Effects of wastewater application on saturated hydraulic conductivity of different soil textures

As metropolitan areas expand, the municipal and industrial uses of freshwater increase. Therefore, water resources for irrigation become limited and wastewater reuse for irrigation becomes a good alternative. For this purpose, the effects of suspended solids in wastewater on the soil physical properties, i.e., saturated hydraulic conductivity, K_s, have to be considered. The objectives of this research were to study the effects of applying freshwater and differently treated wastewater on K_s in the surface and subsurface layers of sandy‐loam, loam, and clay‐loam soils. This effect was studied by investigating the ratio of K_s for wastewater to K_s for fresh water in soil surface as K_r1 and in soil subsurface as K_r2. The results showed that the application of freshwater did not reduce the K_r1 considerably. However, the reduction in K_r1 mainly occurred in soil depth of 0–50 mm due to the application of wastewater. This effect is more pronounced in clay‐loam soil than in loam and sandy‐loam soils. It is concluded that application of wastewater with TSS (total suspended solid) of ≥ 40 mg L^–1 resulted in K_r1 reduction of >50% in different soil textures. However, the K_r2 reduction at soil depth of 100–300 mm is not considerable by application of wastewater for different soil textures. Further, it is concluded that less purified wastewater can be used in light‐texture soils resulting in less reduction in K_r1. Empirical models were developed for predicting the value of K_r1 as a function of amounts of wastewater application and TSS for different soil textures that can be used in management of wastewater application for preventing deterioration of soil hydraulic conductivity.     

Spatial variability of water retention parameters and saturated hydraulic conductivity in a calcareous Inceptisols (Khuzestan province of Iran) under sugarcane cropping

The objective of this study was to quantify inherent spatial variability and spatial cross-correlation of the van Genuchten retention parameters and saturated hydraulic conductivity (K_s) of surface and subsurface layers in a calcareous Inceptisols (Khuzestan province, Iran) under sugarcane cropping. Measurements were performed on 100-cm³ undisturbed soil cores collected at 94 locations along a 30-m-long transect with horizontal sampling distance intervals of 0.3 and 1 m at soil depths of 0–40 and 40–80 cm, respectively. Spatial variability was investigated using conventional statistics and geostatistical techniques. Coefficient of variation (CV) varied from 8.2% (for shape parameter, n at 40–80 cm depth) to 256.7% (for K_s at 0–40 cm depth). The n parameter and saturated water content, θ_s, showed a small-scale spatial heterogeneity with a maximum CV of 11.3% for the first depth and 9.2% for the second depth. Most of the hydraulic parameters at both depths showed a spatial structure and convex experimental semivariograms with dominant spherical models with the influence range of 3.2–41 m. In most cases, the extent of spatial correlation scales of cross-semivariograms for pairs of cross-correlated hydraulic variables was found to be different with reference to those relating to the direct semivariograms of correlated variables.     

晋西北黄土丘陵区土壤饱和导水率的空间分布特征及影响因素

土壤饱和导水率（K_s）是反映土壤入渗性能与土壤持水能力的重要参数，为探究流域尺度下土壤K_s的空间分布特征及影响因素，更好地掌握土壤水文过程与调节机理，选取晋西北黄土丘陵区朱家川流域横向梯度（上游、中游、下游）不同土地利用方式下的土壤（70个样点）为研究对象，采用定水头法测定土壤K_s，并获取样点地形因子和其他土壤理化性质，通过建立土壤K_s偏最小二乘回归模型（PLSR），分析影响土壤K_s空间分布格局的主要因素。结果表明：（1）除土壤容重和砂粒含量为弱变异外，区域土壤理化性质其余因子均为中等变异；土壤K_s在横向梯度下表现为上游 > 中游 > 下游；（2）不同土地利用方式下土壤K_s差异显著（P<0.05），由高到低顺序为林地 > 农地 > 草地；（3）林地（VIP=1.997）与草地（VIP=1.710）利用方式、土壤容重（VIP=1.548）、土壤有机质（VIP=1.323）、大团聚体（VIP=1.266）、粉粒含量（VIP=1.062）和黏粒含量（VIP=1.049）是土壤K_s变化的主要因素，林地利用方式影响程度最大。土地利用、土壤性质、地形因子均是影响黄土丘陵区土壤K_s空间分布的主要因素，是用来模拟预测土壤K_s空间分布的重要因子。     

