Spatial Patterns Of Soil Properties Research Articles

Spatial patterns of ecohydrologic properties on a hillslope-alluvial fan transect, central New Mexico

Abstract Spatial patterns of soil properties are linked to patchy vegetation in arid and semi-arid landscapes. The patterns of soil properties are generally assumed to be linked to the ecohydrological functioning of patchy dryland vegetation ecosystems. We studied the effects of vegetation canopy, its spatial pattern, and landforms on soil properties affecting overland flow and infiltration in shrublands at the Sevilleta National Wildlife Refuge/LTER in central New Mexico, USA. We studied the patterns of microtopography and saturated conductivity (Ksat), and generally found it to be affected by vegetation canopy and pattern, as well as landform type. On gently sloping alluvial fans, both microtopography and Ksat are high under vegetation canopy and decay with distance from plant center. On steeper hillslope landforms, only microtopography was significantly higher under vegetation canopy, while there was no significant difference in Ksat between vegetation and interspaces. Using geostatistics, we found that the spatial pattern of soil properties was determined by the spatial pattern of vegetation. Most importantly, the effects of vegetation were present in the unvegetated interspaces 2–4 times the extent of vegetation canopy, on the order of 2–3 m. Our results have implications for the understanding the ecohydrologic function of semi-arid ecosystems as well as the parameterization of hydrologic models.

Effect of visitors’ pressure on soil and vegetation in several different micro-environments in urban parks in Tel Aviv

The effect of the pressure imposed by visitors on urban soil and herbaceous vegetation was investigated in seven micro-environments in parks in Tel Aviv. Soil properties (organic matter content, soil moisture, soil surface compaction/penetration depth), litter biomass, and herbaceous vegetation characteristics (vegetation cover, number of species, height) were determined in seven micro-environments: oak and pine trees, each under high and under low visitors’ pressure; a herbaceous area without visitors’ pressure; paths; and a resting area. Soil samples were collected from the upper 0–5 cm soil depth. In addition, in the tree micro-environments soil samples were taken at 0.5, 1, 2, and 3 m from the tree trunk. Averages and variances of soil properties and the vegetation characteristics varied among the various micro-environments and according to visitors’ pressure. Soil organic matter and soil moisture contents were significantly higher under oak trees with low visitors’ pressure than in other micro-environments. Litter biomass and penetration depth significantly decreased with increasing visitors’ pressure under pine and, especially, oak. The vegetation cover, number of species, and height of herbaceous vegetation were greatest in the herbaceous area, lower under with the trees where there was high visitors’ pressure and lowest in paths and resting areas. Thus, the soil properties in the oak micro-environment and the vegetation characteristics in the herbaceous area were the most sensitive to visitors’ pressure. For each tree and open area, increasing visitors’ pressure was accompanied by increasing spatial homogeneity of soil and vegetation. A radial spatial pattern of soil properties developed under oak with low visitors’ pressure.

Changes in the spatial variation of soil properties following shifting cultivation in a Mexican tropical dry forest

The role of secondary vegetation in restoring soil fertility during shifting cultivation in the tropics is well known. Yet the effect of secondary succession on the spatial patterns of soil properties has received little attention. To determine whether changes in the plant community as a result of shifting cultivation affect the scale of spatial dependence for biologically important soil nutrients, we sampled three dry tropical forest stands in Campeche, Mexico. These stands represented a gradient of cultivation history: one mature forest stand, a forest fallow that had undergone one cultivation-fallow cycle, and a forest fallow that had undergone two cultivation-fallow cycles. We used an analysis of semivariance to quantify the scale and magnitude of spatial dependence for organic matter content (OM), phosphorus (P), potassium (K), and aluminum (Al) in each stand. The scale of spatial dependence varied with cultivation history, but the degree of spatial dependence did not differ among stands. In the mature forest P and K were autocorrelated over distances >7.5 m. In the forest fallows 48–88% of the variation in soil P and K was autocorrelated over distances up to 1.1–5.1 m. In contrast, the range of autocorrelation for Al (∼2.5 m) did not differ among stands. We conclude that shifting cultivation changes the range of autocorrelation for biologically important soil nutrients at a scale that may influence plant growth. The finer scaled pattern of soil nutrients in forest fallows is likely to persist with continued shifting cultivation, since fallows are cleared every 3–15 years.

