Effect of crop type and cultivar surface area on rates of decomposition in soils

Sustaining the productive capacity of soils has raised interest in the maintenance of soil organic matter through management practices and use of crop residues. While the impact of management practices has been studied, little is done to understand how the charateristics of the residue itself impact the decomposition at the soil surface. This study relates the chemical composition and the surface area of the aboveground residue to the decomposition rates for three cultivars each of three crops: cotton, peanut and sorghum. The rates were determined by mass loss. Change in the residue specific surface area to mass loss was also measured. Findings show that after 14 days, the aboveground residue for the three crops were from the most rapid loss to the slowest: cotton (43%) > peanut (32%) > sorghum (24%). Changes in the specific surface area-to-mass ratio were from the slowest to the most rapid loss: cotton (1.60×10-4) > peanut (1.50×10-4> sorghum (1.20×10-4). Since varietal differences within crops have led to variation in decomposition rates, cultivars with slower decaying residues might be recommended for C sequestration and for erodible lands in semi-arid zones of the Sahel. Likewise, crop residues with faster decomposition rates can be recommended for soil fertility improvement. Key words: Decomposition rate, crop type, crop residue, chemical composition, specific surface area-to-mass ratio.