Showing papers in "Soil Science in 2005"

Influence of soil moisture on near-infrared reflectance spectroscopic measurement of soil properties

Abstract: Near-infrared reflectance spectroscopy (NIRS), a nondestructive analytical technique, may someday be used to rapidly and simultaneously quantify several soil properties in agricultural fields. The objectives of this study were to examine the influence of moisture content on the accuracy of NIRS anal

Comparison of glomalin and humic acid in eight native U.S. soils

Abstract: Two important extractable fractions of soil organic matter (SOM) arehumic acid (HA) and glomalin-related soil protein (glomalin). Optimizing the purity of each fraction is necessary to correlate fraction quantity and molecular characteristics with soil quality. Manipulation of extraction sequence an

Effect of organic carbon on available water in soil

Abstract: A model of the water-holding characteristics of soil is needed to develop a systematic method for determining the value of organic C in soil. In the United States, available water-holding capacity (AWC) in soil is that water retained in soil between field capacity and the permanent wilting point; th

Soil physical properties and aggregate-associated C, N, and P distributions in organic and conventional cropping systems

Abstract: Organic farming, which is growing in popularity, has been proposed as a sustainable alternative to conventional farming practices. However, it is not known how organic farming systems affect soil erosion risk and sediment-bound nutrient transport. Our objectives were to compare soil erosion risk and sediment bound nutrient transport potential for grain-based conventional and organic cropping systems by determining selected soil physical properties and distributions of carbon (C), nitrogen (N), and phosphorus (P) in soil aggregates of the 0-5 cm depth of a Christiana-Matapeake-Keyport soil association. We measured soil bulk density, aggregate stability, aggregate size distributions, and total C, N, and P associated with five soil aggregate size classes in no-till (NT) and chisel till (CT) systems and in an organic system (ORG). No-till soils had lesser bulk density and greater aggregate stability than did CT and ORG soils. Carbon, N, and P concentrations were greater in large (g2.00 mm) and small macroaggregates (0.21 to 2.00 mm) than in microaggregates (l0.21 mm) regardless of cropping system. When nutrient concentrations were combined with aggregate distribution data, the quantity of aggregate associated nutrients was greatest in microaggregates in ORG and CT soils but greatest in macroaggregates in NT soils. These results indicate an increased risk of sediment associated nutrient transport from ORG and CT soils compared with NT soils, since microaggregates in these soils are preferentially lost through sediment transport. The NT cropping system promoted macroaggregate formation and reduced the risk of particulate nutrient transport in this warm, humid region soil.

Compost incorporation increases plant available water in a drastically disturbed serpentine soil

Abstract: Construction activity typically results in the removal of existing topsoil, exposing unconsolidated parent material that is often difficult to revegetate. In areas with serpentine mineralogy, revegetation is even more difficult because of low nutrient concentrations, heavy metal toxicity, and a low Ca:Mg ratio. Because serpentine-tolerant plants typically display xeric morphology, we hypothesized that water stress was a main factor limiting revegetation on serpentine roadcuts and that compost incorporation would increase plant available water (PAW). Four treatments were evaluated for their ability to increase PAW on a large serpentine roadcut: nontilled (ambient), tilled, and two rates of incorporated compost (270 and 540 Mg/ha or 12 and 24% by volume). Soil water release curves and moisture depletion were measured in situ using time domain transmissometry and soil psychrometers from early spring through the dry summer months. Compost incorporation (24% by volume) resulted in greater than a 2-fold increase in PAW and generated more than 4 times more vegetative biomass compared with the nontilled control. In contrast to the in situ method, by the conventional pressure plate method showed significantly less PAW in the 24% compost treatment compared with the nontilled treatment. In situ measurements of PAW agreed well with biomass data, indicating that for this atypical soil, in situ measurements were more accurate. Compost incorporation into a drastically disturbed serpentine soil is a successful revegetation technique that will increase PAW as well as the ability of the plants to access this water resource through greater root proliferation.

