Spatial Patterns Of Soil Properties Research Articles

Spatial patterns of SOC, SON, 137Cs and soil properties as affected by redistribution processes in a Mediterranean cultivated field (Central Ebro Basin)

Mediterranean mountain agroecosystems are sensitive areas to soil degradation due to climatic conditions and anthropogenic pressure from agriculture and grazing practices. Soil redistribution processes affect the spatial variability of soil properties and nutrients, as soil organic carbon and nitrogen (SOC and SON) are linked to soil quality and soil functions. A representative cereal field of rain-fed agroecosystems in a Mediterranean mountain environment where conventional and conservation agricultural practices have been implemented was selected on the northern border of the Ebro valley (NE Spain) to gain a better understanding of the effect of soil redistribution processes on the spatial pattern of soil properties at field scale. One hundred and fifty-six bulk (30–50cm) and 156 topsoil samples (5cm) were collected on a 10×10m grid. Furthermore, 21 soil samples (40cm) were collected at a nearby undisturbed reference site. 137Cs massic activity was measured on bulk and reference soil samples, and SOC and SON were measured on all soil samples. The characterisation of SOC pools into active (ACF) and stable carbon fraction (SCF) was carried out to study SOC pool dynamics. The fallout 137Cs was used in order to identify areas of 137Cs loss and gain and that of soil within the study field. Similar spatial patterns and direct and significant correlations (p<0.01) were found between 137Cs and soil nutrients. As much as 70% of the total study field had lower values of 137Cs inventory than the reference for the area. In addition, there was a generalised loss of soil nutrients. SOC gain was found in less than 1% of the study field and there was a large loss of SON compared to the undisturbed reference site. Higher and significant (p<0.01) contents of soil nutrients were found in topsoil than in bulk samples. Furthermore, there was an enrichment of the relative contribution of ACF to total SOC in sampling points where there was a 137Cs gain in both bulk and topsoil samples as a consequence of the soil redistribution particles by tillage and runoff. Understanding patterns of soil nutrients can be useful for developing or implementing land management strategies to preserve soil quality in Mediterranean agricultural areas.

Derivation of terrain covariates for digital soil mapping in Australia

Digital soil mapping is founded on the availability of covariates that are used as surrogates for the spatial patterns in soil properties. One important subset of covariates represents the patterns due to terrain, and these are typically derived from a digital elevation model at a suitable resolution. When each digital soil mapping exercise requires the calculation of terrain covariates, there is a clear potential for inconsistent methods and for choosing the covariates that are easiest to derive rather than those that are most relevant. The creation of open repositories of relevant terrain covariates that are correctly derived avoids these problems and fosters the application of digital soil mapping and other modelling activities that benefit from landscape properties. This paper describes the creation of a suite of commonly used terrain covariates from the 1-arcsecond (~30 m) resolution digital elevation models for Australia that were released through CSIRO’s Data Access Portal and the TERN Data Discovery Portal. The methods used to derive the terrain covariates are described and their characteristics are identified.

Spatial and vertical analysis of soil properties in a Mediterranean vineyard soil

AbstractSoil physical properties influence vineyard behaviour; therefore, the knowledge of their spatial variability is essential for making vineyard management decisions. Little work has been conducted at high spatial resolution on soil properties at depths lower than 0.30 m which is of special relevance to perennial crops. The objectives of this work were to (i) analyse the spatial and vertical variability of soil depth, particle size fractions and water‐holding capacity (WHC) by geostatistical techniques; (ii) study the causes of the variability, with additional information from classical soil sampling; and (iii) assess the significance of WHC through its relationship with vine vigour. The work was carried out in a vineyard of eight hectares within the D.O.Ca. Rioja (northern Spain). Soil variability was determined via grid sampling at three depth ranges (0–0.30, 0.30–0.60 and 0.60–0.90 m). A conventional soil survey provided additional information on soil variability. Clay, sand and silt fractions, soil organic matter content, WHC and pruning weight were determined. Most soil properties had strong or moderate spatial dependence, with the exceptions of sand at 0.30–0.60 m and silt in the topsoil. Topography and soil erosion caused the spatial variability of soil depth and contributed to the spatial distribution of particle size fractions in the topsoil, while the heterogeneity of parent material influenced the spatial pattern of soil properties at 0.60–0.90 m. The WHC and soil depth spatial distributions related well to that of vine vigour, demonstrating the importance of knowing the spatial variability of these soil properties.