THE RELATION BETWEEN COST AND UTILITY IN SOIL SURVEY

This paper discusses how to compare the utility of soil maps. For three contrasting areas, in Southern England, it compares the utilities of a number of single-property and general purpose (series) soil maps, produced by free and grid survey, at map scales from 1 :20,000–1:70,000. The‘purity’of series mapping units increases with survey effort. Where the soil boundaries had fairly clear external expression free survey was superior to grid survey. On average the purity of maps by grid survey was higher than for maps by free survey at comparable survey effort. The uniformity of soil properties within mapping units was measured by relative variance (RV)= within-unit variance/total variance, (1–RV) indicates the increased precision achieved by the soil map. It increased with survey effort. For series maps by free or grid survey (1–RV) depended on how closely soil properties were associated with profile classes, and on the extent to which soil boundaries could be mapped on their external expression. Free survey was preferred at scales between 1: 100,000 and 1:30,000, when the soil boundaries could be mapped on their external expression, (1–RV) for the profile classes on which the mapping units are defined puts a ceiling to the utility of series maps (grid or free) which is already nearly achieved at map scales near 1:25,000. Except for properties very poorly associated with profile classes, single property maps do not have great advantage over series maps at medium map scales, but they attain higher values of (1–RV) at scales greater than 1: 25,000.     

渝东北紫色土饱和导水率传递函数研究

为研究渝东北紫色土理化性质在垂直空间上的分布情况以及对饱和导水率的影响,进而建立饱和导水率与各理化性质间的关系函数,推求饱和导水率的传递函数,选择渝东北开州区、云阳县等7个区县内45个紫色土典型田块为研究区域,运用Excel 2013和Matlab 2015b软件统计分析后,利用多元非线性回归法推求并验证了渝东北紫色土饱和导水率传递函数模型和模型参数。研究表明:①研究区土壤饱和导水率变化范围在0.16～195.68 cm/d,变化范围广,空间变异系数大,变异性较强;同一采样点深度越大,饱和导水率越小;②土壤饱和导水率与有机质含量有显著的指数函数关系,与饱和含水量有较强的二次函数关系,与土壤容重和土壤颗粒的相关性不大;③本次试验建立的土壤饱和导水率传递函数模型及模型系数检验合格,预测值与实际测算值误差较小,精度良好,可用于渝东北紫色土饱和导水率的预测工作。     

Effects of compaction on soil hydraulic properties,penetration resistance and water flow patterns at the soil profile scale

The aim of this study was to quantify the effects of compaction on water flow patterns at the soil profile scale. Control and trafficked plots were established in field trials at two sites. The trafficked treatment was created by four passes track‐by‐track with a three‐axle dumper with a maximum wheel load of 5.8 Mg. One year later, dye‐tracing experiments were performed and several soil mechanical, physical and hydraulic properties were measured to help explain the dye patterns. Penetration resistance was measured to 50 cm depth, with saturated hydraulic conductivity (K_s), bulk density, and macroporosity and mesoporosity being measured on undisturbed soil cores sampled from three depths (10, 30 and 50 cm). Significant effects of the traffic treatment on the structural pore space were found at 30 cm depth for large mesopores (0.3–0.06 mm diameter), but not small mesopores (0.06–0.03 mm) or macroporosity (pores > 0.3 mm). At one of the sites, ponding was observed during the dye‐tracing experiments, especially in the trafficked plots, because of the presence of a compacted layer at plough depth characterized by a larger bulk density and smaller structural porosity and K_s values. Ponding did not induce any preferential transport of the dye solution into the subsoil at this site. In contrast, despite the presence of a compacted layer at 25–30 cm depth, a better developed structural porosity in the subsoil was noted at the other site which allowed preferential flow to reach to at least 1 m depth in both treatments.     

