Decomposition of rice straw residues and the emission of CO<sub>2</sub>, CH<sub>4</sub> under paddy rice and crop rotation in the Vietnamese Mekong Delta region - A microcosm study

Abstract

This study investigated the influence of soil undergoing different crop rotations on the CH<sub>4</sub>, CO<sub>2</sub> emissions, and decomposition of rice straw. The studied soil undergoing crop rotation systems were rice-rice-rice (SR) and baby corn-rice-mungbean (SB). Two main microcosm set-ups: anaerobic (SR-AN, SB-AN) and aerobic (SR-AE, SB-AE) conditions. Litter bags containing rice stems were inserted into the soil and recollected at different time points for chemical analysing and the gas sampling was collected to measure the CO<sub>2</sub> and CH<sub>4</sub> emissions. The results indicated that the total carbon (TC) decreased around 30%, and the TC removal in anaerobic was significantly higher than in aerobic conditions. The residue cellulose content varied in a range from 68.2% to 78.6%, while the hemicellulose content varied from 57.4% to 69.3% at day 50 after incorporation. There were no significant differences in the total nitrogen removal, cellulose, hemicellulose, and lignin contents among the microcosm set-ups. CO<sub>2</sub> emission increased in all the microcosm set-ups with the treatments without rice straw (CTSR, CTSB) in both aerobic and anaerobic conditions. CH<sub>4</sub> release in the SR-AN treatments did not differ significantly compared with the SB-AN treatments. This study confirmed that the decomposition of rice straw residues is faster in the anaerobic paddy soil condition compared to the aerobic crop rotation condition.