| Nowadays,there are different degrees of soil fertility degradation in various parts of the country,especially in Karst mountain areas with serious rocky desertification,less soil coverage,thin soil and poor quality,which leads to the relative lagging in agricultural industry development and great challenge for food securlty in Karst mountain area.Therefore,it is imminent to evaluate the soil fertility in the mountain areas of Karst,and to evaluate the soil fertility in the Karst mountain area objectively,which is of great significance to the land resources,scientific fertilization,crop layout adjustment and land development and arrangement in the Karst area.In this paper,Tongren,a typical Karst landform,was selected as the research area.Total nitrogen,available phosphorus,quick-acting potassium,organic matter and pH were used as fertility indexes.The fractal interpolation model is used to evaluate the soil fertility in order to evaluate the soil fertility better in Karst and make up for the deficiency of the former.The model is based on the fractal dimension of single fertility index,and the evaluation value of each soil sample is obtained by fractal dimension calculation,through which the empirical grade function is obtained.The evaluation value is classified and through which fractal interpolation model is established,accordingly the comprehensive status of soil fertility in Tongren is obtained.In addition,combining with projection pursuit model,grey correlation model and numerical model,the evaluation results were verified and compared and to analyze the spatial distribution pattern of fertility and abundance and to explore the factors that affect the soil fertility.The main conclusions are as follows:(1)The mean value of total nitrogen in the study area is 1.33g/kg,the mean value of organic matter is 20.24g/kg,the mean value of effective phosphorus is 10.90 mg/kg,and the mean value of available potassium is 126.48mg/kg,all of which are at the medium level.The range of pH is between 4.60~7.90,with a mean value of 6.11 mg/kg,showing a slight acidity.The results of variation coefficient analysis showed that total nitrogen,available potassium,available phosphorus and organic matter all had middle intensity.(2)Based on the geographic statistical analysis module in ArcGIS 10.1,the comprehensive evaluation of soil fertility was evaluated by Kriging interpolation method,and from which the spatial distribution map of soil fertility in Tongren was obtained.In view of the spatial distribution of soil fertility evaluation results,the soil fertility in Tongren is relatively general,which is mainly at insufficient and medium soil fertility level,representing the general level of soil fertility in the whole study area and the trend of distribution is increasing from the southwest to the northeast.(3)According to the comparative analysis of spatial distribution and the result verification analysis,the fractal interpolation model and the other 3 evaluation models have a good similarity in the fertility level distribution area,and the distribution area is more than 40% in the distribution area;The number of samples that had same grade through fractal interpolation with at least the other two kinds of evaluation methods of the 50 sampling samples,totally is 46,accounting for 92% in the total verification points,and only 4 validation samples have statistic difference.The results of the comprehensive study show that the evaluation results of fractal interpolation model coincide with the evaluation results of the other 3 model methods.It also reflects the soil fertility level objectively and scientifically in Tongren,and provides a new technical method for the assessment of soil fertility in the Karst mountain area.(4)The soil fertility showed different results under different factors.The study shows that the soil fertility has significant difference under different soil types;there is a significant correlation between the fertility with the elevation and the degree of the slope.The level of soil fertility in the area below 1000 m in elevation and 15°~35° in slope is better.Meanwhile differences in slope direction also cause differences in fertility.The northeast direction is the shady slope,in which the soil has a better fertility,correspondingly the southwest direction is the sunny slope,in which the soil has poorer fertility,and the soil fertility in the land utilization in Tongren city is the forestland > cultivated land > the garden land. |
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