Hotspots of Nitrous Oxide Emission in Fertilized and Unfertilized Perennial Grasses

Hotspots of nitrous oxide (N2O) emission are thought to contribute substantially to annual emissions from agricultural soils. We observed N2O fluxes from fertilized and unfertilized C-3 and C-4 perennial grasses on a wet silt loam soil in New York, United States during the growing season in 2013, 2014, and 2015 using static chambers. Analysis of N2O hotspots within the research plots revealed that hotspots contributed between 34.3 and 39.1% of the total emissions, and constituted between 0.8% and 5.0% of all flux observations. Hotspots were more frequent and of greater magnitude in the fertilized treatments, and occurred when soil temperature was greater than 9.1 degrees C and soil moisture was between about 40% and 80% water filled pore space (WFPS). A single chamber location in the fertilized switchgrass treatment was consistently a hotspot for N2O emission, suggesting that hotspots maintain a stable spatial pattern over extended periods. The maximum magnitude of N2O hotspot emission exhibited a relationship to soil temperature that is similar to that of the microbial growth rate constant.