Spatial heterogeneity of soil nutrients and pH in tobacco area based on geostatistics: A case study in a karst area of Youyang county, Chongqing

Evaluation of spatial heterogeneity of soil nutrients and pH forms a basis for management of soil nutrients and fertilization in tobacco-growingareas. In this paper, the spatial heterogeneity of soil nutrients and pH in the tobacco-growing area of Youyang county was evaluated using classical statistics and geostatistics. The results indicated rich organic matter and poor availability of phosphorus in the study area; the variation coefficients for eight soil nutrient indicators ranged from 13.11% to 71.46%. The variable coefficient of available phosphorus was the largest among the indicators, while organic matter, total nitrogen and available nitrogen were stable. A significant positive correlation between organic matter and total nitrogen, total phosphorus, available nitrogen and available phosphorus was noticed, while a clear negative correlation between pH and both available phosphorus and potassium was identified. The semivariograms for soil organic matter, total nitrogen, total phosphorus and available potassium were all well fitted using the exponential curve model, while the correlation between pH and available nitrogen fitted well using the spherical model; total nitrogen, total phosphorus, available nitrogen and potassium had moderate spatial correlation, and other soil nutrient indicators showed weak spatial correlation. The spatial distribution of soil nutrients and pH in the east-west direction and the north-south direction area is significantly different, and the variation of spatial distribution in the east-west direction was larger than in the north-south direction. The spatial correlation of soil nutrients in tobacco-growing area of Youyang county is not significant, therefore, it can be concluded that the spatial heterogeneity of soil nutrients is mainly affected by the topography, fertilization, tillage and other potential factors.