Predictive-descriptive models for gas and solute diffusion coefficients in variably saturated porous media coupled to pore-size distribution I. Gas diffusivity in repacked soil

Abstract: The soil gas and solute diffusion coefficients and their dependency on soil total porosity (Φ), fluid-phase (air or water) contents, and pore-size distribution largely control chemical release, transport, and fate in soil. The diffusion coefficients hereby play a key role in both local and global environmental issues including spreading, biodegradation and volatilization of hazardous chemicals at polluted soil sites, and soil uptake, production, and emission of greenhouse gases. In a series of papers, we present new advances in describing and predicting the gas and solute diffusion coefficients in variably saturated porous media, carefully distinguishing between repacked and undisturbed media. Also, we establish direct links between gas and solute diffusivity and pore-size distribution, with further links to pore continuity and tortuosity. In this first paper, a porosity correction term is added to a recently presented model for predicting gas diffusivity in repacked soil. The obtained POrosity-Enhanced (POE) model assumes that increased Φ creates additional interconnectivity between air-filled pores. The POE model is tested against data for 18 repacked soils ranging from 0 to 54% clay, including new data measured in this study for both noncompacted and compacted, high-porosity soils. The POE model accurately predicts gas diffusivity across a wide Φ range up to 0.75 m3 m -3 , whereas the original model is accurate only for Φ up to 0.55 m 3 m -3 . A unifying, two-parameter function for gaseous phase pore continuity (f g ) is suggested. The f g function illustrates developments in gas diffusivity models during the last century, including assumptions behind the increasingly precise prediction models for repacked soil. Last, the POE model is coupled with the widely used van Genuchten (vG) soil-water characteristic model, hereby establishing an accurate and predictive link between soil gas diffusivity and pore-size distribution. The closed-form POE-vG gas diffusivity model is highly useful to evaluate effects of pore-size distribution and soil type on gas diffusivity and gas transport in repacked soil systems.

Leaching of colloids and dissolved organic matter from columns packed with natural soil aggregates

Abstract: Transport of pollutants by colloids and dissolved organic matter (DOM) may increase the leaching of strongly sorbing pollutants (e.g., PAHs, heavy metals, radionuclides, and certain pesticides). A prerequisite for colloid- and DOM-facilitated transport is the release of colloids and DOM from soil. In the present study, the leaching of colloids and DOM from columns packed with natural soil aggregates (2-4 mm) was investigated. Aggregates with different organic matter content were used: Aggregates from Soil 1, with 3.6% organic matter content, and aggregates from Soil 2, with 2.5%. The leaching experiments showed that colloid leaching increased with higher organic matter content. Colloid leaching was strongly affected by the ionic strength of the infiltrating water but less so by the specific type of cation. However, prolonged leaching (20 h) with KCl increased the leaching of colloids, probably because of the ion exchange of naturally occurring polyvalent ions with K + . The accumulated amount of colloids leached during 20-h period was orders of magnitude lower than the amount of dispersible colloids (determined by rotation of soil water mixtures), and the organic carbon fraction (f oc ) of the leached colloids was 3 to 4 times higher than the f oc of the dispersible colloids. The leaching of DOM from Soil 1 was greater, but, relative to the soil organic matter content, it was similar for the two soils. The leaching of DOM was not significantly affected by the chemistry of the irrigation water. Irrigation with solutions of KCl and deionized water increased the hydrodynamic dispersion coefficient on Soil 2, due to swelling of the clay minerals and closure of the soil pores. Irrigation with CaCl 2 led to lower hydrodynamic dispersion, because of shrinking clay minerals. Soil 1 was less sensitive to shrinking and swelling of clay minerals because of its higher organic matter content.

