Preparation Of Acidic Phosphorus-rich Biochar And Its Effect On Soil Phosphorus Availability In Arid Region

Biochar can effectively increase soil fertility.The p H value of alkaline soil is rather high and the content of phosphorus（P）is mostly fixed.Therefore,the application of biochar is limited in the alkaline soil.Thus,it is necessary to find a reasonable way of modification in order to increase the application of biochar in the alkaline environment.In this study,the biochar（CBC,WBC and HBC）is prepared by these raw materials such as cotton straw,wheat straw and halophytes,and modified by phosphate（H₃PO₄）and pyrophosphate（H₄P₂O₇）in order to produce the acidic phosphorus-rich biochar（P-CBC,P-WBC,P-HBC,PA-CBC,PA-WBC and PA-HBC）.With the help of characterization technique of element analyzer,scanning electron microscope（SEM）,energy dispersion X-ray spectroscopy（EDS）,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FTIR）and Raman spectroscopy（Raman）,the structural changes of the original biochar,H₃PO₄and H₄P₂O₇of modified biochar are clarified,as well as their P-binding modes.The P morphology and content variation of the biochar were confirmed by Hedley fractionation extraction method.Through soil culture test,the P morphology and content variation of biochar and soils are measured after different biochar entering into aeolian soil（AS）,greydesert soil（GS）,brown soil（BS）and saline soil（SS）respectively,so as to investigate the response of alkaline soils to different biochar.The main study results are as follows:（1）H₃PO₄and H₄P₂O₇modification are able to significantly affect the physicochemical properties of CBC,WBC and HBC.All unmodified biochar is alkaline and the p H decreases significantly after modified by H₃PO₄and H₄P₂O₇.H₃PO₄and H₄P₂O₇form a granular structure with a high level of P on the surface of the biochar.The surface shape changes.The specific surface area,pore capacity and average pore diameter of the biochar decrease.Moreover,the biochar modified treated by H₄P₂O₇is minimal.The C element significantly decreases,P content increases and aromaticity is reduced in biochar after the modification.（2）Spectral analysis indicates that H₃PO₄and H₄P₂O₇modification are able to disrupt the C-P groups in the original biochar,promote the formation of P-（OH）₃groups,and form P⁺-O,P-O-P and carboxyl（-COOH）on the surface containing P groups and acidic groups.Modification causes the biochar to form a new P2p peak.Compared to the H₃PO₄modified treatment,the relative amounts of C-P-O and C=O and（or）P=O in the H₄P₂O₇modified biochar decrease while the relative amounts of C-O-P,O=P-O,C-O-C and（or）P-O-C and P-O-P increase.Measurement analysis reveals that the modification enhances the P activity in the biochar.Among which the active P content significantly increases by 0.02～14.78 g·kg^-1,and all moderately active P content significantly increases by 0.02～0.90 g·kg^-1（p<0.05）.H₃PO₄and H₄P₂O₇modification increases the P content in HBC by 68.93%and 66.19%,respectively,which is the most.（3）Raw biochar only significantly increases the p H values in the BS soil.Both H₃PO₄and H₄P₂O₇modified biochar may significantly reduce the soil p H of AS,GS,BS and SS.Moreover,there is no significant difference among the soils by applying two types of modified biochar.The H₂O-P content decreases by 1.31～1.50 g·kg^-1and 0.46～0.72 g·kg^-1,respectively after WBC and CBC enter into the soil.H₂O-P content of HBC shows a significant decrease by 0.03 g·kg^-1（p<0.05）on the surface of the biochar only in SS.After adding two types of modified biochar in the soil,the Na HCO₃-Po content in biochar significantly increases by 0.32～2.11 g·kg^-1（p<0.05）.The improvement of P in soil by three types of modified treated biochar is achieved as following:original biochar<H₃PO₄modified biochar<H₄P₂O₇modified biochar.