重庆市四面山不同土地利用类型饱和导水率

[目的]探讨不同土地利用类型和土壤理化性质对饱对导水率的影响。[方法]采用定水头法测定四面山不同土地利用类型的饱和导水率,并运用回归分析,相关分析和主成分分析法分析其与土壤物理因子和有机质的关系,以及影响饱和导水率的主导因子。[结果]各土地利用类型的平均饱和导水率均高于荒地,其顺序为:林地农地草地,林地中天然林饱和导水率大于人工林;饱和导水率随土层深度的增加呈负指数递减规律;饱和导水率与容重呈幂函数关系,与孔隙度呈正相关,与黏粒含量呈负相关;有机质含量的提高对饱和导水率有积极的促进作用。[结论]影响饱和导水率的主导因子是容重、有机质、非毛管孔隙度和毛管孔隙度,其次,土壤机械组成对其也有一定影响。     

Using boosted regression trees to explore key factors controlling saturated and near‐saturated hydraulic conductivity

Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near‐saturated hydraulic conductivities in undisturbed soils with a global meta‐database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta‐databases may strongly over‐estimate prediction performance unless they are validated against each individual data source separately. For such a source‐wise cross‐validation, we estimated the hydraulic conductivity at a tension of 10 cm (K₁₀) and the saturated hydraulic conductivity (K_s) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K₁₀ were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in‐depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K₁₀, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension‐sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for K_s. The direction of the tension‐sequence and the soil texture class were also important, with both coarse and fine‐textured soils generally having larger K_s values than medium‐textured soils.     

石灰岩与白云岩坡地土壤饱和导水率对比研究

[目的]对比研究不同下垫面特征和土地利用方式对两类坡地表层土壤性质及其土壤饱和导水率(Ks)的影响。[方法]以喀斯特地区不同岩性下垫面的石灰岩和白云岩两类坡地表层土壤为研究对象,采用Guleph稳定入渗仪和土壤分析的方法。[结果](1)石灰岩和白云岩表层土壤在受到放牧作用影响后,土壤均呈现显著退化趋势,其容重、黏粒含量增大,孔隙度、有机质含量降低。(2)石灰岩和白云岩两类坡地表层土壤在未受到人为干扰的自然植被条件下,由于表层岩溶带的发育,Ks都很高,平均值分别为328.6和257.2mm/h。其中,石灰岩坡地相比白云岩坡地,Ks具有更高的空间变异性,二者Ks变异系数变化范围分别为90.71%~95.62%和59.60%~67.32%。(3)受到放牧作用影响后,石灰岩和白云岩坡地表层土壤Ks相比自然植被状态下呈显著降低趋势,Ks分别降低52.2%和86.7%,白云岩坡地Ks降低程度大,高于石灰岩坡地。     

陕北水蚀风蚀交错区两种生物结皮对土壤饱和导水率的影响

该文以陕北水蚀风蚀交错区普遍发育的地表和地上两种生物结皮为研究对象，分别以3种非生物结皮（无结皮、物理结皮、去除生物结皮）为对照，使用盘式入渗仪测定其饱和导水率。结果表明：与无结皮土壤相比，两种类型生物结皮均可极显著降低土壤饱和导水率；与去除生物结皮土壤相比，两种类型生物结皮对土壤饱和导水率的降低均不显著；与有物理结皮发育的土壤相比，地表生物结皮对土壤饱和导水率的降低不显著，而地上生物结皮对土壤饱和导水率的降低显著。一方面，两种生物结皮对土壤饱和导水率均有明显降低作用，预示生物结皮在降雨活动中可能会增加径流、降低入渗，阻碍研究区水分亏缺条件下的植被恢复和生态与环境建设。另一方面，与不同的对照相比，生物结皮对土壤饱和导水率的影响截然不同，该结论可在一定程度上解释当前有关生物结皮影响土壤水分入渗方面所存在的分歧。     

Effects of a bentonite–water mixture on soil-saturated hydraulic conductivity

To reduce water loss in light-textured soils, hydraulic conductivity should be reduced by mixing the soils with some soil conditioners, e.g. sodium-bentonite. The objectives of this study were to investigate the effects of irrigation water with different bentonite concentrations (0, 0.05, 0.1, 0.15 and 0.2%) on hydraulic gradient (i) and relative saturated hydraulic conductivity (K _rs) in a laboratory soil column with a loamy sand soil. Addition of sodium-bentonite to the soil increased i throughout each experiment. Furthermore, addition of bentonite reduced K _rs, and a 0.2% bentonite–water concentration after infiltration of 48 mm of bentonite–water mixture (BWM), reduced the K _rs value to 56% of K _s. K _rs was reduced as the concentrations of bentonite increased and its value reached ～0.5 to 0.6 as the infiltration of BWM increased. The lowest value of K _rs and the greatest reduction rate occurred at a bentonite concentration of 0.2%. It is concluded that BWM can be used as a channel liner. Using a 0.2% bentonite concentration resulted in a reduction in the seepage ratio from 1.0 to 0.08.     