Effects of bulk density and soil type on the gas diffusion coefficient in repacked and undisturbed soils

Abstract: The gas diffusion coefficient in soil is affected by several soil physical parameters, including (1) air-filled porosity, (2) bulk density, (3) soil disturbance, (4) the kind of diffusion gases, and (5) soil texture. From the measurement of the relative gas diffusion coefficient (D/D0) of alluvial a

Biological and physical processes that mediate micro-aggregation of clays

Abstract: The aggregation of clays after the addition of organic materials is described. Clays were incubated with or without added organic matter in the form of grass, straw, or charcoal and needed to be dried to a water potential of −1.5 MPa or less to aggregate. It was the fine fraction of the clay (<0.5 μ

Predictive-Descriptive Models for Gas and Solute Diffusion Coefficients in Variably Saturated Porous Media Coupled to Pore-Size Distribution

Abstract: The soil-gas diffusion coefficient (DP) and its dependency on soil type and air-filled porosity (ϵ) controls a multitude of gas transport and fate processes in natural soils, including soil aeration, emission of greenhouse gases, and spreading of volatile organic chemicals. Recent studies show that Dp(ϵ) often differs between repacked and undisturbed soils. This paper revisits two models for predicting DP(ϵ) in undisturbed soil, the three-porosity model (TPM) and the Buckingham-Burdine-Campbell (BBC) model. The TPM is modified by a new expression for predicting DP as a function of ϵ at −100 cm H2O of matric potential (reference point). In the hereby obtained three-porosity-encased (3POE) model, the nonlinearity in gaseous phase pore continuity is assumed to be monotonously increasing with the volumetric fraction of larger pores (drained at −100 cm H2O). To make the model more generally applicable, reference-point DP(ϵ) expressions for other matric potentials than −100 cm H2O are developed from data for 44 soils and can be used in cases where ϵ at −100 cm H2O is not known. Measurements of DP at eight different matric potentials were made on intact soil samples from two fields with volcanic ash soil. The 3POE and BBC models were tested against the measured data and data from literature, comprising 65 soils, and gave similar and accurate predictions. The 3POE model is coupled with the widely used van Genuchten soil-water characteristic (SWC) function to obtain a closed-form model (3POE-vG) that directly relates gas diffusivity in undisturbed soil to pore size distribution. As a low-parameter alternative, the BBC gas diffusivity model is coupled with the Campbell SWC function. Both SWC-coupled gas diffusivity models can assist in analyzing soil type and management effects on gas diffusivity-matric potential relations in undisturbed soils, for example, in relation to improving soil aeration and reducing soil emissions of volatile chemicals.

Migration of silver, indium, tin, antimony, and bismuth and variations in their chemical fractions on addition to uncontaminated soils

Abstract: Metals (Ag, In, Sn, Sb, and Bi) were added to the surfaces of four soil types in columns and exposed to precipitation in a grass-covered field for 18 months. The distributions of the total concentrations and the chemical fractions of the metals were then analyzed to study the metal migration in the soils. The chemical fractionation was performed by using an eight-step sequential extraction technique. Most of the added metals were retained in the uppermost (0 to 2 cm with filter) soil layers, but small portions were moved to the sublayers. Major chemical fractions (>10% in proportion) of the added metals were residual, H 2 O 2 extractable organic-bound (H 2 O 2 -Org), and metal-organic complex-bound (Me-Org) fractions for Ag, Me-Org, residual, carbonate-bound, and H 2 O 2 -Org fractions for In, residual, Me-Org, amorphous metal oxides-bound (am-MeOx), and crystalline Fe oxides-bound fractions for Sn, Me-Org, residual, am-MeOx, and H 2 O 2 -Org fractions for Sb, and H 2 O 2 -Org, am-MeOx, and Me-Org fractions for Bi. Metal migration in soils was mainly associated with the exchangeable, carbonate-bound, and Me-Org fractions. The capacity of soils to retain the metals was in the order Andosol > Fluvisol > Regosol ≅ Cambisol. The mobility of metals was in the order In ≅ Bi > Sb > Ag Sn.

