Soil quality assessment based on soil microbial biomass carbon and soil enzyme activities

Soil quality evaluation is one of most important approach to analyze the effects of soil management practices on soil quality. Using data from a short-term land use experiment (four years) in the Songnen Plain, this study investigated the effect of five land use types including cropland, restored grassland, Leymus chinensis grassland and Leymus chinensis grassland for mowing and Alfalfa forage land on the changes of soil microbial biomass carbon (MBC) and four enzyme activities (catalase, urease, alkaline phosphatase and invertase). Additionally, the soil qualities under different land uses were evaluated using the soil quality index. Results showed that land use treatments had a significant effect on the soil MBC and activities of urease and invertase, whereas no significant differences were found for the activities of catalase and alkaline phosphatase. Grassland colonization significantly increased the soil MBC and soil enzyme activities. Soil invertase activity was the most sensitive indicator to land uses with a sensitivity index greater than 1.94, while soil catalase activity was the least sensitive indicator to land use types with a sensitivity index less than 1.13. Numbers of sensitive index larger than 1.50 at Alfalfa forage land, restored grassland, Lyemus chinensis grassland and Lyemus chinensis grassland for mowing were 4, 3, 2 and 1, respectively, indicating the improvement of alfalfa planting on soil microbial indicators was better than other land use treatments. All the two soil quality indices based on linear and non-linear scoring method can accurately reflect the effect of land uses on changes of soil quality due to the significant positive correlation between the two indices. Conversion from cropland to grassland significantly improved the soil quality in the study area. Soil quality index in the Alfalfa forage land was the highest with a value of 0.89 for linear scoring function and 0.60 for non-linear scoring function, followed by the restored grassland, Leymus chinensis grassland and Leymus chinensis grassland for mowing, and the land use type of cropland has the lowest soil quality index with a value of 0.55 for linear scoring function and 0.30 for non-linear scoring function. Our results indicated that the alfalfa plantation may be a good land use practice for poor soils in the study area.