The Effect of Soil Type on Gaseous Emissions from Flooded Rice Fields in Portugal

Overall rice cultivation in Europe occurs under flooding conditions to control soil temperature, weeds, and pests. The aim of this study was to assess the effects of sandy and clay soils on ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from flooded rice (Oryza sativa L.) fields. A 2-year rice field experiment was conducted in two different soils (sandy and clay soil) during two consecutive seasons in central Portugal. Soil mineral N dynamics and gas fluxes were followed between rice sowing (May) and harvest (October) dates. The NH3 fluxes were measured by the dynamic chamber technique while the N2O, CO2, and CH4 fluxes were measured by the closed chamber technique. Ammonia and N2O emissions did not differ significantly (p > 0.05) among the two soils and were about 10% and 1.5% of the N applied, respectively. In clay soil, CO2 emissions were significantly higher (p < 0.05) in 65% and CH4 emissions were significantly lower (p < 0.05) in 36% relative to sandy soil. The global warming potential (GWP) and yield-scaled GWP were not significantly different (p > 0.05) between the two soils. The yield-scaled NH3 from clay soil was significantly higher (p < 0.05) in 29% relative to sandy soil. The present study suggests that NH3 losses and global warming potential from flooded rice are quite similar among the sandy and clay soil. However, the yield-scaled NH3 was significantly higher in clay soil, in relation with a highest concentration of available ammonium in the solution, while yield-scaled global warming potential was not significantly different among the two soils.