Low-cost CO₂ sensors reveal seasonal and management-driven soil carbon fluxes in a Mediterranean agroecosystem

Soil is the Earth’s second-largest carbon sink, and understanding soil carbon dynamics is critical for sustainable climate mitigation. Monitoring soil gas emissions offers an effective way to track changes in soil carbon storage driven by climate and agricultural practices. This study assessed seasonal soil CO₂ efflux from 5 ha of agricultural land in Merced, California, a Hot-Summer Mediterranean climate region, as it transitioned from flood-irrigated pasture to sprinkler-irrigated cropland. Five distinct land management events or practices were examined: flood irrigation, pasture grazing, soil disking, rainfed winter forage cultivation, and sprinkler-irrigated row cropping. We hypothesize that efflux regimes are primarily driven by seasonal changes in soil moisture, temperature, and vegetation and that land management activities will restructure these conditions to produce distinct efflux responses. Efflux rates were measured using low-cost portable CO₂ sensors during synoptic sampling campaigns from Summer/Fall 2022 through Fall 2024. The highest mean CO₂ efflux occurred during flood (5.1 µmol m⁻² s⁻¹) and sprinkler irrigation (3.5 µmol m⁻² s⁻¹), approximately 2–4× greater than during disking, pasture, or cultivation periods. Ordinary least squares regression identified soil moisture as the strongest predictor of efflux (β = 5.91, p < 0.001), followed by vegetation cover (β = 2.92, p < 0.001), and soil temperature (β = 0.04, p < 0.043). Unsupervised cluster analysis grouped observations into three distinct seasonal regimes: (1) Winter (Pasture), (2) Summer (Flood), and (3) Fall (Disking, Pasture, and Sprinkler). These results mainly supported our hypothesis advancing the understanding of how seasonal and management-driven factors shape carbon cycling in Mediterranean agroecosystems and inform practical strategies for monitoring and managing CO₂. • Multi-year soil CO 2 efflux study in a Mediterranean agroecosystem • Low-cost CO 2 efflux systems enabled high-resolution, field-scale data acquisition • Soil moisture, temperature, CO 2 efflux, and NDVI data across five management events • Soil moisture was the dominant CO 2 efflux predictor across management actions • Seasonal conditions structured CO 2 efflux with management modulating responses