Nitrogen Fertilizer Mineral (commercial) Nitrogen Fertilizer N2O Emissions from Urine and Dung in Pasture

In-field Direct Emissions Crop residue and cover crops ( ABM = aboveground biomass) Nitrogen content of ABM Residue remaining post-harvest Nitrogen in crop residue Ratio of biomass belowground to aboveground (default values available – Alfalfa>wheat >corn>soybean) More below ground biomass, more emissions Nitrogen content of belowground biomass

Figure 1. Infield nitrous oxide emissions components at ARL (kg CO2 eq/ha/yr),

Questions from this slide set: From the slides presented describing sources of in-filed direct emissions of the different cropping systems, as well as the WICST management slide from last Thursday – how might you explain the differences observed in the modeled N2O emissions on the previous slide? How do these modeled results differ from the direct measurements outlined in Table 3?

In-field Indirect Emissions Leaching or volatilization of N CO2 from change in SOC CO2 from urea volatilization Can be eliminated by using other N fertilizer