Soil landscape evolution due to soil redistribution by tillage: a new conceptual model of soil catena evolution in agricultural landscapes

This paper focuses on analysing tillage as a mechanism for the transformation of soil spatial variability, soil morphology, superficial soil properties and development of soil–landscape relationships in agricultural lands. A new theoretical two-dimensional model of soil catena evolution due to soil redistribution by tillage is presented. Soil profile truncation occurs through loss of soil mass on convexities and in the upper areas of the cultivated hillslopes; while the opposite effect takes place in concavities and the lower areas of the field where the original soil profile becomes buried. At sectors of rectilinear morphology in the hillslope (backslope positions), a null balance of soil translocation takes place, independent of the slope gradient and of the rate of downslope soil translocation. As a result, in those backslope areas, a substitution of soil material in the surface horizon with material coming from upslope areas takes place. This substituted material can produce an inversion of soil horizons in the original soil profile and sometimes, the formation of “false truncated soil”. In the Skogstad agricultural field (Cyrus, MN) spatial patterns of soil properties (soil calcium carbonate content) in the surface soil horizons and soil morphology along several slope transects were analyzed. These spatial patterns are compared with those estimated for soil redistribution (areas of erosion and deposition) due to tillage using the Soil Redistribution by Tillage (SORET) model and water erosion using the models Water Erosion Prediction Project (WEPP) and Universal Soil Loss Equation (Usle2D). Results show that tillage was the predominant process of soil redistribution in the studied agricultural field. Finally, some practical implications of the proposed model of soil landscape modification by tillage are discussed. Nomographs to calculated the intensity of the expansion process of the eroded soil units by tillage are proposed for three different patterns of tillage.

Field-scale N fertilizer recommendations: The spatial covariance problem

Theory is needed to estimate field-scale crop response and calibration relationships (soil test versus recommended fertilize r rate) from local scale measurements, in fields with spatially variable soil properties. The objective of this study is to present a theoretical stochastic framework for examining the influence of the spatial variability of soil properties, and covariance between soil properties, on field-scale crop response to fertilizer. An analytical solution of the general stochastic scaling equation is given for the specific case of wheat grain yield response to applied N fertilizer with variable soil-N test and available water in Saskatchewan, Canada. The analytical solution indicates spatial variance of soil properties within fields influences field average yield response to applied fertilizer. The field-scale maximum economic rate of fertilizer N (MERN), depends not only on the average soil properties, but also on (1) the amount of variability of soil properties in the field, and (2) the correlation between the spatial patterns of soil properties (e.g., soil test and available water). For the specific soil examined, positive spatial correlation between soil-N test and available water significantly increases MERN, for the same average soil test and available water. Negative correlation decreases MERN. Key Words: Fertilizer recommendation, soil test, spatial variability, crop response, soil water

Spatial patterns of surface soil properties and vegetation in a Mediterranean semi-arid steppe

In arid and semi-arid areas with sparse vegetation cover, the spatial pattern of surface soil properties affects water and nutrient flows, and is a question of considerable interest for understanding degradation processes and establishing adequate management measures. In this study, we investigate the spatial distribution of vegetation and surface soil properties (biological crusts, physical crusts, mosses, rock fragments, earthworm casts, fine root accumulation and below-ground stones) in a semi-arid Stipa tenacissima L. steppe in SE Spain. We applied the combination of spatial analysis by distance indices (SADIE) and geostatistics to assess the spatial pattern of soil properties and vegetation, and correlation analyses to explore how these patterns were related. SADIE analysis detected significant clumped patterns in the spatial distribution of vegetation, mosses, fine root accumulation and below-ground stone content. Contoured SADIE index of clustering maps suggested the presence of patchiness in the distribution of earthworm casts, fine roots, below-ground stone content, mosses and biological crusts. Correlation analyses suggested that spatial pattern of some soil properties such as biological crusts, moss cover, surface rock fragments, physical crusts and fine roots were significantly related with above-ground plant distribution. We discuss the spatial arrangement of surface soil properties and suggest mechanistic explanations for the observed spatial patterns and relationships.

