Effects of land use type on soil available trace elements in the rocky mountain area of north China

The rocky mountain area of north China is an important functional area for water conservation, sand fixation and soil-water retention in Beijing-Tianjin-Hebei. It is an important barrier to maintain the ecological security of Beijing-Tianjin-Hebei. Soil nutrient conservation capacity is an important factor affecting the construction of ecological engineering. Soil trace elements are an important part of soil fertility and are strongly influenced by land use types. To reveal the effect of land use type on soil available trace elements in the rocky mountain area of north China, the contents of soil available Fe, Mn, Cu and Zn at 0 – 15 and 15 – 30 cm were investigated considering three land use types (cropland, grassland and forestland) in Chongli district, Zhangjiakou City. The results showed that the land use type had significant influence on the content of the soil available trace elements (P < 0.05). Contents of available Fe and Mn in cropland were significantly lower than those in forestland and grassland, with mean values of 10.46 and 10.94 mg·kg^–1, respectively. The available Zn content (average value 2.58 mg·kg^–1) in cropland was significantly higher than that in forestland and grassland. The available Cu content (0.67 mg·kg^–1) in cropland was significantly higher than that in grassland and exhibited no significant difference (P > 0.05) from that in forestland soil. The available trace elements in forestland and grassland soil showed surface polymerization, while that of available trace elements in vegetable plots in 0 – 15 and 15 – 30 cm of soil showed no significant difference. The contents of soil available Fe and Mn were positively correlated with the soil organic matter, but negatively correlated with the content of soil available Cu and Zn. The soil organic carbon content of cropland was significantly lower than that of forestland and grassland, with a mean value of 1.99 g·kg^–1. These results provide a theoretical reference for soil nutrients management and sustainable land use.