Analysis of soil physical properties under different vegetation types in the alluvial fan area of Manas River watershed

Soil physical properties of four vegetation types (Tamarix ramosissima, Halostachys caspica, Nitraria sibirica, Salsola spp.) were investigated in the alluvial fan area of Manas River watershed. The main results showed that in the horizontal direction, soil pH, total salt content and soil bulk density of Tamarix ramosissima were the lowest within the depth of 1m soil profile, and were 8.75, 0.97g/kg and 1.42g/cm super(3), respectively; while soil organic matter content, moisture content, total porosity and capillary porosity of Tamarix ramosissima were the highest and were 9.04g/kg, 16.67%, 45.57% and 36.18%, respectively. It was shown that the Tamarix ramosissima could reduce soil salinity and ameliorate soil structure significantly. In the vertical distance of soil profile, the total salt content of the four vegetation types in 0--20cm topsoil was the highest among different soil layers, so salinity accumulated in the form of salt efflorescence in surface soil. With the increase in soil depth, soil moisture content and soil bulk density showed significant increase, but soil organic matter content, field moisture capacity, total porosity, capillary porosity and non-capillary porosity were significant reduced (P < 0.05). The result of correlation analysis showed that soil organic matter was the main reason resulting in the change of other soil physical properties. Compared with the uncovered ground, soil organic matter content, total porosity and capillary porosity of the four vegetation types within the depth of 1m soil profile were improved significantly, and soil bulk density was reduced significantly, soil organic matter content was increased by 162.94%, 82.94%, 85.59% and 27.94%, respectively; total porosity was increased by 44.90%, 20.83%, 36.06% and 15.80%, respectively; capillary porosity was increased by 58.27%, 30.71%, 43.48% and 25.72%, respectively, and soil bulk density was reduced by 18.86%, 10.86%, 17.14% and 7.43%, respectively. It was shown that different halophytes growing in the saline-alkali soil in arid desert areas can ameliorate the soil quality significantly.