Effects of land use on spatial patterns of soil properties in a rocky mountain area of Northern China

In the rocky mountain area of North China, soil fertility has decreased with severe soil and water losses under various land uses. Land use has been proven to affect soil fertility spatial distribution patterns at larger scales. However, less information is available about these effects in field scale plots. Soil samples were collected at 2-m intervals by grid sampling from an area (18 × 18 m) within three land use types (poplar woodland, rotation cropland with peanut and sweet potato, and peach orchard). Soil properties including soil particle composition, soil organic matter, total nitrogen (TN), nitrate nitrogen (NO3 −-N), total phosphorus (TP), and available phosphorus (AP) were measured for each sample. The spatial variability and spatial pattern of the soil properties were assessed for the three contrasting land use types. NH4 +-N, NO3 −-N, and AP in the peach orchard and NO3 −-N in the poplar woodland exhibited strong variation (coefficient of variance >100 %). Other properties showed moderate variations. With annual plowing and fertilization, soil properties in the rotation cropland had less variability and greater spatial autocorrelated ranges. The spatial dependences of sand content, TN, NO3 −-N, and SWC in both the peach orchard and the rotation cropland were weaker than those in the poplar woodland, but the spatial dependences of TP and AP in the peach orchard were stronger than those in either the rotation cropland or the poplar woodland. Human activities such as plowing, fertilization, and harvesting had obvious effects on the spatial variability and spatial pattern of soil properties.

Hierarchical analysis of vegetation dynamics over 71 years: soil–rainfall interactions in a Chihuahuan Desert ecosystem

Proliferation of woody plants in grasslands and savannas is a persistent problem globally. This widely observed shift from grass to shrub dominance in rangelands worldwide has been heterogeneous in space and time largely due to cross-scale interactions among soils, climate, and land-use history. Our objective was to use a hierarchical framework to evaluate the relationship between spatial patterns in soil properties and long-term shrub dynamics in the northern Chihuahuan Desert of New Mexico, USA. To meet this objective, shrub patch dynamics from 1937 to 2008 were characterized at patch and landscape scales using historical imagery and a recent digital soils map. Effects of annual precipitation on patch dynamics on two soils revealed strong correlations between shrub growth on deep sandy soils and above-average rainfall years (r = 0.671, P = 0.034) and shrub colonization and below-average rainfall years on shallow sandy soils (r = 0.705, P = 0.023). Patch-level analysis of demographic patterns revealed significant differences between shrub patches on deep and shallow sandy soils during periods of above- and below-average rainfall. Both deep and shallow sandy soils exhibited low shrub cover in 1937 (1.0% +/- 2.3% and 0.3% +/- 1.3%, respectively [mean +/- SD]) and were characterized by colonization or appearance of new patches until 1960. However, different demographic responses to the cessation of severe drought on the two soils and increased frequency of wet years after 1960 have resulted in very different endpoints. In 2008 a shrubland occupied the deep sandy soils with cover at 19.8% +/- 9.1%, while a shrub-dominated grassland occurred on the shallow sandy soils with cover at 9.3% +/- 7.2%. Present-day shrub vegetation constitutes a shifting mosaic marked by the coexistence of patches at different stages of development. Management implications of this long-term multi-scale assessment of vegetation dynamics support the notion that soil properties may constrain grassland remediation. Such efforts on sandy soils should be focused on sites characterized by near-surface water-holding capacity, as those lacking available water-holding capacity in the shallow root zone pose challenges to grass recovery and survival.

Improving the Prediction Accuracy of Soil Mapping through Geostatistics

This research aimed to implement and compare the accuracy of different interpolation methods using cross validation errors for interpolating the spatial pattern of soil properties. This paper investigates whether the use of kriging, instead of traditional interpolation methods, improves the accuracy of prediction of soil properties. To this end, various interpolation (kriging) techniques that rely on the spatial correlation between observations to predict attribute values at ensampled locations are studied. Geostatistics provides descriptive tools such as semivariograms to characterize the spatial pattern of continuous and categorical soil attributes. The maps obtained from Ordinary Kriging, Inverse Distance Weighting and splines show clearly that the map from Universal Kriging (UK) is better than the other three interpolation methods. Therefore, UK can be considered as an accurate method for interpolating soil (EC, pH, CaCO3) properties.

