The Soil Moisture Content Research Of The Artificial Forest And Farmland In Xi'an Area

The soil plateau is situated at half arid and moist area, where the rainfall is little and concentrates, and the underground water buried depth is deep, which cause the soil moisture to be especially important in vegetation construction of the loess plateau. Surface evaporation and plant' s transpiration cause the soil moisture to be serious lost, and the dry layer has appeared in soil under some vegetation, especially under the artificial forest and grass vegetation displayed outstandingly. The dry layer not only influences the vegetation' s growth and renewal, but also threatens the following vegetation' s construction. Therefore, the research into the soil moisture change has an important practical significance to promote artificial forest' s normal growth, the forestry development and the ecological environment construction, as well as reduce the environmental disaster which possibly creates to in the loess plateau.Through the soil moisture content determination from zero to six meter of different artificial forest land and farmland in northern suburb, southern suburb and eastern suburb of Xi' an and Xianyang area, this article has studied the soil moisture restoration condition and consumption process of the artificial forest land and farmland in this local after a rainy year, as well as change rule of the soil moisture and influence factors and so on. The light manpower drill is used to gather sample, and the depth of drill hole is six meter, the sampling spacing is ten ceilometers, generally sixty samples are gathered each hole. The determination of soil moisture content adapted drying weight method which has been considered accurate and reliable. The places of Xi' an area were elected to be studied including Wujiafen, Miaopotou village in southern suburb, and Chang' an area of the southern suburb, as well as Pangxi village in Xianyang area and so on. Kinds of the artificial forest trees were chosen including the Chinese parasol, the French parasol, the polar, the cedar, the Chinese scholar tree and the White wax woods and so on. In addition, for the contrast, some determinations to the soil moisture content of weed places have also carried on.The annual precipitation of 2003 was 883mm, which is higher than the normal average annual precipitation, belongs to a rainy year of the Xi' an area. In 2004, the annual rainfall of Xi' an area reached 517.2 mm, is lower nearly 100m m than multiannual average precipitation, therefore, it belongs to the poor water year. In 2005 the precipitation of Xi' an area reaches 570 mm, which belongs to the normal precipitation year. Through the determination and analysis to soil moisture content of artificial forest land and farmland in the different precipitation years, we have obtained the below knowledge.(1) The soil moisture content under different artificial forest of Xi' an area is different. The research indicated, moisture content consumption of broad-leaf parasol and poplar tree is less than that of needle deodar cedar, but the moisture content consumption of the oriental arbor-vitae is least. Among the kinds of trees chosen, the soil moisture content from high to low in turn is that the Chinese parasol is highest, the French parasol tree is higher than the poplar tree and the white wax woods, the deodar cedar lowest. The main reason for the moisture content difference of artificial forest land is that different kind of trees' growth speed is different. But farmland, including wheat land and corn field, soil moisture content generally is high.(2) In the identical area, the precipitation and the length of precipitation season exist difference, creates the yearly dynamic change of the soil moisture. In rainy year the soil moisture content of artificial forest land is high, but in poor rainfall year and the normal precipitation year, the soil moisture content is low, even the dry layer appears.(3) The findings demonstrated, that under the condition that the precipitation surpasses 883.2 mm in 2003. The increased moisture content caused the soil to do the level to vanish, studied the area general soil moisture until 2006 to be still higher, only had the minority artificial forest land to do the level to appear once again. In the abundant year soil layer restores moisture content may maintain the planted forest more than 4 years" normal growths. However, because the planted forest soil moisture spending rate is quicker in Xi' an, after infers the abundant water year about 6 years, the more universal appearance the soil dry layer will appearance in this area.(4) Thcsampling place apple forest thickness of stand bigger in Xian yang, after passes through the abundant water year more than three years of moisture contents consumptions, therefore the soil dry layer grows once again, the more the center age apple forest trees age bigger, the level growth to be stronger.(5) The different type land utilization way is not same regarding the soil moisture degree of utilization, weed soil moisture content is bigger than the farmland, the farmland water content is bigger than the planted forest.(6) Because the soil dry layer is the moisture content transmission insulating layer, it vertically severed the precipitation to enter infiltrates the military supplies ground water the way. Therefore the soil dry layer not only to be able the indicator vegetation growth not to be normal, moreover had instructed the local water cycle is normal or not. At the year precipitation achieved above 800mm the abundant water year, the planted forest soil dry layer has already to vanish in Xi' an area, moreover could not appear after in the abundant water year two years soil dry layer, the water circulation restored normally in the short time. However, passes through three years half consumption, the planted forest soil moisture clearly reveals reduces, some already appeared soil dry layer, if the next year still for the normal year or the poor water year, the soil dry layer phenomenon also will continue to aggravate. The soil dry layer grew to instruct the local water cycle fell into once more not normally circulates the condition.(7) Although this area before 2003 has grows the weak dry level existence, but grows well from the planted forest looked, this local and the precipitation similar loess plateau half moist area is an area which basically is suitable for to afforest, but because the soil moistures insufficient, the forestation elected slow-growing tree seed, and should suitably reduce the thickness of stand...