Surface Soil Texture Research Articles

Thermodielectric effects on radar backscattering from wet soil

Thermodielectric interactions between free and bound soil water at different soil textures and frequencies affect radar backscatter. Simulations with a semi-empirical backscatter model show a potential for temperature corrections in inference of water content. A new thermodielectric response backscatter difference index was derived for remote mapping of surface soil texture.

Simple

A model predicting seedling emergence is described and applied to sugarbeet (Beta vulgaris L.). The input variables are the soil surface texture, soil temperature, rainfall, aggregate size distribution and position in the seedbed, sowing depths, characteristics of the seeds (initial seed mass distribution, germination time, and hypocotyl elongation distributions). A three‐dimensional seedbed layer is created where the aggregates and seeds are placed. Soil water content is assumed not to limit sugarbeet emergence (sowing conditions in northern Europe). The time needed to reach the soil surface is calculated using germination thermal time, soil temperature, the presence or absence of aggregates, and the hypocotyl elongation function. The ability of seedlings to break through the soil surface is a function of crust development and moisture. The seedling growth after emergence is calculated with reference to seed mass distribution, emergence delay, and the presence or absence of mechanical obstacles. The emergence prediction was tested in field experiments with four seedbeds, from fine earth to cloddy structure, and a sowing depth of 17 to 35 mm. The predicted number and sizes of clods encountered by seedlings and the calculated hypocotyl length were not significantly different from measured ones. Predicted germination times were longer than the observed ones (differences <5°C d); final rates were well predicted. Predicted vs. measured final emergence rates differed by less than 10%; changes with time differed from 15 to 30°C. This was due to the hypocotyl elongation functions, which must be improved. Further improvements will be to predict soil water content variations and effects on emergence via water stress and soil strengthening.

Analysis of temporal variation and species-site relationships of witness tree data in southeastern Pennsylvania

Witness tree species – site relationships are described with respect to parent material, soil drainage, and soil surface texture in Lancaster County, southeastern Pennsylvania. Quercus velutina Lam. and Carya were positively associated with "limestone" parent materials and well-drained, loamy sites. Quercus velutina was strongly associated with "acid shale and sandstone" parent materials and well-drained, upland soils. Quercus alba L. was most abundant on parent material classes associated with stream valleys and coves while Qurecus prinus L. and Castanea dentata (Marsh.) Borkh. were positively associated with well-drained, rocky sites on "quartzite" parent materials. Procedures were then developed to test for significant changes in witness tree species frequencies over the 100-year period of metes and bounds surveys in Lancaster County. These tests revealed that Quercus coccinea L., Nyssa sylvatica Marsh., and early successional species were surveyed much later than Quercus rubra L., Q. alba, and Carya spp. Agricultural land clearing, cutting for firewood, selective logging, and the charcoal-iron industry all probably contributed these species changes. Overall, abundances of minor species appear to be much more sensitive to these early settlement land uses. Given the extent of metes and bounds surveys, these tests for temporal variations may be applied to witness tree data throughout the eastern United States.

Analysis of temporal variation and species-site relationships of witness tree data in southeastern Pennsylvania

Witness tree species – site relationships are described with respect to parent material, soil drainage, and soil surface texture in Lancaster County, southeastern Pennsylvania. Quercus velutina Lam. and Carya were positively associated with "limestone" parent materials and well-drained, loamy sites. Quercus velutina was strongly associated with "acid shale and sandstone" parent materials and well-drained, upland soils. Quercus alba L. was most abundant on parent material classes associated with stream valleys and coves while Qurecus prinus L. and Castanea dentata (Marsh.) Borkh. were positively associated with well-drained, rocky sites on "quartzite" parent materials. Procedures were then developed to test for significant changes in witness tree species frequencies over the 100-year period of metes and bounds surveys in Lancaster County. These tests revealed that Quercus coccinea L., Nyssa sylvatica Marsh., and early successional species were surveyed much later than Quercus rubra L., Q. alba, and Carya spp. Agricultural land clearing, cutting for firewood, selective logging, and the charcoal-iron industry all probably contributed these species changes. Overall, abundances of minor species appear to be much more sensitive to these early settlement land uses. Given the extent of metes and bounds surveys, these tests for temporal variations may be applied to witness tree data throughout the eastern United States.

