Impact of water/fertilizer management on methane emission in paddy fields and on global warming potential

Methane (CH₄) is a key greenhouse gas, second only to CO₂ in term of contribution to global warming.Paddy field, as an important source of CH₄ emission, has significant implications for global warming and climate change.In order to understand the main factors of CH₄ emission in paddy fields and its impact on global warming, this study calculated potential global warming and sought measures to mitigate CH₄ emission in paddy fields.To do so, we collected data on CH₄ emission in paddy fields in China using literatures published before 2015(including journals and doctoral and master dissertations) and documented in CNKI net, ScienceDirect and SpringLink.Then daily CH₄ emission, global warming potential (GWP) and associated factors influencing CH₄ emission in paddy fields in China were analyzed using regression and factorial analyses.The results showed that daily emission of CH₄ in paddy field and GWP due to CH₄ emission increased with increasing soil organic matter (SOM).The order of daily CH₄ emission from paddy field was:late paddy field of double cropping rice > early paddy field of double cropping rice > single cropping paddy field > late paddy field of rice-wheat rotation.GWP due to CH₄ emission in late paddy field was more than that in early paddy field for double cropping rice.The order of daily CH₄ emission from paddy fields with different fertilizer managements was:ST (straw turnover) > NO (chemical nitrogen fertilizer with organic manure) > NF (chemical nitrogen fertilizer)≈ BI (biochar).Water management significantly affected CH₄ emission from paddy fields with the order of continuous flooding (CF) > field drying (FDF) > flooding-drying alternation (FD) > control irrigation (CI).Proper water management also significantly reduced GWP due to CH₄ emission.The order of GWP due to CH₄ emission in early paddy fields, late paddy fields and single cropping rice paddy fields was also as follows:CF > FDF > FD > CI.The results suggested that CH₄ emission was influenced by many factors, including soil SOM content, water and fertilizer management, and basic soil conditions.However, agricultural management activities (e.g., water and fertilizer management, fertilizer amount, fertilizer type) played a major role in CH₄ emission in agricultural lands.This was influenced by soil nutrient conditions (soil SOM content and C:N ratio), climatic conditions (crop growth period, temperature and precipitation during growth period), management practices (fertilizer and water management), rotation system, and other factors.For a more accurate inventory of greenhouse gas emission and proposal of effective mitigation policies, it was critical to use appropriate prac-tices suitable to specific climatic, soil and cropping conditions, combined with rational nitrogen fertilizer application rate and water management.