Seasonal and Annual Methane and Nitrous Oxide Emissions Affected by Tillage and Cover Crops in Flood-Irrigated Rice

Soil tillage plays an important role in methane (CH4) and nitrous oxide (N2O) emissions in flood-irrigated rice production. Hence, this study measured the effects of soil tillage and cover crops on the seasonal and annual CH4 and N2O emissions in flood-irrigated rice. A field experiment was conducted for two agricultural years with conventional tillage (CT), minimum tillage (MT), no-tillage (NT), and NT with Persian clover (Trifolium resupinatum) (NT+PC). The effect of different tillage systems on CH4 emissions, which occur predominantly in rice cultivation, depends on the impact of tillage and the amount of straw remaining at the time of rice seeding. When straw incorporation in MT and CT reduces the quantity of straw remaining relative to NT, lower CH4 emissions occurred in the CT and MT. In contrast, when the amount of straw remaining on the soil is similar among the types of soil tillage, lower CH4 emissions occurred in the NT. The effect of tillage on annual N2O emissions was unclear, although the highest in-season N2O emissions occurred in the NT, where the highest water-filled pore space values were recorded in both years. High N2O emissions during rice cultivation occurred in the CT after nitrogen fertilization. The effect of the cover crop in the NT varied as a function of the performance of the clover. When the PC biomass production was satisfactory in the second year, annual CH4 and N2O emissions increased by 8 % and 23 %, respectively. The seasonal and annual quantification of CH4 and N2O emissions is important to reduce the uncertainty of the effect of different land management systems on CH4 and N2O emissions.