Greenhouse Gas Fluxes As Affected By Urea Fertilizer, Nitrification Inhibitor, and Biomass Sorghum Residue Application to Soil.

A portion of nitrogen (N) fertilizers applied for crop production may be lost via leaching or gaseous emissions.  Nitrification inhibitors are designed to inhibit nitrification, the microbial conversion of ammonium to nitrate, a highly mobile form of N most prone to loss. The objectives of this study were to determine the impact of nitrapyrin on NH₃, N₂O and other greenhouse gas (GHG) emissions as well as the effects of biomass sorghum residue on the efficiency of the nitrification inhibitor and nutrient cycling. A greenhouse study was designed to quantify gas fluxes from soils amended with N fertilizer, nitrification inhibitor, and sorghum residue. Experimental treatments included every combination of the treatment scenarios with or without urea N fertilizer, Instinct II^© nitrification inhibitor, and sorghum biomass residue, with 3 replications. Each treatment was mixed with Weswood silty clay loam soil and then added to the top 15 cm of a 30-cm PVC column, which contained unamended soil in the lower portion. Emissions of CO₂, N₂O, CH₄, and NH₃ were measured with a mobile-FTIR gas analyzer integrated with a LI-COR chamber twice a week for 5 weeks then once a week for an additional 3 weeks. Gas measurements were taken at the same time of day over the 59 day period and soil samples were collected at days 0, 7, 14, 28, and 59 for NH₄ and NO₃ analysis. Treatments with sorghum residue significantly increased cumulative CO₂ emissions while reducing NH₃ emissions over those without residue. Nitrapyrin treatments showed significantly less cumulative N₂O emissions, but significantly more NH₃ and CO₂ emissions than treatments without the inhibitor. Treatments with N fertilizer exhibited increased N₂O, NH₃, and CO₂ emissions. These results provided valuable information on how nitrification inhibitors and bioenergy crop residues influence C and N cycling and GHG losses.