Soil organic carbon sequestration rates in two long-term no-till experiments in ohio

Abstract: The effectiveness of no-till (NT) farming in reducing loss of soil organic matter (SOM) depends on climate and soil properties. Soil samples were obtained from two long-term experiments that were designed to study the impact of tillage systems on crop yields. However, the objectives of this experiment were to assess the impact of NT on soil organic carbon (SOC) sequestration rate and other soil properties and to estimate historic depletion of SOC under different soil management practices with reference to the undisturbed wooded control. The two long-term experiments in Ohio studied were those sited at South Charleston and Hoytville. The South Charleston (83° 30' W and 39° 48' N) experiment was established in 1962 on Crosby silt loam (fine mixed, mesic Aeric Ochraqualf). The site has long-term annual temperature and precipitation of 10.8 °C and 1043 mm, respectively. Tillage treatments for continuous corn (Zea mays) were NT, chisel plow (CP), and moldboard plow (MP). The Hoytville (84° 04' W and 41° 03' N) experiment was established in 1987 on Hoytville clay loam (fine, illitic mesic Mollic Epiaqualfs) soil. The site has long-term annual temperature and precipitation of 9.9 °C and 845 mm, respectively. There were two crop rotations: (i) 2-year corn-soybean (Glycine max) rotation with NT and subsoiling and (ii) 3-year corn-soybean-oat (Avena sativa) rotation with NT, CP, and rotational tillage soil management. The Hoytville clay site is poorly drained, has higher clay content, and higher and more even by distributed antecedent level of SOC in the soil profile than does the South Charleston silt loam soil. No-till increased SOC and N pools in the 0 to 5-cm layer in silt loam soil but had no effect in clay soil. The rate of SOC sequestration in the silt-loam soil under NT was 175 kg C ha -1 y -1 . The silt loam soil had higher SOC and N stratification ratios in NT than in MP and CP treatments, whereas the stratification ratios were low and similar in all treatments in the clayey soil. For both soils, there were no differences between tillage treatments in several soil properties including texture, available water capacity, hydraulic conductivity (K s ), and cation exchange capacity. The NT decreased soil bulk density and pH in the 0 to 15-cm layer in the silt loam soil. The plow till treatments had a small impact on soil aggregation in clayey soil. The decline in water-stable aggregates with reference to NT was no more than one sixth. In the silt loam soil, however, the water-stable aggregates in plow till treatments were merely one third of that in the NT treatment. The historic loss of the SOC pool for 0 to 30-cm depth under agricultural land use was 25 to 35% in silt loam and 19 to 25% in the clayey soil.

Phosphorus availability to barley from manures and fertilizers on a calcareous soil

Abstract: High concentrations of animal production in the United States have increased the concern about the environmental fate of phosphorus (P) in manures. We conducted a growth chamber study to develop phosphorus source coefficients (PSCs) for manures and fertilizers typically land applied and incorporated

Phosphorus leaching through intact soil columns before and after poultry manure application

Abstract: Recent application of manure can increase phosphorus (P) loss from soil in subsurface flow (e.g., drainage water). This study investigated vertical leaching of P through two soils. Eight 30- and 50-cm-deep, intact soil columns (30-cm diameter) were collected. Columns were irrigated periodically (2.4 cm day -1 ) before and after surface application of poultry manure (85 kg total P ha -1 ), continuing for 11 weeks after the application. A dye tracer (FD&C blue No. 1) was used to identify the presence of active macropores at the bottom of each column, and to compare properties of undyed soil matrix material with dyed soil bordering active macropores. Before manure application, concentrations of total P (TP) in leachate did not exceed 0.57 mg L -1 , with dissolved reactive P (DRP) a minor fraction of leachate TP (averaging 7%). Manure application resulted in significant increases in leachate P concentrations, with DRP averaging 72% of leachate TP. No significant differences in leachate DRP and TP concentrations were observed between 30- and 50-cm-deep columns or between soils, either before or after manure was applied, reflecting considerable variability in leachate P trends. In many columns, P concentrations in leachate peaked soon after manure application, with maximum DRP concentrations ranging from 1.1 to 11.2 mg L -1 . In other columns, concentrations increased slowly over time, but maximum DRP concentrations were only 0.19 to 0.55 mg L -1 . Different temporal trends in leachate P concentrations were unrelated to trends in flow. Increased P sorption saturation of soil bordering macropores in subsurface horizons, due to elevated Mehlich-3 P and depleted Mehlich-3 Al, points to the importance of macropores as preferential flow pathways for P. Results of this study highlight the significant, but temporally and spatially variable, nature of P leaching in manured soils.

