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Soils are highly variable spatially due to the combined effects of physical,chemical,and biological processes that operate with different intensities and at different scales.Understanding the spatial variability of soil properties is essential in determining local fertilizer needs of tobacco.The spatial variability of soil nutrients in terrain with a typical gentle slope was comprehensively analyzed by a combination of geostatistics with a Geographic Information System(GIS) platform.Scatter diagrams of the spatial distributions of soil nutrients were then quantitatively constructed.The study potentially provides theoretical bases not only for the use of management zones(MZs) of tobacco fields in gentle mountain-terrain slopes,which are field subdivisions that have relatively homogeneous attributes of landscape and soil conditions,but also for decision-making with respect to precision fertilization.Soil samples(0—20cm) were taken at 88 points on an approximately 25-m grid using a global positioning system to define sample locations.The results showed moderate levels of spatial variability of four measures of nutrient contents in the research region.The contents of soil OM,TN,AN and AP values were low,and their means were 8.89 g/kg,26.76 mg/kg,1.92 mg/kg and 130.23 mg/kg,respectively.Organic matter(OM) with a nugget/still ratio 30.9%,and available K(AK) with a nugget/still ratio 31.1%,could be modeled with an exponential model.The nugget/still ratios of available N(AN) and available P(AP) were 37.7% and 26.4%,respectively,and they could be well modeled with a spherical model.As a result,all the nutrients exhibited a moderate spatial correlation.The range of soil OM,AN,AP and AK values were 61.8 m,76.3 m,70.5 m and 57 m,respectively.The fractal dimension(D) of AK was the highest,followed by OM and AN,and AP was the lowest.Anisotropic analyses and trend analyses all showed that OM and AP were even strongly anisotropic.AN and AK showed the widest scope in isotropism.The spatial distributions of the four measures of soil nutrients in the study region,which were influenced by elevation and slope and represented some regularity,were characterized by the mean contents of all nutrients being low in the north central area with a relatively steep slope,while being high in the comparatively flat northeast and south regions.

The spatial variability of soil total nutrient levels, which may be greatly affected by parent material, plays an important role in both agriculture and environment, especially with regard to soil fertility and soil quality. Little research has been done that addresses the spatial characteristics of total nutrients. Soil samples (0–20 cm) were taken from 111 points on an approximately 20-m grid in March 2009 using a global positioning system (GPS) to define sample locations. Sixteen soil total chemical properties were analyzed by classical statistical and geostatistical methods. Soil aluminum (Al), calcium (Ca), chromium (Cr), copper (Cu), nitrogen (N), sodium (Na), silicon (Si), strontium (Sr), titanium (Ti), and vanadium (V) exhibited strong spatial dependence, with the nugget–sill ratios ranging from 3.39% (Na) to 23.53% (Si). Soil barium (Ba), iron (Fe), potassium (K), manganese (Mn), phosphorus (P), and zinc (Zn) had moderate spatial dependence, with nugget–sill ratios of 3.39% to 23.53%. The spatial...

Spatial variability in soil properties has long been observed within uniformly managed fields. Understanding the spatial characteristics of soil properties would be helpful in the development of site-specific management. Uniform management results in overapplication in areas with high nutrient levels and underapplication in areas with low nutrient levels. The objective of this study was to quantify the degree of spatial variability of soil properties. This is important to tobacco quality across flue-cured tobacco (Nicotiana tabacum) plantation fields. Fourteen soil properties were analyzed by geostatistical techniques. Soil organic matter (OM) had significantly positive correlations with active soil OM, total N (TN), available N, available phosphorus, available potassium, Cu, Fe, and Mn. Soil TN, Zn, cation exchange capacity, and silt showed strong spatial dependence, with nugget-sill ratios ranging from 3.39% to 23.43%. Other soil properties showed moderate dependence, with nugget-sill ratios of 30.87% to 49.99%. Spatial dependence ranged from 34.3 m (Zn) to 376.3 m (Mn). The OM contour map showed highest similarity with that of TN. Variography and kriging are useful tools for soil-sampling strategies and variable-rate application in site-specific farming.

Present nutrient management recommendations for flue-cured tobacco (Nicotiana tabacum) in Central China are typically uniform for large regions. This results in over-application in areas with high nutrient levels and under-application in areas with low nutrient levels. An 87-ha tobacco field was selected to define management zones (MZs) for more precise soil nutrient management. Our objectives were to: (1) quantify the spatial variability of soil fertility variables, and (2) delineate the MZs by the combined usage of principal component analysis (PCA) and fuzzy cluster algorithm. To achieve these objectives, soil samples (0-20cm) were taken from 81 points on an approximately 100-m grid in March 2007. Soil samples were analyzed for pH, organic matter (OM), total nitrogen (TN), alkalytic nitrogen (AN), available phosphorous (AP), available potassium (AK), and cation exchange capacity (CEC). Spatial variability was assessed and spatial distribution maps constructed using geostatistical techniques. PCA and fuzzy cluster algorithm were then performed to delineate MZs; fuzzy performance index (FPI) and normalized classification entropy (NCE) were used to determine the optimum cluster number. Results showed that the optimum number of MZs for this study area was three and analysis of variance indicated the heterogeneity of soil fertility among different MZs. The defined MZs provide a basis of information for site-specific fertilizer management in the tobacco-planted field.

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.