Gone with the Wind: Soil Respiration Source Depending on Residue Placement in an Irrigated Corn System in Colorado

Soils have the potential to mitigate greenhouse gas emissions by storing carbon in the form of soil organic carbon (SOC). Conventional agricultural practices have decreased native soil organic carbon (SOC) stores, thereby releasing large amounts of the greenhouse gas, carbon dioxide. Agricultural practices that minimize soil disturbance, such as no-till (NT) have the potential to rebuild SOC, increasing soil health and decreasing greenhouse gas emissions. However, in some cases, NT paradoxically results in a decrease in SOC storage over time, suggesting that slower residue decomposition might not equate to more long-term SOC sequestration. To determine the relative importance of residue addition and disturbance on residue-C loss, we implemented 5 treatments with either no residue or ¹³C labelled residue applied to either the surface or incorporated into soils that were either disturbed (i.e., tilled) or undisturbed. Soil respiration fluxes were measured for the following 12 months and partitioned into residue- or soil-derived respiration. Results indicate that residue addition increased total carbon dioxide (CO₂) flux compared to no residue addition, disturbance did not affect total CO₂ flux, and incorporated residue-derived respiration was higher than that of the surface-applied residue. These results indicate that NT initially decreases residue decomposition and could increase soil health, but higher summer temperatures and delivery of irrigation water may change the magnitude and direction of these trends.