Predictive-descriptive models for gas and solute diffusion coefficients in variably saturated porous media coupled to pore-size distribution. III. Inactive pore space interpretations of gas diffusivity

Abstract: Accurate description of the soil-gas diffusion coefficient (Dp) as a function of air-filled (e) and total (Φ) porosities is required for studies of gas transport and fate processes. After presenting predictive models for Dp in repacked and undisturbed soils (Part I and II), this third paper takes a more descriptive approach allowing for the inclusion of inactive air-filled pore space, e in . Three model-based interpretations of e in are presented: (1) a simple power-law model (labeled Millington-Call) with the exponent (V) taken from Millington (1959; Science 130:100-102), and expanded with a constant e in term (= 0.1 m 3 m -3 ), (2) a model (SOLA) based on analogy with solute diffusion and assuming a linear increase in pore continuity from zero at the threshold air-filled porosity where gas diffusion ceases (e th ) to a maximum at e = Φ, (3) a power-law model (VIPS) assuming variable e in that linearly decreases from a maximum at e = e th to zero at e = Φ. Assuming e th = 0.1 m 3 m -3 , all three models satisfactorily predicted Dp in 18 repacked soils. The difference between the three models is mainly pronounced for higher-Φ soils, and each model has its own advantage. The SOLA model together with similar models for solute diffusivity allows a direct comparison of pore continuity in the soil gaseous and liquid phases, suggesting large differences in tortuosity and inactive fluid-phase between the two phases. The low-parameter Millington-Call model could account for variability in measured Dp along a field transect (Yolo, California) by varying e in with ±0.03 m 3 m -3 3 and is applicable for stochastic gas transport simulations at field scale. The mathematically flexible VIPS model highly accurately fitted D P (e) data for undisturbed soil, illustrating the large possible variations in e th and V. The VIPS model is coupled with the van Genuchten (vG) soil-water characteristic model, yielding a closed-form expression for Dp as a function of soil-water matric potential. The VIPS-vG model is useful to illustrate the combined effects of pore size distribution and inactive pore space on soil-gas diffusivity.

Mobility of natural radionuclides and selected major and trace elements along a soil toposequence in the central Spanish pyrenees

Abstract: We thank the EEC project >VAHMPIRE> (EN AA 123431. PL. 1995-1999) and CICYT project >RADIERO> (REN2002-02702) for financial support.

Temperature effects on iron reduction in a hydric soil

Abstract: For soils to be considered hydric, they must demonstrate both saturation and anaerobic conditions in the upper part of the soil. Although several technologies are available for monitoring of soil water tables, documentation of reducing conditions is more problematic. This has led to recent interest in the use of IRIS (indicator of reduction in soils) tubes. IRIS tubes are lengths of PVC pipe coated with ferrihydrite paint, which are inserted into the soil to document reducing conditions. Observations from preliminary studies led us to postulate soil temperature will affect the degree and rate of reduction and removal of ferrihydrite from the IRIS tubes. To quantify the impact of soil temperature on ferrihydrite reduction and removal from IRIS tubes, a time series experiment was designed such that IRIS tubes were placed into a hydric soil for time periods ranging from 7 to 28 days, between February and June, 2004. Water tables were monitored daily, Eh was measured at depths of 10, 20, 30, 40 and 50, cm on a weekly basis, and soil temperature was recorded every 4 hours. Removal of ferrihydrite from IRIS tubes was not constant during periods of anaerobiosis and was related to soil temperature. At temperatures below 2 °C, there was essentially no measurable ferrihydrite reduction, even though soil redox potentials fell within the Fe(II) stability field. As soil temperatures increased between 2 and 8 °C, the quantity of ferrihydrite reduction increased with time. At soil temperatures between 8 and 20 °C, substantial (35% to 45%) ferrihydrite paint was reduced and removed from IRIS tubes within 7 days. For a given temperature, there was greater reduction of ferrihydrite in zones closer to the soil surface, presumably due to higher amounts of oxidizable organic matter in near surface horizons.