Plant species effect on the spatial patterns of soil properties in the Mu-us desert ecosystem, Inner Mongolia, China

Although Artemisia ordosica Krasch. and Sabina vulgaris Ant. are the dominant shrub species in the Mu-us desert ecosystem, they differ in their botanical traits. We investigated the spatial patterns of soil properties using geostatistical analysis to examine the effect of plant species on these spatial patterns. Comparison among three microsite types (under A. ordosica, under S. vulgaris, and the opening between vegetation) showed that A. ordosica generally had less effect than S. vulgaris on local soil properties. The long life-span, prostrate life-form, and evergreen leaf-habit of S. vulgaris may lead to a higher accumulation of organic and fine materials under S. vulgaris. The range of spatial autocorrelation found in the mass of organic matter on the soil surface was smaller than that of the coverage of S. vulgaris (11.5 m) which corresponded to the canopy patch size of this species, and was longer than the canopy patch size of A. ordosica. The ranges of total C and N, and pH (11.7–15.6 m) were similar to that of S. vulgaris. The range of available P (106.3 m) was comparable to that of the coverage of A. ordosica (86.2 m) considered to be the scale of the distribution of this species. The ranges of silt+clay and exchangeable K, Ca, and Mg (31.0–46.7 m) were not related to plant presence, and were similar to that of topography (43.1 m).

Plant induced fertile islands as possible indicators of desertification in a succulent desert ecosystem in northern Namaqualand, South Africa

Zones of nutrient enrichment beneath shrubs, the so called 'fertile islands', are the result of a range of interacting physical and biotic concentrating mechanisms. These concentrating mechanisms lead to specific spatial patterns of soil properties across a landscape and it has been suggested that disruption of the normal patterns into more aggregated 'fertile islands' might be a useful index of desertification in semi-arid regions. The objective of this paper was to determine whether 'fertile islands' are as characteristic a feature of succulent deserts as they are of shrub dominated deserts. Results indicate that, even in a community dominated by succulent species fertile islands develop under extremely arid conditions and that the degree of development is dependent on plant dynamics. Long-lived species showed greater concentration effects. However, the patterns of nutrient accretion in islands are very different to shrub invaded grasslands in North America. In particular nitrogen accretion dominated the 'fertile islands' in Namaqualand, and we suggest that these islands are more ephemeral than carbon and phosphorus dominated islands reported for other systems. These more dynamic islands are a consequence of rapid community dynamics since the Namaqualand region is characterised by many short-lived perennials which turnover generations very rapidly in response to environmental conditions. Using the development of 'fertile islands' to assess desertification as applied elsewhere might be inappropriate in Namaqualand because of the different patterns of community dynamics underlying the formation and characteristics of these islands.

Use of spatial patterns of soil properties and wheat yield in geostatistics for determination of fertilizer rates

Researchers traditionally conduct fertilizer experiments on small, replicated areas at university or governmental research centers. This approach has two problems: (1) extrapolation of the results to large cropped fields requires taking into account the impacts of spatial variability of soil properties on the optimum amount and type of fertilizer to apply and (2) farmers have limited access to the research work, particularly in developing countries, which limits the information transfer needed for farmers to adopt the recommended fertilizer techniques. With these problems in mind, field and laboratory investigations were conducted on a farmer's field to study the spatial patterns of some soil properties and wheat yield using geostatistics for determination of fertilizer rates. The field was divided into four parallel transects, and soil samples were collected at 15‐m intervals along each transect. These soil samples were analyzed for different physical and chemical properties. A uniformity trial was conducted on wheat in the field. Classical statistical and geostatistical techniques were used to describe the variability in measured soil properties and wheat yield. Most of the soil properties and wheat yield had a very high coefficient of variation. Variability in soil properties and wheat yield was best described by a linear model. The potential wheat yield was estimated using the relationship between wheat yield and lime content, and was used in determining nitrogen (N) fertilizer rates for different areas. The effects of soil variability on crop growth and profitability of fertilizer used were also demonstrated to the farmers.

