CH4 and N2O Emissions in a Rice Field

First Measurements in the Uruguayan Productive System

Resumo

Irrigated rice fields are major sources of two important greenhouse gases (GHG), methane and nitrous oxide. As an initial step towards obtaining local information, emissions of CH₄ and N₂O from rice paddy soil were measured by the static chamber technique in greenhouse and field experiments conducted in eastern Uruguay. In the greenhouse experiment, the effect of two flooding moments (21 and 45 days after emergence) and nitrogen fertilization (0 and 50 kg N ha^-1) on gas emissions was studied. Early flooding and nitrogen fertilization tended to increase N₂O emissions. In the field experiment, effect of winter soil cover crop and nitrogen fertilization (0 and 82 kg N ha^-1) were tested. Higher CH₄ fluxes were observed mainly during the reproductive stage of the plant in the N-fertilized treatment with ryegrass winter crop. N₂O flux peaked at flushing. Results indicate that the use of cover crops might increase GHG emissions during the rice cycle. Despite differences in agronomic management practices employed in Uruguay, CH₄ and N₂O fluxes are within magnitudes previously reported for rice fields worldwide.