Habitat Selection by Northern Sagebrush Lizards (Sceloporus graciosus graciosus) in the Columbia Basin, Oregon

Habitat selection by northern sagebrush lizards (Sceloporus graciosus graciosus) was investigated on the US Navy's 19,400-ha Naval Weapons Systems Training Facility Boardman near Boardman, Oregon, as part of an integrated multi-resource research program. The objectives of the study were to determine what plant communities these lizards occupied and what specific habitat components they selected within these types. In general, northern sagebrush lizards occupied plant communities dominated by big sagebrush (Artemisia tridentata) and antelope bitterbrush (Purshia tridentata) and largely avoided communities dominated by gray rabbitbrush (Chrysothamnus nauseosus), cheatgrass (Bromus tectorum), and western needleand-thread grass (Stipa comata). Usage within bitterbrush and sagebrush habitats was determined by comparing habitat characteristics at sites occupied by lizards (n = 15 per plant community) with sites randomly located within each plant community (n = 15 per plant community). Results showed that these lizards selected for areas with significantly higher than average bare soil coverage and significantly lower than average coverage of grass, litter, and lichen. Furthermore, all sites occupied by lizards were located in sandy soils even though this soil type represented only about half of the surface soil texture available. Overall, northern sagebrush lizards selected for sand blows with approximately 20% shrub coverage and avoided areas with loamier soils covered (stabilized) with grass, litter, or lichen.

Scaling up from field to region for wind erosion prediction using a field-scale wind erosion model and GIS

Factors that affect wind erosion such as surface vegetative and other cover, soil properties and surface roughness usually change spatially and temporally at the field-scale to produce important field-scale variations in wind erosion. Accurate estimation of wind erosion when scaling up from fields to regions, while maintaining meaningful field-scale process details, remains a challenge. The objectives of this study were to evaluate the feasibility of using a field-scale wind erosion model with a geographic information system (GIS) to scale up to regional levels and to quantify the differences in wind erosion estimates produced by different scales of soil mapping used as a data layer in the model. A GIS was used in combination with the revised wind erosion equation (RWEQ), a field-scale wind erosion model, to estimate wind erosion for two 50 km 2 areas. Landsat Thematic Mapper satellite imagery from 1993 with 30 m resolution was used as a base map. The GIS database layers included land use, soils, and other features such as roads. The major land use was agricultural fields. Data on 1993 crop management for selected fields of each crop type were collected from local government agency offices and used to ‘train’ the computer to classify land areas by crop and type of irrigation (agroecosystem) using commercially available software. The land area of the agricultural land uses was overestimated by 6.5% in one region (Lubbock County, TX, USA) and underestimated by about 21% in an adjacent region (Terry County, TX, USA). The total estimated wind erosion potential for Terry County was about four times that estimated for adjacent Lubbock County. The difference in potential erosion among the counties was attributed to regional differences in surface soil texture. In a comparison of different soil map scales in Terry County, the generalised soil map had over 20% more of the land area and over 15% greater erosion potential in loamy sand soils than did the detailed soil map. As a result, the wind erosion potential determined using the generalised soil map was about 26% greater than the erosion potential estimated by using the detailed soil map in Terry County. This study demonstrates the feasibility of scaling up from fields to regions to estimate wind erosion potential by coupling a field-scale wind erosion model with GIS and identifies possible sources of error with this approach.