Grassland community composition drives small-scale spatial patterns in soil properties and processes

The presence and activity of individual plants can affect soil resource availability and microbial processes, and can influence the spatial scale over which soil properties vary. While soils have been found to differ under plants of differing growth form (i.e. grasses vs. trees), few studies have focused on small-scale soil differences under comparably-sized species. Here we investigate how two types of C-3 grasses influence patterns in soil properties and processes at scales of less than one meter in a California grassland. To understand how native perennial grasses differ from invasive annual grasses in their effects on soils, we used cross-semivariogram analysis to quantify the degree and scale of spatial heterogeneity in soil properties and processes in experimentally-seeded grasslands. We then used mapping techniques to correlate spatial patterns of soil properties and processes with the cover of annual and perennial grasses aboveground. We found that many soil properties and processes belowground were spatially-correlated with the aboveground presence of annuals or perennials. Soil moisture became more heterogeneous with increasing amounts of perennial cover, suggesting that perennial bunchgrass individuals take up more water and produce zones of resource depletion in comparison with soils directly under annual grasses. The association of belowground resources and activity with the two types of grass suggests that the historical shift from perennial to annual dominance in California grasslands led to changes in the small-scale spatial structure of soil properties and processes in these systems. These changes may alter ecosystem function and could potentially perpetuate invasive annual grass dominance.

Apparent Electrical Conductivity in Correspondence to Soil Chemical Properties and Plant Nutrients in Soil

Spatial variability and relationship between soil apparent electrical conductivity (ECa), soil chemical properties, and plant nutrients in soil have not been well documented in Malaysian paddy fields. For this reason precision farming has been used for assessing field conditions. ECa technique for describing soil spatial variability is used for soil data acquisition. Soil sampling provides the data used to make maps of the spatial patterns in soil properties. Maps are then used to make recommendations on the variation of application rates. The main purpose of the authors in this study was to generate variability map of soil ECa within a Malaysian rice cultivation area using VerisEC sensor. The ECa values were compared to some soil properties after delineation. Measured parameters were mapped using kriging technique and their correlation with soil ECa was determined. Through this study the authors showed that the EC sensor can determine soil spatial variability, where it can acquire the soil information quickly.

Litterfall and associated nutrient pools extend beyond the canopy of scattered eucalypt trees in temperate pastures

Scattered paddock trees are a keystone feature of temperate grazing landscapes of Australia. However, our understanding of their influence on their immediate environment, and specifically the spatial distribution and characteristics of litter, is still limited. Here, we quantified the spatial pattern of litter around 4 Eucalyptus species (Eucalyptus melliodora A. Cunn. Ex Schauer, E. viminalis Labill., E. blakelyi Maiden and E. michaeliana Blakely) in grazing landscapes on the Northern Tablelands of NSW, Australia. We examined the effect of species and soil parent material (basalt, granite and meta-sediments) on litter chemistry and chemical pools. Between 54–145 kg of litter was found around individual trees and litter density consistently declined with distance from the tree (330 g.m−2 in the inner canopy to 4 g.m−2 in the open paddock). However, an equivalent quantity of litter was found beneath and beyond the canopy indicating that a large quantity of the litter and nutrients fell beyond the edge of the canopy. Overall, leaf litter accounted for 23 to 34% of litterfall and had larger nutrient concentrations and pools than bark or stick litter. Most litter nutrients concentrations were independent of tree species or parent material but our results suggest that P, K and S were removed in foliage prior to abscission whilst Ca and Fe concentrations increased. The spatial patterns of litter distribution around scattered trees coincide with spatial patterns in soil properties that are frequently observed in these environments, and provide strong evidence of a significant link between these factors. Our results suggest that the removal of scattered trees from pastoral landscapes in this region of Australia will result in the loss of a significant litter input to the soil surface and will diminish this potentially important source of soil nutrients.

