砒砂岩不同类型区土壤氮磷养分特征

砒砂岩区生态环境脆弱，侵蚀剧烈，研究不同类型砒砂岩区土壤氮（N）、磷（P）养分特征，可为该区的植被恢复及生态修复提供理论依据和数据支撑。该研究以内蒙古准格尔旗什布尔太沟裸露区、二老虎沟覆土区和特拉沟覆沙区为研究对象，根据流域长度分别在什布尔太沟、二老虎沟和特拉沟的沟口至沟头处，各选5、8和4个断面，共计17个土壤断面，于各断面不同坡位，采集共计153个样点的土样，测定0～20 cm土层全氮（Total Nitrogen，TN）、氨氮（Ammonia Nitrogen，AN）、硝态氮（Nitrate Nitrogen，Ni）、全磷（Total Phosphorus，TP）及速效磷（Available Phosphorus，AP）含量。结果表明：1）砒砂岩土壤TN含量0.24～1.39 g/kg、AN含量5.07～30.70 mg/kg、Ni含量0.76～5.87 mg/kg、TP含量0.10～0.57 g/kg及AP含量0.97～7.63 mg/kg。2）覆土区土壤N、P养分平均含量最高，覆沙区次之，裸露区最低；同类型区内土壤AN、Ni和AP含量相关系数较高，整体上速效养分间的相关性相对更强。3）同类型砒砂岩区，坡顶与坡底附近，土壤TN、AN、Ni、TP和AP含量相对较高；阴坡土壤AN、Ni和AP整体养分水平高于阳坡。综上，可根据砒砂岩不同类型区不同坡位土壤N、P养分特征，因地制宜地进行植被恢复，遏制该区水土流失强度，促进砒砂岩区生态系统修复。

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.