Study On Spatial Heterogeneity And Suitability Evaluation Of Tobacco-growing Soil Nutrient In Jiange County

The growth, production and quality of flue-cured tobacco are largely subject to the influence of soil nutrients and fertilization management. Soil is co-affected by structural factors like climate, topography and parent material and human random factors like tillage practices and fertilization management, which makes the soil nature of high spatial heterogeneity. Only by a full understanding of its status and variation could the soil nutrients be well managed. This research combined statistical method with GIS technology to study the status and spatial variability of tobacco planting soil nutrients in Jiange, Guangyuan; The factor data of topographic characteristics extracted from DEM data reflects the spatial distribution of soil nutrients under this terrain condition; Comprehensive assessment on tobacco planting soil suitability was carried out by calculating weights adopting membership function and entropy value method to master the spatial distribution of soil suitability for scientifically precise management of tobacco planting soil; and further providing references for fertilizer management of tobacco planting soil nutrients in Jiange. The main results are as follows:(1) Status of Tobacco-planting soil nutrient in Jiange county pH variation coefficient of tobacco planting soil in the study area is 8.336%, deemed as weak variability. The variation coefficient of the rest of the nutrient indexes are varying from 10%～100%, within the scope of medium variability. Soil pH value is 7.85, alkaline. The average content of organic matter is 15.079 g/kg, the average content of total nitrogen is 0.877 g/kg and the average content of exchangeable magnesium is 83.952 mg/kg, all within the range of nutrient deficiency level. For trace elements, the average content of available iron and sulfur is 22.851 mg/kg and 38.040 mg/kg respectively, both within the scope of rich tobacco planting soil level; while the average content of soil alkali-hydrolyzable nitrogen, available phosphorous, rapidly available potassium, available zinc, boron, manganese and copper are all within middle level of abundance-shortage range. The contents of organic matter, total nitrogen, and exchangeable magnesium of the sampling sites are within the scope from deficiency to medium, among which,72.84%,52.08% and 56.87% of the sampling sites are of deficient level, respectively; The contents of alkali-hydrolyzale nitrogen and rapidly available potassium are within the scope from deficiency to abundance, but their distribution in sampling sites are irregular; The contents of available zinc, manganese and copper are within the scope from extreme deficiency to abundance, among which, most of the sampling sites have medium content; For available phosphorus, boron and sulfur, their contents are distributed in whole deficiency-abundance scope, and respectively 39.62%,42.81% and 27.48% of the sites are among medium scope; The content of available iron is among the scope from medium to abundance, while 77.96% of the sampling sites contain abundant iron. As the soil nutrient contents show different abundance rank deficiency condition, it is necessary to manage the differentiation. Contents of indicaters like soil nutrients pH, organic matter, total nitrogen, alkali-hydrolyzale nitrogen and available boron could meet normal distribution, while the contents of rest of the indicators could also obey the normal distribution characteristics after natural logarithm conversion.(2) Nutrient spatial variation characteristics of tobacco-planting soil in Jiange county Co/(C+Co) of Soil pH, alkali-hydrolyzale nitrogen, available phosphorus, copper, sulfur and exchangeable magnesium are less than 25%, their contents are relatively stable. With intense spatial correlation, structural factors play a leading role in its spatial variation; While the Co/ (C+Co) of organic matter, total nitrogen, rapidly available potassium, available boron, available zinc, manganese and iron are varying from 25% to 75%. They are subject to the co-influence of structural factors and random factors, which reflects a moderate spatial correlation. After a semi-variance theory model fitting, spherical model is best for organic matter, nitrogen and available boron, while for the rest of nutrient indicators, Gaussian model is appropriate. Effecting factors of the 13 tobacco planting soil nutrients in the study area work on different scales, varying within12～1773m, with a significant difference.Adopting ArcGIS software to do Kriging interpolation on tobacco planting soil nutrient indicator sampling points, based on semi-variance function and the optimal model. After interpolation, grading the soil nutrient according to abundance-deficiency standards, then drawing spatial distribution picture of the soil nutrients in the study area. Intuitive understanding of tobacco planting soil nutrients distribution pattern in the study area could provide guidance for the fertilization management in tobacco production, and work out appropriate fertilization management practices for different towns with different levels of nutrient indicators.(3) Suitability evaluation of tobacco-planting soil in Jiange county Tobacco soil nutrients in the study area are correlated to the terrain factors there. Various indicators of soil nutrients are negatively correlated to the elevation and slope. Available nitrogen, rapidly available potassium, zinc, iron and manganese showed a significant negative correlation with elevation and slope at p<0.01; But soil nutrients showed no significant correlation with the slope aspect. Nutrients content of the soil in the study area show a decreasing trend with the increasing of elevation within the range of 400-880m above sea level, and exhibit a difference in maximum nutrient elevation for different nutrients; nutrients content of the soil also decreases with the increase of slope; while in different slope aspect level, the distribution of soil nutrients diversify, showed no obvious pattern. Tobacco planting in the study area are dense at low mountain slopes with an altitude of 520-760m, slopes within 5～15°, semi-shady slopes and semi-sunny slopes, and the average content of the soil nutrients are high in these places.According to the scoring results of soil nutrients integrated fertility index (IFI), its suitability is divided into five levels. Applying ArcGIS software to generate the assessment distribution picture of the soil nutrients suitability. Comprehensive fertility distribution of Jiange tobacco planting soil nutrients could be learned from the picture, and precise management could be carried out based on the evaluation results.