We applied four treatments of biogas slurry g/hm² (CK.0; L.0.125 t/hm²; M.0.250 t/hm²; and H.0.375 t/hm²) and biochar (B0.0; B1.40 g/hm²; B2.80 g/hm²; and B3.120 t/hm²) through a randomized blocks design with three repeated blocks in three 16-year-old poplar plantations respectively in the northern Jiangsu Province. The afforestation time was the same throughout the poplar plantation, and the condition throughout the poplar plantation was relatively consistent. Through statistical calculation, we analyzed the effects of biogas slurry and biochar.

Without the biochar application (treatment B0), the oribatida density in three soil layers within all the biogas slurry treatments was higher than in the control treatment (CK). Oribatida density in the soil layer at 0-10 and ≥10-25 cm increased with biogas concentration. Oribatida density in three soil layers decreased when biochar concentration increased. Oribatida density in soil layer 0-10 cm significantly increased under biogas slurry treatment M with biochar treatment B1, and under biogas slurry treatment H with biochar treatment B3.

Oribatida density significantly increased when concentration of biogas slurry increased on the scale of 0-0.375 t/hm². However, biochar treatment decreased the oribatida density. Further research such as accumulation of heavy metals and physicochemical properties is needed prior to scientific use of biochar and biogas slurry.