Investigations on the nano manure-originated biochar in reducing phosphorus leaching potential from vegetable soils: An evidence of colloidal phosphorus variation.

Colloidal phosphorus (CP) is the main form of soil P easily loss to aquatic environment inducing water eutrophication. Biochar could impact soil properties and further regulate soil CP loss, while the effect of the nano-sized part with high activity is unclear. This study investigated the control effect and mechanism of manure-originated biochar with bulk and nano sizes on CP leaching potential in the vegetable soils with high legacy P and degree of P saturation (DPS). Results showed that the bulk-sized biochar increased soil CP by 39.9 % in comparison with control (2.72-6.46 mg kg-1), ascribed to the drastic rise of soil H2O-P and DPS relative to the slightly improved maximum adsorbed P (Qmax). By contrast, the nano-sized biochar, originated from various manure, possessed more functional groups (-COOH and -COH in FTIR spectrum) and were unstable (low carbon content and absolute value of Zeta potential), contributing to the retention of soil CP via adsorption and cementation roles. Meanwhile, the nano-sized biochar remarkably improved soil amorphous Fe/Al oxides contents and P adsorption capacity (high Qmax but low DPS), decreasing colloidal compounds release proved by low colloidal components (Fe, Al, Ca, and TOC) and high NaOH-P in soils, thereby significantly reducing soil CP by 41.2 % compared with control. Therefore, it could be an effective and alternative agronomic measure using nano-sized biochar to regulate CP loss from soils, especially with high P leaching potential.