Abiotic efflux of CO₂ from soil is often attributed to dissolution of carbonates, and therefore not expected to occur in soils with a low pH. However, another abiotic source of CO₂, less constrained by pH, may arise from reactions that oxidize natural soil organic matter and reduce metal oxides. Studies of redox reactions between phenolic compounds and Fe and Mn oxides in soil have been focused mainly on the environmental fate of both oxidants and reductants and formation of organic matter. We measured CO₂ formed during 3-hour, room temperature (22±2 ^oC), incubations of samples of archived soils and from an ongoing crop diversity study. Subsamples (8 g. ODE) of each soil, were treated (5 ml) with water, or solutions of glucose (0.029 M), or gallic acid (0.025 M). For each soil, subsamples amended with H₂O or with the glucose solution produced little CO₂ and were nearly identical to each other, while CO₂ quickly formed after treatment with gallic acid regardless of pH. The net increase in CO₂ due to gallic acid, observed from the 18 archived soils, ranged from less than 0.5 to more than 80 mg CO₂-C kg^-1 soil. Significant treatment effects were observed in samples from the crop diversity study with more (Tukey’s P≤0.05) net CO₂ from a small grain-fallow treatment compared a 5-year rotation treatment, 19.04 and 15.77 mg CO₂-C kg^-1 soil, respectively. This study suggests abiotic reactions capable of rapidly producing a burst of CO₂ can occur in a wide range of soils following inputs of simple phenolic compounds and be impacted by management regimes. We suggest these are redox reactions in soil linked to Mn or Fe metal oxides and when considered together with fluctuations of carbon inputs to soil and redox cycling, might be a larger contributor to C emissions than previously accounted for.