Abstract: Due to the massive amount of residue produced during shale oil extraction, enhancing the resource utilization of oil shale residue is of critical importance. We conducted a field experiment with four treatments (0, 3, 6, and 9 kg·m^-2 oil shale residue added to sandy soil), following a randomized block design. We analyzed soil physicochemical properties, heavy metal contents, enzyme activities, and microbial biomasses under different treatments. The relationships between soil microbial biomass stoichiometry and soil properties were clarified, and the feasibility of improving sandy soil with oil shale residue was explored. The results showed that adding oil shale residue to sandy soil could improve soil structure and enhance soil fertility. The addition of 6 kg·m^-2 oil shale residue resulted in an increase of 90% and 29% in soil water content and porosity, respectively, while bulk density decreased by 7%. The contents of organic carbon, alkalinehydrolyzable nitrogen, and available phosphorus were increased by 31%, 26%, and 97%, respectively. The activities of catalase, urease, phosphatase and sucrase were enhanced by 59%, 86%, 18%, and 37%, respectively. Microbial biomass carbon, nitrogen, and phosphorus were increased by 18%, 64%, and 136%, respectively. However, compared with the addition of 6 kg·m^-2, the treatment of 9 kg·m^-2 oil shale residue addition significantly decreased soil urease, phosphatase, and sucrase enzyme activities as well as the carbon, nitrogen, and phosphorus contents in microbial biomass. Soil microbial biomass carbon, nitrogen and phosphorus were positively correlated with soil water content, porosity, organic carbon, alkaline-hydrolyzable nitrogen, available phosphorus, and catalase, urease, phosphatase and invertase activities. Soil organic carbon was the main factor affecting soil microbial biomass stoichiometry. Therefore, the optimal addition amount of oil shale residue is 6 kg·m^-2, which can enhance microbial activities, the activity of soil enzymes, nutrient transformation and cycling, and soil environment.

Key words: sandy soil improvement, oil shale utilization, soil enzyme activity, microbial entropy, Horqin Sandy Land