Dilemma of organic matter input to mitigate climate impact of rice paddies

Abstract

Soil can act as either a source or sink of atmospheric carbon (C). Organic matter application can sequester carbon dioxide (CO₂) through negative emission technologies. However, in rice paddies, organic matter application can significantly increase methane (CH₄) emissions, offsetting potential climate benefits. We compared the effects of organic matter types on net climate impact by quantifying annual gaseous fluxes and soil C stock changes with CO₂ equivalents. All organic amendments increased CH₄ emissions (7–30 Mg CO₂-eq. ha⁻¹) compared with the no organic matter treatment (NPK). However, the increases in soil C stock (9–11 Mg CO₂-eq. ha⁻¹) were insufficient to shift the system from a net C source to a net sink, even when combined with water management strategies. In contrast, biochar increased CH₄ emissions but enhanced soil C stock, leading to a net negative emission effect without compromising rice productivity. Given that rice paddies account for about 11 % of anthropogenic CH₄ emissions, organic matter application requires careful evaluation to avoid exacerbating climatic impacts.