Pedo-transfer functions for estimating the hydraulic properties of paddy soils in subtropical central China

Pedo-transfer functions (PTFs) have been widely used to estimate soil hydraulic properties in the simulation of catchment eco-hydrological processes. However, the accuracy of existing PTFs is usually inadequate for use. To develop PTFs for local use, soil columns were collected from a double rice-cropped agricultural catchment in subtropical central China. The PTFs for saturated soil hydraulic conductivity (K_s) and parameters (θ_s, α, and n) of the van Genuchten model for the soil water retention curve (SWRC) were obtained based on soil’s basic properties, and compared with models developed by Li et al. in 2007 and Wösten et al. in 1999, respectively. Our results indicated that K_s in the range of 0.04–1087 cm d^?1 and θ_s in the range of 0.34–0.51 cm³ cm^?3 were both well estimated with the R²_adj of 0.72 and 0.87, respectively, but α (0.04–0.65 cm^?1) and n (1.05–1.21) were relatively poorly predicted with the respective R²_adj of 0.38 and 0.55, despite the use of more input parameters. Our local derived PTFs outperformed the other two existing models. However, if the local PTFs for paddy soils are not available, the Wösten et al. 1999 model can be proposed as a useful alternative. Therefore, this study can improve our understanding of the development and application of PTFs for predicting paddy soil hydraulic properties in China.     

Estimation of saturated hydraulic conductivity from double‐ring infiltrometer measurements

This research aims to determine soil vertical saturated hydraulic conductivity (K_s) in situ from the measured steady infiltration rate (I), initial soil properties and double‐ring infiltrometer (DRI) test data. Characterizing the effects of these variables on the measured steady infiltration rate will enable more accurate prediction of K_s. We measured the effects of the ring diameter, head of ponding, ring depth, initial effective saturation and soil macroscopic capillary length on measured steady infiltration rates. We did this by simulating 864 DRI tests with the finite element program HYDRUS‐2D and by conducting 39 full‐scale in situ DRI tests, 30 Mini‐Disk infiltrometer experiments and four Guelph Permeameter tests. The M5′ model trees and genetic programming (GP) methods were applied to the data to establish formulae to predict the K_s of sandy to sandy‐clay soils. The nine field DRI tests were used to verify the computer models. We determined the accuracy of the methods with 30% of the simulated DRI data to compare I/K_S values of the finite element models with estimates from the suggested formulae. We also used the suggested formulae to predict the K_s values of 30 field DRI experiments and compared them with values measured by Guelph Permeameter tests. Compared with the GP method, the M5′ model was better at predicting K_S, with a correlation coefficient of 0.862 and root mean square error (RMSE) of 0.282 cm s^?1. In addition, the latter method estimated K_svalues of the field experiments more accurately, with an RMSE of 0.00346 cm s^?1.     

Effect of long‐term swine‐manure application on soil hydraulic properties and heavy metal behaviour

This study evaluated the effect of 13 years of swine‐manure application on the changes in soil hydraulic properties, and as associated physicochemical properties, with a focus on heavy metal mobility. Various soil hydraulic properties were measured, including soil water retention (SWR), saturated field hydraulic conductivity (K_fs) and unsaturated field hydraulic conductivity (K_funsat) using a disc infiltrometer. Heavy metal mobility was evaluated with a sequential extraction procedure. At 0–30 cm soil depth in the heavily manured plot (SMhigh plot), SWR at 0 to ?100 kPa was significantly larger than in plots amended with a standard amount of manure (SMstd plot) or with chemical fertilizer (CF plot). K_fs and K_funsat values in both manure‐amended plots were less than in the CF plot under dry soil conditions but greater than those of the CF plot under wet soil conditions. Furthermore, K_fs and K_funsat did not necessarily increase with manure application rates. On the other hand, high‐mobility metal fractions, such as the exchangeable fraction of Zn, and the CH₃CO₂Na‐extractable fraction of Zn and Mn, and the metal–organic complex fractions of Zn, Cu and Mn, increased with the greater manure application rate. In addition, low‐mobility metal fractions, the organically bound fractions of Zn, Cu and Mn in the high SM plot and the easily reducible metal oxide fraction of Mn in both manure‐amended plots were probably affected and released into high‐mobility fractions. This indicated that manure application changed the soil redox conditions by improving the soil structure, depending on the water content of soil pores. Despite the reduction of K_fs and K_funsat by heavy manure application, the transport of high‐mobility metal fractions with either surface water flow or infiltration water flow could be controlled by soil water content at the beginning of a rain or irrigation event.     

