Dr Pauline Chivenge1, Dr Bjoern Sander1
1International Rice Research Institute, Metro Manila, Philippines
The sequestration of C in soils is generally considered a win-win situation because it improves soil quality and mitigates greenhouse gases in the atmosphere. However, in lowland rice soils the sequestration of C in soil is often associated with increased greenhouse gas emissions, which can be detrimental to climate change mitigation. For example, rice straw incorporation into the soil increases soil organic C and is considered important for recycling nutrients, and is advisable over burning as the latter causes respiratory health problems. However, the decomposition of straw under submerged conditions causes formation of phenolic compounds, which affect N availability and crop growth, and increases greenhouse gas emissions, particularly methane. Methane production under anaerobic decompositon of organic matter in lowland rice contributes about 10% of the global anthropogenic methane gas emissions in the agriculture sector. N fertilizers increase rice yields and soil organic C, but also increase methane emissions depending on rate of application. This poses challenges on how to improve rice yields and foster soil organic C sequestration while reducing greenhouse gas emissions, and finding the optimum balance remains fundamental for rice ecosystems. The following questions remain petinent for lowland rice systems: Is it possible to simultaneously sequester carbon in rice soils and reduce greenhouse gas emissions? Can the carbon sequestration-greenhouse gas reduction benefits be achieved concurrently? Are we chasing contradictory aims? This review considered these issues, dynamics, and realities with an attempt to analyze the trade-offs and synergies between soil organic C sequestration and greenhouse gas emissions.