Causes of soil erosion and its effect on agricultureAbstract：soil erosion has a serious damage to agricultural, which can cause huge economic losses. The comprehensive management of soil and water is very important to develop our agriculture, control flood disaster, and promote the sustainable and healthy development of the national economy. Based on this, this paper expounds the main impact of soil erosion on agricultural in China, and puts forward the corresponding countermeasures.Keyword: soil erosion; damage on agriculture ; Nutrient loss; control and conservation.Recent years, with the rapid development of China's economy, to development our country`s industries we have sacrificed the much of our surrounding environment .It caused serious damage to the environment, the temperature rise, climate anomalies, flash floods and debris flow increased, especially the large area of forest and grasses have been disappeared, such phenomenon of soil erosion in China is more serious than before . China's field area is large, and the topography of the region has great differences, the situation of soil erosion, is also different in must places .to understand the situation of soil erosion, the cause of its further research, and its harm to agriculture , so as to achieve the development of modern agriculture, the development of the national economy.1 causes of soil erosionSoil erosion not only damage the local ecological environment and agricultural production conditions, resulting in poor people living in poverty, but also for the lower reaches of the river to bring serious damage to the flood of cement sand". Where the people's lives and property are severely lost, regardless of the towns and villages, the people's life and property, regardless of the urban and rural areas. Sediment deposition in lakes, reservoirs, river bed, the entire national economic construction is very far-reaching, in the provinces (regions) of varying degrees, there are such problems. China is a mountainous country, mountain area accounts for the land area of 2 / 3, and our country is the world on most widely distributed loess. Terrain fluctuation in mountainous and hilly areas. The loess or loose weathered crust is very prone to erosion in the absence of vegetation protection. In most parts of our country belongs to the monsoon climate, rainfall concentrated, the rainy season precipitation often with annual precipitation of 60% to 80% and heavy rainstorms. It is easy to cause soil erosion. The geological conditions and climatic conditions are the main factors causing the loss of soil and water loss in China. It can be divided into natural factors and human activities. The natural factors affecting soil erosion are: (1) the climate, such as precipitation, precipitation distribution, rainfall intensity, wind speed, air temperature, relative humidity and sunshine; (2) the topography, such as slope, slope length, slope shape, elevation, relative elevation, gully density; (3) geology, main the lithology and tectonic movement, rock weathering, hardness, water permeability for the occurrence and development of gully erosion and collapse, landslide, debris flow, Shan Hong erosion are closely related; (4) soil, soil erosion is the main object, the soil permeability, corrosion resistance, impact resistance great impact on soil erosion; (5) the vegetation factors, the main function of vegetation to prevent soil erosion, the rainfall interception of water conservation, soil improvement, holding small climate conditions, and can prevent the shallow landslide and erosion in a certain extent, vegetation destruction, soil erosion will intensify. Human activity isthe cause of soil and water loss occurrence, development or the soil and water loss can be controlled the dominant factor intensified human activities of soil and water loss are: deforestation, unreasonable use of land, land reclamation on steep slopes, slope farmland, overgrazing, shovel for digging turf. Indiscriminate disposal of slag, waste soil and so on. The destruction of surface vegetation, surface lose the protection of green vegetation, desertification, dump heavy rain, easy cause soil erosion. The formation of the Loess Plateau ", its myriad landscape, be reduced to fragments" is human caused by unreasonable use of land. China has a large population, food and fuel demand and other pressure, in the case of low productivity, land reclamation, one-sided emphasis on food production, ignoring the development of agriculture, forestry, animal husbandry and forestry, the only suitable for forest, animal husbandry and the use of land is also turned into agricultural fields. A large number of reclamation on steep slopes, even steep slope more and more poor, poorer and more cultivation, the vicious circle of ecological system; forest deforestation, and even arbitrary digging for roots, lawn, trees dropped, so that the surface of the bare, which are added to the soil and water loss. In addition, some of the basic construction does not conform to the soil and water conservation requirements, for example, unreasonable construction of roads, factories, coal mining, Quarrying and other, and the destruction of vegetation, reduce the slope stability, caused a landslide, collapse, debris flow and other more serious geological disasters.2 the impact of soil erosion on Agriculture2.1 soil erosion has increased the natural disasters such as flood, drought and other natural disasters.China's northwest land area is vast, about the total area of land, the impact of China's climate characteristics, a year of rainfall concentrated in the summer, autumn two season, and more in the form of heavy rain, and in the spring, winter two season precipitation is very little, if the water loss is not enough water, it will seriously dry early, pose a huge threat to agricultural production. In the southeast of China, the impact of the monsoon climate, the annual rainfall is relatively large, but the impact of the larger, often floods, droughts and other disasters. In regions such as Yunnan, Guizhou, annual precipitation although are mostly higher, but soil and water loss in the area serious, the formation of "surface water is expensive, such as oil, brawl groundwater flow situation, plagued by serious people's daily life and agricultural production.2.2 causes a large number of fertile lossOne is to lead to land degradation, farmland destruction, so that people lose the foundation of survival, threatening the national food security. China's per capita possession of arable land area is far below the world average, the contradiction between people and land, serious soil erosion and exacerbated this contradiction. China's loss of soil erosion and the loss of arable land