Tree species-mediated spatial patchiness of the composition of microbial community and physicochemical properties in the topsoils of a tropical montane forest

To evaluate the importance of plant–soil feedbacks in forest ecosystems, it is fundamental to understand the spatial range within which plant species control soil physicochemical and microbial properties. We investigated the spatial pattern of soil properties associated with canopy trees in a tropical montane forest on Mt. Kianbalu, Borneo. We analyzed soil physicochemical properties and microbial communities (biomarker lipid abundance) as a function of soil depth and distance from the tree trunk of a conifer ( Dacrydium gracilis ) or a broadleaf tree ( Lithocarpus clementianus ). The concentration of condensed tannins and fungi-to-bacteria were higher beneath Dacrydium than beneath Lithocarpus . Furthermore, carbon-degrading enzyme activities were lower beneath Dacrydium . These effects of the tree species were more distinct on soil properties beneath the tree crown than on those outside the tree crown. These effects appeared to be largely due to differences in litter chemistry, and the distinct set of soil properties formed corresponding to the above canopy crown. In conclusion, the species-rich forest on the tropical mountain contains spatially distinct units of soil properties associated with canopy trees, and this spatial pattern can influence ecosystem dynamics in the forest through plant–soil feedback effects.

Spatial Relationships of Phosphorus Sorption in a Seasonally Saturated Constructed Wetland Soil

Constructed wetlands can be important sinks of P in agricultural landscapes; however, the long‐term ability of these systems to retain P often diminishes with time. This study used a spatially explicit statistical approach to characterize spatial patterns of soil properties and their correlation with P sorption in an 11‐yr‐old, seasonally saturated, constructed wetland receiving runoff from irrigated agriculture. The results were used to link the spatial pattern of P sorption with hydrologic, biogeochemical, and pedologic processes. A spatial sampling design was used and soil samples were measured for total P, bioavailable P, P sorption index (PSI), total C and N, texture, oxalate‐ and dithionite‐extractable Fe and Mn, pH, electrical conductivity, water‐extractable Mg, Ca, and Na, and sedimentation rate. Wetland hydrodynamics was a primary factor shaping the spatial distribution of wetland soil properties, creating three distinct hydrologic and biogeochemical zones (e.g., sediment deposition, transition, and Fe oxide transformation). Soil properties with the strongest correlation to the PSI included oxalate‐extractable Fe, clay, total C, and silt. In the sediment‐deposition zone, sedimentation was the dominant process influencing P sorption, contributing fresh sediments with reactive surfaces for P sorption. In contrast, the Fe oxide transformation zone received little sedimentation, resulting in greater exposure time for surface sediment alteration. Increased exposure resulted in dissolution of crystalline Fe oxides and reformation of poorly crystalline Fe oxides in a thin oxidative lens at the sediment–water column interface, thus increasing P sorption capacity. This spatially explicit investigation of P sorption in seasonally saturated wetland soils provided a robust framework within which to evaluate the wetland soil processes controlling P sorption capacity and the efficacy for long‐term sorption potential.

Predicting runoff from semi-arid hillslopes as source areas for water harvesting in the Sierra de Gador, southeast Spain

The effectiveness of water harvesting systems collecting surface runoff form rangeland hillslopes in semi-arid regions is difficult to predict, since the hydrological response at the outlet depends on the heterogeneity of hydrological processes. The lack of continuous runoff pathways, due to the irregular spatial patterns of soil properties and the variety of antecedent soil moisture conditions directly influence runoff generation and control discharge into the water harvesting cisterns. The aim of this paper is to evaluate the effectiveness of semi-arid hillslopes in generating runoff for water harvesting systems. Runoff was estimated by the STREAM expert-based model which was applied to three semi-arid hillslopes (0.4 to 6 ha). On the one hand the STREAM model rules were adapted to the regional conditions i.e. an antecedent precipitation index was adjusted to local soil moisture conditions and the rainfall duration was defined as the total rainfall event quantity and the effective rainfall duration (P-tot/t(eff)). On the other hand, the distribution of rock outcrop and vegetation cover along the slopes was used to define homogeneous hydrological units. Final infiltration capacities were attributed to these hydrological units based on values found in the literature. The prediction performances are acceptable for the three water harvesting systems with an RMSE of 13.9 m(3). It was shown that the rainfall/runoff model was more sensitive to the duration of the storm than to the antecedent soil moisture conditions. The use of a unique set of hydrological parameters for the three water harvesting systems on representative hillslopes allows the runoff prediction from any rangeland hillslope within the same region. Furthermore, the spatial patterns of soil surface characteristics are crucial for collecting runoff at the outlet of the system. Model runs demonstrated that degradation of vegetation and sealing of very small areas within flow paths can lead to an increase of annual runoff by as much as a factor two. (C) 2009 Elsevier B.V. All rights reserved.

