Characteristics of soil nutrient distribution in high-altitude meadow ecosystems with different management and degradation scenarios

In two high frigid meadow soil series of northwest Sichuan with different management and degeneration gradients,distribution characteristics of different soil nutrients were analyzed for three soil layers (0～20cm,20～40cm,40～60cm). The influence of management type and degradation degree on high frigid meadow soils was then discussed. Results show that soil organic matter, total nitrogen and phosphorus in natural pastures increase significantly after fencing and tillage. At the same time, available nitrogen and phosphorus contents increase remarkably. But the tendencies in 20～40cm and 40 ～60cm soil depths show a lesser magnitude due to soil layer compaction. A steady decrease in organic content is observed with the increase of meadow degrading level. With increasing depths, soil organic matter content decreases. Within the 0～20cm soil depth at increasingly aggravated degradation, soil organic content decreases by 32.6% and 52.1%.Changes in total nitrogen and phosphorus follow the above trend of organic matter, while change in total potassium is largely insignificant. Comparison with lightly degraded meadow, moderately and heavily degraded meadows own 1 5.1% and 28.6% decreased available nitrogen, 25.4% and 59.4% decreased available phosphorus. After fencing, tillage, vegetation rehabilitation is improved, degraded land soil nutrient content increases. However, tillage enhances soil penetration, mineralization and eluviation, resulting in lose of soil organic matter and NO₃-N, subsequently reducing soil carbon accumulation. Further more, plowing destroys inherent grass growing soil layer leading to sand-bed becoming dominant degenerated meadow features. Thus,tillage measures should be applied prudent ially in the sub-alpine rangelands of northwest Sichuan.