Effects of salt ions on silicon dissolution in biochar and soil
To understand the dissolution characteristics of silicon in biochar amended saline soils as influenced by salt ions,we prepared wheat straw biochar(WS300-WS700)and cotton straw biochar(CS300-CS700)at different temperatures and investigated the kinetics of silicon in different extractants(H2O,CaCl2,and NaCl solutions),dissolution by successive extractions,and the effect of biochar on the dissolution of silicon in soil.We observed that the kinetic dissolved concentration of silicon in biochar peaked on the third day,decreased,and then fluctuated steadily.Silicon dissolution in H2O and NaCl solutions was higher in biochar prepared at 500℃and 700℃than in biochar prepared at 300℃.The cumulative dissolution of silicon in all wheat and cotton straw biochar was highest with H2O solution extraction,whereas biochar silicon dissolution was lowest and almost zero with CaCl2 solution extraction,except for WS300.More silicon was leached from wheat straw biochar than from cotton straw biochar.In the H2O solution,WS700 showed the highest cumulative silicon dissolution of 1 146.10 μg,while CS300 leached the lowest amount in CaCl2 solution extracts.Trends in cumulative leaching of silicon from biochar-treated soils were consistent with biochar:soil silicon dissolution was greatest from the WS700 treatment extracted in H2O solution,followed by the CaCl2 solution extraction and least in NaCl solution.This could be attributed to the soil itself having a higher dissolution of silicon in the CaCl2 solution than in the NaCl solution.Scanning Electron Microscopy-Energy-Dispersive X-Ray(SEM-EDS)and X-ray Diffraction(XRD)characterization revealed that the decrease in silicon dissolution from biochar in saline extraction may be due to the reaction of ions with soluble silicon,which is subsequently adsorbed onto the biochar surface.Biochar for saline soil amendment increases silicon dissolution in soil and reduces inhibition of silicon dissolution by salt ions.
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