Mapping field‐scale spatial patterns of size and activity of the denitrifier community

There is ample evidence that microbial processes can exhibit large variations in activity on a field scale. However, very little is known about the spatial distribution of the microbial communities mediating these processes. Here we used geostatistical modelling to explore spatial patterns of size and activity of the denitrifying community, a functional guild involved in N-cycling, in a grassland field subjected to different cattle grazing regimes. We observed a non-random distribution pattern of the size of the denitrifier community estimated by quantification of the denitrification genes copy numbers with a macro-scale spatial dependence (6-16 m) and mapped the distribution of this functional guild in the field. The spatial patterns of soil properties, which were strongly affected by presence of cattle, imposed significant control on potential denitrification activity, potential N(2)O production and relative abundance of some denitrification genes but not on the size of the denitrifier community. Absolute abundance of most denitrification genes was not correlated with the distribution patterns of potential denitrification activity or potential N(2)O production. However, the relative abundance of bacteria possessing the nosZ gene encoding the N(2)O reductase in the total bacterial community was a strong predictor of the N(2)O/(N(2) + N(2)O) ratio, which provides evidence for a relationship between bacterial community composition based on the relative abundance of denitrifiers in the total bacterial community and ecosystem processes. More generally, the presented geostatistical approach allows integrated mapping of microbial communities, and hence can facilitate our understanding of relationships between the ecology of microbial communities and microbial processes along environmental gradients.

Surface modelling of soil pH

In addition to classical methods, namely kriging, Inverse Distance Weighting (IDW) and splines, which have been frequently used for interpolating the spatial patterns of soil properties, a relatively more accurate surface modelling technique is being developed in recent years, namely high accuracy surface modelling (HASM). It has been used in the numerical tests, DEM construction and the interpolation of climate and ecosystem changes. In this paper, HASM was applied to interpolate soil pH for assessing its feasibility of soil property interpolation in a red soil region of Jiangxi Province, China. Soil pH was measured on 150 samples of topsoil (0–20 cm) for the interpolation and comparing the performance of HASM, kriging, IDW and splines. The mean errors (MEs) of interpolations indicate little bias of interpolation for soil pH by the four techniques. HASM has less mean absolute error (MAE) and root mean square error (RMSE) than kriging, IDW and splines. HASM is still the most accurate one when we use the mean rank and the standard deviation of the ranks to avoid the outlier effects in assessing the prediction performance of the four methods. Therefore, HASM can be considered as an alternative and accurate method for interpolating soil properties. Further researches of HASM are needed to combine HASM with ancillary variables to improve the interpolation performance and develop a user-friendly algorithm that can be implemented in a GIS package.

Spatial heterogeneity of soil properties and vegetation–soil relationships following vegetation restoration of mobile dunes in Horqin Sandy Land, Northern China

