Effect Of Grazing Disturbance On Soil Physical And Chemical Properties In Mountain Forest-Arid Valley Ecotone In The Upper Reach Of Minjiang River

Grazing disturbance was one of the most main anthropogenic interference factors in the ecotone between dry valley and mountain forest in upper reaches of the Minjiang River. Livestock have an impact on vegetation and soil environment through the ways of intaking, Trampling, excrement, also, the processes of palatability intaking, nutrients conversion, and excreta return affected soil nutrient cycling. Those changed the original ecosystem structure and functional characteristics, and were the important factor that caused the heterogeneity of vegetation and soil. Four typical vegetation types were selected in the ecotone between dry valley and mountain forest in upper reaches of the Minjiang River, that is black locust forest, berberis brushwood, grassland, and poplar-willow forest. Used line transect methods, and based on the grazing-path, from far to near, grazing disturbance included light, medium and heavy intensity in this paper, and to explore the impaction of soil properties under different grazing intensity in this area. The main results were as follows:(1)With grazing intensity developing, soil bulk density was increasing, compared to light disturbance intensity, soil bulk density of black Locust forest, berberis brushwood, grassland, and poplar-willow forest was respectively improved10.31%,23.21%,10.00%,15.42%,6.12%,7.55%,6.50%,13.36%. But the mean of soil total porosity, capillary porosity and non-capillary porosity in all vegetation types were reducing, they were46.49%,50.75%,52.56%;39.43%,41.59%,44.38%;6.89%,6.34%,8.67%respectively, compared to light disturbance intensity, the mean of soil total porosity, capillary porosity and non-capillary porosity under medium and heavy intensity reduced10%,13%;6.28%,11%;26.87%,20.53%respectively.(2) With grazing intensity developing, the contents of soil organic matter in black locust forest decreased linearly, compared to light disturbance intensity, they dereased respectively6.25%、25.77%under medium and heavy intensity, while the contents of soil organic matter in berberis brushwood, grassland, and poplar-willow forest showed the variation characteristics that decreased firstly, and then increased. Compared to light disturbance intensity, the contents of soil organic matter under medium and heavey intensity respectively decreased17.48%,9.31%;35.83%,30.96%;25.83%,8.19%.(3) With grazing intensity developing, the change trends of soil pH and soil nutrient were different, and the same as one soil nutrient in various vegetation types. For example, soil nitrogen content in black locust forest is light(2.13g·kg-1)>medium (1.80g·kg-1)> heavy intensity(1.55g·kg-1), but it becomes light(2.29g·kg-1)>heavy (2.17g·kg-1)>medium intensity(1.90g·kg-1) in berberis brushwood. Soil phosphorus content in black locust forest almost unchanged under different grazing intensities, they are respectively0.11mg·kg-1,0.10mg·kg-1,0.11mg·kg-1; soil phosphorus content in berberis brushwood is light (0.07g·kg-1)<medium(0.09g·kg-1)<heavy(0.11g·kg-1), however, light(0.08mg·kg-1)>medium(0.06mg-kg-1)>heavy(0.05mg·kg-1)in poplar-willow forest. Soil available potassium content in black locust forest is heavy(777.08mg·kg-1)>light(433.40mg·kg-1)>medium(344.66mg·kg-1); and so on.(4)Overall, for the characteristics of soil physical and chemical, the difference are significant between0-1Ocm and10-20cm soil layers, as well as among various vegetation types. The correlation analysis shows that there are correlations between soil physical and soil chemical characters, the correlation degrees are also various among different vegetation types, grazing disturbance intensity and soil nutrients.