is about 1000000 acres per year. Mountainous region of northern China, karst area in Southwest China and the upper reaches of the Yangtze River, have a considerable proportion of farmland tillage layer soil has drained, parent material exposed bedrock, completely lost the capacity of agricultural production. According to the scientific investigation, according to the current loss rate projections, 50 years after the Northeast Black Soil Zone 14000000 acres of arable land will be lost.2.3 every year the process of soil erosion takes a large amount of nutrients in the soilChina's annual loss of a large number of soil containing large amount of nitrogen, phosphorus, potassium and other nutrients, equivalent to more than 4000 million tons fertilizer,which is China's annual total output of chemical fertilizer, such as the 1978 I between the Kuomintang and the Communist Party of China production 436.8 million correct fertilizer, coincided with the year the loss of soil nutrient contents unchanged. According to the survey data show that the annual loss of soil nutrients in Shandong province can be converted into a million fertilizer Jiangxi annual loss of soil nutrients is equivalent to the use of about 10 million fertilizer. In some areas, the loss of water and soil erosion is too serious, the application of chemical fertilizers has been unable to compensate for the loss of nutrients. Agricultural ecosystem is a chain of energy conversion and storage, and the soil nutrient is the material basis of crops to achieve energy conversion, only to give adequate nutrients, crops can be stored in the form of carbohydrates more energy, to achieve high yield. At present, the soil nutrient loss, application of chemical fertilizers alone is not enough, and long-term excessive use of chemical fertilizer may cause the deterioration of the quality of the soil, the fertility decline, vegetation coverage density decreased, and form a vicious circle.3 Prevention and control of soil erosionAt present, China's soil erosion has not been cured effectively, but in some place there is still a trend of expansion. The management of soil erosion is an urgent and arduous strategic task faced by the sustainable development of our country.3.1 Comprehensive management of soil erosionSoil erosion is caused by the movement of surface runoff on the slope. The basic principle of the anti - smelting measures is to reduce the runoff of the slope, slow down the runoff speed, improve the soil water absorption ability and the ability to resist the erosion, and try to raise the erosion datum. In taking control measures, we should start with the formation of surface runoff, along the route of the runoff, the measures to local conditions, the combination of prevention and treatment. Only take a variety of measures to comprehensive control and focus on governance can make it work.3.2 Afforestation and grassConstruction of forest and grass vegetation is always watershed soil and water loss is one of the important measures, has a significant effect on the improvement of the ecological environment in the region. To take the most stringent measures, strict control of deforestation, deforestation, land reclamation, land to grow crops, overgrazing, Mining Quarrying and man-made damage to the ecological environment behavior disrupted geomorphic activity, to protect and develop the existing vegetation and soil and water conservation facilities as the focus, follow the principle of suitable tree and strengthen measures of soil preparation, do a good job in the management and protection of the enclosure, comprehensively improve the forestation survival rate and preservation. Reforestation and afforestation of barren hills and slopes with grass.3.3 Scientific research on water and soil conservationConstruction of forest and grass vegetation is always watershed soil and water loss is one of the important measures, has a significant effect on the improvement of the ecological environment in the region. To take the most stringent measures, strict control of deforestation, deforestation, land reclamation, land to grow crops, overgrazing, Mining Quarrying and man-made damage to the ecological environment behavior disrupted geomorphic activity, to protect and develop the existing vegetation and soil and water conservation facilities as the focus, follow the principle of suitable tree and strengthen measures of soil preparation, do a good job inthe management and protection of the enclosure, comprehensively improve the forestation survival rate and preservation. Reforestation and afforestation of barren hills and slopes with grass.3.4 Rational allocation of water and soil resourcesUsing the successful experience of foreign countries to solve the problems in the implementation of water and soil erosion prevention and control policies, to further optimize the comprehensive improvement of soil resources and improve the land conditions, to ease the contradiction between human and land. To harness of soil erosion in China is a long-term and arduous should have sufficient knowledge, we must adhere to the overall planning, focused, do according to one's abilities, step by step implementation of specified in the national ecological environment construction plan of soil and water loss control task. Continue to adhere to the existing successful experience, and vigorously implement the small river basin as a unit, comprehensive prevention and control of the technical route and measures to do a good job of demonstration, focus on breakthrough, the overall advance, accelerate the process of soil erosion prevention and control.3.5 Continuous capital investment management to reduce soil erosionThe state should set up special funds for water and soil conservation, and to ensure that the capital investment continued and stable growth; at the same time, formulate relevant policies, support and attract social capital targets, tasks and performance assessment of cadres, establish a sound leadership to actively participate in the management of soil erosion, forming a stable, diversified funding to protect the target responsibility system, layer upon layer.4 ConclusionThe impact of soil erosion on agricultural resources in many aspects, and it caused huge economic losses, we have to take long term measures to protect our environment and agriculture land. Comprehensive measures must be based on sustainable development for the purpose, not only the immediate interests to dark, to master the local actual situation, the comprehensive treatment. The relevant departments should enhance the understanding, strengthen the comprehensive management of the intensity, in order to ensure the smooth implementation of the management objectives planning.。