Soil Quality Evolvement Mechanism Of Sand-Fixing Forests In The Area Of Yulin In Maowusu Sandland

Sand-fixing forests in the Area of Yulin in Maowusu Sandland had been researched in this thesis. Through representative investigation and Laboratory analysis, we studied general and systemic researches on soil physical properties, soil chemical properties and soil biological properties of different species and stand age of sand-fixing forests, discussed the evolution rules of soil quality of sand-fixing forests and the effect of sand-fixing forests protect soil. The results showed as follows:1. There were remarkable differences on soil moisture, soil bulk density and soil porosity in Salix psammophila, Hippophae rhamnoides, Hedysarum mongolicum, Hedysarum scoparium and Pinus sylvestris forests.In 0-5cm soils layer, the soil moisture of Hedysarum scoparium forest was biggest. The soil bulk density of 20 years Pinus sylvestris var. mongolica forest was least. The soil porosity of 20 years Pinus sylvestris var. mongolica forest was biggest. In 5-20cm soils layer, the soil moisture of Hippophae rhamnoides forest was biggest. The soil bulk density of Hedysarum scoparium forest was least. The soil porosity of Hedysarum scoparium forest was biggest. The soil moisture and soil porosity of 0-5cm soil layer were bigger than that of 5-20cm soil layer obviously in shrubbery, while the soil bulk density of 0-5cm soil layer were less than that of 5-20cm soil layer. With the forest stand age, the soil moisture and soil porosity increased, while the soil bulk density decreased.2. There were remarkable differences on soil organic substance, nitrogen, phosphor, potassium and pH in Salix psammophila, Hippophae rhamnoides, Hedysarum mongolicum, Hedysarum scoparium and Pinus sylvestris forests.In 0～40cm soils layer, organic substance and total nitrogen of soil was: Hedysarum scoparium forest>Salix psammophila forest>Hedysarum mongolicum forest>Hippophae rhamnoides forest>20 years Pinus sylvestris var. mongolica forest>Bare sand; total phosphor and available phosphor of soil was: Salix psammophila forest>Hedysarum scoparium forest>Hedysarum mongolicum forest>Hippophae rhamnoides forest>20 years Pinus sylvestris var. mongolica forest>Bare sand; available potassium of soil was: Hedysarum scoparium forest>Hedysarum mongolicum forest>Hippophae rhamnoides forest>Salix psammophila forest>20 years Pinus sylvestris var. mongolica forest>Bare sand; With the forest stand age increased, organic substance, total nitrogen, available nitrogen, total phosphor, available phosphor, total potassium and available potassium increased, while the pH decreased. In soil profile, the soil nutrients in top layer of Sand-fixing forest were a little higher than in sub-top layer except available nitrogen and pH; the effects of Hedysarum scoparium forest and Salix psammophila forest on soil chemical properties are remarkable.3. There were remarkable differences on the number of soil bacterium, actinomyces, fungi and the activity of urease, sucrase, catalase, alkaline phosphatase in Salix psammophila, Hippophae rhamnoides, Hedysarum mongolicum, Hedysarum scoparium and Pinus sylvestris forests.In 20 years sand-fixing forests, the number of bacterium, actinomyces and fungi under Pinus sylvestris var. mongolica forest and Hedysarum scoparium forest was biggest. The urease activity under Hedysarum scoparium forest and Hippophae rhamnoides forest was biggest. The sucrase activity under Pinus sylvestris var. mongolica forest and Salix psammophila forest was biggest. The catalase activity under Pinus sylvestris var. mongolica forest and Hippophae rhamnoides forest was biggest. The alkaline phosphatase activity under Salix psammophila forest and Hedysarum scoparium forest was biggest. With the Soil layer depth increased, the bacterium quantity, actinomyces quantity, fungi quantity, urease activity, sucrase activity, catalase activity and alkaline phosphatase activity decreased. With the forest stand age increased, the bacterium quantity, actinomyces quantity, fungi quantity, urease activity, sucrase activity, catalase activity and alkaline phosphatase activity increased.4. There were remarkable differences on the effect of soil quality protection in Salix psammophila, Hippophae rhamnoides, Hedysarum mongolicum, Hedysarum scoparium and Pinus sylvestris forests.In 20 years sand-fixing forests, the sediment transport rate of Hedysarum mongolicum forest was least, while the windbreak effect was best. The sediment transport rate of Hippophae rhamnoides forest was most, while the windbreak effect was worst. With the forest stand age increased, the sediment transport rate decreased, while the windbreak effect increased. In 0～10cm soils layer, the number of clay (Particle size<0.05mm)content of sand-fixing forests were bigger increased.5. There were distinct differences on the effect of improve soil quality in Salix psammophila, Hippophae rhamnoides, Hedysarum mongolicum, Hedysarum scoparium and Pinus sylvestris forests.The coverage of lichen was: 40 years Pinus sylvestris var. mongolica forest>20 years Pinus sylvestris var. mongolica forest > Hedysarum mongolicum forest> Salix psammophila forest > Hedysarum scoparium forest >Hippophae rhamnoides forest. In 20 years sand-fixing forests, the litter under Hedysarum scoparium forest was most, the litter under Hippophae rhamnoides forest and Hedysarum mongolicum forest was least. With the forest stand age increased, the litter under sand-fixing forests gradually increased and improve soil fertility.