Optimum biochar preparations enhance phosphorus availability in amended Mollisols of Northeast China

Biochar amendment to soils can improve soil P availability, but details on the optimum application of biochar to black soils in Northeast China are limited. Three types of biochar were produced at six pyrolysis temperatures (between 200 and 700 [degrees]C) and then added to black soil samples. P adsorption-desorption isotherms were fitted by the Langmuir model to evaluate the changes in soil P adsorption-desorption after biochar amendment. Changes in P adsorption and desorption depended on biochar feedstock type and pyrolysis temperature. When pyrolysis temperature increased up to 400 [degrees]C, P sorption maximum ([Q.sub.m]) of soybean pod (SP) and soybean straw (SS) biochar-amended soils were enhanced from 855.65 and 428.84 mg [kg.sup.-1] to 1666.67 and 1547.62 mg [kg.sup.-1], respectively, while a further increase in the pyrolysis temperature lowered the adsorption capacity. However, P adsorption of corncob (CC) biochar amended soils declined from 1428.57 mg [kg.sup.-1] to 556.70 mg [kg.sup.-1] as pyrolysis temperature increased. Higher P desorption in SP and SS compared with CC indicated that SP and SS biochar produced at higher than 400 [degrees]C pyrolysis temperatures were considered to be the optimum biochar to enhance P availability in the black soils of Northeast China. Key words: Batch equilibrium method, biochar amendment, black soil, feedstock type, pyrolysis temperature, phosphorus adsorption and desorption.