Study On Spatial Variability Of Soil Nutrients And Quantitative Evaluation Of Cultivated Land Fertility In Hanzhong

Spatial variation of soil nutrients is universal. Long-time human activities lead to the obvious changes of distribution and spatial characteristics in soil nutrients. The study of the spatial variability of soil nutrients is the foundation and precondition of quantitative evaluation of cultivated land fertility. In recent years, with the development of economy and the expansion of urban scale, the quality of cultivated land were continually decreasing. The blind, unreasonable fertilization have led to the degeneration of soil fertility, the imbalance of regional supply, and the low utilization of fertilizer. Consequently, it has some important and realistic significance to analyze the spatial variability pattern and potential productivity for the soil nutrients of the current cultivated land, guide precision fertilization, change soil environment, and promote continual development of farmland resources.This study takes Hanzhong in Shanxi province as the study area, based on Formulated Fertilization Project of Shaanxi Province, which have widely collected and analyzed foundational data, using the traditional statistical, geostatistics and GIS technology to analyze the spatial variability characteristics and influencing factors of soil nutrients(total nitrogen, available potassium, organic matter, available phosphorus and pH value). The study combined Delphi and AHP(Analytic Hierarchy Process method) to establish soil nutrients fertility evaluation system to evaluate the cultivated land fertility level simultaneous. The results and achievements of this study listed as follows:In the researched area, the average concentration of total N, available K, available P, OM were 1.130 g/kg, 109.277 mg/kg, 18.217 mg/kg and 23.0 g/kg, and average levels of these soil nutrients are in middle. The pH of soil is in 5.1~8.5, with an average value of 6.67, entirety being weak acid. Compared with background value of region in different scales, the results showed that nutrient contents make a big difference with greater regional differences. According to the coefficient of variation, the soil nutrient are shown as a medium spatial variability besides pH, and the variation coefficients is expressed as the following, available P>available K> total N> OM. The coefficient of variation of pH belonged to the low intensity.The spatial variation of soil nutrients were analyzed by using Spatial Autocorrelation Index and Semi-variance analysis of geostatistics methods. The conclusion indicates that the significant spatial autocorrelation of soil nutrients are existed. And the spatial variation were combined effect of both structural factors and random factors. The Global Moran’s I Index is expressed as the following, available K<OM<available P<total N<p H. Z(I) were greater than 2.58, which suggested the characteristics of spatial aggregation demonstrated clearly. The most optimal semi-variance function model of soil total N and available P were spherical model, while soil available K, OM and pH were exponential model. The nugget to sill ratio of soil total N and pH were 15% and 21.5% respectively, and soil available K, available P and OM were 45.1%, 49.9% and 42.7% respectively, and soil available P were lowest, which indicated soil available N and p H has significant spatial correlation while available K, available P and OM existed medium spatial correlation, and available P weakly which made it influenced by random factors largely. The spatial variation of soil total N is strongest at the northeast-southwest direction mostly. The spatial variation of soil available K and pH were change apparently at the south-north direction with the change of distance, while soil OM changed significantly if the distance above 110 km.The spatial distribution characteristics of soil nutrient. The total N of soil in the researched areas has the characteristics of remarkable spatial distribution, which were rich in the central and southeast region, in the northeast region weakly. Soil available K were high in the north and low in the south generally, and shown continuous echelon change in the northern area, presented large of patches in the central part and flaky shapes or mission shapes in the other area. Soil available P has a spatial distribution structure which in zonal distribution with the whole and in massive distribution with the part, and it changed rapidly in the large regions, which presented a pattern that low-side among high from west to east. The OM of soil were high in the east and low in the west generally. Soil pH was appeared a spatial pattern that in zonal distribution with the whole and in massive distribution with the part from west to east, and presented alkaline in the northwest and slight acid in the southwest of the whole city.Analyzing the influence factor of soil nutrients spatial variation, the results showed that there are significant negative correlations between soil total N and elevation, slope and aspect. Each topographical factors effected on the soil pH were not significant. Meanwhile, there are significant correlations between elevation and soil nutrients such as the OM, available K and available P, reached over 0.01 level. Beside available K, the spatial variability of soil nutrient influenced by soil types mostly. The distribution of available K in the soil of yellow brown soil and limestone soil has a significant difference by using analysis of variance and multiple test.According to the evaluation of cultivated land fertility, the total farmland area of the researched region is 393752 hm2. The area ration of grade I is 17.24%, grade II 13.46%, grade III 24.30%, grade IV 40.68%, and grade V 4.32%. The grade I land were basically distributed in river valley plain and terrace near the river of Hantai, Chenggu, Nanzheng. The grade II land were mainly distributed in the valley and plain regions in Nanzheng, Mianxian and Yangxian, which terrain sloped gently. The grade III land were distributed mainly in the low hilly area mostly and some region under incomplete irrigation conditions or weak farm infrastructure, which has condition of good light and heat. The grade IV land were basically distributing in the low hill and partial low mountain region. The grade V land were mainly distributing in the western middle and high mountain region. It is demonstrated that there are significant differences among productivity of cultivated land in different soils and landform types.