Nitrification Inhibitor Impacts Soil Trace Gas Emissions and Nitrogen Cycling.

Losses of applied N fertilizers from agronomic fields represent both an economic loss and an environmental quality concern.  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 N2O, NH3, CO2, and CH4 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 N2O, NH3, CO2, and CH4 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.