Global potential and synergistic benefits of soil amendments for saline-alkali soil amelioration, soil carbon sequestration, and plant productivity: A meta-analysis

Saline-alkali land is a critical arable land reserve, but severe soil salinity-alkalinity threatens ecosystem health and agricultural production security. Organic amendment (OA), inorganic amendment (IA), and organic-inorganic composite amendment (OIA) have been widely used for saline-alkali land rehabilitation, but their effectiveness and synergistic effects in alleviating soil salinity-alkalinity, increasing soil organic carbon (SOC) and plant productivity remain debated. To address these knowledge gaps, based on 3763 observations from 215 studies, we combined a global meta-analysis with machine learning-based spatial prediction models to quantify the effects of OA, IA, and OIA on soil electrical conductivity (EC), pH, SOC content, plant productivity and their comprehensive improvement benefits (CIBs), identify their key drivers, compare the rehabilitation performance of different soil amendments under key environmental factors and future climate scenarios, and map the global distribution of optimal rehabilitation strategies for saline-alkali land. The results showed the OA, IA, and OIA were all effective rehabilitation measures, significantly reducing soil EC and pH and increasing SOC content and plant productivity, with CIBs of 34.7%, 27.5%, and 31.2%, respectively. The effectiveness of soil amendments was driven by initial soil factors, especially soil salinity-alkalinity, C:N ratio, and soil texture. Among soil amendments, OIA was better suited to rehabilitating severely salinized soils. OA and OIA were more favorable for SOC sequestration in high initial C:N ratio soils and had greater synergistic effects for SOC sequestration and plant productivity in sandy and clayey soils, while reducing dependence on irrigation and mineral N inputs. IA showed no advantage over OA or OIA across major initial soil factors, with its rehabilitation benefits requiring irrigation and higher N input rates. Global spatial predictions showed that OA and OIA had broader applicability, and their CIBs remained higher and more stable than those of IA under future climate scenarios. These results highlight the need to prioritize soil amendments involving organic inputs (OA or OIA) in rehabilitation strategies to synergistically achieve soil amelioration, soil carbon sink enhancement, and food security.