Study On Soil Moisture Of Artificial Pinus Tabulaeformis In Loess Hilly Region

In this research, after the study of different stand density and different landform of artificial Pinus Tabulaeformis in Yichuan County on the Loess Hilly Region. And based on the long term data system, the soil water characteristics of artificial Pinus Tabulaeformis and its'relationship with the stand structure were analyzed, the mechanism and stability of interaction effects between community and environment were discussed. The results showed as follows:1. Stand density and tiny terrain had some influence on the characteristics of stand structure. The fine roots of different sites were mainly distributed in 0-60cm soil layers, its biomass accounts for 82.45%-96.37% of total fine roots, and it reduced gradually with the increasing of soil depth and very obviously below 20cm soil layer. With the increasing of stand density, the fine root biomass, DBH and crown diameter decreased, but the height increased. The growth of low-density stand was the best among several different sites. Viewd from the tiny terrain, the height and the diameter were the biggest on the upper of both shady slop and sunny slope, but the fine root biomass were least.2. With the increasing of the stand density, the soil bulk density, total porosity, capillary porosity and hold water performance had improved generally. The soil bulk density in low-density stand was 3.65% lower than that of high-density, while total porosity, capillary porosity and water capacity were 4.62%, 3.79% and 5.13% higher than of high-density,. The physical properties of soil on shady slop were better than that of sunny slope, as total porosity, capillary porosity and capacity were 1.08%, 0.63% and 0.60% higher. The improvement of physical properties of soil on the lower part were more obviously than other parts, both on shady slop and sunny slope. The soil bulk density, total porosity, capillary porosity and hold water performance in surface layer(0-20cm) were improved obviously. The improvement effects decreased with the increasing of soil depth.3. There were obvious vertical and seasonal changes of soil water with different densities and different terrain. Viewed from the vertical change, the soil water content decreased with the increasing of soil depth (P<0.05). It could be divided into the surface soil layer, water use layer and water stability and regulation layer. Viewed from the seasonal change, It could be divided into the soil moisture accumulation period (Last Oct. to May.), the soil moisture subsidise period (May. To Aug.) and the soil moisture recovery period (Aug. to Oct.). There were significant seasonal and annual variations of soil water content for rainfall reason, and showed 1 to 2 months lag. Viewed from stand density, the average soil water content in 0-300cm layer of different density showed: low-density (12.2%)> mid-density (11.9%)> high-density (11.8%). Viewed from the slope direction and positions, the soil water from top to bottom along the slopes showed the tendency of first increased and then decreased both on shady slop and sunny slope, the lower of shady slope (15.4%)> the lower of sunny slope (14.3%)> the upper of shady slope (13.4%)> the upper of sunny slope (13.3%)> the middle of sunny slope (13.0%)> the middle of shady slope (12.7%). But in 2002, the change on sunny slope was abnormal, the middle (13.1%)> the lower (11.1%)> the upper (11.0%).4. After being logged, the soil water of the artificial Pinus Tabulaeformis forest of 26-year-old on semi-cloudy slope got compensation and recovered, the soil water ecological conditions had met the needs of forest renewal after three rainy seasons. During early peroid of logging, the soil water content was just 10.3%, after that time, comparing with the end period of rainy season, except the 12th year-old forest which decreased 2.2%, soil water of 1st, 2nd, 3rd, 20th, 21st and 22nd year-old forest increased 5.3%, 4.3%, 2.8%, 2.4%, 5.3% and 3.7% respectively. The depth of recovery reached deeper than 200cm.5. Viewed from the availability of soil water, low-density woodland's was better than other woodlands'. The middle and the upper sites'were better than lower site's. There were relationships among soil physical indexes, roots and soil characteristics of different sample sites, therefore, the roots could improve the soil physical properties, and it was beneficial to the stability of the planted forest.