| The Three Gorges Reservoir on the Yangtze River middle reaches of China has become a core dominant industry of citrus and plays a vital role of economic and social development. However, the Three Gorges reservoir area citrus orchards are mostly built in the mountainous and hilly areas, and complex topography, soil parent material, soil texture and fertility were quite different. Now the average yield of oranges in Chongqing is only 9000 kg/hm2 due to complex spatial differences in soil fertility and blind fertilizer mainly. So investigation of the soil and leaf's spatial variability at microscale in citrus orchards will provide a basis of variable rate fertilizer applicator and improve the level and International competitiveness of citrus industry. In this study, we carried out research on the microscale spatial variability of nutrients at Late-maturing navel orange of Tiefo Village Fengjie County (A area, Sloping terrain at low altitude) and Hamlin sweet orange of Zhong County, Willow Village Zhongxian County (B area, Multiple hilly terrain at high altitude), and explored the techniques of sampling. DGPS orientation and visualization of quantitative expression systematically. The main results are as follows:1) Soil available nitrogen, exchangeable Mg and some micronutrients of A area were higher than B significantly, however, the exchangeable Ca was on the contrary. Whilst, the available N, Cu, Zn, exchangeable Ca and Mg of A and B areas were medium level variation with coefficient of variation in the range of 15.76%-72.63%,and the micronutrients variability of A area was lower than B area. The soil exchangeable Ca, available Fe, Mn, Cu of A area and the exchangeable Ca showed a normal distribution, however, the exchangeable Mg, Zn and N of A area and N, exchangeable Mg, available Fe, Mg, Zn and Cu of B area are the lognormal distribution. The variation of soil nutrients is different, the variation of same Nutrition in different soil types are also not the same. Whilst, the exchangeable Ca of A and B significant negative correlation with available micronutrients indicated that they were antagonistic.2) Total Ca, Mg, Fe and Mn of citrus leaf in A area were significantly higher than in B area, however, total Zn and Cu of A area were lower than B area. And the major trace elements content decreased in order: Fe> Mn> Zn> Cu. The total nutrients of citrus leaf were with the coefficient of variation from 18.34% to 96.59% which belonged to the mid-intensity variability. Whilst, the total Ca, Fe, Mn, Cu of A area and Ca, Cu of B area showed a normal distribution, and the others presented the lognormal distribution. The total Ca with Mg, Mn and Cu of A and B areas'citrus leaves nutrients were significant negative correlation, respectively, which indicated that they were antagonism.3) The correlation of soil nutrients with leaf nutrients of A and B areas was analyzed, the results showed that the ratio of soil available Ca and Mg was highly significant positive correlation with leaf Ca, and significantly negatively correlated with leaf Mg, Fe, Mn, and the above results indicated that the proportion of soil available Ca and Mg played an important role of plant absorption of middle element and trace elements. Whilst, soil available N, Fe, Mn, Cu showed a significant positive correlation with leaf total Mn.4) The soil available Mg and leaf total Fe of A and B areas adapted to spherical model, and the soil available Zn and leaf Cu adapted to exponential model, Gaussian model for the leaf Mn. Whilst, the soil exchangeable Ca and Cu, available Zn and Cu and leaf Cu content has a strong spatial correlation. The interpolation results showed that the soil N, exchangeable Ca, available Fe, Mn, Cu were abundant, however, the soil exchangeable Mg and available Zn were extremely scarce in A area.Whilst the exchangeable Ca. available Mn were abundant,but the soil N, exchangeable Mg.available Fe. Cu, Zn were extremely scarce in B area.The contents of leaf total Ca, Fe, Mn were in the appropriate level and above.but the contents of leaf total Cu were in the Extreme deficiency leve in A area.The contents of leaf total Ca were abundant.but the contents of leaf total Mg.Cu were extremely scarce in B area5) Topography of the spatial affected the distribution of soil nutrients. The available N. Fe content and the slope rating was significantly negatively correlated, the greater the slope, soil N, Fe loss more easily, and its content is relatively low. And the leaf nutrient content is mainly affected by soil nutrient content, whilst, nutrient content of citrus leaves decreased with the increscent of the slope.6) According to Cochran formula, Cameron methods, standards of soil and leaf nutrient classification, and the given relative sampling error with spatial analysis derived from interpolation map. a scientific sampling plan can be developed and significantly reduce the cost of experiments and sample number, whilst, it also can minimize the error due to the blind random sampling and greatly improving the representativeness and accuracy of the sample.
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