Stock and distribution of total and corn-derived soil organic carbon in aggregate and primary particle fractions for different land use and soil management practices

Abstract: Land use, soil management, and cropping systems affect stock, distribution, and residence time of soil organic carbon (SOC). Therefore, SOC stock and its depth distribution and association with primary and secondary particles were assessed in long-term experiments at the North Appalachian Experimental Watersheds near Coshocton, Ohio, through *13C techniques. These measurements were made for five land use and soil management treatments: (1) secondary forest, (2) meadow converted from no-till (NT) corn since 1988, (3) continuous NT corn since 1970, (4) continuous NT corn-soybean in rotation with ryegrass since 1984, and (5) conventional plow till (PT) corn since 1984. Soil samples to 70-cm depth were obtained in 2002 in all treatments. Significant differences in soil properties were observed among land use treatments for 0 to 5-cm depth. The SOC concentration (g C kg*1 of soil) in the 0 to 5-cm layer was 44.0 in forest, 24.0 in meadow, 26.1 in NT corn, 19.5 in NT corn-soybean, and 11.1 i n PT corn. The fraction of total C in corn residue converted to SOC was 11.9% for NT corn, 10.6% for NT corn-soybean, and 8.3% for PT corn. The proportion of SOC derived from corn residue was 96% for NT corn inmore » the 0 to 5-cm layer, and it decreased gradually with depth and was 50% in PT corn. The mean SOC sequestration rate on conversion from PT to NT was 280 kg C ha*1 y*1. The SOC concentration decreased with reduction in aggregate size, and macro-aggregates contained 15 to 35% more SOC concentration than microaggregates. In comparison with forest, the magnitude of SOC depletion in the 0 to 30-cm layer was 15.5 Mg C/ha (24.0%) in meadow, 12.7 Mg C/ha (19.8%) in NT corn, 17.3 Mg C/ha (26.8%) in NT corn-soybean, and 23.3 Mg C/ha (35.1%) in PT corn. The SOC had a long turnover time when located deeper in the subsoil.« less

Relationship between soil color and temperature in the surface horizon of mediterranean soils: a laboratory study

Abstract: Changes in color parameters with increasing temperatures over the range of 20 to 700 °C were studied in samples from the uppermost surface layer of the A horizon of various typical Mediterranean soils. Because changes in soil color during heating relate to the formation of Fe hydrous oxides species (such as maghemite and hematite) that increase the red color, and the close relationship between the redness rating index (RR) (a color index that is easily measurable) and hematite content, we studied the potential relationship between such an index and the temperature reached by soil samples over the range of 20 to 700 °C. The variation of the RR index with temperature was found to be similar in large soil groups. This allows the estimation of the temperature reached by a soil sample from the increase in redness rating index, provided the variation of RR with temperature for the soil group concerned has previously been determined. This study provides a first approximation to the estimation of the temperature level reached by the soil during a fire and the soil damage by effect of vegetation burning, which depends on the temperature reached. The soil temperature increase by fire is short-lived, but the changes induced in the color and other soil properties by fire are more or less permanent.

