| Renhua County is a typical agricultural county in mountainous area which is located in the north of Shaoguan City, Guangdong Province. With population growth and economic development, the contradiction between local cultivated land resources and social demand is becoming more and more obvious. As for Renhua County, an important problem is how to use the limited cultivated land resources effectively and improve total productivity in cultivated land. In addition, it has been more than 20 a after the second national soil survey, so the spatiotemporal conditions of soil nutrients in local cultivated land have a great change after years of exploitation. Hence, assessing cultivated land productivity and understanding the spatiotemporal evolutions of soil nutrients in Renhua County, will be great significant for the scientifically exploitation and utilization of cultivated land and grain production, which can provide scientific decision-makings for agricultural management department of Renhua.This study collected 2439 soil samples of cultivated land in Renhua from 2007 to 2009 and analyzed their main physical and chemical properties. Then 12 evaluation factors and some methods such as spatial analysis, hierarchy analysis, fuzzy mathematics, comprehensive index and so on were selected to assess the cultivated land fertility level in Renhua. Meanwhile, combined with the 2nd nation soil survey data, GIS method was used to analyze the spatiotemporal evolution characteristics of soil nutrients in Renhua. The research results are as follows:(1) In the soil of cultivated land in Renhua County, the content of organic matter that is between 20-30 g.kg is wholly at the middle level; the content of total nitrogen is mainly between 1.0 and 1.5 g.kg-1(56.07%) which indicates moderate level; the ratio of area with in shortage(<10 mg.kg-1) available phosphorus is only 1.14% that indicates wholly area in rich. The content of available potassium area is in shortage(<100 mg.kg-1) which indicates the area is lack of potassium. Compared to the 2nd nation soil survey, the weighted average content of organic matter is decreased from 29.11 g.kg-1 to 25.14 g.kg-1 with 13.64% extent and the areas with decreased content of that mainly are some towns such as Daqiao, Zhoutian, Changjiang and Hongshan; the weighted average content of total nitrogen is slightly decreased from 1.43 g.kg-1 to 1.37 g.kg-1 and the areas with decreased content of that mainly are some towns such as Changjiang, Fuxi, Zhoutian and Daqiao; the weighted average content of available phosphorus is greatly increased from 13.76 mg.kg-1 to18.83 mg.kg-1 with 36.85% extent and the areas with increased content of that widely distribute in various towns of Renhua, and Danxia, Huangkeng, Daqiao, Zhoutian and Hongshan are the key towns; the weighted average content of available potassium is greatly decreased from 66.19 mg.kg-1 to 40.87 mg.kg-1 with 38.25% and the content of that in the whole county has been decreased. Overall, in the recent 20 a, the contents of organic matter and available potassium have been decreased while available phosphorus has been increased, and the content of total nitrogen has not been changed with slightly decreased. Organic fertilizer should be more applied, rational use of nitrogen, phosphate and potash fertilizers should be strengthened and the content of available potassium in soil should be increased in the future agriculture production.(2) The cultivated lands in Renhua are 213240.32hm2 which are divided into 8 levels from class 1 to class 8. Wherein high-yield cultivated lands are 2777.87hm2, accounting for 13.02%, middle-yield cultivated lands are 10187.78hm2, accounting for 47.74%, and low-yield cultivated lands are 8374.73hm2, accounting for 39.24% in the whole county. Overall, in Renhua County, the quality of cultivated lands is not high and the proportion of middle and low-yield cultivated lands are comparatively large. High-yield cultivated lands mainly distribute in some wide valleies-alluvial plains surrounding the towns of Danxia, Dongtang and Shitang; middle-yield cultivated lands mainly distribute rivers-alluvial plains and upper and middle parts of wide valleies-alluvial plains surrounding each town; and low-yield cultivated lands distribute every towns in Renhua County, but the towns of Changjiang and Huangkeng are most wherein distribute talus slope zones in low hills, depressions between hills and alluvial dams. It is match between the distributions of the classification of cultivated land fertility and geomorphic type. The cultivated lands with highest quality concentrate plains and wide valleies-alluvial plains in Renhua County. |
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