Improvement of hard saline–sodic soils using polymeric aluminum ferric sulfate (PAFS)

• PAFS exhibited better performance than gypsum in ameliorating saline–sodic soils.
• Hydrolysis of PAFS promoted the dissolution of CaCO3 in saline–sodic soils.
• Coagulation of PAFS improved soil micro-aggregates and water permeability.
• PAFS rapidly reduced the sodicity and salinity of hard saline–sodic soils.
• PAFS amendment resulted in higher yields in the first year of rice cultivation.

Highly dispersed hard saline–sodic soils are important agricultural land reserves in the world. These soils are difficult to be ameliorated by conventional amendments because of poor soil properties. The objectives of this study are to screen a highly efficient inorganic polymer soil amendment using laboratory experiments and to evaluate its effectiveness in soil improvements and grain yield promotion under paddy field conditions using field experiments. Compared with control soils cultivated with rice for one year without PAFS treatment, the pH of the 0–8 cm and 8–16 cm layers of PAFS-treated soil decreased from 10.70 and 10.75 to 8.94 and 9.99, respectively, soil CaCO3 contents decreased by 29.49% and 16.19%, respectively, and contents of silt-plus-clay particles decreased by 46.06% and 14.55%, respectively. Soil saturated hydraulic conductivity increased from 0.05 mm d−1 to 40.01 mm d−1 and soil bulk density decreased from 1.55 g cm−3 to 1.29 g cm−3 in the 0–8 cm soil layer. Soil exchangeable Na+, exchangeable sodium percentage (ESP), and salinity (ECe) in the 0–8 cm soil layer were reduced by 61.92%, 63.23%, and 45.61%, respectively; in the 8–16 cm soil layer, the corresponding values decreased by 34.91%, 34.57%, and 37.47%, respectively. Rice yields with PAFS application in the first year of cultivation were as high as 4.66 t ha−1. By contrast, rice yields without PAFS application were only 0.83 t ha−1 in plots cultivated with rice for one year and 1.55 t ha−1 in plots cultivated with rice for two years. Therefore, PAFS is effective for amending hard sodic soils.