Reclamation of forest soils with excavator tillage and organic amendments

In early 1994, a research project was initiated to evaluate the success of several techniques aimed at restoring productivity to degraded soils on landings near Vama Vama Creek, 44 km east of Prince George in Central British Columbia. Soils were developed from morainal parent materials, the usual surface soil texture was silt loam. Two organic amendments were used in this study, including freshly prepared wood chips and old sawdust. An excavator equipped with a site preparation rake was used to till the soils to a depth of 0.50 m. Organic amendments were subsequently added to the plots, and either left as a mulch or incorporated into the surface 0.20 m of the soil. Nitrogen was applied to all plots at a rate of 225 kg N ha −1, which represents about one-third of the 500–700 kg ha −1 that was estimated to be required to compensate for N immobilization during decomposition of the woody residues. Survival was good for all treatments, but after 3 years, trees were growing best in areas that were treated with tillage alone. Trees growing on areas where old sawdust was used as an amendment had more volume than trees growing in areas where wood chips had been used. Control plots with no treatment had intermediate growth. Soil temperature and chemical properties were evaluated for their effect on growth.

Mineralogy and genesis of selected soils and their implications for forest management in central and northeastern British Columbia

Soil properties in central and northeastern British Columbia are strongly influenced by parent materials because of geologically young till, glaciolacustrine, and glaciofluvial deposits. We examined pedogenesis on various parent materials to support studies of long-term forest productivity. We sampled nine pedons developed on till (Bobtail, Lucille Mountain, Skulow Lake, Log Lake, Topley, and Kiskatinaw), glaciofluvial (Bowron), and glaciolacustrine (Aleza Lake 1, 2) deposits. The Skulow Lake pedon is distinctive in the occurrence of talc, while the Lucille Mountain pedon has the only clay fraction in which kaolinite is absent. Other pedons on till contain mica, kaolinite, chlorite, smectite, and vermiculite. The Bowron pedon has mica, kaolinite, and chlorite, while the Aleza Lake pedons have mica, kaolinite, chlorite, and 2:1 expanding minerals. In pedons with low amount of 2:1 expanding clays in the C horizon, mica and chlorite appear to degrade into 2:1 expanding clays, while in pedons with C horizons containing 2:1 expanding clays, mica and chlorite seem stable and the formation of hydroxy-interlayered clays is the predominant process. Podzolization and lessivage are major pedogenic processes, while redoximorphic processes are observed in some pedons with illuvial Bt horizons. Significant soil compaction hazards are presented by the medium and fine soil surface textures. Although clay-rich Bt horizons may benefit soil nutrient regimes, conservation of nutrient-rich forest floors is important, given the low S contents in mineral soils. High contents of feldspars in these soils provide a large reserve of nutrients such as Ca and K. Key words: Clay minerals, parent material, podzolization, lessivage

Alpine and Subalpine Wetland Vegetation on the Bogong High Plains, South-eastern Australia

The botanical composition and structure of wetland vegetation from seven sites in the alpine and subalpine tracts of the Bogong High Plains was sampled in 1995 and 1996. Sites were in the vicinity of Mts Nelse, Cope and Fainter. Sampling was based on contiguous 1-m2 quadrats along transects 20−70 m long across each wetland. Samples were ordinated using non-metric multidimensional scaling (NMDS). Floristic variation was assessed both within selected individual wetlands, and between wetlands from different regions. The relationship between the ordinations and environmental variables such as soil surface texture, soil depth and the amount of bare ground was tested by fitting vectors. Three dominant vegetation assemblages were identified. Closed heath, of hygrophyllous, scleromorphic shrubs such as Richea continentis and Baeckea gunniana, the rush Empodisma minus and the moss Sphagnum cristatum occurred on the deeper peats. Low open heath of Epacris glacialis and Danthonia nivicola occurred on shallow peats. Herbfields of Caltha introloba and Oreobolus pumilio occurred on stony pavements in two different physiographic situations―on relatively steep slopes (10−20°) at the head of wetlands, and on flat ground (slope < 2°), below the head of wetlands. The pavements on the steeper sites appeared to be associated with periglacial features such as solifluction lobes and terraces. Those on the flatter ground appeared to have been derived more recently. Wetlands in the Mt Cope region consisted of closed heath, low open heath and pavement herbfield in various proportions. Wetlands on Mt Fainter, which are subject to heavy trampling by cattle, were in a degraded condition, with a low cover of major hygrophyllous mosses and shrubs, and a high cover of introduced species. Long-ungrazed wetlands in a 50-year exclosure at Rocky Valley had high cover of closed heath, no pavements, numerous ponds and virtually no entrenched drainage channels or exposed peat. The Caltha herbfields are significant features nationally, both floristically and geomorphologically. Alpine and subalpine wetlands have been listed under the Victorian Flora and Fauna Guarantee Act 1988, and continued grazing by cattle is not compatible with the conservation objectives for this alpine vegetation type.

