The application of amendments improves properties of salt-affected soils across China

Soil salinization is a major threat to global arable productivity. Chemical amendments are widely used to improve salt-affected soils and have been proven to be effective. However, the effectiveness of amendments varies across different regions and depends on field management practices. To quantify the improvement effects of different amendments on salt-affected soils and how amendment application affects plant productivity and soil properties, we compiled 2061 pairs of data from 92 studies about amendments across China to conduct a meta- analysis. We found that amendments application improved soil quality by reducing soil pH, electrical conductivity (EC), and exchangeable sodium percentage (ESP) with 3.9 %, 18.1 %, and 43.4 %, and improved soil nutrients by increasing soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) with 33.6 %, 37.7 %, 35.0 %, 55.3 %, and 32.3 %, and subsequently increased plant emergence rate and yield with 16.2 % and 52.2 % regardless of amendment types, respectively. Specifically, applying mixed amendments led to a significant reduction in soil EC by 33.6 %, whereas the application of inorganic compound decreased soil EC by 8.6 %. Furthermore, biochar application significantly increased SOM by 58.4 % and TN by 46.2 %, while gypsum application increased SOM and TN with only 20.9 % and 17.4 %, respectively. Field management, soil properties, and climate all significantly affected the improvement effect after amendments application. The effects of improving salt-affected soil were strongly correlated with the amount and duration of amendments application, followed by the initial soil salinity and alkalinity. Our findings indicated that the selection of soil amendments should consider not only their quantity but also factors such as cost, the longevity of their effects, and environmental safety.