Spatial variability of soil properties in a tobacco field of central China

Present nutrient management recommendations for flue-cured tobacco (Nicotiana tabacum) in central China are typically uniform for large regions. This results in overapplication in areas with high nutrient levels and underapplication in areas with low nutrient levels. Therefore, understanding the spatial variability of soil nutrients is essential in determining local fertilizer needs of tobacco. The objectives of this study were to (i) quantify the spatial variability of soil properties across tobacco plantation fields and (ii) generate contour maps for these variables. Soil samples (0-20 cm) were taken from 81 points on an approximately 100-m grid in March 2007 using global positioning system to define sample locations. Seven soil chemical properties and texture were analyzed by geostatistical techniques. Soil pH, total N, sand, and clay showed strong spatial dependence, with nugget/sill ratios ranging from 16% to 20%. Soil organic matter, available phosphorus (AP), available potassium (AK), cation exchange capacity, and silt showed moderate spatial dependence, with nugget/sill ratios ranging from 30% to 50%. Soil alkalytic N showed no spatial dependence (pure nugget effect) at the chosen sampling interval. Ranges of spatial dependence varied from 274 m (total N) to 1066 m (cation exchange capacity). The clearly patchy distribution and low extrinsic component of variability for AP and AK indicated that spatial distribution maps for AP and AK could be used for the basis of site-specific fertilizer application.