Characteristics of soil nitrogen and phosphorus nutrients in different Pisha sandstone areas

The Pisha sandstone area has been subject to highly intense soil erosion in the semi-arid regions in China, particularly in the reaches of the Yellow River. The typical area of Pisha sandstone is characterized by the soil nitrogen (N) and phosphorus (P) nutrient characteristics, indicating the ecologically fragile rock with the water infiltration. Therefore, it is very necessary to explore the influencing factors behind the restoration of degraded vegetation and ecological environment in this area. In this study, the study area was located in Zhungeer Banner, Ordos, Inner Mongolia, China. The Shibu Ertai-gully, Er Laohuo-gully and Tela-gully were used to represent the exposed, the soil-covered, and the sand-covered Pisha sandstone area, respectively. A total of 17 soil profiles were collected from the mouth to the head of three gullies with 5, 8, and 4 profiles, respectively, depending on the length of the catchment. Nine sampling points were selected at the different slope positions in each section. The soil samples were collected from a total of 153 sampling points. After that, the soil samples from 0-20 cm soil layers were tested for nitrogen and phosphorus to determine the levels of Total Nitrogen (TN), Ammonia Nitrogen (AN), Nitrate nitrogen (Ni), Total Phosphorus (TP), and Active Phosphorus (AP). A correlation analysis was carried out on the distribution characteristics of soil nitrogen and phosphorus contents in the study areas. The results are indicated as follows. 1) The soil N and P contents were ranged from 0.24-1.39 g/kg for TN, 5.07-30.70 mg/kg for AN, 0.76-5.87 mg/kg for Ni, 0.10-0.57 g/kg for TP and 0.97-7.63 mg/kg for AP. 2) The maximum content of soil N and P nutrient was found in the soil-covered Pisha sandstone area, followed by the sand-covered Pisha sandstone area, and the minimum in the bare Pisha sandstone area. The AN, Ni and AP contents of soil N and P were more significant than the TN and TP contents. The correlation coefficients for the soil AN, Ni, and AP content within the same type of Pisha sandstone area were ranged from 0.45 to 0.95. The correlation between the active nutrients was relatively stronger than the full amount of nutrients in the context of the totals as a whole. 3) The levels of soil TN, AN, Ni, TP, and AP were much higher at the top and bottom of the slope than those at the slope surface (upper part, middle, and lower part of the slope) in the same type area of the Pisha sandstone soils. The soil AN, Ni, and AP nutrient contents were relatively higher on the shaded slopes, compared with the sunny slopes in the same type of Pisha sandstone. Consequently, some suggestions can be given during the ecological restoration of the area to choose reasonable ecological management, according to the characteristics of the nitrogen and phosphorus nutrient content levels of the different types of Pisha sandstone soils. This finding can provide a sound reference for the ecological restoration in the Pisha sandstone region.