Co-application of microalgae and biochar to achieve yield enhancement and climate change mitigation in saline-alkali soil

Assessment of soil response to climate-smart agriculture practices may assist in better management decisions in sensitive ecosystems. Despite the approved role of sole biochar or microalgae application in yield stability and climate resilience, their synergistic effects have not been well discovered, especially in fragile saline-alkali land. Here, in a three-year agricultural field by three doses of microalgae application (0, 30, 60 L ha^-1) combined with two biochar application rates (0, 30 t ha^-1), we explored the individual and combined effects on sunflower yield, soil carbon (C), greenhouse gas (GHG) emissions, and carbon footprint (CF). As expected, solely microalgae fertilizer application caused minimal changes in SOC storage, while biochar application had a more predominant effect on SOC storage, indicating that biochar was a key contributor to SOC storage. Notably, the synergistic effects of biochar and microalgae on yield enhancement, SOC storage, and emission reduction were stronger than each factor separately, confirming the positive complementarity effects of such dual application. Combined biochar with high-dose microalgae achieved an average increased yield and SOC storage by 58% and 24%, respectively, and reduced GHG emissions and CF by 18%-31% and 101%, respectively. Therefore, our findings shed new light on the essential roles of biochar and microalgae’ synergistic effects on enhancing crop yield and mitigating climate change in saline-alkali land.