Optimizing rice-crayfish systems with direct seeding: Impacts on greenhouse gas emissions and economic performance

Abstract

The rapid expansion of rice-crayfish (RC) systems has raised concerns about increased methane (CH₄) emissions due to prolonged field flooding, especially in long-term practices. While direct seeding (DS) is widely used to reduce CH₄ in rice cultivation, its efficacy and economic viability in RC systems remain unclear. This study aimed to compare DS versus transplanting (TP) in RC systems cultivated for 5 (RC5) and 15 (RC15) years. Results showed that under TP, CH₄ emissions were 22.0 % higher in RC15 than in RC5. Implementing DS reduced CH₄ emissions by 49.9 % in RC5 and 30.1 % in RC15—mainly during the initial drainage stage—reducing the global warming potential (GWP) by 44.5 % and 27.3 %, despite increased nitrous oxide emissions. Mechanistically, DS suppressed methanogenesis by increasing soil redox potential, as indicated by a 14.1–50.9 % reduction in mcrA gene abundance, while increasing the abundance of ammonia-oxidizing bacteria genes. The reduced effectiveness in RC15 reflected altered emission drivers, as significant CH₄-WFPS correlations observed in RC5 (R² = 0.96) were absent in RC15 (R² = 0.09), limiting water management benefits. Although DS reduced rice yields in RC5 (12.1–10.0 t ha⁻¹), yields remained stable in RC15 (11.8 vs 12.3 t ha⁻¹). Economically, DS improved net ecosystem economic benefits by 3.5 % in RC5 and 12.8 % in RC15 systems, driven by lower crop establishment costs and reduced GWP-associated environmental costs. This study demonstrates that DS is a viable strategy for balancing environmental sustainability with economic profitability in RC systems, though optimal management is modulated by system age.