Tracking the fate and recycling of 13C-labeled glucose in soil

Abstract: A short-term incubation of soil amended with 13 C-glucose was conducted to determine the extent of labeled C recycling that might occur within the microbial community. Changes in the production and isotopic composition of CO 2 and biomass suggest that two phases of microbial activity occurred after the glucose addition. The initial phase due directly to the metabolism of the added glucose was characterized by an increase in biomass and a high growth efficiency. A second phase appeared to be driven by less available substrates (e.g., cell wall structures, soil organic matter) and characterized by insignificant changes in biomass but significant generation of CO 2 suggestive of low growth efficiency. Glucose-C supported 12 to 73% of the CO 2 -C evolved and 17 to 21% of biomass-C, suggesting glucose was the principle energy rather than a C source during the 15- to 48-hour phase of the incubation. Variation in δ 13 C composition of individual phospholipid fatty acids (PLFA) during the incubation indicated that different components of the microbial community played different roles in the cycling of the added glucose. The most enriched δ 13 C values were initially those PLFA associated with Gram-positive bacteria, suggesting they were responsible for much of the initial incorporation. By contrast, at the end of the 48-hour incubation, 4 of 24 PLFA biomarkers were not labeled with 13 C. Actinomycetes, however, probably played a larger role in the use of recycled glucose-derived C, as suggested by the enrichment in 13 C of 10-methyl 18:0 PLFA after the exhaustion of glucose. Results from this study show that the element of time needs to be considered carefully in the interpretation of any stable isotope labeling and biomarker study.

Evaluation of maturity and stability of pruning waste compost and their effect on carbon and nitrogen mineralization in soil

Abstract: To study the maturity and stability degree of pruning waste, four compost samples originated from pruning waste, leaves, and grass clippings were collected each from a different pilot pile at different stage of the composting process: initial nondecomposed material (C1); 2 months old at the end of t

Loss of Nitrate-Nitrogen by Runoff and Leaching for Agricultural Watersheds

Abstract: The loss of nutrients in runoff and leaching water from agricultural land is a major cause of poor water quality in the United States. Scientists (NRCS) developed a technique to estimate the impact of agricultural watersheds on natural water resources. The objectives were to apply the technique on W

Andic soils of the inland Pacific Northwest, USA : Properties and ecological significance

Abstract: Holocene tephra from the cataclysmic eruption of Mount Mazama in southwestern Oregon is an important component of many soils east of Cascade Mountains in the Pacific Northwest region. This article examines ecologically important properties of these tephra-influenced soils. Characterization data from 886 soil horizons (384 pedons) of the region meeting criteria for andic soil properties or subgroup classification as andic or vitrandic intergrades in Soil Taxonomy were used to compare morphological, chemical, and physical properties. Mazama tephra typically comprises a significant portion of a surface mantle with textures ranging from silt loam in areas distal to the tephra source to very gravelly loamy coarse sand in proximal locations. Tephra has been mixed to varying degrees with other parent materials across the region. On average, volcanic glass only comprises 31.1% of the 0.05 to 2-mm fraction and has a bimodal distribution, suggesting that some tephra was deposited with significant quantities of dust or, that since deposition, considerable reworking and mixing of glass has occurred. Oxalate-extractable Al ranges from 0.04 to 5.4% and provides the best indicator of colloidal surface activity as indicated by P retention. Cation exchange capacity (CEC) determined at field pH (ECEC) averages 7.8 cmol c kg -1 and is less than one-third the CEC determined at pH 8.2, indicating considerable variable charge and relatively low capacity of these soils to store and supply nutrient cations. Mineralogical data suggest that a reduced pool of secondary Al may be limiting allophane formation in soil horizons with less tephra influence. Volumetric water-holding capacity of ash-influenced horizons is as much as twice that of underlying horizons and underscores the importance of tephra in seasonally dry, forested ecosystems of the Inland Northwest region.