Quantitative methods were used to examine soil properties and their spatial heterogeneity in a 0-year fenced mobile dune (MD0), an 11-year fenced mobile dune (MD11) and a 20-year fenced mobile dune (MD20) in Horqin Sandy Land, Northern China. The objective of the study was to assess the effect of vegetation restoration on heterogeneity of soil properties in sand dunes and to provide a concept model to describe the relationship between vegetation succession and spatial heterogeneity variation of soil properties in the dunes. The results showed that the average values of vegetation cover, species number and diversity, soil organic carbon (C), total nitrogen (N), and electrical conductivity (EC) increased with the increase in fenced age of mobile dunes, while soil water content (0–20 cm) showed the reverse trend. Geostatistical analysis revealed that the spatial heterogeneity of soil organic C, total N, EC, very fine sand content, and soil water content (0–20 cm) increased from MD0 to MD11 with succession from sand pioneer plant to shrub species then decreased from MD11 to MD20 due to continuous development of herbaceous plants. Canonical correspondence analysis (CCA) showed that there was a relatively high correspondence between vegetation and soil factors, suggesting that the major gradients relating soil organic C, total N, EC, pH, slope, very fine sand content, and soil water content are the main factors for the distribution of dune plants and account for 68.1% of the species-environment relationship among the three sites. In addition, the distribution of the sand pioneer plant was positively related to the relative height of the sampling site and soil water content, and that of most herbaceous plants were determined by soil organic C, total N, EC, pH, and very fine sand content in mobile dunes. The conceptual model of relationship between vegetation succession and spatial heterogeneity of soil properties in mobile dunes suggests spatial patterns of soil properties are most strongly related to plant-induced heterogeneity in dune ecosystems prone to wind erosion, and conversely, the magnitude and degree of spatial heterogeneity in soil properties can influence the plant distribution pattern and vegetation succession of mobile dunes.

Eco‐Geophysical Imaging of Watershed‐Scale Soil Patterns Links with Plant Community Spatial Patterns

The extent to which soil moisture and nutrient availability control the structure, function, and diversity of plant communities has aroused considerable interest in the past decade and remains topical in light of global change. Numerous plant communities are controlled either by water or soil nutrient availability, and yet spatial patterns of soil properties affecting resource pools, such as texture, are often poorly delineated at the landscape level. Traditional soil survey methods, developed for land evaluation, remain largely qualitative, based on the subjective analysis of the soil surveyor and often using vegetation patterns to demarcate soil boundaries. To date, no independent method of determining the properties of soil root‐zone spatial patterns has been developed for use at the landscape scale, resulting in a knowledge gap between observed aboveground vegetation patterns and the distribution of belowground soil properties. The objective of this work was to determine whether a quantitative link could be observed between bulk soil electrical conductivity, used as an indicator of soil texture, and the plant community spatial pattern using geophysics. By comparing the geophysical signal with plant community patterns, we have discovered distinct vegetation niches corresponding to distinct zones of bulk soil electrical conductivity. A hierarchical ranking of the mean bulk soil electrical conductivity for each plant community type follows a power‐law structure.

A conceptual model of coastal dune ecology synthesizing spatial gradients of vegetation, soil, and geomorphology

Patterns of coastal dune vegetation are closely related with soil conditions controlled by geomorphic forms and processes. This study developed a conceptual model integrating these relationships in a spatially explicit manner. A rectangle of 180 × 280 m containing 126 grids of 20 × 20 m was established in the Sindu coastal dunefield in west Korean Peninsula. Sampling from each grid determined 11 soil properties and identified percent cover of 21 woody and herbaceous plant species. Digital elevation models were generated by topographic survey and used to derive eight topographic parameters. Redundancy analysis and canonical correspondence analysis examined the effect of geomorphic factors on edaphic characteristics and the edaphic influence on spatial distribution of vegetation, respectively. The spatial pattern of soil properties and plant species were inferred from spatial interpolation techniques. In the foredune area, distance from the coastline was a significant indicator of soil nutrients derived from the marine sources by aeolian processes. This favored the dominance by Elymus mollis. Moisture-tolerant species (e.g., Calamagrostis epigeios) had high cover in the acidic soils of dune slacks, which covaried with wetness index, an indirect measure of the depth to the freshwater table. Vegetation–soil interactions (e.g., nitrogen fixation by legumes) were important in secondary dune areas, with topographic effects less significant. Vegetation, soil, and geomorphic factors are closely connected in a causal chain across a whole dune area. Our model thus addresses the importance of integrating foredune, dune slack, and secondary dune into one continuous system.

