Objective  To study the improvement effect of urban sewage sludge addition on soil of rare earth mine wasteland, and the strengthening effects of adding bagasse and soil conditioner on the basis of sewage sludge, and provide a theoretical guidance for soil improvement of rare earth mining areas and utilization of urban sewage sludge resources.

Method  The soil of rare earth mine wasteland was selected as research object. Three treatments including adding sewage sludge (T1), adding sewage sludge and bagasse (T2), adding sewage sludge, bagasse and soil conditioner (T3) were set. The soil of rare earth mine wasteland was used as control (CK). Canavalia gladiata was chosen as test material to verify soil improvement effect through pot experiment. The physicochemical properties of testing soil and C. gladiata growth indexes were determined, and the soil improvement effects of different treatments were comprehensively analyzed by principal component analysis and fuzzy membership function analysis.

Result  Compared with the control, three treatments greatly improved the physicochemical properties of soil in mining area, promoted the growth of C. gladiata and the absorption of N, P and K nutrient elements. T1 reduced soil bulk density by 27.64%, increased total porosity by 23.91%, increased capillary water holding capacity by 42.41%, increased the content of organic matter by 11.01 times, and meanwhile greatly increased the contents of total P, alkaline hydrolytic N, available P and available K. The soil physical properties of T2 were better than those of T1, with organic matter content increased by 25.9% and pH increased by 0.32. The soil pH (7.22) of T3 was the highest, which was 49.17% higher than T2, and the contents of available P and available K increased by 0.46% and 11.05% respectively. The total plant biomasses of T2 and T3 were significantly higher than those of T1 and CK, and there was no significant difference between T2 and T3. The accumulations of N, P and K per plant reached the maximums in T2, which were 934.43, 172.07 and 931.35 mg respectively, and significantly different from other treatments. The average subordinate function values of CK, T1, T2 and T3 were 0.06, 0.56, 0.83, 0.90 respectively, and the soil improvement effects were ranked as T3>T2>T1.

Conclusion  The addition of urban sewage sludge significantly improves the soil of mining area, and the improvement effect is significantly enhanced by adding bagasse and soil conditioner on the basis of adding sewage sludge.