Effect of cracks on soil characteristics and crop growth in subsided coal mining areas

To determine the effects of cracks on soil characteristics and crop growth in subsided coal mining areas, field investigation and laboratory analysis were conducted for the contents of soil water and available nitrogen, soil microbial characteristics and physiological properties of crops at points with different distances from soil cracks. The results showed that soil cracks conduced to the loss of soil water and nitrogen. The closer the sampling site was to the soil cracks, the lower were the contents of soil water and available nitrogen. The cracks had no effect on the contents of soil water and available nitrogen at sampling sites beyond 120 cm from the cracks. The change in the contents of soil water and available nitrogen led to changes in soil microbial characteristics. The closer sampling site was to a soil crack, the lower were the activities of soil enzymes (urease and sucrase) and soil respiration rate. The crack had no effect on soil microbial characteristics at distances beyond 90 cm from the cracks. The crack had significant effect on chlorophyll content and photosynthetic rate of wheat, but had no effect on chlorophyll content of wheat at distances beyond 60 cm from the cracks. At jointing stage, the cracks showed a significant effect on wheat leaf photosynthetic rate within 0 60 cm from the cracks. The cracks had no effect on wheat leaf photosynthetic rate at distances beyond 60 cm from the cracks. However, at flowering stage, the crack had no effect on wheat leaf photosynthetic rate at distances beyond 90 cm from the cracks. The cracks had different effects on yield traits of winter wheat. The cracks had significant effect on plant height, unit stem weight and grain number per ear of wheat within 0 60 cm from soil cracks. The crack had no effect on yield traits of wheat at distances beyond 90 cm from the cracks. The crack reduced spike number and yield of wheat. The closer the sampling site was to the cracks, the higher was the reduction in spike number and yield of wheat. Compared with the distance of 120 cm from the cracks, spike number and yield of wheat within 0 30 cm from the cracks dropped by 43.7% and 53.3%, respectively. Thus soil cracks caused loss of soil water and nitrogen that in turn decreased soil quality and crop yield.