| Through the research of paddy field sampling investigation, combined with the actual situation of paddy field in Changsha, the characteristics and spatial variation of soil nutrients such as available nitrogen, available phosphorus, available potassium and organic matter were mainly analyzed. Using the fuzzy comprehensive evaluation method to evaluate the Integrated soil fertility in paddy field, and through the ArcGIS making integrated soil fertility spatial distribution map, to more intuitive understanding of paddy field fertility distribution conditions and the overall level in this area, which is helpful for scientific reasonable fertilization, and also providing basic data and theoretical basis for the healthy and stable development of the production and management of main crops, ecological agriculture, organic agriculture in this area. The main conclusions of the study are as follows:1. The content of organic matter in paddy fields in Changsha was low, with an average of 1.31%, which was slightly higher than that of natural soil, root layer was greater than the depth and the surface on the soil profile. The spatial distribution of organic matter gradually decreases from the north to the south.2. The average content of available nitrogen was 19.61mg/kg. The available nitrogen content was lower than the whole country, and also lower than that of natural slope soil. Soil profile showed that the surface layer was greater than the root than the depth. The spatial distribution increases gradually from north to south.3. Available phosphorus content and available potassium content are both at high level, mean values were 22.83 mg/kg and 444.00mg/kg. The distribution in the soil profile of available phosphorus and available potassium were basically consistent with the natural soil. The difference was that the deep content of available phosphorus is more than the surface layer and the root, while the content of available potassium decreased from the surface layer to the deep layer, and the decreasing rate was fast. The spatial distribution of available phosphorus was high in the middle and south, the east and the west was relatively low. Available potassium was descending from the east and west sides to central trend in spatial distribution.4. From the results of comprehensive evaluation of soil fertility, the level of soil fertility in paddy field was generally low. From the soil profile, the root layer soil fertility level was better than the surface layer, the deep layer is the lowest. Soil impoverishment appeared in the surface layer firstly, and the root layer soil fertility was more ideal than the surface.5. From the distribution of soil comprehensive fertility level, the surface soil fertility level of paddy field in Changsha is low; the distribution area of the five and six grades is the most extensive, the sum of the area is 2158.67km2. While the one or two and three grades of the soil in the root layer is wide. The plots with high fertility level were significantly more than the surface layer. The highest level of fertility is in the central and southern Ningxiang and the border area between Changsha County and Liuyang. The fertility level of the deep layer is very low. |
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