Objective  Fertility and enzymatic activity of the saline-alkali soil in relation to land use were analyzed for ecological improvements and restoration.

  Method  At sites on Songnen Plain in western Jilin province, the effects on organic carbon, total nitrogen, invertase, urease, alkaline phosphatase, and catalase of the saline-alkali soils under different types of land use as paddy farming field (N₁), dry farming field (N₂), wetland (S), and grassland (C) were compared.

  Result  The organic carbon contents in the soils ranged 9.70–16.27 g·kg⁻¹ under N₁, 3.85–11.58 g·kg⁻¹ under N₂, 2.14–2.97 g·kg⁻¹ under S, and 5.25–11.24 g·kg⁻¹ under C. and the total nitrogen, 1.83–2.32 g·kg⁻¹ under N₁, 0.45–0.76 g·kg⁻¹ under N₂, 0.34–1.28 g·kg⁻¹ under S, and 0.88–2.04 g·kg⁻¹ under C. and the total T/N, 2.29–7.11 under N₁, 8.89–15.28 under N₂, 2.00–6.42 under S, and 4.20–5.97 under C. The activities of various enzymes were urease (60.64–286.49 μmol·d⁻¹·mg⁻¹)＞alkaline phosphatase (9.22–48.05 μmol·d⁻¹·mg⁻¹)＞catalase (9.14–9.68 μmol·d⁻¹·mg⁻¹)＞sucrase (0.06–7.82 μmol·d⁻¹·mg⁻¹) and decreased along the depth of the soil layers. The invertase significantly correlated with C/N at P＜0.05, the urease with C/N at P＜0.01, the alkaline phosphatase with the organic C at P＜0.01 and with the total nitrogen at P＜0.05, while the catalase with total nitrogen at P＜0.01 and with C/N at P＜0.05. The redundant analysis indicated that the activities of invertase and urease were mainly regulated by the pH and bulk density, while those of alkaline phosphatase and catalase largely affected by the moisture content and electric conductivity of the soil.

  Conclusion  Land use exerted significant effects on the organic carbon, total nitrogen, and enzyme activity in the saline-alkali soils which gradually decreased from the surface to the deeper layers. Paddy farming on the land fostered the nutrient accumulation and increased the enzymatic activities in the soil. Thus, the type of land use was considered more ecologically friendly than wetland or grassland for the regions of saline-alkali soil.