Carbon sink in cropland soils and the emission of greenhouse gases from paddy soils: a review of work in China

This paper discusses the dual contribution of rice paddy soils to atmospheric greenhouse effect. On one hand, the paddy soils store more organic carbon than the upland soils by 12–58% in China. The amount of organic carbon stored in paddy soils increased by 120.8–584.0 Tg (Teragram=$\text{10}{}^{12}\text{g}$) in 0–100 cm soil depths due to the conversion of upland soils to paddy soils in the past 600 years in China. On the other hand, the paddy soils are another important source of atmospheric CH₄. Among the factors governing the CH₄ emission, the water regime was mainly reviewed in this paper. Mid-season aeration is one of the means to mitigate the CH₄ emission and also contribute to the higher rice yield. However N₂O emission does occur during the drainage period, and its global warming potential (GWP) is higher in long term. Therefore, it is important to properly control the water regimes and judiciously use nitrogen fertilizers in paddy soils in order to maximize its sinks and minimize its sources of atmospheric greenhouse gases (GHGs).