Effects of Burning of Sugarcane and Maize Residues on Different Forms of Carbon in Some Soils of Khuzestan Province

Burning of crop residues has adverse impacts on soil and environment. Limited information is available about the effects of crop residue burning on different forms of soil carbon. A factorial experiment with a complete randomized design was conducted to evaluate the effects of burning of sugarcane, and maize residues and different sampling depths as experimental factors on different forms of organic carbon including microbial biomass (MBC), permanganate-oxidizable (POX), total organic carbon (TOC), fine particulate organic carbon (FPOM) and coarse particulate organic carbon (CPOM) in some soils of Khuzestan Province. Composite soil samples with three replications were taken from 0-5, 5-15, and 15-30 cm depths in 5 points of the selected two sugarcane and two maize farms before and after burning of the plant residues. According to the results, the amounts of TOC (from 7.2 to 9.0 g kg-1 in maize and 13.2 to 14.2 g kg-1 in sugarcane farms), CPOM (from 1.4 to 1.6 g kg-1in maize and 2.7 to 2.85 g kg-1in sugarcane farms) and FPOM (from 2.3 to 3.1 in maize and 3.8 to 4.5 in sugarcane farms) were significantly increased in the soil 0-15 cm depth, due to the burning of both crops residues. The results also indicated that the burning of residues decreased the amounts of MBC (from 155 to 123 mg kg-1in maize and 112 to 65 mg kg1in sugarcane farms) and POX (from 240 to 209 mg kg-1in maize and 362 to 315 mg kg-1in sugarcane farms) in the soil 0-5 cm depth. Also, the MBC and POX values in 5-15 and 15-30 cm depths were lower than those in 0-5 cm depth of the soil. However, burning of the sugarcane and maize residues had no influence on the amounts of MBC and POX parameters. The results also implied that the amounts of TOC, MBC, POX, FPOM and CPOM were affected by the type of residues. Accordingly, the TOC, POX, FPOM and CPOM values were higher in sugarcane farms, but maize farms showed higher amounts of MBC (128.7 mg kg-1 vs. 60.8 mg kg-1).