Geo‐ecological soil features and the vegetation pattern in an arid dune area in the Northern Negev, Israel

AbstractSoils are suggested to be an important factor influencing the vegetation pattern. In order to prove this hypothesis in an arid and sandy Negev ecosystem of longitudinal dunes and interdune corridors near Nizzana, Israel, the distribution of soil units and plant communities were compared on a very small‐distance level. The Nizzana site has a size of nearly 100 ha. 250 soil pits with 3–5 horizons were mapped and sampled within the soil geographical monitoring. Soil water capacity and cation exchange capacity were estimated from the field data. In addition 176 plots of 100 m2 were established around the soil pits with emphasis on plants, coveting the environmental gradient across the dune ridges. Plant mapping plots were arranged into groups with the same dominating perennial species and a key for the vegetation mapping was developed. In the investigated desert site topography, soil surface crust, soil texture and salt content partly can explain the distribution of plant communities. A soil classification proposal is based on these parameters and is a useful tool to indicate correlations between soil units and the vegetation pattern. Nevertheless, dependent on topography and surface and/or subsurface water flow as well as the occurrence of “fertile islands” the moisture and nutrient regimes influence the vegetation pattern with respect to plant growth to a greater extent than the soils themselves.

Presidedress soil nitrogen test for corn in Virginia

The presidedress soil nitrate test (PSNT) and the presidedress tissue nitrogen test (PTNT) have been developed to assess residual soil nitrogen (N) sufficiency for corn (Zea mays L.) in the humid eastern U.S. We conducted field studies at 47 sites during 1990 and 1991 to evaluate the use of the PSNT and PTNT for corn in Coastal Plain, Piedmont, and Appalachian Ridge and Valley regions of Virginia. Seven rates of fertilizer N (0, 45, 90, 135, 180, 225, and 270 kg/ha) were applied at corn height of 0.40 to 0.50 m and replicated four times in a randomized complete block design. Whole corn plants and soil to a depth of 0.30 m were sampled when corn height was 0.15 to 0.30 m to estimate available soil N prior to the application of fertilizer N treatments. Corn grain yield response to fertilizer N was used to assess residual soil N availability. Nitrogen concentration of whole corn plants at 0.15 to 0.30 m height was not an accurate indicator of plant‐available soil N. Corn yields were maximized without sidedress N at the 19 sites where soil NO3‐N was at least 18 mg‐kg‐1 and at the 17 sites where soil (NO3+NH4)‐N was at least 22 mg‐kg‐1. The PSNT predicted corn N sufficiency regardless of soil physiographic region or surface texture; however, the critical values for NO3‐N and (NO3+NH4)‐N were 3 to 5 mg‐kg‐1 lower than those established in Pennsylvania and Maryland, where cooler soil temperatures may permit greater residence time of inorganic N.

An appraisal of soil phosphorus testing data for crops and pastures in South Australia

