Fig. 1

Soybean grain yield under different organic material and nitrogen levels. Note: Fig. 2019 A and 2020 B represent the soybean aboveground dry weight in the 2019 and 2020 growing seasons. R2, R5, and R8 stages represent the blooming flower stage, beginning seeds stage, and fully mature stage of soybean. Nitrogen treatment N0, N1, N2, and N3 represent 8.4 kg ha ^− 1, 22.5 kg ha ^− 1, 45 kg ha ^− 1, and 67.5 kg ha ^− 1 N, respectively. Fertilizer treatment CK, BC, and BF represent no fertilizer control, biochar, and biofertilizer. The point and error bars represent the mean and standard deviation of the three-replicate data. Different lowercase letters indicated a significant difference between treatments at 0.05 (p < 0.05) probability levels