Rice straw management practices and GHGs emission

The global warming potential (GWP) of rice (Oryza sativa L.) farming is approximately four times greater than wheat or maize cultivation. Rice paddy mainly contributes to methane (CH4) emission due to the anaerobic conditions of flooded fields but also releases nitrous oxide (N2O) during draining cycles and nitrogen fertilization. A proper straw management, such as incorporation into soil, increases soil organic matter content and improves soil fertility, but may enhance CH4 emissions due to increased fermentation of organic matter in flooding condition. On the contrary, burning crop residues is considered to have a high environmental impact by producing air pollutants (e.g. particulate matter (PM) and volatile organic compounds (VOC)). In this framework, the quantification of GHG emission from different rice-straw managements is needed to develop effective agricultural practices for the reduction of rice global warming potential. This could be particularly relevant in Italy, which is Europe’s largest rice producer accounting for 53% of European production. The aim of the present study is to compare the climate impact of two different rice straw management practices - straw incorporation versus straw burning - in the Po valley. CO2, CH4 and N2O flux exchanges will be measured during two rice cultivation seasons. A further aim will be to assess the emission of air pollutants from crop residues burning by sampling and identifying volatile organic compounds (VOC). The field experiment will be conducted in two rice plots where two different residue management will be tested: in the first one, the residual straws will be incorporated into the soil whereas in the second scenario the rice straw will be burned. Gas measurements will be performed using the following methods: 1) CO2 and CH4 fluxes will be monitored at ecosystem level using the Eddy Covariance (EC) methodology, a standard micrometeorological method for the direct measurement of CO2, CH4, water vapor and heat fluxes over a large area and at a high temporal resolution. 2) NO2 emissions from soil will be measured in real time using a dynamic chamber coupled to an infrared gas detector (LICOR 7820). 3) VOC composition from burning straw will be determined with GC–MS analysis. 4) Soil samples will be collected to quantify soil nitrogen (total and mineral) and soil organic carbon (SOC) content. The knowledge gathered in the present project will contribute to the development and implementation of good agricultural practices in rice cultivation. In addition, the data collected will represent an important contribution to the Italian GHGs emissions inventory.