Data from more than 580 field experiments conducted in South Australia over the past 30 years have been re-examined to estimate extractable soil phosphorus (P) levels related to 90% maximum yield (C90) for 7 crop species (wheat, barley, oilseed rape, sunflower, field peas, faba beans, potato) and 3 types of legume-based pasture (subterranean clover, strawberry clover, annual medics). Data from both single-year and longer term experiments were evaluated. The C90 value for each species was derived from the relationship between proportional yield responsiveness to applied P fertiliser rates (determined as grain yield in crops and herbage yield in ungrazed pastures) and extractable P concentrations in surface soils sampled before sowing. Most data assessments involved the Colwell soil P test and soils sampled in autumn to 10 cm depth. When all data for a species were considered together, the relationship between proportional yield response to applied P and soil P status was typically variable, particularly where Colwell soil P concentration was around C90. When data could be grouped according to common soil types, soil surface texture, or P sorption indices (selected sites), better relationships were discerned. From such segregated data sets, different C90 estimates were derived for either different soil types or soil properties. We recommend that site descriptors associated with the supply of soil P to plant roots be determined as a matter of course in future P fertiliser experiments in South Australia. Given the above, we also contend that the Colwell soil P test is reasonably robust for estimating P fertiliser requirements for the diverse range of soils in the agricultural regions of the State. In medium- and longer term experiments, changes in Colwell soil P concentration were measured in the absence or presence of newly applied P fertiliser. The rate of change (mg soil P/kg per kg applied P/ha) appeared to vary with soil type (or soil properties) and, perhaps, cropping frequency. Relatively minor changes in soil P status were observed due to different tillage practices. In developing P fertiliser budgets, we conclude that a major knowledge gap exists for estimating the residual effectiveness of P fertiliser applied to diverse soil types under a wide range of South Australian farming systems.

Desert Plant Communities in Human‐Made Patches‐‐Implications for Management

We measured productivity and diversity of annual plant communities in human—made pits and mounds (20 ° 30 ° 100 cm) in the Northern Negev of Israel. We differentiated the species according to propagule size, dispersal mode, and geographical distribution in Israel. Our results in 28 experimental units containing a pit, a mound, and a portion of the undisturbed surrounding "matrix" showed that species richness, total plant density, and biomass yield were higher in the pits and mounds than in the matrix. Soil moisture at 0—15 cm depth was higher in the pits, but lower in the mounds relative to the matrix. Species with larger propagules (>5 mm) became more abundant, and those with tinyseeds (<1 mm) became less abundant, in the human—made patches relative to the undisturbed matrix. Wind—dispersed species and those with secondary dispersal by runoff were denser in pits and mounds, while short—distance rain dispersers were more abundant in the matrix. "Edge" species, occurring in the study site at the edge of their geographical distribution in Israel, increased more in density, species richness, and biomass than general "core" species, for which the study site is in the center of their distribution. The annual plant community responded to changes in three environmental factors: (1) microtopographic structure from flat surface to mounds or pits, which function as traps for seeds; (2) soil surface texture from densely packed to loose soil in pits and mounds, which provide suitable sites for larger propagules; (3) soil moisture availability, increasing in the pits but decreasing in the mounds relative to the matrix. The relevance of the study was discussed in relation to (1) combating desertification, (2) sustainable arid land use, and (3) species conservation.

Deterministic uncertainty in landscapes

AbstractDeterministic complexity (chaos) may be common in geomorphic systems, but traditional definitions may have limited practical utility for empirical geomorphology. These definitions are based on sensitivity to initial conditions, which in geomorphology are both unknown and unknowable. Further, chaos analysis depends on distinguishing deterministic complexity from stochastic complexity. This is problematic in geomorphology because some stochastic complexity is virtually always present in addition to any chaos that may be present. While it is important to recognize that some complex, apparently random patterns may derive from inherent non‐linear system dynamics, this is of limited use in explaining process–response relationships or mechanics of landscape evolution. A more general term, which subsumes chaos, is deterministic uncertainty, i.e. uncertainty associated with an identifiable but unknown or uncertain source. An analysis of landscape entropy shows that such underlying constraints produce spatial patterns which are apparently chaotic. For the case of geologic controls, the apparent contribution of deterministic chaos to the landscape entropy is a direct non‐linear function of the extent of geologic constraints. However, the underlying constraints and their contribution to observed spatial patterns can also be interpreted in non‐chaotic terms. Examples are given, involving geologic constraints on stream channel networks and parent material control of surface soil textures. Because both randomness and chaos may be more apparent than real, the concept of deterministic uncertainty is more useful in process geomorphology than that of chaos.

