Spatial Variation And Its Application Of Soil Nutrients Based On GIS And Geostatistics

Spatial variation of soil features is universal. However, a plot is often seen as an even unit in traditional agricultural productivities. And it is fertilized according to peasants' practice in production or the fertilizing recommendation for a large scale by local agricultural technical organization. As a result, imbalance of nutrients' supply and low utilization ratio of fertilizer is doomed for the lack of efficient measures to deal with specific situation. Besides, the underground water is easily polluted for the excessive fertilizer in local area. In response, it is necessary and important, which fully understanding the spatial variation laws underlying in soil characteristics and the couplingmechanism lying between the growth of the plants and soil properties, and defining proper managerial units of soil nutrients. It is not only the foundation to realize the management of so-called "Suit our measures to differing conditions in terms of locality, time, and issue involved", but also the pre-condition of the sustained utilization of soil resources.By using such methods and technology as investigation, chemical analyses, traditional statistics, geostatistics, ecological methods and 3S, this paper carries out following researches, which selected Liutang Branch of Houhu Farm in Jianghan Plain as experimental region. Partâ… , spatial variation laws underlying in soil nutrients was posted, scale-offect and its forming momentum were discussed, and multi-scale nested simulation model was introduced. It has important theoretical meaning on comprehending features spatial variation deeply, predigesting and optimizing scenario of soil sampling, and advancing the research on spatial variation. Partâ…¡, different scenario for soil nutrient management was put forward, which was aimed to excavate quality potential of crop, exert predominance of agricultural resources, or obtain the most economy incomes. Results can be used as theoretical guidance and basis of decision-making for application of precision agriculture in China. The main conclusions of the research are summarized as follows:1 Spatial variability of soil nutrients145 samples were collected under nested scenario, which is constructed by 400m, 100m, and 50m. pH value, CEC, organic matter, total nitrogen, available nitrogen, available phosphorus, available potassium, available iron, available copper, available zinc and available boron content were mensurated. It was analyzed by using traditional statistics. Result shows that, content of soil nitrogen, phosphorus, and potassium is in the medium level; organic matter content is on the low side, which leads to the low ability of nutrients adsorption; Available copper and available iron content are relatively high, and available zinc is obviously lack in research area.Comparing the precision of spatial estimation under different datasets, the dataset which contains 145 samples was selected to obtain soil characters' distribution. By geostatistics, spatial structure of soil variables was discussed, and the spatial distribution map was drawn. It is discovered that, all of variables have semi- variance structure, and spherical model fits best for semi-variogram. But, spatial structure features of different variable are distinct. Physical characters of soil, organic matters, total nitrogen, and available nitrogen, mainly affected by humidity and heat, and the spatial variation assumes subdued in the whole region. Available potassium and phosphorus are mainly influenced by random factors, and the variation seems unstable. Spatial variation of trace elements is affected by random factors most (available iron excepted).2 Scale-offect and the nested simulation of spatial distribution for soil nutrientsTotal nitrogen was taken as an example. With geostatistical methods, characteristics of spatial variation on three scales were obtained respectively, and discussed the existence of scale-offect and its performance. Result shows that, spatial variation of TN lies in each scale; affected by different factors, various structure being formed; scale-offect thus plays obviously.By Univariate method, momentum of spatial variation of soil nitrogen on each scale is discussed. In 400m sampling scale, dissimilarity of landuse is the main reason for the formation of nitrogen spatial variation; in 100m sampling scale, difference of agrotype and topography affected distribution of soil nitrogen most, and the influence from distinctness of management level between managers only appears in local area; in 50m sampling scale, diversity of agrotype and managers are momentum of nitrogen variation.Based on nested theory of geo-science, several nested models were conducted in description of soil nitrogen distribution. Result shows that, precision of the 3^rd model is the best, in which spatial structure in large scale is obtained by simple kriging method based on 145 points' data, then be emendated according features on mid or small scales. 3 Relationship between exertion of quality potential of cotton and soil propertiesThrough principle component analyses, quality indexs of cotton can be represented by three components, which is satin degree, productive capability, and ventilate capability. Satin degree represents trimness and intensity of fibre, and it is influenced by total nitrogen (organic matter) and pH value of soil; productive capability describes length and elongation capability of fibre, which is decided by germ plasm, and it is also affected by soil available iron; ventilate capability is relative with available iron content in soil prominently, which indicates that satisfying crops' demand on trace elements is propitious to improve ventilation of cotton yarn.4 Suitability evaluations on tillageBased on niche-fitness model, grid for 50m^*50 meter is taken as evaluation unit; we calculate the niche-fitness value of different crops, and obtain the suitability for crops and regional restrictive factors. Results indicate that the niche-fitness value in this area is in medium and high side which can be able to meet basic requirement of crops, the 1, 2 level is primary. Soil suitability for different crops in the southwest of study area is high, which is related to the ascendant status of soil natural attribute such as soil profile structure, organic matter and available nutrient. Contrarily, soil suitability for crops in the southeast and northwest of study area is on the low side. It is proved that available boron and available zinc are the primary niche factors that restrict tillage productive potential in this area.On the other hand, based on the niche-fitness of different crops, optimization rotation program of evaluation units for exertion resource advantage or optimization economy scenario are obtained. Results indicate that the suitable area of rice and wheat is maximal in the each season. Under the optimization resource advantage scenario, area of optimization planting type about rice-wheat rotating pattern is maximal and rice-rape rotating pattern is next. Under the optimization benefit scenario, area of optimization planting type about cotton-wheat rotating pattern is maximal and rice-wheat rotating pattern is next. According to field survey, the latter planting type is in accord with the actual situation. 5 Regionalization of soil nutrient managementThrough principle component analyses, soil elements are represented by two components. The first component characterizes maintenance capability on nutrients, and, accommodating level of soil nitrogen and potassium; the second component describes supply status of trace elements and available phosphors. According to frequency histogram, two components are graded respectively. Overlaying classification maps of principle components and regional management map of pH, regional management program of soil nutrients is obtained based on nutrients status quo. There are 14 blocks under this scenario; A₂-B₁-P₂ region is the largest one, which accounts for 30% of the whole area; and the average area of these regions is about 38.28hm². Then, overlaying soil map, chorography, and optimization rotation map under optimization economy scenario, stable regionalization of soil nutrients management is achieved. There are 42 blocks under this scenario; A₂-B₁-12b-P₂-E₂-R₁ region is the largest one, which accounts for 16% of the whole area; and the average area of these regions is about 12.76hm².