Reclamation of Saline–Alkali Soils Using Fulvic Acid: Mechanism and Field Effects

Fulvic acid is an organic soil amendment used to ameliorate salinealkali soils and to alleviate the negative effects of soil salinization on crops. However, scientific tests of many fulvic acid products have given very mixed results. A meta-analysis of 16 case studies on the field applications of fulvic acid was conducted. The results show that, compared with the control, fulvic acid generally reduced the soil electrical conductivity by 0.15 dS m−1. However, for fields with high groundwater tables and poor drainage, the effect of fulvic acid on promoting downward salt leaching was limited. Fulvic acid treatment reduced soil pH from 8.48 to 8.38, yet for fields with high CO32− and HCO3− contents, the soil pH may increase after fulvic acid addition. The mechanisms by which fulvic acid reduces soil electrical conductivity and pH are mainly colloid adsorption and ion exchange. Fulvic acid can promote the uptake of nutrients such as nitrogen and phosphorus by crops, and increase crop yield by 40.5%. However, both nutrient use efficiency and yield increasing rate decreased with increasing soil salinity. Fulvic acid was more effective in ameliorating moderately saline soils.