Mechanistic insights into saline-alkali soil amelioration mediated by food waste-derived organic fertilizer

• Enzyme-hydrolyzed food waste-derived organic fertilizer was used to improve saline-alkali soil. • 2% FWOF application reduced soil pH and increased soil organic carbon by 95.6%. • Optimal FWOF dosage promoted seed germination and enhanced microbial diversity. • Excessive FWOF dosage may lead to increased salinity to affect soil and plant health. • FWOF for saline-alkali soil amelioration provided a dual-benefit circular economy strategy. The escalating burden of food waste and the widespread prevalence of saline-alkali soils present urgent global challenges that threaten both environmental sustainability and food security. Conventional composting of food waste to organic fertilizer suffers from large space demands and long processing time. Here, we propose a dual-benefit strategy that converts food waste into organic fertilizer (FWOF) via rapid enzymatic hydrolysis for effective soil amelioration and resource valorization. A 2% FWOF application optimally reduced soil pH and increased available phosphorus, total nitrogen, and organic carbon by 56.31%, 16.41%, and 95.79%, respectively, leading to a substantial enhancement in soil fertility while keeping electrical conductivity below phytotoxic thresholds. In contrast, higher doses (5-10%) caused excessive salinity and suppressed seed germination. FWOF also restructured microbial communities, enriching Firmicutes and Actinobacteria by about 40% while accelerating soil humification, a process essential for improving soil productivity. This study provides the first integrated mechanistic evidence that food waste-derived fertilizer can simultaneously achieve sustainable waste valorization and saline-alkali soil restoration. The proposed dual-benefit strategy offers a cost-effective, scalable, and circular economy-based solution for both urban waste management and amelioration of saline-alkali soil.