Large old trees influence patterns of δ13C and δ15N in forests

AbstractLarge old trees are the dominant primary producers of native pine forest, but their influence on spatial patterns of soil properties and potential feedback to tree regeneration in their neighbourhood is poorly understood. We measured stable isotopes of carbon (δ13C) and nitrogen (δ15N) in soil and litter taken from three zones of influence (inner, middle and outer zone) around the trunk of freestanding old Scots pine (Pinus sylvestris L.) trees, to determine the trees' influence on below‐ground properties. We also measured δ15N and δ13C in wood cores extracted from the old trees and from regenerating trees growing within their three zones of influence. We found a significant and positive gradient in soil δ15N from the inner zone, nearest to the tree centre, to the outer zone beyond the tree crown. This was probably caused by the higher input of 15N‐depleted litter below the tree crown. In contrast, the soil δ13C did not change along the gradient of tree influence. Distance‐related trends, although weak, were visible in the wood δ15N and δ13C of regenerating trees. Moreover, the wood δ15N of small trees showed a weak negative relationship with soil N content in the relevant zone of influence. Our results indicate that large old trees control below‐ground conditions in their immediate surroundings, and that stable isotopes might act as markers for the spatial and temporal extent of these below‐ground effects. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Spatial pattern and heterogeneity of soil properties in sand dunes under grazing and restoration in Horqin Sandy Land, Northern China

Applying a combination of classical and geostatistical methods, we identified soil properties and their spatial variation in a 5-year grazed sand dune (GSD5) and a 20-year recovered sand dune (RSD20) in Horqin Sandy Land, northern China. The paper assesses the effect of grazing, topography and vegetation restoration on spatial heterogeneity of soil properties. The results showed that soil organic carbon, total nitrogen, very fine sand (0.1–0.05 mm) content and their coefficients of variation were lower in GSD5 than in RSD20, while soil water contents (0–20 cm and 20–40 cm depths) were higher in GSD5 than in RSD20. Geostatistical analysis revealed that the spatial structured variance accounted for the largest proportion of total sample variance in soil properties at the measured scale under grazing and restoration. The spatial autocorrelation ranges were 66.30 m for soil organic carbon and 50.80 m for total nitrogen in GSD5 less than those in RSD20 (70.00 m and 76.10 m, respectively), while the spatial autocorrelation ranges of soil particle size fractions and soil water contents in RSD20 were less than those in GSD5. Kriging-interpolated maps also showed that the heterogeneity of soil organic carbon and total nitrogen and their degree of patch fragmentation were higher in GSD5 than in RSD20. These results suggested that continuous grazing resulted in an increase in spatial variability of soil nutrient and a decrease in spatial variability of soil particle size fractions and soil water content. Soil organic carbon and total nitrogen of sand dunes are associated closely with soil particle size fractions, relative height of sampling site and vegetation cover. Spatial patterns of soil properties are most strongly related to grazing, topography and plant-induced heterogeneity in sand dune ecosystems prone to wind erosion.

Spatial Variation of some Soil Physico-Chemical Properties of an Alfisol in Southwestern Nigeria

An analysis of spatial patterns of soil properties is important for efficient soil sampling, prediction of soil properties at unsampled sites and developing site-specific farming practices. Spatial variation of soil acidity (pH in water), soil organic carbon (C), total nitrogen, available P, exchangeable K, Mg and clay content were evaluated for some soils under fallow at Ajibode, southwestern Nigeria. The spatial distribution patterns of these soil properties, the range of spatial correlation from semivariance analyses, as well as the required sampling density for fertilizer recommendations were examined. The soil properties exhibit different patterns of statistical distribution. Available P, Mg and K were positively skewed while pH, C, and clay were near normal for 0 – 15 cm soil depth. At a soil depth of 30 – 60 cm, available P was skewed and kurtotic while Mg was skewed. Clay distribution was near normal irrespective of soil depth. Spatial analysis indicated that C, pH, Mg, Clay, Total N and K (for 0 – 15 cm soil depth) and pH, available P, C, Mg and Ca (30 – 60 cm soil depth) are related (spatial dependence) within a distance of 30 – 60 cm. The spatial dependence of the properties studied was weak to moderate. Sampling spacing of 30 – 60 m is appropriate for soil fertility assessment in the test area. A sample size of 37 core samples per hectare is required to adequately predict the mean of soil properties with 5 % allowable error. Keywords : Spatial variability, Soil properties, Semivariogram, Southwestern Nigeria. Nigerian Journal of Soil and Environmental Research Vol. 7 2007: pp. 82-91