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.