Identifying biotic and abiotic processes of reversing biochar-induced soil phosphorus leaching through biochar modification with MgAl layered (hydr)oxides

Biochar (BC) as a increasing widely adopted soil amendments showed potential threat to soil P leaching, but the relevant mechanisms were not clear enough and relevant strategy should be proposed to address the P leaching induced by BC application. In this study, effects of ordinary corn straw BC, and a fabricated Mg/Al-LDHs modified biochar (LBC) on soil P availability, adsorption, fraction and mobility were compared and investigated by conducting the column and incubation experiments at biochar to soil rate of 1 %, 2 % and 4 % (w/w). Chemical sequential extraction methods and various solid-state method (i.e., three-dimensional excitation emission matrix (EEM), x-ray diffraction (XRD), scanning electron micrograph (SEM) and P K-edge X-ray absorption near edge structure (XANES)) were utilized to give deep insights into the P mobilization and immobilization mechanisms by respectively applying the BC and LBC. Results of incubation experiments showed that applying the LBC reduced the labile P with significant Ca\\P transformation to Al-retained P, while ordinary BC promoted the Fe/Al-P transformation to labile dibasic calcium phosphate and monobasic calcium phosphate evidenced by the EEM analysis, in-situ XANES investigation and chemical sequential extraction methods. Results of phosphatase and microbial analyses indicated that the decreased labile P after 30 days' incubation and the mitigated P leaching in LBC treatment were dominantly ascribed to abiotic processes of inorganic P transformation and (de) sorption. This research gave deep insights into abiotic and biotic processes of ordinary biochar promoting soil P leaching, and important implications for applying engineered biochar in reducing P leaching and improving soil productivity.

Automated summary

This study compared the effects of ordinary biochar and modified biochar on soil phosphorus and investigated the mechanisms of phosphorus mobility and immobilization. The results showed that the modified biochar reduced soluble phosphorus and transformed it into immobilized phosphorus, while the ordinary biochar promoted the transformation of phosphorus into soluble calcium phosphate. Additionally, abiotic processes played an important role in phosphorus transformation and sorption.