Decomposition rates of plant residues under different land uses

-1 (dry weight) were incubated in laboratory, in triplicate. CO 2 emitted from soil was measured after 20, 40, 60, and 80 h of incubation, and the amount of released C was calculated (mg C g -1 soil). The difference between the amount of C added by the plant residue and C liberated as CO 2, was named residual C. The C loss was greater and residual C retained was lower (p<0.05) for Alfisols where alfalfa was applied than for those were wheat straw was added, which was a function of the biochemical composition differences between the alfalfa and wheat straw residues. Regarding the land use, residue C loss was lower (p<0.05) in woodland ( Haematoxylon campechianum and Bucida buceras ) soils (rates from -0.12 to -1.02 µg g -1