Effect of areas of land used for engineering construction on soil moisture and nutrient in the alpine steppe regions of the Qinghai-Tibet Plateau

The area of land used for engineering construction greatly affects the restorable degree of destroyed natural steppe on the Qinghai-Tibetan Plateau. An experiment was carried out to disclose the effect of land use for engineering construction on the conservation of water, potential nutrients, and present nutrients of soil in land that had been used for engineering construction and had experienced identical restoration periods. This study showed that the soil moisture content did not different between land used for engineering construction and natural steppe when the area used for construction was below 254 m2. Furthermore, the soil moisture of land used for engineering construction was smaller than that of natural steppe when the area used was 583 m2 (P<0.05). The organic matter content at a soil depth of 0-10 cm in land used for engineering construction was bigger and that at a depth of 10-20 cm was smaller than that of natural steppe when the area used for engineering construction was below 254 m2. However, the organic matter content at both soil depths in land used for engineering construction was smaller when the area used was 583 m2 (P<0.05). The soil total nitrogen content did not differ between land used for engineering construction and natural steppe when the area used was 55 m2. The soil total nitrogen, ammonium nitrogen, and nitrate nitrogen contents of land used for engineering construction were significantly lower than those of natural steppe (P<0.05) when the land used for engineering construction was over 156 m2. The amplitudes of these declines in nitrogen content correlated with the area of land used for engineering construction. The total phosphorus content at a soil depth of 0-10 cm first increased and then decreased as the area of land used for engineering construction increased (P<0.05), peaking at 156 and 254 m2. The available phosphorus contents at soil depths of 0-10 and 10-20 cm first decreased and then increased as the area of land used for engineering construction increased, reaching nadirs at 156 and 254 m2. The total potassium and available potassium contents in soil first increased and then decreased as the area of land used for engineering construction increased, peaking at 254 m2. The total potassium and available potassium contents of land used for engineering construction were lower than those of natural steppe when the area used was over 254 m2, and they were bigger than those of natural steppe when the area used was below 254 m2. These results suggested that the conservation of water, potential nutrients, and present nutrients in the soil of land used for engineering construction were similar to those of natural steppe when the area of land used for engineering construction was below 254 m2, but differed in larger areas, when all the tested areas had experienced identical restoration periods.