[Meta-analysis of Organic Carbon in Sandy Soil in Response to Amendment Application]

Proper application of soil amendments can effectively increase the accumulation of soil organic carbon （SOC） in poor soils, thereby enhancing soil fertility level. The impacts of different types of amendments on the SOC content of sandy soils varies widely. Investigating the effects of various amendments on the SOC content of sandy soils and associated key controlling factors provides a scientific basis for formulating strategies to enhance the fertility of sandy soils. A data set was established with 617 pairs of data from 114 published studies that reported the effects of amendment application on SOC content of sandy soil during 1987 and 2023. Meta-analysis was used to quantitatively analyze the effects of amendment application on the SOC content of sandy soil globally under the conditions of various amendment types and application rates, climates, and soil properties. This study also investigated the major controlling factors for the changes in SOC in sandy soil after amendment application using regression analysis and random forest model. The research results showed that： ① Amendment application significantly increased SOC content by 61% on average in sandy soils and the application of inorganic amendment increased SOC in sandy soils （161%） to a significantly greater extent than that of organic amendment （37%） and compound amendment （54%）. ② The application amount and duration of inorganic amendments had no significant effect on the increase of SOC in sandy soil. Among the organic amendments, the increase of SOC in sandy soil was enhanced with the increase in the application amount of biomass carbon and organic fertilizer and decreased with the application duration of the amendment. ③ Climatic conditions, the amount and duration of amendments, and soil physicochemical properties combined explained 88% of the variability in SOC response in sandy soils. The magnitudes of SOC change due to amendment application significantly decreased with increased average annual temperature, initial SOC content, and soil pH, however, positively correlated with aridity, soil bulk density, and sand content. The application of amendments significantly increased SOC content in sandy soils. The type and application amounts of amendments, climatic conditions, and soil properties strongly regulated SOC in response to amendments. Therefore, the type and amounts of amendment, climate, and soil conditions should be comprehensively considered when applying amendments to effectively increase the organic carbon content and fertility level of sandy soils.