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.