Evaluating Shrub‐Associated Spatial Patterns of Soil Properties in a Shrub‐Steppe Ecosystem Using Multiple‐Variable Geostatistics

AbstractGeostatistics are often calculated for a single variable at a time, even though many natural phenomena are functions of several variables. The objective of this work was to demonstrate a nonparametric approach for assessing the spatial characteristics of multiple‐variable phenomena. Specifically, we analyzed the spatial characteristics of resource islands in the soil under big sagebrush (Artemisia tridentata Nutt.), a dominant shrub in the intermountain western USA. For our example, we defined resource islands as a function of six soil variables representing concentrations of soil resources, populations of microorganisms, and soil microbial physiological variables. By collectively evaluating the indicator transformations of these individual variables, we created a new data set, termed a multiple‐variable indicator transform or MVIT. Alternate MVITs were obtained by varying the selection criteria. Each MVIT was analyzed with variography to characterize spatial continuity, and with indicator kriging to predict the combined probability of their occurrence at unsampled locations in the landscape. Simple graphical analysis and variography demonstrated spatial dependence for all individual soil variables. Analysis also showed that ensembles of variables were not randomly distributed, but rather were correlated systematically within the landscape. Maps derived from ordinary kriging of MVITs suggested that the combined probabilities for encountering zones of above‐median resources were greatest near big sagebrush. As the selection criteria for defining a resource island became more stringent, the area of the resource island decreased. Cross‐variography revealed that big sagebrush was more positively correlated with MVIT resource islands than were grass species, the other major plant type.

Soil properties and their variations on two contiguous hillslopes in Northeast Brazil

Information on spatial distribution of soil properties in a landscape is not only required for soil mapping and classification but also for soil management. Spatial patterns of soil properties in a landscape are the results of systematic variations in pedogenic processes controlled by environmental factors of which landscape position is important. In northeast Brazil, Lithosols (Ustorthents) whose surface horizons are directly underlain by lithic or paralithic contacts occupy upper slope positions with steep gradient; the Cambisols (Ustropepts) occupy the mid- and lower slope positions. In some cases Non-Calcic Brown soils/Planosol (Haplustalfs) occupy lower slopes. We examined the properties of two contiguous hillslopes in granitic and gneissic saprolite to determine whether there were any systematic variations among landscape positions and to interpret pedogenesis in the hillslopes. Particle size distribution, and the Ti content of sand plus silt and saprolite showed that the two hillslopes were formed on different parent materials. At Site 1, soil property variations along the slope, measured by standard deviation from the means, were attributed to variability in parent material rather than to landscape position. Except for solum thickness, which increased systematically downslope, variations in sand, clay, ECEC and pH were not related to landscape position. Increasing solum thickness downslope was explained by the effect of erosion on the upper, and deposition at the lower slopes. Silt and organic carbon contents at Site 1, and Fe o and Fe d contents at Site 2 significantly decreased downslope. One possible explanation for this trend, in addition to erosion and deposition, is the effect of slash and burn agriculture on the lower slopes, and the changes in redox conditions caused by periodic waterlogging.

Estimation of soil properties and wheat yields on complex eroded hills using geostatistics and thematic mapper images

Better assessment of large scale patterns in soil fertility, erosion, and crop productivity is needed to address environmental concerns in the steeply rolling dryland farming region of eastern Washington. Spatial variability of organic carbon, soil phosphorus, and wheat yields measured on several 655 m long transects in complex eroded hills of the Palouse region of eastern Washington was studied using classical statistics and geostatistics. In addition, Landsat Thematic Mapper images of bare soil at the study site were used to estimate organic matter content in blocks having an area of 28.5m × 28.5 m. Classical statistical analysis showed moderate coefficients of variation in soil properties (25–50%) and wheat yields (30%). Spherical semivariograms of soil properties and wheat yields showed strong spatial dependence, with a range of influence on the order of from 70 m to 145 m. The semivariogram for Landsat estimated organic matter was almost identical to that for organic matter measured in the surface transects. The cross-semivariogram between measured organic matter and wheat yields also exhibited strong spatial dependence, with a range of influence of about 120m. Organic matter, soil phosphorus, and wheat yield were interpolated at unsampled locations using block kriging and block cokriging techniques. Excellent agreement was obtained between kriged wheat yields and wheat yields cokriged from Thematic Mapper estimates of organic matter. Satisfactory agreement was obtained between kriged soil phosphorus and cokriged soil phosphorus based upon remotely sensed organic matter. Results of this study provided strong evidence for nonrandom spatial patterns in soil properties and crop yields. These spatial patterns are associated with changes in surface organic matter content across the landscape resulting from extensive erosion and exposure of subsoil. Geostatistical techniques provide a powerful tool for interpolating ground measurements of soil properties and crop yield over large areas in combination with estimates of organic matter obtained from Thematic Mapper images.

