| Rudong County, situated in the southeastern part of Jiangsu Province, is in the lower reaches of the Changjiang River and close to the Yellow Sea. It has an area of 1872 km2, 1.622 million mu of which is farmland. The average amount of farmland for each person is 1.4 mu, which is below the national level and over the provincial level that is 1.3 mu per person. Farming mainly consists of rice, wheat, cotton and vegetables which are harvested twice every year. The 2nd national soil survey shows the main problems with soil fertilizers in this area as follows: 1. The low content of organic compounds keeps decreasing. The average content of organic compounds in 20-cm-thick soil is 14.2g/kg, which, compared with that of 1974, has reduced by 0.9g/kg. Only 105,000 mu of farmland, 6.5% of the total, contains over 20g/kg of organic compounds while 161,000 mu, about 10% of the total, contains less than 10g/kg of organic compounds. The decrease of organic compounds has caused the hardening of the furrowing layer, the worsening of soil structure and the lessening of holding water and fertilizer. 2. The maladjusted soil nutrients show great inconsistency. The average content of nitrogen is 0.91g/kg, which is below the average level, and it is 0.6-1.2g/kg in 80% of the farmland. There is a great lack of phosphorus. The content of quick-acting phosphorus is 4mg/kg on average and less than 5 mg/kg in 70% of the soil. The littoral soil contains some potassium while most soil lacks it. The content of quick-acting potassium is 138mg/kg on average and less than 80mg/kg in 15% of the soil. The whole soil condition is that nitrogen, phosphorus and potassium. 3. The yield of rice is high while the fertilizing structure is unreasonable. That leads to the result that output is larger than input. The proportion of organic and inorganic fertilizers is 3:7 and that of nitrogen, phosphorus and potassium is 1: 0.35: 0.20.For a long time, agriculture has mainly aimed at the single and total yield. The fertilizers are mainly nitrogenous fertilizer, phosphorus fertilizer and low-density composite fertilizer. Thus in the area arises the problem called "Emphasizing on fertilizer while overlooking organic fertilizer; emphasizing on nitrogenous fertilizer while overlooking nitrogenous potash fertilizer; emphasizing on macroelements and overlooking microelements ". The costs of fertilizers keep high. The natural environment and the quality of crop products for agricultureare getting worse and worse. And the people's health is greatly threatened. In order to keep up with the development of farm products without environmental pollution, there is great need to adjust fertilizers, to control pollution, and to develop the producing ability of soil. Only in that way can the consumers' need for high-qualified farm products be met, the competitive ability in domestic and international markets be improved, and the strategic adjustment of agricultural structure and the sustainable development of agriculture be promoted.The research takes Rudong County for example and is based on the continual investigation into the main types of soil, the typical soil nutrients and crop fertilizers in the area. The research also analyzes the soil quality of farmland after the 2nd national soil survey, especially the dynamic evolvement of the soil nutrients and fertilizer input and the yield of the main crops. It is linked with Stat. data and does research into the demanding rule of the main crops' need for soil nutrients and fertilizers in the efficient agricultural ecosystem. The research brings forward proper countermeasures of soil fertilizing and managing, which provides the basis for the adjustment and optimization of planting structure , the control over agricultural pollution and the construction of bases of crop products without environmental pollution, and promoting the sustainable development of agriculture in Rudong County.
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