Soil Quality Evaluation In The Urban-Rural Marginal Area

The urban-rural marginal area is a connection belt and transition zone between the city construction district and the immense rural, which characteristics is neither similar with the typical city nor with the rural. The urban-rural marginal area is a special belt in which urbanization, industrialization and agri-intensivism happen most drastically in our country. As a result of the numerous importation of agricultural pollutants, garbage and industrial wastes, the urban-rural marginal area has became a combination which have the high concentration of land use and the high intensity of soil quality succession. A series of problems happen, such as the level of soil fertility decline, soil environmental quality deteriorates, and soil ecosystem functions weaken. All of these constrain the economic development of urban and rural and the steadily improving of human health in China.In the paper, taken Xiema town of Chongqing City as a case, the distribution and classification evaluation of fertility indicators and environmental indicators are first analyzed. Then, the membership evaluation of soil fertility quality and environmental quality is carried out. Finally, the soil synthesize evaluation is conducted. Conclusions as the following are drawn:1. The level distribution pattern of soil fertility in the urban-rural marginal area is not obvious, with the different changes of the physical and chemical indicators. This is influenced by the complicated land use, farming systems, crops and matrix. The profile distribution pattern of soil fertility in the urban-rural marginal area is obvious. The soil pH and total phosphorus is increased with deeper soil depth, otherwise the soil organic matter, total nitrogen, available nitrogen, available phosphorus and available potassium is reduced with deeper soil depth, The profile distribution pattern of total potassium is not obvious.2. According to the soil physical and chemical classification indicators, the bulk density is tighter, the clay content is low. In accordance with the classification indicators of soil nutrients, the soil organic matter content which is in and below III level accounts 74.47 percent, the overall level of organic matter is beside the middle. The soil total N content which is in and overhead III level accounts 98.73 percent, the overall level of total N is high. The soil total P content which is in and below III level accounts 98.73 percent, the overall level of total P is low. The available P varies severely; the higher and lower value accounts a certain proportion. The overall level of available K is beside the middle.3. In accordance with national environmental standards for II level, the single-factor pollution index of Cd is at the level of mildly contaminated, the single-factor pollution index of Cu is at the level of safety. The ration of Cd pollution degree in heavy pollution, moderate pollution and light pollution are respectively 17, 19.1, and 31.9 percent. The ration of Cu in light pollution degree is 19.15 percent, and the others are in the safety degree. According to Chongqing heavy metal background value, the index of potential ecological hazard4.Taken organic matter, total N, available N, total P, available P,, total K, available K pH, clay content, bulk density for the evaluation indicators, the soil fertility quality is evaluated with Fuzzy mathematics and Gray system methods. The results are both very good correlation. Compared the results of the two methods, the index of Fuzzy mathematics has the better resolution than the index of Gray system. The indicators more relevant for the Soil fertility index are available K, available P, available N, soil organic matter, pH. These should be given priority in selection of indicators for soil fertility evaluation5. Taken the total Cd and Cu as indicators, the soil environmental quality is evaluated with Gianni Merlo index method. Gudging from the soil environmental quality index, 73.4 percent of the soil samples have been contaminated. The soil of urban-rural marginal area has been seriously polluted.6. Based on the soil fertility quality evaluation environmental quality evaluation, the soil quality composite evaluation is conducted. Judging from the soil quality composite index, the soil quality in urban-rural Marginal Area is below the middle level. This is a combined result of soil productivity degradation and soil pollution.