Carbon Mineralization from Winter Cereal Cover Crops in an Organic No-till Soybean Production System.

Selection of crop and management practices greatly influence the balance of soil organic carbon in the agricultural soils. Cover crops not only supply organic carbon but also play an important role in maintaining long-term sustainability by weed suppression, nutrient supply, and improving soil physical structure. However, limited information is available on the impact of cover crops on carbon inputs and cycling in organic cropping systems. We conducted field and laboratory incubation studies to estimate the carbon mineralization rate of winter cereal cover crops. We hypothesized that the organic matter decomposition and carbon mineralization rates may vary among winter cover crops depending on the amount and composition of residues. Five cereal cover crops (Haybet barley, TAM exp. oat, Elbon rye, Glenn hard red spring wheat, and Fannin hard red winter wheat) and a cereal-legume combination (Rye- hairy vetch) were planted in early November and terminated on early April using a roller-crimper prior to planting soybean under organic management. Polyester mesh litterbags (30x30 cm²) with three different residue rates (0.5x, 1x, and 2x) were used in the field experiments. Cover crop residues were also used in a laboratory incubation study for 180 days to estimate the carbon mineralization rate in a controlled environment. Carbon dioxide (CO₂) evolved during the incubation period was measured periodically using a LICOR 840A CO₂/H₂O gas analyzer. Faster rate of decomposition was observed for rye-vetch and TAM exp. oats residues in the litterbag experiment. Residue weight was reduced by 50% in the first 50 days and 64% tissue lignin was decomposed in 112 days. Higher residue rates took a longer time to mineralize and increased the carbon in active and slow release pools.