Spatial variability of physico-chemical properties and hydraulic characteristics of a gravelly calcareous soil

Due to the existence of gravelly soils and the lack of sufficient research on such soils, this study was carried out on a gravelly calcareous soil. Selected physico–chemical and hydraulic soil attributes were determined at 69 points on a nested-sampling design. Hydraulic characteristics including unsaturated hydraulic conductivity (K _ψ) and sorptivity coefficient (S) at six applied tensions of 0 to 0.2 m, and sorptive number (α) and macroscopic capillary length (λ) at five applied tensions of 0.03 to 0.2 m were determined using a tension disc infiltrometer. Hydraulic and chemical soil attributes were the highest and the lowest variants, respectively. The maximum and minimum values for the coefficient of variation (CV) in all the measured physico-chemical and hydraulic soil attributes were obtained for α_0.2 and soil pH, respectively. Minimum, maximum, mean and variance values of K _ψ, S and α decreased as applied tension increased. Although the pattern was reversed for λ. The majority of soil attributes showed the spatial structure with dominant spherical and exponential models for physico-chemical and hydraulic attributes, respectively. Range values of semi-variograms were obtained between 4.6 m (for α_0.03) and 211 m (for clay, gravel content and soluble Mg). In general, range values were 99.60, 82.05 and 40.2 m for physical, chemical and hydraulic soil attributes, respectively, indicating that the physical soil attributes influenced neighboring values over greater distances than the other soil attributes. This enables soil scientists to use measured soil physical data over greater distances to estimate attributes in the unsampled locations.     

干粉PAM溶解时间对土壤饱和导水率的动态影响

本试验选取两种质地土壤(黏壤土和砂壤土),采用3种干粉PAM施用水平(0、22.5 kg/hm~2和45 kg/hm~2),测定土样在10.25 mm/h入渗速度下的土壤饱和导水率(KS),然后根据土样团聚体含量和稳定性及团聚结构的微观图片,分析干粉PAM影响下土壤结构的变化特征,进而说明干粉PAM溶解时间对KS的影响机理。结果表明:施用PAM后,KS随干粉PAM在水中溶解时间的延长而逐渐减小,最终趋于稳定;干粉PAM溶解时间较短时,PAM处理的KS高于对照,其中PAM施用水平45 kg/hm~2时砂壤土KS提高幅度最大,较对照提高26.87%,但不同PAM施用量处理间的KS差异不显著。干粉PAM溶解时间足够长时,PAM处理的KS均显著低于对照,其中PAM施用水平45 kg/hm~2时黏壤土KS降低幅度最大,较对照降低10.86%,但是不同施用量处理间KS差异不显著。从影响机理上分析,PAM主要是通过增加土壤团聚体含量及稳定性来提高KS;而干粉PAM溶解时间足够长时,由于PAM易吸附土壤颗粒,水解后的PAM分子链不断伸张延长,堵塞了土壤孔隙,加上PAM本身的黏滞特性,从而降低了KS。研究干粉PAM溶解时间对KS的动态影响,可以为PAM在改善土壤导水能力方面的应用提供理论依据。     

