Straw management effects on global warming potential and yield-scaled greenhouse gas emissions in a subtropical rice ecosystem

ABSTRACT

Global warming potential (GWP) of rice paddies depends on straw management. This study evaluated methane (CH₄) and nitrous oxide (N₂O) emissions and soil C stocks to determine GWP and yield-scaled GWP under different strategies and intensities of rice straw management in a subtropical climate. We hypothesized that decreasing soil management intensity and straw incorporation in the soil would reduce GWP. Methane fluxes were substantially higher during the rice growing season than in the off-season, while the opposite was observed for N₂O fluxes. The cumulative emissions of CH₄ during the growing season among the straw management strategies evaluated ranged from 165.8 to 586.0 kg ha^-1. Annual CH₄ emissions were lower when soil and straw received some type of management compared to no-tillage. Daily N₂O fluxes ranged from -2.8 to 201.7 g ha^-1 day^-1; cumulative N₂O emissions during the off-season ranged from 455.2 to 2816.5 g ha^-1. During the off-season, strategies to reduce N₂O emissions include post-harvest straw incorporation using a disc harrow, winter straw removal, and ryegrass cropping. Soil organic C stocks ranged from 35.96 to 38.36 Mg ha^-1. Straw management using a disc harrow reduced soil organic C stocks, with more adverse effects than straw removal. Soil and rice straw management did not affect rice grain yield, with an average of 10.4 Mg ha^-1. Methane emissions were the main component of GWP in all straw management systems. The contribution of N₂O emissions to GWP was small and mostly (>85 %) determined by off-season emissions. Yield-scaled GWP ranged from 0.64 to 1.06 Mg CO₂eq Mg^-1 yield and was lower when soil and straw management systems occurred shortly after the rice harvest. Our results indicate that soil and straw management immediately after rice harvest reduces CH₄ emissions, GWP, and yield-scaled GWP.

nitrous oxide; methane; flooded rice; global warming potential; rice straw