Water efficient rice production - Short-term benefits at the expense of long-term fertility?

While many agricultural practices have resulted in loss of soil organic carbon (SOC), paddyrice production often presents favourable conditions for carbon sequestration. At the sametime, it is a major source of methane emissions and a large water user. The introduction ofwater saving irrigation (WSI) practices, such as alternate wetting and drying (AWD) andmid-season drainage (MSD), have been suggested as strategies for decreasing the large waterdemands of paddy rice production. With the removal of anaerobic conditions during thegrowing season, they may also lower CH4 production and reduce the global warmingpotential of rice production. However, the long-term impact of WSI on SOC - an indicator ofsoil health and fertility - has been little explored. Through a meta-analysis we assessedthe effects of WSI on SOC storage and GHG emissions. AWD and MSD reducedemissions of CH4 by 52.3%, and increased those of CO2 and N2O by 44.8 and 30%respectively. WSI reduced CO2-equivalent emissions by 52% but increased thesoil-to-atmosphere flux of carbon by 24% when compared to flood irrigation. Moreover, WSIdecreased SOC concentrations by 8.2% when compared to flood irrigation. WhileWSI affects SOC and greenhouse gas emissions, it has been shown to potentiallyhave little effect on rice yield. However, evidence of yield stability is limited toshort-term (1-2 years) experiments, whereas soil properties change over decades.Therefore, care should be taken when assessing the long-term sustainability of theseirrigation practices because WSI can decrease soil fertility. The development offuture irrigation strategies should consider long-term effects and trade-offs betweenwater savings, fertility, other ecosystem services and climate change mitigation. [ABSTRACT FROM AUTHOR]