Spectroscopic studies on the phosphorus adsorption in salt-affected soils with or without nano-biochar additions

Biochar amendment may be an effective solution of maintaining phosphorus (P) and sustaining agricultural production in salt affected soils. However, the behavior of P adsorption in salt-affected soils with nano-biochar (nB) amendment is unclear. Batch adsorption experiments were conducted to investigate the impacts of different levels of soil salinity amended with nB at rates of 0, 0.10%, 0.20%, and 0.50% (w/w) on the P adsorption isotherm and also, mechanisms of P adsorption by using spectroscopic analysis. The results showed that P adsorption increased with increasing soil salinity with or without nB addition. Under level of 120 mg P L−1, adsorption capacity of P increased from 992.8 mg kg−1 for high saline soil (S5) to 1144.0 mg kg−1 after treated with 0.20% nB. The results of P adsorption were agreed with Langmuir and Freundlich isotherm models. Fourier transform infrared analysis (FTIR) of nB showed that the surface of nB decorated with oxygenated functional groups which play an important role in the adsorption of P anions. Analyzes of FTIR and XRD indicated that the main adsorption mechanism for P adsorption on nB in salt affected soils was surface precipitation. Our findings suggest that the nano-biochar amendment in salt affected soils can be a promising enhancer for P adsorption. •Five soil samples with different levels of salinity were amended with nano-biochar at different rates.•Maximum adsorption of P on saline soils higher than non-saline.•The adsorption capacity of P values increases by increasing nano-biochar rates.•Surface precipitation was the dominating mechanism for P adsorption on nano-biochar.