FIELD WIND EROSION

The quantity of soil material transported by wind will decrease with height above the surface. Airborne samples were obtained at five levels above four soils. Mass distribution with height differs for materials in saltation or in suspension. A technique was developed to mathematically describe the two modes of transport so the total quantity being transported could be determined by integrating the two equations. Transition height, where the transport mode changes from saltation to suspension, is termed TSS. TSS decreases as surface soil texture changes from a fine sandy loam to a loam, indicating a higher percentage of the eroded material is moving at a greater distance above the soil surface. TSS increases as roughness of the soil surface increases, indicating a decrease in the suspension component and that the majority of eroded material is moving close to the soil surface.

Soil texture and granulometry at the surface of Mars

The physical behavior of the Martian surface soil has been characterized remotely by both photopolarimetry and radiometry. The degree of linear polarization defines a coefficient b which is related to the top surface soil texture and is calibrated in terms of grain size, or as a fraction of the area exhibiting uncovered clean rocks. This coefficient b was recorded with the instrument VPM (Visual Polarimeter Mars) on board Soviet orbiter MARS 5 in 1974. The radiometric thermal inertia coefficient I is essentially a measurement of the soil compaction, or an effective average particle size in the soil texture, through the few decimeters below the top surface sensed by polarimetry. The instrument IRTM (Infra Red Thermal Mapper) was used on board the Viking spacecraft between 1976 and 1982. The polarimetric scans raked a strip covering two contrasting regions, the dark‐hued Mare Erythraeum and the light‐hued Thaumasia. Over these wide areas, several smaller typical terrains were characterized by the three parameters A (albedo), b (related to top surface grain size) and I (underlaying compaction or block size). The large dark region Erythraeum is characterized everywhere by a uniform polarization response, despite the large geomorphological diversity of the surface. The values of A and b indicate a ubiquitous coating or mantling with small dark grains of albedo 12.7%, with a radius of 10 to 20 μm. Thermal inertia coefficient I indicates that the sub‐surface is divided in pieces around 300 to 600 μm in size. A simple model consisting of sand‐size particles completely coated with 15 μm black grains is compatible with both measurements. Conversely, the brighter terrain Thaumasia discloses a large variety of soil properties. A typical location with albedo 16.3% has a surface covered with orange grains, probably very dispersed in size, for which the largest grains are 20 to 40 μm. The subsurface is divided into pieces 180–300 μm or smaller, if cemented. On the basis of terrestrial analogs of the Martian soil (Morris et al., 1990), it is surmised that the near‐surface soil on the dark areas could be tachylite sand‐size grains surficially coated by cohesive black particles of titanomagnetite. The bright orange grains in the Thaumasia‐like terrains could be made of the weathered (palagonitized) basalt glass particles of sideromelane, as found in terrestrial analogs (Singer, 1982), Thaumasia is known to be a source area for dust storm production. The observed soil texture provides the large grains needed for saltation to occur, causing the intermixed small grains to be ejected from the surface and carried by wind.

Relationship between peanut yield and soil classification of Ultisols in southeastern Alabama

Farmers have often observed that peanut ( Arachis hypogaea L.) produces better on some soils than others, even when receiving the same management practices. This study was conducted to determine the validity of relating peanut yields to a soil classification system in the southeastern US. On-farm peanut experiments conducted from 1972 to 1988, consisting of 164 farms from seven counties of Alabama USA, were compiled for analysis. All experimental sites were identified by soil series, surface-soil texture, and slope. Yields were significantly affected by year and soil series, but yields were not significantly different based on a fertility capability classification system. Surface-soil texture and slope accounted for only a very small portion of yield variations. Soil series appeared to be a more reasonable means for predicting yields, although it may need to be modified to account for the influence of depth to an argillic horizon.

