Rational Sampling Density of Tobacco-planting Soil Dependent on Different Topography

Topography influences the density of soil sampling points for precise fertilization. In the case of high phosphorus and potassium fertilization for flue-cured tobacco, the soils in areas of plain, broad valley, narrow valley and gentle slope were sampled by 50 m×50 m grids and the available nutrients in soil samples were tested. The results showed that by Cochran formula,individual sample for plain, valley and gentle slope represented an area of 1.92, 1.01-1.56 and0.73 ha, respectively at a confidence level of 90% and a relative error of 15%; by geostatistical method, the maximum sampling space for precise nutrient management were 234.0, 134.4-177.5and 58.2 m for plain, valley and gentle slope, respectively. It indicated that sampling densityshould be increased gradually from flat to slope.