CH4 and N2O emissions and their potential control by rice biomass biochar: The case of continuously flooded paddy fields in Indonesia - A review

Methane (CH4) and nitrous oxide (N2O) are the two most important greenhouse gases (GHG) from flooded paddy fields in Indonesia. This review aims to characterise CH4 and N2O emissions from flooded paddy fields by published data analysis and to examine the potential of biochar from rice straw (RSB) and rice husk (RHB) to mitigate the emissions in Indonesia. A comparison of various box-plot datasets of CH4 emissions showed that the different types of flooded paddy field soil cause varying amounts of CH4 emissions from various regions in Indonesia. Sequentially, CH4 emissions of flooded paddy fields from highest to lowest are Alluvial of Kalimantan and Sulawesi, Andisols of Java, Ultisols of Sumatra, Alfisols of Java and Bali and Inceptisols of Java and Bali, with a mean of 1062, 505, 446, 135 and 64 kg ha-1 season-1, respectively. The organic amendments application combined with chemical fertilisers is the principal driver of anthropogenic CH4 emissions from paddy fields. However, N chemical fertiliser application contributes only about 0.37% of the N2O flux, 0.69 kg ha-1 season-1. The produced biochar number was insufficient effectively to reduce CH4 and N2O emissions, at least 20 tonnes ha-1 year-1, in addition to the pyrolysis process to produce biochar, releasing CH4 emissions. Yet, with its recalcitrant properties and continuous application, RSB and RHB potentially reduce CH4 and N2O emissions from paddy fields.