Soil quality assessment of reclaimed land in the urban-rural fringe

The expansion of the urban-rural fringe (URF) has greatly boosted the economy, but haphazard building and chaotic management have severely harmed the soil, particularly valuable arable land resources. The majority of studies have focused on the regional identification of URF, with little research on the influence of URF on soil quality. The soil quality index (SQI) method was used in this study to compare the soil quality of reclaimed land (FKD) in the URF to nearby grain fields (GD), open-air vegetable plots (CD), and facility vegetable plots (DP) in Daxing District, Beijing, China. The results indicated that the SQI of FKD was much lower than that of other land utilization types. Soil organic carbon (SOC), nitrogen, and phosphorus levels were low in FKD and might be improved with proper fertilization in subsequent management. The contents of Na, Mg, Ca, Fe, and total po-tassium (TK) in FKD were not statistically different from those in GD and CD, but the urease and sucrase activities in FKD were significantly lower than those in the other three land use patterns. A minimum data set including SOC, available phosphorus, TK, clay, Mn, and Zn was obtained for soil quality assessment using principal component analysis with Norm value and correlation analysis. Soil trace elements were standardized using an "optimum is better" scoring function using the 75th percentile of the element background values as the threshold. To our knowledge, this is the first time in soil quality assessment that the 75th percentile of the element background value for a specific soil type has been chosen as the optimum value.