Rice straw management practices and GHGs emission

Agriculture contributes to anthropogenic global warming by causing emissions of important greenhouse gases (GHGs) such as methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) [1]. Among the agronomic crops, rice (Oryza sativa L.) represents a major concern to scientific community, because its global warming potential is approximately four times greater than that of wheat or maize [2]. Rice paddies accounts for ~48% of greenhouse gas emissions and contributes ~ 22% and ~11% of total agricultural methane and nitrous oxide emissions, respectively [3,4]. The anaerobic environment of soil under flooding conditions mainly contributes towards the CH4 emission whereas during draining cycles and the fallow period, the upper layers of soil may remain aerobic, determining a considerable amount of N2O emissions [5,6]. Good management practices are key factors to mitigate GHG emission from agriculture, including from rice paddies. Among the best agricultural practices identified as “climate smart” is the incorporation of residues into the soil as it leads to a sustained increase in organic matter [7], contributing to soil carbon sequestration and improving soil fertility [8]. On the contrary, burning crop residues is considered to have a high environmental impact by producing carbon monoxide, CH4, N2O and other nitrogen oxides (NOx) [7]. However, in rice paddies, leaving rice straw on soil surface and flooding may result in increased CH4 emissions due to enhanced fermentation of organic matter. In this framework, it is urgent to quantify the emission of GHG (CO2, CH4 and N2O) from rice paddies and to establish the actual global warming impact that rice straw incorporation versus burning might have, to develop strategies for effective climate change mitigation. This could be particularly relevant in Italy, which is Europe’s largest rice producer accounting for 53% of European production [9].