Acidification Status Of Purple Soil And Its Mechanism In Chongqing

Soil acidification is one of the important process of soil degeneration, which lead to decrease of pH, lose of base and nutrient, enhancement of aluminum and heavy metals activation, consequently resulting of deforestations and desease of crops' yield. Once the acidified leaching water enters into water bodies, such as lakes, rivers, etc, it would cause acidification of them and death of fish. The effect of soil acidification on terrestrial and aquatic ecosystem will increase with time. Therefore, soil acidification is one of the serious environment problems in the world.Soil acidification is a slow natural process. However, human activities had rapidly accelerated the process in recent decades. There are two artificial factors that effect on soil acidification, one is acid precipitation caused by air pollution, another is abuse of chemical fertilizer. Because a large region of acid rain occured in south of China, many researched had focused on soil acidification caused by acid precipitation and had neglected that caused by chemical fertilizer. The method that simulated acid deposition on soil was usually adopted to reveal the effect of acid precipitation on mobilization of chemical element in soil. This method could not to quantitatively analyse and express the degree of soil acidification, because it lacked of dynamic field monitoring documents and relative cases. In this paper, aimed at the limits of previous studies, the purple soil in Chongqing, which was serious damaged by acid precipitation, was selected as study objective. The study carried out through investigating region of soil acidification, leaching experiment of simulated acid rain and consulting long-term monitoring documents of experiment in field soil, aimed to discover between acid precipitation and fertilization which lead to soil acidification, then understand the current status of soil acidification and mechanics through macroscopical and microcosmic ways.The investigation of soil acidification in this paper based on the data of the soil investigation of Chongqing in 1980's and the report on the environment quality of vegetable base of Chongqing in 2002. At the same time, the representative soil samples from Chongqing were collected to analysis the pH, exchangeable acidity, exchangeable aluminum and acidic buffering ability. Changes in soil acidity of Chongqing in recent two decades were known by comparing the data of two stages.The status purple soil acidification in Chongqing was showed by investigation. In the middle of 1980's, soil acidification only occurred in some regions rather than all of the Chongqing. Comparing to the 1980's,the alkaline purple soil of farm in Chongqing had decreased. However, the acidic purple soil had increase in some degree. The soil pH had decrease, but the exchangeable acidity and exchangeable aluminum had increase. It could be predicted that the area of soil acidification have expanding trend and that the degrees of soil acidification have deepening trend.In order to request the effective factors of soil acidification in vegetable base, two-factor, four-level was designed in the leaching experiment by simulated acid rain. This experiment included treatment with simulated rain of four pH levels (pH3.5, pH4.5, pH5.5 and pH6.5) and fertilizer in four doses (Control, Organic fertilizer, Chemical fertilizer, Organic and Chemical fertilizer). The soil chosen for model experiment was neutral and acid gray-brown purple soil. Prior to be put into the plastic columns with 5.4cm diameter and 30 cm of height, the air-dry soils were ground to < 3.0mm, then mixed with the fertilizer as required. The soil in each column was 595.6 grams in weight, 20 centimeters in height. According to the annual mean precipitation of Chongqing in recent years, the precipitation in this experiment was chosen as the 70% of 1200mm, which deduct the stream on the earth's surface. The volume of the every-month rainfall was applied on the basis of its monthly distribution characteristic. The leaching speed in 100ml per hour and 1c...