| Soil nutrient is one of the most important properties of soil. The precise prediction and analysis of nutrient content and characteristics is the prerequisite to realize the zoning management of nutrient, rational use of land and sustainable development. The study of the spatial distribution and influencing factors of regional soil nutrient based on spatial prediction and statistical research, are important methods to achieve scientific farming in line with local conditions. The status of soil nutrient in apple orchard affects its yield and quality. The excess use of fertilizer on apple cultivation, unreasonable fertilization structure in this area, would seriously affect the local apple quality and industrial development, so it is necessary to analyze the distribution characteristics and influencing factors of soil nutrient in orchard, and realize the scientific management of soil nutrients.In this paper,the soil nutrient of apple production area in Xunyi County,Shaanxi Province was taken as the research object. The database of soil nutrient and influencing factors of apple orchards were established respectively in this study, based on the data of soil sampling points,remote sensing images, DEM and soil types in apple orchards. The general statistical characteristics and the adaptability of geostatistical spatial prediction model of soil nutrients,including organic matter, alkali hydrolysable N, available P and available K,were studied by traditional statistics, spatial statistics and GIS. The spatial distribution map of soil nutrients were drawn, and the comprehensive evaluation of soil nutrients was carried out by the improved TOPSIS. The correlation analysis and linear regression analysis were used to establish the linear regression model of influencing factors, and the influence of each influent factor on soil nutrient was quantitatively analyzed. The management system of soil nutrients of apple orchard was developed by C# and ArcEngine. The results provide theoretical and technical support for regional orchard nutrient mapping, zoning management, precision fertilization and sustainable development of apple production area.The main achievements of this study are as follows:(1) From the perspective of geostatistical spatial prediction and mapping, the adaptability of Ordinary Kriging and Cokriging to the mapping of nutrient distribution in apple orchards was studied, and a scientific scheme for the digital mapping of apple orchards was provided. In the aspect of comprehensive evaluation and mapping of nutrients, an objective method of determining the weight of soil nutrient by using principal component analysis is put forward,which accords with the law of mathematical statistics and improves the objectivity of research results. The integrated nutrients were studied, objectively and accurately, by improved TOPSIS, and the rationality and feasibility of this method were demonstrated. At the same time, the correlation analysis and multiple linear regression analysis were applied to the analysis of influencing factors of soil nutrient, and the rationality and reliability of the method were proved. The influence weight of influencing factors on soil nutrient was analyzed objectively and quantitatively, and the nutrient management system of apple production area was explored.(2) The spatial distribution of soil nutrients in apple area of the study area was uneven, and was with moderate variability. The decrease order was: available K > available P> organic matter> alkali hydrolysable N. According to the grade classification standard of soil nutrients on apple in Weibei District of Shaanxi Province, organic matter, alkali hydrolysable N,available P and available K belonged to Grade?,?,? and ? respectively, which indicated that the content of available hydrolysable N was low, organic matter and available P were medium, available K was high. Therefore, it is necessary to adjust the fertilization structure and increase the amount of nitrogen fertilizer. The optimal fitting variogram models of organic matter, alkali hydrolysable N, available P, and available K were, respectively, index,index, index and Gaussian. Under the best fitting variogram model, the mapping accuracy of Ordinary Kriging on alkali hydrolysable N was higher than that of Cokriging, but the Cokriging had better adaptability to the organic matter, available K and available P in the orchard. The spatial distribution pattern of organic matter is decreasing from Zhitian, Puyuan and Tuqiao Town in the east to the west and the middle, and the area ratio of the low-content area was larger. In addition to the part area of Tuqiao Town, alkali hydrolysable N was decreasing from Zhitian Town-Tai Town and Zhanghong Town-Yuandi Town to the two sides of the study area. The spatial distribution of available K was scattered, and the average content of available K of the orchard is high. The high value area of available K was located in Tai Town, Zhengjia, and Tuqiao Town. Available P showed a decrease trend from Chengguan Town and Chidao - Zhangbasi Town to the two sides of the study area, in addition to the west area of Tai Town and the south area of Yuandi Town.(3) The comprehensive evaluation of soil nutrients showed that the integrated nutrients of orchard in the study area belonged to middle and lower levels. The minimum value of Ci of the orchard was 0.131, the maximum was 0.685, the average was 0.358, the standard deviation was 0.092, and the variation degree was moderate. The distribution of the integrated nutrients decreased from the west to the east, in addition to the east area of Qiupo-tou Town,the middle area of Zhitian Town and Tuqiao Town. The distribution area of high-value was consistent with that of the dark loessial soil, and most of the low-value areas were mainly distributed in the area of the loessial soil. The area ratio of extremely high zone, high zone,medium zone, low zone, and extremely low zone was 7.189: 20.432: 27.533: 31.217: 13.628.The percentage of middle and lower area took up 72.378% of the study area, and mainly distributed in the east of research area.(4) The correlation analysis showed that there were significant correlations between organic matter and elevation, aspect in the orchard. The available hydrolysable N was significantly correlated with slope, aspect and soil type, and was extremely significantly correlated with elevation. Available K was extremely significantly correlated with elevation,slope and aspect.Available P was extremely significantly correlated with elevation, and was significantly correlated with aspect. The quantitative analysis of linear regression showed that the content of organic matter was affected by elevation, aspect, and vegetation coverage, soil types. The available hydrolysable N was mainly affected by topographic factors and soil types. Available K was related to topographic factors, especially the altitude factors. Available P was mainly affected by elevation and aspect. The information management system of soil nutrients on apple was developed, based on C# and ArcEngine10.1, with Geodatabase as the database platform. There were data management and browsing, attribute and spatial query, thematic map and fertilizer recommendation function in the system, which had advantages of simple operation, pertinence and practicability. The management of data, basic processing and spatial visualization were realized by this system, and for recommended fertilization in apple production area. |
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