| In the hill region of the Loess Plateatu,serious soil and water loss and arid climate are the two main ecological problems. In order to estimate the effect of soil and water conservation of plantation correctly, and offer scientific bases to the research on areal water cycle, we selected Robinia pseudoacacia,Hippophae rhamnoides,Caragana Korshinskii and grass land which have come into being for more than 30 years by natural succession as a control in Ansai County. We investigated the relationship between the age of forest and the hydraulic propertities of soil by using field experiment and interior analysis.The main results are as follows:1.As the age of stands increased, the aboveground biomass,aboveground litters and the underground biomass of different forests increased. Hippophae rhamnoides and Caragana Korshinskii came into being matured early comparing with Robinia pseudoacacia. At the early stage of forests, the plantation grew fast, having ecological effect, but grew slowly afterwards.2.The specific root length of young forest is longer than that of matured forest. For Robinia pseudoacacia, the specific root length of 10 years old was 2.4 times longer than that of 30 years old; for Caragana Korshinskii, the length of 14 years old was 0.7 times longer than that of 24 years old, and 0.4 times longer than that of 50 years old; for Hippophae rhamnoides, the length of 15 years old was 0.4 times of that of 24 years old. The results showed that the young forest have more abilities to use water and nutrients.3.Plantation have significant effects on soil aggregate,bulk density,soil porosity and organic matter content. Clay particle in wood land was below 10%, organic matter content was between 4.53g/kg～9.23g/kg, both in a low level.4.The soil water characteristic curve equation isθ= AS-B, the correlation coefficient was high, the value of A was between 10.697～22.454, averaged 14.674. The results showed that the water holding capacity of plantation decreased with the clay particle content decreasing. As the age increased, field water capacity,effective water content,water holding capacity and drought resistance increased. At the low suction stage, the specific water capacity of soil in Caragana Korshinskii land was higher than that in Robinia pseudoacacia and Hippophae rhamnoides land. At the high stage, there was a little difference among them.5.Soil hydraulic conductivity was higher at the matured stage when the saturated hydraulic conductivity of Robinia pseudoacacia land was higher than that of Hippophae rhamnoides and Caragana Korshinskii land. Soil saturated hydraulic conductivity decreased significantly as the soil layer was deeper.6.Soil water can be supplied by rain water when it is rainy. In October 2007, soil water content in 0～140cm layer was more than 10%, it was even 13~18% high in 100cm and the soil of 200cm layer can be supplied.7.Correlation analysis was used to investigate the relationship between soil hydraulic properties and physical properties,root system properties. The results showed that the aggregation was better, the water holding capacity was higher. Soil hydraulic conductivity was mainly affected by soil aggregate and soil porosity, and there was a positive correlation between them. There were affinities between water holding capacity,soil hydraulic conductivity and root system biomass,root length,surface area. The water holding capacity of soil with a great root system biomass and small specific root length was high, soil hydraulic conductivity was high when the root surface area was big and the root was long. |
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