Yunnan The Chenggong Region Soil Erosion <sup> 137 </ Sup> Cs Tracer Study

Soil erosion is one of the most severe environmental problems today. China is among the countries with the most serious situation of soil erosion, especially in the red hilly area of the south which is the most important reservation of agricultural products. Soil erosion does not only bring geological disasters, but also has great impact on Chinese sustainable development of agriculture.This paper's sampling sites is at the basin of the south-eastern slope of Song Shan mountain of Cheng gong County in Yunnan Province. According to the Mass Balance Model built by Yang et al. (1998) applied for cultivated land and the soil profile distribution model for uncultivated land separately, we study the soil erosion of lands with different uses, using Caesium-137 measurements converted to soil erosion rates.This study confirms that the reference inventory of Caesium-137 is 962.34 Bq/m~2 in this area. Three kinds of land in the basin are monitored by the Caesium-137 inventories respectively: ranged from 51.05 to 669.36Bq/m~2 of land covered with wild grass, 39.48 to 1231.08 Bq/m~2 of dry farmland ranged and 0 to 1518.51 Bq/m~2 of woodlands with secondary masson pines; corresponding to Caesium-137 inventories, medium-term soil erosion rates are respectively2078.751～17553.9t/km~2·a, 230.94～17784.87t/km~2·a and 0～1990.64t/km~2·a).According to the standards of the Ministry of Water Resources , the whole region belongs to the area of middle to high intensity of erosion, and in some areas the erosion has been so serious that needs to be highly noticed. In accordance to the experimental results and the field survey, the soil erosion slightly at most of the woodlands covered by secondary masson pines on the top of the Song shan mountain, because of higher vegetation and the less devastating impact from human activities. However, it is much higher of the erosion rate of land with wild grass and dry farmland than that of the woodlands with secondary masson pines. The possible reason is that the human farming, such as ploughing, disturbs the soil. Meanwhile the favorable protective methods, like constructing terraces, have not been taken. It is concluded combining the test result and the actual situation of the survey that, Caesium-137 tracer technology of soil erosion is quite suitable for the Yunnan region, which deserves further promotion for better service for people's production and daily life.In order to develop the agriculture of Yunnan, people should first prevent soil erosion effectively. We propose to carry out protection to natural forests, and return farmland to forests and grasslands in practice. With the western development strategy, it is suggested to implement watershed management and continually enhance the level of soil erosion control.