Effects of land subsidence resulted from coal mining on soil nutrient distributions in a loess area of China

Underground coal-mining results in severe land subsidence then changes soil nutrient distributions. Soil organic matter (SOM) and total nitrogen (TN) are critical indicators of soil quality and play a key role for plant growth. However, fewer scholars pay attention to the soil nutrient distributions in mining subsidence areas. In this study, a total of 64 soil sampling points, taken from 4 different plots (one unmined plot, two subsided plots and one reclaimed plot), were collected from No.3 Anjialing underground coal mine in the loess area of China. SOM and TN at the depths of 0-20, 20-40, 40-60 and 60-80 cm in these sampling plots were measured. The classical statistics and geo-statistics were used to analyze the vertical and horizontal spatial variability of SOM and TN. The mechanisms of the effects of coal mining subsidence on soil nutrient distribution were revealed based on the distribution of the surface cracks of subsided plots. All of SOM and TN at the depth of 0-20 cm in subsided plots were less than those in unmined plot. Below the depth of 20 cm, TN in subsided plots were higher than those in unmined plot and SOM were less than those in unmined plot. SOM in reclaimed plot were higher than those in subsided plots; however, TN did not exhibit a clear regularity. Land subsidence increased horizontal spatial heterogeneity of SOM and TN distributions. The crack width, crack depth and the distance between sampling point and edge of crack were the main influence factors resulting in horizontal spatial heterogeneity of SOM and TN. This study can provide a theoretical and technical reference for land rehabilitation in subsided lands in loess area.