Spatial Variability Of Soil Quality In The Dry Valley Along A River's Length Of The Hengduan Mountains

Typical dry valley in the Hengduan Mountains of southwest China is very susceptible to soil degradation and ecological deterioration due to environment fragility and special climate of dry and monsoon pattern. Soil physical and chemical properties along the river and altitudinal gradient have been studied, and characteristics of changes in soil properties and their contributing factors along the river and altitudinal gradients are also probed. In order to assess the impacts of environmental gradients and long-term land use patterns on soil fertility quality of dry valleys soils, soil physical and chemical fertility regime in dry valley of Heishui River in Ningnan and Puge County, one first order branch of the Jinsha River, have been monitored.1 Changes in soil physical properties along the river gradients. Soil physical parameters degradation present zonal differentiation in the upper reach, middle reach and lower reach, such as graved content, macro-aggregate, hydraulic conductivity, bulk density and so on.2 Changes in soil chemical properties along the river gradients. Soil organic matter and available nitrogen showed the same tendency. The results show that organic matter and nitrogen content were easy to degrade at Tuomugou and Hulukou town. Soil available phosphorus along the river gradients was higher at Puge County. Soil exchangeable cation and exchangeable base increase along with the river gradients except Puge and Qiaowo town. Soil chemical fertility quality of Heishui Valley could beclassified three categories along the valley.3. Changes in soil chemical properties along altitudinal gradients. There was no difference in soil organic matter of all elevations. Available nitrogen and available phosphorus along Masangping altitudinal gradients were highest from 1100m~1200m asl.; while along Ningnan altitudinal gradients they were highest from 1100m~1200m asl, and would decrease with elevation. Available nitrogen and available phosphorus along Hulukou altitudinal gradients deteriorated greatest from about 700 m asl.Soil exchangeable Ca, Mg and base along Masangping altitudinal gradients were highest at 1400m asl. and exchangeable K was lowest in riverbank. Soil exchangeable cation and base decreased along Ningnan altitudinal gradients with elevation while increased above 2000m asl. Soil exchangeable Ca, Mg, Na and base along Hulukou altitudinal gradients decreased with elevation while soil exchangeable K increased with elevation.4. Impacts of land use patterns on soil fertility. Soil fertility parameters degrade quickly after exploitation of wasteland. Soil fertility was improved under paddy cultivation and kailyard. Cluster analysis of soil chemical fertility of dry valley show that soil exchangeable base/exchangeable Ca, exchangeable K/exchangeable Mg, organic matter / available nitrogen / total nitrogen / total phosphorus/available phosphorus, pH reflected soil fertility quality integratedly, and assessment indices of soil chemical fertility quality in dry valley could be established based on these parameters.