Optima 3300 rl

The biochar and BMC were finely ground, and passed through ≤ 2-mm sieve for further analysis.
The pH and electrical conductivity (EC) were measured by using a digital pH and conductivity meter (Aquamax KF, GR Scientific, UK), at a solid: deionized water ratio of 1:5 (w/v). The CEC was measured by extracting the samples with 1N sodium acetate solution (pH = 8.2) (Sumner and Miller, 1996) . Acid neutralizing capacity (ANC) was determined by using the potentiometric titration method (Johnson, 1990) . The SSA was measured by the Brunauer-Emmett-Teller (BET) adsorption method. Total C and N were determined by a CHN analyzer (PE-2400, Perkin Elmer, USA). Other nutrient contents (e.g., P, K, Ca, Mg, Zn, Cu, Fe, and Mn) in the biochar and BMC were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP -OES) (Optima 3300 RL, Perkin Elmer, USA) after digestion with HNO3-HCl mixture [3:1(v/v)] in a microwave digestion system (Discover @ SPD, CEM Corporation, USA). The crystal structure, morphology, and surface chemistry of BMC were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy(Supplementary Information).