Soil Erosion in Southeastern China of Red Soil Area —Causes, Effects and Countermeasures

3 Water Resources Bureau, Jiangshu, Province Abstract: Soil erosion causes soil degradation in the low hilly red soil region in the subtropical China. With the objectives to understand the cause, effects and countermeasures of soil erosion we conducted field studies at different scales. Land use changes contribute to the main causes for the serious soil erosion by water. The land use was changed significantly after the foundation of China and caused severe soil erosion. The first change was from the natural vegetation of secondary forest mixed of pine trees and broad-leaved trees into tea plantations (Camellia sinesis) during the period of the Great Leap Forward in late 1950s. The second change happened during the period of Reformation of Rural Land Tenure System in the late 1980s and the early 1990s, when farmers were allowed to make their own decision on land use. The tee trees and the untapped secondary forest were reclaimed for cash crops like peanut (Archis hypogaea) and fruit trees like edible citrus and chestnut (Castanea mollissima). Our catenary studies clearly prooved that the soil loss at a rate of 12 cm—16 cm per year led to the accumulation of sediments at the footslope under peanut cultivation irrespective of the soil parent material, either from Quaternary clay or from sandstone. The soil profiles showed that soil loss was at a rate of 12 cm—16 cm per year as accumulated at the toeslope position irrespective of the soil parent material, either from Quaternary clay or from sandstone. Selective transportation and distribution along the slope and clay lessivation in the soil profile resulted in the soil stratification in soil texture. These processes increased the environmental risks through intensified interflow after high input of agricultural chemicals. The results from the erosional plots of different farming systems indicates that the maximum soil losses for conventional farming systems amount to 21.23 Mg ha -1 a -1 . The enrichment ratio of soil nutrients is higher than 1.2, ranging from 2.57 to 6.19 for soil organic matter and from 1.90 to 2.45 for soluble N. In a small watershed with an erosion gully, where the plinthic horizon was exposed due to water erosion, the soil loss ranges from 53.4 Mg ha -1 a -1 to 256.32 Mg ha -1 a -1 . The modulus of soil loss by far exceeds the annual soil loss reported in the loess plateau in China, equivalent to the annual soil loss of 85 mm in depth within ten year. The loss of available soil nutrients by runoff and soil sediment can be as high as 10.84 kg ha -1 for NO3-N and 16.72 kg ha -1 for available K even though the soil has a very poor soil fertility. The innovative tillage and techniques of restoration of vegetation in bare land are developed to reduce soil erosion significantly. The soil loss under the minimum tillage with straw mulching is averaged 0.5 Mg ha -1 a -1 to 1.5 Mg ha -1 a -1 . After restoration of the vegetation cover in the bare land soil loss due to erosion hardly happens. The complex techniques of engineering and biological measures are established for the establishment of plantation in the infertile acid soil. The new tillage techniques and the restoration of the plants not only reduce the soil erosion, but also improve soil fertility as well as the soil physical properties, which strengthen soils against soil erosion. Macro-aggregates >1 mm and plant available soil water are increased, four years after reclamation. Although seriously erosion has been retarded due to restoration and conservation of vegetation, soil