| The Tai Lake area is the developed district of Jiangsu province, and it is famous for its rice and fishery. The economy of Tai Lake area has being developed rapidly since the 80's of 20 centuries. The percentage of agriculture on the GDP was decreasing since that time. There are some negative effects with the development of industry, such as the decreased cultivated land and the increased pollution of Tai Lake. These negative effects threatened the food safety in quantity and quality.Yixing city has abundant natural resources and varieties of topography. The economy of Yixing city has being developed rapidly like other cities in south Jiangsu since the 80's of 20 centuries. But the total area of cultivated land and yield of agricultural product are being decreasd. We surveyed the soil fertility and fertilization status of tilth, analyzed the evolution of soil fertility and the problems of management soil and fertilization in Yixing city in order to conduct agricultural practice.The main results showed that soil fertility in Yixing city has changed apparently from the second national soil survey. At present, the average contents of soil organic matter, total nitrogen, available phosphorus, available potassium, available boron, available zinc, available copper, available manganese, and available iron are 26.2 g kg-1, 2.2 g kg-1, 14.0 mg kg-1, 56.0 mg kg-1, 0.44 mg kg-1, 1.74 mg kg-1, 3.85 mg kg-1, 17.0 mg kg-1, and 109.0 mg kg-1 respectively. As compared with the corresponding values in 1981, the content of soil OM increased slightly, while soil total nitrogen increased significantly. The soil available phosphorus was remarkably increased compared to that in 1981, but the soil available potassium was quickly decreased from 78 mg kg-1 to 56 mg kg-1 at the same period, which resulted in the lack of soil available potassium in most area. And furthermore, the soil where the available potassium is in severe lack accounted for 1/3 in all cultivated land in Yixing city now. Although the status of soil available boron and zinc was improved somewhat, there are still 2/3 of tilth lack of boron and 1/3 lack of zinc.The results on fertilizer survey showed that the total rate of fertilizer application in Yixing city had being increased from 1980 to 1998. But it decreased after 1999. The application of chemical fertilizer per 666.7 m2 was increasing with time. The total amount of organic and inorganic fertilizer application was 143,900 tons in Yixing (25,300 tons as pure nitrogen) in 1980 while it was 126,000 tons in 2002 (43,000 tons as pure nitrogen). The pure nutrients application rate per 666.7 m2 was 11.88 kg in 1981 while it was 45 kg in 2002. The application of chemical fertilizer increased significantly while the application of organic fertilizer including straw decreased remarkably from 1980 to 2002, which resulted in the unsteady soil fertility. The economic efficiency of nitrogen fertilizer application decreased in recent years. The ratio of nitrogen, phosphorus, and potassium application was not suitable and the application rate of nitrogen was significantly higher than both of phosphorus and potassium.The actualities and developing tendency to the soil and fertilizer of Yixing city are relevant to food safety and the development of sustainable agriculture. We should take effective measures to control the decrease of tilth, to improve tilth quality, to fertilize reasonably and economically, and to increase agricultural input. We should set up healthy monitoring system of soil quality and information managementsystem of soil resources in order to manage soil quality dynamically. We should set up complex nutrients management system which includes organic and inorganic nutrients to make sure the best efficiency of nutrients input. We should also set up monitoring net system of fertilizer information and fertilizer effect to distribute reasonably fertilizers in different districts and improve the level of macro decision-making. And finally, we should set up training organization in order to enhance peasants' environmental an... |
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