Effect of patterns of straw returning to field on methane and nitrous oxide emissions during rice-growing season in a rice-wheat double cropping system
Although straw returning of rice is a primary way of straw utilization, excessively returning not only affected the crop growth but also went against the eco-logical environmental protection of farmland. The objective of the study was to estimate the flux of methane (CH_4) and nitrous oxide (N_2O) emission in a rice-wheat double cropping system influenced by different patterns of straw returning to field. A six-year field experiment was conduc-ted in Suzhou, Jiangsu province, and straw returnings to field were set as rice straw returning (R), wheat straw returning (W), both rice and wheat straw returning (RW) and no straw returning (CK) treatments. The methan and nitrous oxide emissions were measured by static chamber-gas chromato-graphic technique. The results showed that total CH_4 and N_2O emissions, global warming potential (GWP) and GWP per unit yield were significantly influenced by patterns of straw returning to field. Total CH_4 emissions followed the order of RW (233. 04 kg/hm~2) > W (197. 99 kg/hm~2) > R (122. 14 kg/hm~2) > CK (97. 07 kg/hm~2). Total N_2O emissions were R > W > RW > CK. Compared with CK, RW (10. 54 t/hm~2) and R (10. 36 t/hm~2) significantly increased grain yield. Seasonal global warming potentials (GWPs) of CH_4 and N_2O and GWPs per unit grain yield were higher in R, W and RW plots than those in CK plots. These results indicate that straw returning to field boosted CH_4 and N_2O emissions and wheat straw returning to field played a key role in increasing CH_4 emission.