Influence of Enhanced Rock Weathering on Carbon Dioxide (CO2) and Nitrous Oxide (N2O) Emissions Following Soil Rewetting in a Southern California Cropland

Enhanced rock weathering (ERW) is a climate change mitigation technology that has been proposed to capture inorganic carbon (C) in soils and catalyze negative C emissions at large scales. ERW involves the application of finely crushed silicate rock minerals to soils to increase the weathering rate and maximize soil as a natural, long-term CO2 sink. It is currently unknown if, and to what degree, ERW may influence soil health and C storage. Co-deployment of inorganic and organic amendments, such as compost and biochar, may also impact the ability of soils to sequester C, but those potential synergies have not yet been explored. In addition to soil C pools, greenhouse gas (GHG) emissions represent key C budget components needed to quantify the net movement of C and nitrogen (N) in or out of a system. Southern California croplands represent significant sources of GHG emissions and undergo frequent drying-rewetting events, with soils remaining dry throughout the summer and rewetting during winter. These events induce significant and rapid pulses of GHG emissions immediately following rewetting, likely due to increased soil heterotrophic respiration and stimulated microbial activity. We studied soil GHG emissions at the field scale following rewetting irrigation events in two crop types. In February 2022, we measured CO2 and N2O emissions at a field trial of furrow irrigated corn (Zea mays) and flood irrigated alfalfa (Medicago sativa) in Imperial Valley, CA. Measurements were taken daily for two weeks following irrigation. The treatments included no amendment, crushed meta-basalt rock, and a combination of rock and organic amendments (compost, and biochar). Continuous GHG measurements were taken from closed, dynamic soil chambers using a Picarro G2508 Cavity Ring-Down Spectrometer. During GHG measurements, we took auxiliary measurements of soil and air temperature, soil moisture, pH, and extractable N. Our results indicate that rock amendments, alone and in combination with compost and biochar, significantly decreased N2O emissions in corn plots. We also found that combination treatments decreased CO2 emissions in corn. These results highlight the potential of EWR as a C sequestration and climate change mitigation tool in California croplands.