Mitigating methane and enhancing rice productivity: an integrated assessment of biodegradable PLA mulch and microalgal biofertilizers in submerged rice cultivation

Rice paddies are a significant source of methane (CH4), yet mitigation options that maintain yield under continuous flooding remain limited. This study evaluated the effects of biodegradable polylactic acid (PLA) mulch and biofertilizer on greenhouse gas emissions, plant performance, and greenhouse gas intensity (GHGI) in a factorial field experiment with eight different treatments combined across two rice varieties. Stage-integrated assessment of CH4 and CO2 fluxes was measured at tillering, flowering, and harvest. CH4 emissions were strongly growth-stage dependent, with the highest emissions occurring during the flowering stage, particularly in the high-emitting BF-888 no-mulch treatment. The PLA mulch reduced flowering stage CH4 emissions by 40%–70% relative to no-mulch in several treatment combinations, despite causing a modest increase during tillering. CO2 fluxes exhibited a relatively uniform temporal pattern across growth stages, with limited variation among treatments and no significant effects of mulch or biofertilizer. GHGI varied sharply across treatments, with the highest value (GHGI ≈ 8.1) occurring in Microalgal 888 without mulch due to elevated flowering-stage CH4 emissions. On the contrary, PLA Mulch x biofertilizer (New San Pa Tong) and No Mulch by No Fertilizer (SP) treatments produced GHGI values below 1.0, indicating more efficient emissions per unit yield. Generally, PLA mulch did not uniformly suppress CH4 but redistributed emissions across growth stages, reducing late-season peaks and improving GHGI when paired with suitable fertilizer variety combinations. The outcomes demonstrate that PLA mulch and biofertilizers can contribute to low-emission rice production when applied in conjunction with context-specific management strategies.