Influence of γ-PGA on greenhouse gas emissions and grain yield from paddy rice under different rice varieties

Background: Significant efforts have been devoted to assess the effects of the poly-gamma-glutamic acid (gamma-PGA) on crop growth, yield and quality, soil water retention and fertilizer use efficiency. However, few studies have evaluated the effects of gamma-PGA on greenhouse gas (GHG) emissions and grain yield from paddy fields with different rice varieties. Methods: In the present study, a split-plot field experiment was performed to comprehensively evaluate the effects of gamma-PGA concentrations (i.e., no application [P0] and 25.0 kg ha(-1) of gamma-PGA fermentation solution [P1]) and rice varieties (i.e., conventional rice [Huanghuazhan, H], red rice [Gangteyou 8024, R] and black rice [Black indica rice, B]) on the grain yield, GHG emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), net ecosystem economic profit (NEEP) and carbon footprint (CF) during 2022 and 2023 rice-growing seasons in central China. Results: Application of gamma-PGA significantly affected the GHGs emissions, NEEP and CF. Compared with P0 treatments, P1 treatments significantly increased the NEEP by 1.2-11.2 %, and decreased the GWP by 12.9-35.4 %, the GHGI by 16.5-35.9 % and the CF by 13.8-26.2 % in 2022-2023. Application of gamma-PGA showed a tendency to increase the yield. Under gamma-PGA application condition, R treatment exhibited the lowest GWP, GHGI and CF, and the highest yield and NEEP compared with B and H treatments. Conclusion: Our results suggest that gamma-PGA application is an ecological agricultural management to increase rice yield, reduce greenhouse gas emission and increase economic benefit, and its advantage is more significant for red rice than for other rice varieties.