Mitigation of greenhouse gases emission affected by no-tillage and winter cover crops in a subtropical paddy rice ecosystem

ABSTRACT

Paddy rice production based on traditional soil management emits large amounts of methane (CH₄) into the atmosphere. This study assessed the potential of no-tillage (NT) and winter cover crops (WCC) to mitigate net greenhouse gas (GHG) emissions in a subtropical paddy rice ecosystem. A long-term (20-yrs) experiment was evaluated regarding the effect of NT combined with winter fallow or three WCC (ryegrass, white oat, and birdsfoot trefoil) on seasonal CH₄ -C and nitrous oxide (N₂O-N) emissions and on soil organic carbon (SOC) stocks in comparison to conventional tillage (CT) under winter fallow in a Gleysol of Southern Brazil. The changes in SOC were used as a proxy for annual net carbon dioxide (CO₂) exchanges in the soil-atmosphere, taking the CT treatment as a reference. The GHG balance (summation of CH₄ , N₂O and CO₂ emissions multiplied by their global warming potential of 34, 298, and 1, respectively) and emissions intensity of GHG emissions were calculated. Across winter managements, NT decreased 25 % of GHG emissions in comparison to CT system. This effect was mainly related to the decrease of seasonal CH₄ -C emissions (31-113 kg ha^-1) and by promoting SOC accumulation (0.45-0.65 Mg ha^-1yr^-1) in comparison to CT system, since soil N₂ O-N emission was not affected by management practices. Increased soil CH₄ -C emissions offset the positive effect of WCC on SOC accumulation compared with winter fallow. Based on our findings, NT mitigates net GHG emissions in subtropical paddy rice ecosystems, but no additional effect is observed combining NT with WCC.

nitrous oxide; methane; tillage systems; net balance of GHG; lowland