Short-term modulation of mineral phosphorus fractions by functionalized biochars in different alkaline soil types

There remains a gap of knowledge regarding the functionalization of modified biochar types to enhance phosphorus (P) availability in arid soils. Therefore, original biochar (OB) derived from pyrolyzed Dodonaea viscosa feedstock at 500 °C was functionalized using ball milling (BMB), chemical oxidation (CHB), and biological activation (BIOB) to study their short-term effect on mineral P dynamics in charosphere of different soil types. Elemental and XRD analyses of OB and BIOB pointed to considerable amounts of P (0.95 and 0.71%) with a presence of P-containing minerals. EDS spectra of BIOB-amended soils showed elevated peaks of C (61.39–76.94%) confirming the exterior coating of soil granules by modified biochar through biofilm formations of extracellular polymeric substances secreted by the niche of B. subtilis. Biochar application motivated the formation of microaggregate fractions (the main sink of orthophosphates; < 0.25–0.05 mm) relative to unamended treatment. Fractional amounts of different P forms showed alterations following biochar application with a significant increase of the labile P pool, including soluble (53.86–870.25%) and exchangeable (92.71–982.92%) fractions. The high functionality of modified biochars modulated P dynamics in the soil-biota-plant system through secretion of solubilizing compounds (BIOB), increasing soil wettability and controlling the strength of reactive metal ions responsible for phosphate fixation (BMB), and releasing of acidifying compounds responsible for amending soil pH (CHB). Modulating effects of biochar on P dynamics in the soil-biota-plant system was able to transform higher amounts of residual P fractions into labile forms relative to the soil-biota system. Biochar application enhanced soil’s potential to supply phytoavailable nutrients to maize seedlings. Findings from this study, therefore, provide insights regarding functionalization of fit–for–purpose forms of modified biochar tailored in improving P phytoavailability in arid soils.