Single‐Tree Influence on Earthworms in Forest Soils in Eastern Kentucky

AbstractVegetation may affect earthworm populations directly through inputs of litter and leachates, and indirectly through alteration of soil properties. This study examined the characteristics of earthworm populations on an area where small‐scale spatial patterns in soil properties were previously shown to be due to the influence of individual trees and understory species. Earthworm densities in the O horizon and in the upper 20 cm of mineral soil ranged from 0 to 20 and from 0 to 80 individuals/m2, respectively. Density was significantly lower in mineral soils under both yellow poplar (Liriodendron tulipifera L.) and eastern hemlock (Tsuga canadensis [L.] Carr.) when rhododendron (Rhododendron maximum L.) was present in the understory, compared with under the same two tree species when rhododendron was absent. Bimastos parvus Eisen, a species characteristic of inhospitable sites, was dominant on rhododendron plots, but was replaced by Komarekiona eatoni Gates and Eisenoides carolinensis Michaelsen in the absence of rhododendron, especially on plots under yellow poplar. In mixed‐species forests, abundance and species composition of earthworm assemblages are spatially variable in correspondence with patterns of soil properties and of the occurrence of tree and understory plant species.

Regional and Catenary Variations in Properties of Borolls of Southern Saskatchewan, Canada

AbstractThe spatial pattern of soil properties results from systematic variations in the type and intensity of soil‐forming processes and from random variations superimposed on the systematic variations. We examined the thickness of A horizons and depths to CaCO3 at 21 sites in southern Saskatchewan to determine whether systematic differences occurred among soil‐moisture regimes of Borolls and among landform elements in catenas. The mean thickness of A horizons was thinnest for the aridic Borolls (x̄ = 15.3 cm) and ustic Borolls (x̄ = 15.2 cm) and thickest in the udic Borolls (x̄ = 18.4 cm), reflecting the regional moisture gradient. The regional differences in mean depth to CaCO3 were contrary to the expected pattern: mean depths were smallest for the ustic Borolls (x̄ = 29.9 cm) and greatest for the aridic (x̄ = 34.1 cm) and the udic (x̄ = 34.9 cm) Borolls. A consistent pattern was associated with landform elements in soil catenas. The smallest means for both properties were associated with shoulder and backslope elements with convex across‐slope curvatures, and the greatest means for footslope elements with concave across‐slope curvatures. The range in mean values of the two properties among landform elements within a catena was consistently an order of magnitude greater than the regional differences among soil subgroups.

Vegetation change in a Poplar Box (Eucalyptus populnea) Woodland. Effects of tree killing and domestic livestock.

Results are summarized for a number of separate studies which investigated the effects of killing the trees, and of grazing by domestic livestock on herbage biomass, densities of grasses, forbs and woody plants and some surface soil properties in poplar box woodlands. Some temporal changes in vegetation and spatial patterns in soil properties occurred in all treatments. Forb and grass densities increased from 1966 to 1970 and 1972 respectively and then declined. Surface soil pH, micro-relief, salt content and litter biomass were generally higher at the tree bole than between the tree canopies. Herbage biomass was highest where trees had been killed but the killing of trees did not have a direct effect on the densities of either grasses or shrubs. The increased growth of herbage is attributed to an increase in the availability of water and nitrogen. The vegetation changes following tree killing with livestock excluded are summarized in the form of changes in the proportions of the grasses, shrubs and trees; grass proportion increased for the first six years following tree killing after which grasses tended to be replaced by shrubs. The density of shrubs increased following the exclusion of livestock. Shrub densities were less in experimental grazed plots than in ungrazed plots but still increased with time. With grazing by livestock, herbage biomass was highest adjacent to trees and the percentage of bare soil increased away from trees. Changes resulting from interactions between the grazing and killing treat- ments mainly related to soil compaction and water infiltration. It is suggested that shrub encroachment in the poplar box lands may arise because of fluctuations in grazing pressure resulting from large paddock and property sizes and variability in rainfall. Little of the available herbage is grazed during abnormally wet years, thus there is an effective release from grazing at a time when germination of shrubs is likely to occur.