Remediation of saline soils by a two-step process: Washing and amendment with sludge

•We evaluated the effect of a two-step process on remediation of saline sodic soils.•Washing saline-sodic soil with CaCl2 decreased pH and ESP values of WS.•Amendment with sludge residues enhanced phys-chem-biological properties of WS.•Highest germination indices were obtained at low ratio of sludge addition (1% w/w).•The two-step process shows promise for restoration of saline-sodic soils.

Soil salinization is a serious land-degradation problem that affects soil, plants and groundwater within ecosystems. In this work, the effect of washing saline-sodic soils with CaCl2 at 2% (w/v) and amendment with composted and dry sewage sludge was evaluated in a remediation assay. The effectiveness of amendments to improve the soil fertility was investigated with seed germination assays of Raphanus sativus L. Two different organic wastes were used: sewage sludge composted with pruning wastes (CP) and thermally dried sewage sludge (T) at rates of 1 and 2% (w/v) on organic matter basis. In general, there was an increase of germination percentage in the amended washed soils. The best indices were obtained at the 1% amendment dose with CP. The low exchangeable sodium percentage (ESP) in washed-amended soil (3 to 6 times lower than that of saline-sodic soil) could partially explain the increase in seed germination percentage of R. sativus L. The incorporation of organic amendments to washed soil also seemed to be beneficial as a step in the restoration process according to the chemical characteristics, especially by increasing the level of nutrients such as carbon, nitrogen, and phosphorus. A significant multiple linear regression of radish germination index in terms of pH values, sodium adsorption ratio of soil (SAR), and different forms of nitrogen (NH4+ and NO2−) was found.Overall, saline-sodic soil washing with CaCl2 followed by addition of organic amendments seems to be a promising strategy for restoration of such soils with simultaneous improvements of cation balance and nutrient/organic matter contents.

Graphical abstractDownload full-size image