宁南山区草地植被恢复方式对土壤饱和导水率的影响

为评价宁南山区草地植被不同恢复方式对土壤入渗性能的影响,以不同植被群落的饱和导水率为研究对象,采用逐步回归研究退耕农地、禁牧荒地、封育草地导水率的变化及影响因子,并探讨了其作用机制。结果表明：3种植被恢复方式均有利于0-40 cm土壤饱和导水性能提高;各土层土壤饱和导水率均随植被恢复而不断提高,0-5 cm土层改善作用最为明显;农地退耕序列和荒地禁牧序列5-40 cm土层、封育草地序列0-40 cm土层土壤饱和导水率随土层深度下降而降低;影响土壤饱和导水率的因子为土壤有机质因子和土壤结构因子;3种植被恢复方式土壤有机质质量分数与Ks均呈显著的线性相关关系,在该区域有机质质量分数越高,Ks增加越快;土壤有机质积累是土壤饱和导水率提高的根本动力。因此,草地封育更利于提高使该地区土壤导水性能提高,促进生态恢复。     

Analysis on pedodiversity and spatial subset representativity—the German soil map 1:1,000,000

Knowledge about spatial soil variation in terms of measured pedodiversity, as well as the spatial distribution of soils in terms of spatial subset representativity, offers the possibility to estimate the quality and variance within a soil map. Additionally, it can help to identify representative sample locations. Demonstrated at the German soil map at a scale of 1:1,000,000, this study describes a methodology to analyze the distribution of taxonomical pedodiversity using the Simpson index and a new approach to derive representative spatial subsets based on a modified χ²‐test (χ_m²), which can be used as monitoring areas. To analyze the spatial composition of the soil map and to detect differences in the underlying mapping schemes of the German soil map 1:1,000,000, three different spatial data structures were studied: (1) the entire soil map, (2) the soil map segmented into geomorphological regions, and (3) the soil map segmented into the Federal States of Germany. Representative patches of varying sizes were statistically derived for all spatial subsets as well as the entire soil map ranging from 20 km × 20 km up to 70 km × 70 km. The results show that the measured pedodiversity is linked to both the geomorphology as well as the political borders of the Federal States. On the one hand, this reveals the uncertainty of measuring pedodiversity on the basis of soil‐class maps as the spatial representation of pedodiversity is influenced by the different mapping traditions and methods applied in the 16 Federal States of Germany. On the other hand, it allows the analysis of the aggregation schemes of different landscapes. The presented approach helps to understand large soilscapes and to compare different soil maps of different states and countries as well as to enhance the soil map with additional information. Furthermore, the representative patches can be used to select soil‐monitoring areas.     

青海省东部不同土地利用方式下土壤饱和导水率分布及其影响因素

研究高寒地区土壤饱和导水率分布特征及其影响因素可为评估脆弱生态系统水源涵养能力和构建区域水文模型提供参数.通过测定青海省东部南北样线24个样点(0—30 cm)土壤基本理化性质和饱和导水率(Ks),分析了不同土地利用方式下Ks分布特征及其影响因素.结果表明:Ks均值表现为林地(1.89 cm/h)>草地(1.62 cm...     

SPATIAL VARIABILITY OF SOIL PHYSICAL PROPERTIES IN A REGION OF THE LOESS PLATEAU OF PR CHINA SUBJECT TO WIND AND WATER EROSION

The analysis of the spatial variability of soil properties is important for land management and construction of an ecological environment. The objectives of this study were to investigate the spatial variability of saturated hydraulic conductivity (K_S), total porosity (TP), capillary porosity (CP) and bulk density (BD) in relation to land use in a 0·54 km² watershed on the Loess Plateau. Topsoil samples (0–5 cm) from 154 sites within the watershed were collected and analyzed by classical and geostatistical statistics in the summer of 2009. The results from the classical statistical analyses indicated that TP, CP and BD had low variability whereas K_S had high variability with the watershed. Farmland had significantly lower BD and higher TP and CP than grassland, shrubland and woodland (p < 0·05). Geostatistical analyses revealed that the K_S semivariogram was best fit by a spherical model, the CP semivariogram was best fit by an exponential model and the TP and BD semivariograms were best fit by Gaussian models. The nugget to sill ratios and fractal dimension values indicated that all four soil properties had strong spatial dependence. Moran's I analysis showed that a 100‐m sampling interval would be adequate for detecting the spatial structure of the four soil physical properties within the watershed. Spatial interpolation maps could provide useful information for precision agriculture practices and ecological management. Copyright © 2011 John Wiley & Sons, Ltd.