Abstract

We evaluated the mode of decomposition in relation to biochemical quality of plant residues and land use. Alfisols under different uses (woodland, grassland and cultivated soils) mixed with alfalfa (Medicago sativa L.) and wheat straw (Triticum aestivum L.) in doses of 10 t ha^-1 (dry weight) were incubated in laboratory, in triplicate. CO₂ 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 CO₂, 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 /day), and greater in grassland (Gramineae) and cultivated soils (Sorghum vulgare and Yucca sp.) (rates from -0.28 to -1.37 µg g^-1 /day). We conclude that the C loss, by decomposition, increases in order of woodland > grassland > cultivated soils, and less residual C is retained.

Key words: Organic matter, organic wastes, alfisols, land use, soil respiration.