Coal mining subsidence on soil nutrients and enzymes of artificial forest in northern China

Quantification and evaluation ofthe spatiotemporal changes in soil quality is importantto understand soil degradation mechanisms and restore the damaged land productivity. However, the effects of coal mining subsidence on the spatial and temporal characteristics of soil quality are not well understood. We investigated the contents of pH, organic matter (OM), total nitrogen (TN), nitrate nitrogen (NN), ammonia nitrogen (AN), total phosphorus (TP), available phosphorus (AP), available potassium (AK), total potassium (TK), cation exchange capacity (CEC), sucrase activity (SA), urease activity (UA), phosphatase activity (PA), catalase activity (CA) and dehydrogenase activity (DA) in the coal mining subsided area. The results showed that the contents of TN, NN, AN, TP, AK, TK, SA, UA, PA, CA and DA exhibited significant (P < 0.05) differences among the four seasons. Compared with the upper layer (0-20 cm), the lower layer (20-40 cm) contained higher contents of AN, NN, TN, TP and TK but lower contents of SA, UA, PA, CA and DA. The NN, AP, TP, AK and UA were identified as key indicators in the minimum dataset using principal component analysis. The seasonal changes of soil quality index (SQI) were in the following order: winter (0.707), spring (0.681), summer (0.616), and autumn (0.563). The spatial changes of SQI were highest for middle slope position 3 (0.508), followed by lower slope position 4 (0.507), top slope position 1 (0.446), upper slope position 2 (0.442), and bottom slope position 5 (0.437). Based on these spatiotemporal changes in soil quality, it was suggested that the application of multiple land use types may be a useful method for land reclamation and the interest of local farmers in the coal mining subsided area.