Methane and Nitrous Oxide Emissions in Lowland Rice Production As Affected by Fallow Management.

Rice (Oryza sativa L.) is the main staple food produced in tropical Asia, where two rice crops are often grown each year on submerged soils. Submerged rice soils are known to be a source of methane, but relatively little research has examined the effects of management during the fallow between rice crops on emissions of methane and nitrous oxide during an entire annual cycle with two rice crops and two fallow periods. We examined the effects soil submergence, tillage, soil drying, and crop residue retention during the fallow between rice crops on emissions of methane and nitrous oxide during both the fallow and the subsequent rice crop. Prolonged drying of soil with or without tillage during the fallow — rather than periodic or continual soil submergence during the fallow — reduced methane emissions throughout the subsequent period of rice cropping. Soil drying and tillage during the fallow resulted in formation of nitrate and emission of nitrous oxide during the fallow, but nitrous oxide emissions during the subsequent rice crop were small regardless of fallow management. The results indicate that management practices between rice crops should be considered when estimating emissions of methane and nitrous oxide from rice production systems.