Soil-climate feedback loops identified between precipitation variability and soil N2O and CH4 fluxes in switchgrass

Grant Falvo (1), Carmella Vizza (1, 2), Sarah Roley (2), G. Philip Robertson (1)
1 Michigan State University, W.K. Kellogg Biological Station, Hickory Corners, Michigan. 2 Washington State University, School of the Environment, Richland, Washington.

Presented at the All Scientist Meeting and Investigators Field Tour (2021-09-23 to 2021-09-23 )

Changing precipitation regimes may alter the net exchange of greenhouse gases from agricultural soils. This may in turn produce positive, or negative climate-soil feedback loops. This study evaluated the net exchange of N2O and CH4 from unfertilized soils planted to Panicum virgatum in Southwest Michigan, measuring responses to four different precipitation regimes. Using rainout shelters equipped with irrigation systems, equal amounts of precipitation were applied either once every three days, once every twenty days or once every thirty days. An ambient precipitation treatment was maintained as a reference. Static gas flux chambers were installed in each treatment, with four replicates arranged in blocks. Fluxes were measured weekly, as well as before and after irrigation events. Precipitation regimes significantly influenced N2O and CH4 fluxes, especially in the days before and after irrigation events. Soil CH4 fluxes were generally negative (i.e. net sink), and increasing time between irrigation events strengthened the CH4 sink. Soil moisture at the time of gas sampling predicted CH4 fluxes, with drier soils having stronger sink strength than wetter soils. N2O fluxes were variable, with some fluxes immediately post-irrigation being higher or lower in the twenty- and thirty-day interval treatments. Cumulative CH4 fluxes for the study period were more negative in the treatments that had longer periods between irrigation events, while cumulative N2O fluxes were more positive. When expressed in 100-year radiative forcings, N2O dynamics overshadowed the CH4 dynamics. Thus, precipitation regimes with more time between rainfall events may result in greater contributions to global climate change.