Nitrogen fertilizer application in the rice-growing season can stimulate methane emissions during the subsequent flooded fallow period

摘要

Winter-flooded rice paddy field (FR), characterized by water conserved in the field during the fallow period, is a typical cropping system in southwest China, leading to considerable methane (CH_4) emissions. The effect of nitrogen (N) fertilization on CH_4 emissions during rice-growing seasons is well studied in FR, further studies covering N fertilizer applied in the rice-growing seasons affects CH_4 emissions during the subsequent fallow period is needed. Therefore, a field experiment was conducted in an FR of Sichuan province, China, with conventional N fertilized (CN) and N unfertilized (NN) treatments. The cumulative CH_4 emission from CN treatment during the rice-growing season and the subsequent fallow period was 389 ± 29.4 and 158 ± 31.2 kg C ha~(-1), which were increased by 29.5% and 395% in comparison with the NN treatment, indicting N applied during the rice growing-season significantly facilitated CH_4 emission during the subsequent fallow period. During the rice-growing season, higher CH_4 emission from CN treatment could be attributed to elevated soil dissolved organic carbon (DOC) content that might have provided sufficient substrates for CH_4 production. During the fallow period, as compared to NN treatment, higher CH_4 emissions from CN treatment could be explained by greater linear regression slopes between CH_4 fluxes, soil temperature and DOC to dissolved inorganic N (DIN) (DOC/DIN) ratio. Moreover, the structural equation model (SEM) described that the soil temperature exhibited the most significant effects on CH_4 emissions for both treatments during the rice-growing season and subsequent fallow period. These findings are a major step forward to showing that N fertilizer applied in the rice-growing season could also affect CH_4 emission during the subsequent fallow period, accompanying other soil parameters controlling CH_4 emission.