Study On The Soil Physical And Chemical Properties Of Alpine Meadow Under Different Degradation Degrees

Based on the investigation and analyses on the plant communities of alpine meadow in Jinqiang River valley of Tianzhu Country, Gansu Province, three representative sampling plots were selected according to the degradation degree and utilizing pattern, and they were marked as light-degraded meadow (LD); moderately degraded meadow (MD) and heavily degraded meadow (HD). The differences and the soil physical and chemical properties were studied. Meanwhile, the relationships among soil nutrient contents were analyzed.1. Characteristics of plant communities of degraded alpine meadowBecause of long-term continuous grazing pressure, the grassland degraded in different degrees and the species diversity, richness and evenness of plant communities were obviously decreased. The dominant plant species (Kobresia spp., Polygonum viviparum) of plant communities were replaced by forbs and poisonous grasses (Oxytropis spp., Pedicularis spp., Gentiana spp.). The total coverage and aboveground phytomass of grassland decreased along with the degraded degree. Compared with MD and LD, the coverage of HD decreased by 40% and 20%, and the aboveground phytomass decreased by 24.92% and 15.89%, respectively.2. Soil properties of degraded alpine meadowThe soil physical properties showed remarkable vertical variation pattern with the soil depth. The soil moisture decreased gradually (0 to 5cm increased in upper layer and then decreased in lower layers), on the contrary, the bulk density of soil and soil pH value increase gradually increased. With the degradation degree, the soil moisture decreased gradually but the bulk density of soil and soil pH increased.3. Change of soil organic matter content of degraded alpine meadowSoil organic matter content showed an decrese and then invrease trend within 0cm to 5cm along with the degradation degree, and within 5cm to 10cm, it gradually reduced. The difference of soil organic matter content within 0cm to 5cm among sampling sites was significant (p<0.01), and no significant difference within 5cm to 10cm (except LD). This suggested that the the soil degradation in upper larer was more serious than that in deeper soil layer. In general, the soil organic matter content within 0cm to 10cm gradually reduced along with with the grassland degradation degree.4. Change of soil nitrogen content of degraded alpine meadowAlong with the increase of soil degradation degree, the soil nitrogen content within 0cm to 10cm showed a decrease and then increase trend. The soil nitrogen content within 0cm to 5cm reduced, and the trend within 5cm to 10 cm was same with that of 0cm to 10cm. Howevr, the available nitrogen content showed an increasing trend along with the degradation degree and the difference was significant (p<0.01), this trend was opposite to the total nitrogen content.5. Change of soil phosphorus content of degraded alpine meadowAlong with the soil degradation degree, the total soil phosphorus content within 0cm to 10cm layer presented a decrease and then increase trend. But in general, it showed a decrease trend. The available phosphorus content revealed a trend of decline along with the degradation degree and the difference was significant (p<0.01) among sampling sites.6. Relationship between soil nitrogen and phosphate contentsWithin 0cm to 10cm layer, The relationships among total nitrogen, total phosphorus, available phosphorus and available nitrogen were significant (p<0.05). The contents between available phosphorus and other nutrients positively correlated (p<0.01) and negatively correlated with available nitrogen. The available nitrogen content was negatively correlated with other nutrients7. Relationship between SOM and soil nitrogen and phosphate contentsSOM was positively correlated with total nitrogen, total phosphorus and available phosphorus (P<0.01), and negatively correlated with the available nitrogen (p<0.01). The soil total nitrogen, total phosphorus and available phosphorus contents increased along with SOM. SOM showed negative correlation with available nitrogen. The regression equation between SOM and soil nutrients as follows: y=31.049x-52.486, r~2=0.855(for total nitrogen); y=-0.330x+308.362, r~2=0.329(for total phosphorus); y=20.851x-20.485, r~2=0.524 (for available phosphorus); y=452.801x-22.453, r~2=0.822(for available nitrogen).