南方双季稻田稻草还田的碳汇效应

利用长期稻草还田定位试验和短期不同稻草还田模式试验，研究稻草还田对南方双季稻田土壤固碳、甲烷排放和综合碳汇的影响.结果表明： 稻草还田能增加土壤有机碳，长期还田的耕层土壤碳汇年增长率为0.07 t C·hm^-2·a^-1，土壤有机碳的表观转化率随着稻草还田量的增加而减少.稻草还田导致稻田甲烷排放量显著增加，其中，NPK添加稻草（NPK+RS）处理早、晚稻期间甲烷排放通量比仅施NPK分别增加了75.0%和251.5%（P<0.01）.稻田甲烷排放随着稻草还田量的增加而增加，在水稻产量和耕作方式相近的条件下，稻草（茬）的甲烷表观转化率接近.综合土壤固碳和甲烷排放的稻田净碳汇，NPK+RS处理负碳汇效应显著，基本与其水稻生物固碳接近，比稻草不还田处理（NPK）增加158.3%；不同还田模式中，稻草覆盖免耕处理能显著减少甲烷排放，其净碳汇（负值）比高桩翻耕处理减少50.9%，有利于水稻高产稳产.

Carbon sequestration effects of rice straw return in double season paddy field in Southern China

In a long-term site-specific experiment with rice straw return (RSR) and in a short-term experiment with different RSR modes, this paper studied the effects of RSR on the soil organic carbon (SOC) sequestration, methane emission, and net carbon sink in a double season paddy field. RSR increased the SOC content, and the annual increasing rate of soil carbon sink in plow layer (0-15 cm) under long-term RSR was 0.07 t C x hm(-2) x a(-1). With the increasing amount of RSR, the apparent SOC transformation rate decreased. RSR promoted the methane emission from the paddy field significantly, and the methane emission flux in treatment RSR plus NPK during early- and late rice growth seasons increased by 75.0% and 251.5% (P < 0.01), respectively, compared with that in treatment NPK. The methane emission increased with the increasing amount of RSR. Under the similar tillage mode and rice yield, the rice straw returned had the similar apparent methane transformation rate. Considering the soil carbon sequestration and the net carbon sink after methane emission in the paddy field comprehensively, treatment RSR plus NPK had significant negative effect on the carbon sink which was basically approached to the bio-fixation of carbon by rice and increased by 158.3%, as compared with treatment NPK. Among different RSR modes, rice straw mulching plus no tillage decreased soil methane emission significantly, with the net carbon sink decreased by 50.9% as compared with the treatment high stubble plus tillage, and benefited the high and stable yielding of rice.