Combined effects of straw and water management on CH4 emissions from rice fields.

Water and organic amendments are the two most important factors that control methane (CH4) emissions from rice fields, the combined effect of which on CH4 emissions has been rarely studied. Thus, a field experiment in a split-plot design was conducted to investigate the combined effect of straw and water management on CH4 emissions. Main plots had water treatments: continuous flooding (CF), flooding - midseason drying - flooding (FDF), and flooding for transplanting - rainfed (RF); and subplots had straw treatments: straw incorporated into soil (SI), straw mulching (SM), and without straw. Results showed that the presence of water layer led to substantial increase in CH4 emissions which were enhanced by straw application. Cumulative CH4 emissions were influenced by water, straw, and their interactions significantly (P < 0.05). The cumulative CH4 emissions were 505.3, 241.2, and 56.5 kg ha-1 for CF, FDF, and RF, respectively. By contrast, SI under CF, FDF, and RF increased CH4 emissions by 265.4, 271.4, and 175.6 kg ha-1, respectively. And SM under CF, FDF, and RF increased CH4 emissions by 213.3, 112.8, and 14.6 kg ha-1, respectively. The results indicated that SM resulted in less CH4 emissions compared with SI, especially in plots frequently with absence of water layer. Besides, SM had a potential to increase rice yield in rice paddies that had a lack of water. Therefore, in-season straw application should be avoided in lowland rice paddies, and straw mulching is practical in rice paddies lack of water.