Delineating potential management zones for cotton based on yields and soil properties

Abstract: Procedures to delineate management zones as a basis for making variable rate applications of fertilizers within a field have not been well defined.. The objective of this study was to evaluate a framework of procedures for delineating potential management zones. with data collected from 1-ha grids on an irrigated cotton (Gossypium hirsutum L.) field in Texas from 1998 through 2000. Selected measurements included lint yield, soil pH, exchangeable Ca 2 + and Mg 2 +, K saturation, sand and clay content, depth to free carbonate layer, depth to caliche, NO 3 -N, available P, elevation, and slope. Data were processed with k-means cluster analysis, multivariate analysis of variance (MANOVA), and discriminant analysis. Cluster analysis allowed grouping lint yield and soil properties into high and low yielding classes by their data structure. Using the most significant linear combination in terms of distinguishing 2+ 2+ two yield classes from MANOVA, soil pH, extractable Ca and Mg , K saturation, clay content, and soil N to P ratio were identified as variables that were most related to cotton yield classification and resulted in two potential management zones. The lowest misclassification rate (27%) appeared in the two classes developed from the six influential variables and misclassification mostly located near the pivot boundary and near high to low or low to high yield transition areas, possibly due to changes in soil properties coupled with differences in weather-year patterns in the3 years. Combined with other information, the delineated high and low yield . classes can serve as potential management zones for making detailed management prescriptions for irrigated cotton on these soils. (Soil Science 2005;170:371-385)

Grassland management effects on soil surface properties in the Ozark Highlands

Abstract: Much of the research regarding the effects on soil properties of grazing and land-use conversion from native prairie to pasture and hay meadows has been concentrated in the northern Great Plains where the climate is relatively cool and dry However, little research has been conducted to ascertain similar effects on soil properties in the much warmer and wetter mid-southern latitudes The objective of this study was to characterize the effects of prairie conversion to agricultural grasslands on soil properties in the Ozark Highlands of northwest Arkansas Three native prairie sites were identified with adjacent grazed or hayed grasslands on silt-loam soils Four prairie-agricultural grassland comparisons were made for this study, with each comparison occurring on the same soil-mapping unit Conversion of native prairie to grazing and hay harvesting created significantly (P < 005) higher bulk density, soil pH, and extractable P, Mg, and Mn within the top 10 cm There was a significantly (P < 02) larger difference in electrical conductivity, extractable K, Na, and Fe, but a significantly smaller difference in total N and C and organic matter concentration, in the top 10 cm between prairie-grazed and prairie-ungrazed landuse combinations Overall, soil surface properties of agricultural grasslands in the Ozark Highlands were similar to those of native, undisturbed prairie, indicating that either negligible responses occurred following conversion, parameters recovered to original equilibrium levels, or the magnitudes of agricultural inputs following conversion were too low to change equilibrium levels substantially The baseline soil data generated in this study for undisturbed prairie and agriculturally managed grasslands can serve as standards for assessing impacts of high-input agriculture and future land-use changes in the Ozark Highlands

Erosional effects on soil physical properties in an on-farm study on alfisols in west central Ohio

Abstract: Tillage effects on soil properties are often site-specific functions depending on the type of soil, climate and topography of the area. This on-farm study designated to investigate the effects of no-till (NT) duration, degree of erosion, and chisel tillage-alternate year with manure (MCT) and annual

Effects of root density distribution models on root water uptake and water flow under irrigation

Abstract: Water uptake by roots greatly influences water distributions in soil-plant systems. It is essential to understand root water uptake patterns to estimate accurately water movement through the systems. In this study, six empirical root density distribution models were incorporated into a water flow model to study their effect on root water uptake and soil water movement. Two main distributions of root systems, i.e., cylindrical and conical shapes, were considered. Root water uptake with these models was evaluated at three levels of irrigation, about 0.3, 0.7 and 1.0 of total potential transpiration, with three root depths in a sandy loam soil and a silt loam soil. High irrigation levels reduced difference of root water uptake from different root depths in both soils. In the sandy loam soil, a shallow root depth could enhance difference in root water uptake among different root distribution models, whereas a greater difference was found within larger root depths in the silt loam soil. The models with the conical shape resulted in an average of 13% higher leaching in the sandy loam soil than were seen with the cylindrical shape. Contributions from different parts of the root system to the total root water uptake were varied with the different models, as were the distributions of water pressure head and water flux in the soil profiles.