Solute Leaching in Crop Row vs. Interrow Zones

AbstractThis was a pilot study to investigate overall differences in solute leaching from soil beneath row vs. interrow zones of a row crop. Overall leaching could be minimized by exploiting such differences. Strontium bromide was uniformly applied to two, 7.2 by 6 m plots on Bosville fine sandy loam (fine, mixed, thermic Albaquic Paleudalf) planted in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Within each plot, the surface soil texture varied from fine sandy loam to fine sandy clay loam. Soil water status was monitored with tensiometers. After the vegetative growth stage, soil samples were taken along five transects perpendicular to the crop rows at 0.2‐m intervals, to a depth of 0.5 m. Sampling locations corresponded to row, quarter‐row, and interrow positions. In the fine sandy loam half of the corn plot, there was significantly more leaching of Br below the 0.5‐m depth in the interrow positions than in the row positions. This appears to be related to the soil water status, since soil conditions in the fine sandy loam half of the corn plot were, on the average, drier under row positions than under interrow positions. Overall leaching was less under soybean than under corn. Simplified two‐dimensional simulations of solute transport in row‐interrow zones further enhanced our understanding of the effects of net flux differences between those zones, overall net flux, and soil and crop type. The simulations indicated that overall leaching could be slowed by enhancing the differences in evapotranspiration between the row and interrow zones.

EFFECTS OF PESTICIDE, SOIL, AND RAINFALL CHARACTERISTICS ON POTENTIAL PESTICIDE LOSS BY PERCOLATION -A GLEAMS SIMULATION

ABSTRACT Potential pesticide loss in soil percolate is influenced by pesticide persistence and sorption by soil constituents (organic matter). Pesticide persistence, expressed as half-life (ti/2), changes with soil depth as microbial activity and soil properties change. Little is known, however, how these changes influence potential pesticide transport out of the root zone. Objectives of this study were to investigate relative differences in potential pesticide losses from the root zone by percolation due to 1) different soil surface and subsurface textures and pesticide ti/2 and 2) interactions between pesticide ti/2 and timing of rainfall after pesticide application. The GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model and a 50-year historical rainfall record at Tifton, Georgia, were used to simulate pesticide losses by percolation from three soils ranging in surface texture from sand to sandy clay loam. Hypothetical pesticides had surface ti/2 of 5, 15, 30, and 60 d and a range of subsurface ti/2 (2.5-360 d), and were applied to continuous com {Zea maize, L.) at 2 kg ha~ ^ as surface spray at planting each year on 1 April. Simulated pesticide losses by percolation increased with increased surface and subsuiface t|/2 and decreased with increased KQC (adsorption constant based on soil organic matter) values. Potential pesticide leaching was greatest for Lakeland sand and least for Greenville sandy clay loam. Rainfall timing affected simulated pesticide loss by percolation, especially for nonpersistent pesticides. For short pesticide ti/2 (0-5 d), excessive rainfall events within 1 ti/2 were largely responsible for simulated pesticide loss by percolation. Results indicate that changes in pesticide t|/2 in surface and subsurface horizons of different soils influence potential pesticide leaching from the root zone, and models (i.e., GLEAMS) can be used to provide comparative analysis of soil-pesticide-climate interactions. For example, depending on soil type and pesticide K^^ and surface Xyp^ values, potential leaching losses increased two to seven times as subsurface tiy2 increased six times.

Variations in Surface‐Layer Color, Texture, pH, and Phosphorus Content Across Prairie Dog Mounds

AbstractSpatial variations of soil surface color, texture, pH, and phosphorus content were studied so the effects of relict and modern prairie dog (Cynomys ludovicianus) pedoturbation on soil surface properties will be more predictable in southwestern South Dakota. When first formed, prairie dog mounds are made of surface soil. In time, lower‐layer materials are added to the surface. The overall textural variation usually increases with pedoturbation because the original surface layer has a different texture than the subsoil. The mound pH is usually greater than the adjacent soil because calcareous subsoil is deposited in the mound. With time, the mound pH decreases as carbonate leaches and the color becomes darker as organic matter accumulates. The color hue gradually changes to a 10YR if the subsoil was not originally a 10YR hue. Fecal and skeletal phosphorus are deposited in and on the mound to increase areal variation in phosphorus content as a mound continues to be used.