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

Abstract

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 13C abundance method can be used to determine the flow of C from C4 residues and soil organic matter (C3-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 13C 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 13C 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 13 C 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 13C abundance method could determine the degree of ‘priming effect’ in soils amended with C4-C residues.