Short-term mineralization of maize residues in soils as determined by carbon-13 natural abundance

Studies of soil organic matter equilibria must include estimates of C turnover. The objective of this study was to provide data on how the natural C-13 abundance method can be used to determine the flow of C from C-4 residues and soil organic matter (C-3-source) in a short-term incubation. Corn residue was added at a rate of 5.7 mg C g(-1) soil to two soils, a clay and a sandy clay loam. During the course of a 35-day incubation in a CO2-free system, CO2-C and C-13 natural abundance of the respired CO2 were measured. About 20% of the corn residue-C added was mineralized in both soils as determined from the CO2 respired and the C-13 natural abundance of the respired CO2. Mineralization of the added residues was also calculated as the difference of the total amount of the respired CO2-C between the control and the corn residue-treated soils divided by the total amount of corn residue-C. Values were 35% for the clay soil, and 30% for the sandy clay loam soil. The difference in values calculated from the C-13 natural abundance and the difference method was due to mineralization of the indigenous soil organic C resulting from the addition of corn residues. Use of the natural C-13 abundance method could determine the degree of `priming effect' in soils amended with C-4-C residues.