Understanding a Soaked Activated Coke Waste’s Impact on Phosphate Adsorption and Utilization, and Pak Choi Growth in Saline-Alkali Habitats

Soaked activated coke waste (SACW) refers to the fine porous particles (diameter < 1 mm) of activated coke which is immersed in dilute nitric acid aqueous solution to remove excess salts and heavy metals. In the study, the feasibility of SACW in improving phosphorus (P) utilization and plant growth under saline-alkali conditions was studied.

The mechanism of phosphate adsorption by SACW in saline solutions were evaluated by a series of solution experiment, meanwhile a soil culture experiment was conducted to access the effect of SACW combined with phosphate fertilizer on growth of pak choi (Brassica rapa L. ssp. chinensis) in saline soils.

The adsorption capacity of phosphate by SACW was decreased with increasing salinity concentration, and the effect of co-existing salt ions on phosphate adsorption was ordered as: SO₄²⁻> Cl⁻> Na⁺. The adsorption isotherm of phosphate by SACW showed a heterogeneous phosphate adsorption process, in which precipitation and ligand exchange were the main adsorption mechanisms. The SACW combined with low amounts (0.1 g kg^− 1) of phosphate fertilizer significantly decreased the concentration of soil active P and improved that of moderate active P, meanwhile promoting the growth of pak choi in 0.2% saline-alkali soil. Correlation analysis showed that the improved soil properties could increase soil Oslen P concentration, thus enhancing the uptake of P by plants and improving the growth of pak choi.

The SACW could improve the efficiency of P utilization by improving soil properties, and thus promote the growth performance of pak choi under saline conditions.