沼液作为一种有机肥，富含多种营养元素及氨基酸、腐殖酸、吲哚乙酸等物质，能有效提高土壤肥力，减少化肥投入。生物炭是生物质经高温裂解产生的化学性质稳定的高度芳香化富碳固体物质，能缓释沼液的养分。采用沼液与生物炭混施杨树人工林，探讨土壤动物优势类群甲螨（oribatida）个体密度的响应，为进一步深入了解土壤动物及其生态过程，以及人工林的科学经营提供参考。

采用野外控制试验，在同一年份造林、立地条件相对一致的16年生杨树人工林内联合施用不同用量沼液和生物炭，沼液样方大小为10 m×12 m，施液量分别设置对照（0 t/hm²，编号CK）、低用量（0.125 t/hm²，编号L）、中等用量（0.250 t/hm²，编号M）和高用量（0.375 t/hm²，编号H）4个处理；再于每个沼液样地内设置4个不同生物炭施用量，即：对照（0 t/hm²，编号B0）、低用量（40 t/hm²，编号B1）、中等用量（80 t/hm²，编号B2）和高用量（120 t/hm²，编号B3）4个处理。通过计算各土层甲螨的个体密度，分析各用量沼液与生物炭联合施用对不同土层（0～10、≥10～25、≥25～40 cm）中甲螨类群分布规律的影响。

在单施沼液试验中(不施用生物炭), 3个土层中甲螨的个体密度均大于对照组(不施用沼液)；其中，0～10、≥10～25 cm土层甲螨个体密度均随着沼液施用量的增加而增大；而在施用生物炭试验中，B1、B2、B3处理的生物炭均降低了3个土层甲螨个体密度。在同一生物炭处理下，仅B1与施沼液M，及B3与施沼液H混施处理下的0～10 cm土层中，甲螨个体密度显著高于其他处理，其余各处理组对土层甲螨个体密度无显著影响。

单施用沼液，显著增加了甲螨的个体数量，在本试验设置的0～0.375 t/hm²范围内，甲螨的个体数量随施液量的增加而增加；而在所有沼液用量处理下，同时施用生物炭均降低了甲螨的个体数量，显示出显著的抑制作用，但其重金属累积或土壤理化性质等作用机制还有待深入。

Biogas slurry is a type of liquid residue formed after anaerobic fermentation of animal and crop waste. It contains a huge number of amino acids, humic acid, indole acetic acid, and other substances, as well as N, P and K in their ionic state. To improve yields and quality of crops, fertilizer has been overused in the past few years, and this could cause land degradation. As a type of liquid residue produced after anaerobic fermentation of animal and crop waste, biogas slurry can effectively improve soil fertility and reduce the use of fertilizer. Biochar comes from pyrolysis of crop wastes and other organic materials. Biochar can absorb biogas slurry and increase nutrient retention. Soil fauna is an important part of the ecosystem. Oribatida mites plays an important role in soil’s biological and ecological process. This study aimed to reveal the effects of biogas slurry and biochar on oribatida density in different soil layers (i.e. 0-10, ≥10-25 and ≥25-40 cm), providing a theoretical basis for the scientific use of biogas slurry and biochar.

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.