Maize and Soybean Litter‐Carbon Pool Dynamics in Three No‐Till Systems

After harvest, the litter‐C pool contributes 20 to 23% of the total C present in maize ( Zea mays L.)‐based agricultural ecosystems. Therefore, understanding litter‐C pool dynamics is important in determining the overall C dynamics of the system and its potential to sequester C. We examined litter‐C production and in situ decomposition of maize and soybean [ Glycine max (L.) Merr.] litter using four annual litter cohorts (2001–2004) in three no‐till management regimes: irrigated continuous maize, irrigated maize–soybean rotation, and rainfed maize–soybean rotation. Litter inputs, i.e., litter‐C production, was 20 to 30% higher in irrigated fields than the rainfed field, and maize produced approximately twice as much litter C as soybean. Litter losses, i.e., decomposition, were highly variable, but overall, after 3 yr of decomposition, only 20% litter C remained on average. We fit decomposition models to our data to predict litter‐C accretion after 10 yr of management. While management and annual variation were important in fitting the model, tissue type increased model fit most, suggesting a strong role of litter physical structure in decomposition. The predicted 10‐yr standing litter pool was 15 and 35% higher in the irrigated maize field than the irrigated or rainfed maize–soybean rotations, respectively. Our data clearly show that the litter‐C pool is highly dynamic, with as much as a 60% increase within 1 yr. Thus, short‐term C sequestration estimates in agricultural ecosystems largely reflect litter‐C pool changes, which are primarily driven by litter inputs and not decomposition differences.