Decomposition of rice straw and microbial carbon use efficiency under different soil temperatures and moistures

The management of crop residues has become an important aspect of sustaining long-term fertility in cropping systems. Incorporation of crop residues can change microbial processes, which affect nutrient availability and hence crop yield. Carbon (C) use efficiency by soil microorganisms during rice straw decomposition was determined in a rice paddy soil, under aerobic and anaerobic (flooded) conditions at different temperatures (5, 15, and 25°C). Flooding had a tendency to reduce C mineralization and enhance methane (CH4) production; however, with decreasing temperature CH4 production became negligible. Our study showed that anaerobes recycled fermentation waste products during the long-term incubation resulting in a lower net residue-C mineralization in flooded systems compared to non-flooded conditions. As a result, we observed similar microbial production under flooded and non-flooded conditions even though anaerobes decomposed less straw-C than aerobes. These results indicate that a significant amount of decomposition occurred under flooded conditions, but because substrate use efficiency was higher, less straw-C was mineralized compared to aerobic conditions. Kinetic analyses of C mineralization curves confirmed that the C mineralized in the flooded treatment was mainly from labile pools with significant amounts coming from more recalcitrant pools, such as cellulose and lignin depending on temperature. The results are discussed in relation to nutrient availability in rice cropping systems.