Wheat straw management affects CH4 and N2O emissions from rice fields

A 3-year field experiment was conducted in Jiangsu Province, China from 2004 to 2006 to investigate CH4 and N2O emissions from paddy fields as affected by various wheat straw management practices prior to rice cultivation. Five methods of returning wheat straw, no straw, evenly incorporating, burying straw, ditch mulching and strip mulching, were adopted in the experiment. Evenly incorporating is the most common management practice in the region. Results showed that compared with no straw, evenly incorporating increased CH4 emission significantly by a factor of 3.9–10.5, while decreasing N2O emission by 1–78%. Methane emission from burying straw was comparable with that from evenly incorporating, while N2O emission from burying straw was 94–314% of that from evenly incorporating. Compared with evenly incorporating, CH4 emission was decreased by 23–32% in ditch mulching and by 32% in strip mulching, while N2O emission was increased by a factor of 1.4–3.7 in ditch mulching and by a factor of 5.1 in strip mulching. During the rice-growing season, the emitted N2O was negligible compared to that of emitted CH4. No significant difference in grain yield was observed between ditch mulching, burying straw, evenly incorporating and no straw. Compared with no straw, the grain yield was increased by 27% in strip mulching. Based on these results, the best management practice for returning wheat straw to the soil is strip mulching wheat straw partially or completely onto the field surface, as the method reduced CH4 emission from rice fields with no decrease in rice yield.