Fig. 1

Effects of different concentrations of SPSB on soil chemical properties in a continuous cropping system. CK (no biochar), S1 (2.5% w/w biochar + soil), S2 (5% w/w biochar + soil), S3 (7.5% w/w biochar + soil). AK, available potassium; AHN, alkali-hydrolyzable nitrogen; AP, available phosphorus; SOM, soil organic matter. The significant differences are determined by the Tukey test, with different lowercase letters indicating significant differences between groups (P < 0.05)