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.