bluuebunny/crossref_metadata_2025 huggingface dataset:
Silica Associated with Fragipan and Non‐Fragipan Horizons
Authors: Steinhardt G. C. , Franzmeier D. P. , Norton L. D.
Published: July 2010

All horizons of two fragipan soils and one nonfragipan soil were extracted with a sodium citrate‐bicarbonate‐dithionite (CBD) reagent and 0.5N NaOH. Both produced a maximum in extractable silicon (Si) in the fragipan horizon, but NaOH extracted about 10 to 40 times as much Si as did CBD. This Si appears to be a critical part of the fragipan, because in the nonfragipan soil, extractable Si shows no subsurface maximum at the depths in which fragipans occur.
A Simple System for Repeated Soil Resistance Measurements at the Same Spot
Authors: Nadler Arie , Magaritz Mordekcai , Lapid Yigael , Levy Y.
Published: July 2010

An AC (alternating current) generator and a multi‐electrode probe (MEP) were used for field measurement of bulk‐soil electrical conductivity (ECa). The MEP enabled unlimited, repeated, fast measurements of ECa at a certain spot. The MEP was operated by a portable, inexpensive, sine‐wave AC generator for obtaining ECa values based on the four‐electrode method.
Estimating the Soil Water Dependence of the Electrical Conductivity Soil Solution/Electrical Conductivity Bulk Soil Ratio
Authors: Nadler Arie
Published: July 2010

A procedure is developed to calculate the ratio between electrical conductivity (EC) solution (ECw) and EC of bulk soil (ECa) as a function of soil water content (θ). This ratio, (F), changing nonlinearly with θ, is used to calculate soil solution salinity from measurements of bulk soil electrical conductivity. Obtaining F‐θ relationships for intermediate and low soil moisture levels by an accurate theoretical model is impractical due to the complicated interdependence of several solid‐ and liquid‐phase parameters. Therefore an empirical approach was adopted to obtain the complete F‐θ relationship by superimposing the complete suction‐water retention relationship on two F‐θ measurements at the same θ values. The experimentally determined F‐θ curve overlaps the theoretically calculated F‐θ relationship at high soil water contents and the empirically obtained F‐θ relationship at low soil water content. Examples are given for several soil types.
Calculating the Depths of Soil Moisture Control Sections from Laboratory Data
Authors: Zobeck T. M. , Daugherty L. A.
Published: July 2010

Calculations of the upper and lower boundaries of a soil moisture control section are illustrated using only the depth, bulk density, and saturated, −1/3, and/or −15 bar water contents, and amount of coarse fragments of the soil horizons. It is recommended that the difference between the −50 to −100 cm and −15 bar water contents be used for determining and defining the soil moisture control section in medium to fine‐textured soils. Both moisture contents are reasonable approximations of physically or biologically significant moisture levels and easily determined in the laboratory. The definition would then correspond to the familiar available water‐holding capacity (AWC) value currently in use.
Stratified Profiles: Characteristics of Simulated Soils in a Beef Cattle Feedlot
Authors: Norstadt Fred A. , Duke Harold R.
Published: July 2010

Profile combinations of clay loam, sand, clay loam over sand, and sand over clay loam were used to study salt movement and mineral nitrogen (N) transformations in a beef cattle feedlot. These soils were placed in lysimeters located in a feedlot stocked at the rate of one animal, weighing 270 to 450 kg, per 15.2 m2. The feedlot was bedded with sawdust and stocked continuously. After the lysimeters were in use 4 years, cores were removed for physical and chemical analyses. Each profile combination affected salt movement and mineral N transformations differently. Sand over clay loam was the superior combination to retard nitrate‐N (NO3‐‐N) movement and retain salt. In this configuration organic matter apparently moved from the manure pack through the sand along with NO3‐‐N and may have enhanced denitrification in the clay loam layer. The effect of location within the feedlot and depth increment within a given soil fill and their interaction were not important variables influencing profile chemical characteristics.
The Physical Swelling of Clays in Solvents
Authors: Murray R. S. , Quirk J. P.
Published: July 2010

The physical swelling of two illitic clays has been measured, at zero matric potential, in a series of organic solvents with different functional groups. The results show that a significant linear correlation exists between the observed swelling and the static dielectric constant of the liquid. This behavior is compared with the intracrystalline swelling of montmorillonite and is discussed in relation to the mechanism of swelling of clay systems.
A Field Study of Solute Dispersion in a Shallow, Unconfined Aquifer
Authors: Leland D. F. , Hillel D.
Published: July 2010

A natural gradient tracer test was performed to (i) characterize the patterns of variation of saturated hydraulic conductivity (Ks) and longitudinal dispersivity (αL) in a shallow, unconfined aquifer in a sandy soil on a sloping site and to (ii) examine scale effects on quantification of αL. Chloride tracer was injected into the saturated zone, and its downslope movement was monitored by means of multilevel samplers.

Results show that the mean value of Ks derived from the tracer test was in close agreement with values obtained independently on undisturbed core samples and from double‐ring infiltrometer tests performed in situ. Results also indicate a nonuniform distribution of velocity on both vertical and horizontal transects at right angles to the mean direction of flow. Values of αL, calculated using a simplified solution of the two‐dimensional advective‐dispersive equation, show a nonuniform distribution of αL in the profile and reveal that increasing the scale of measurement vertically at right angle to the flow leads to larger measured values of dispersivity. The effect was observed with a change in scale from point measurements to averages taken over the 60‐ to 75‐cm thickness of the profile's saturated zone. The frequency of sampling is also shown to have a significant effect on quantification of αL.
Water Infiltration and Redistribution in a Silt Loam Subsoil with Vertical Worm Channels
Authors: Bouma J. , Belmans C. F. M. , Dekker L. W.
Published: July 2010

Infiltration and redistribution of water in a fine silty, mixed, mesic Fluventic Eutrochrept with macropores (dominantly vertical worm channels) were studied with physical and morphological techniques. Infiltration rates in individual worm channels were measured and channel morphology was studied by excavation after adding methylene blue and gypsum. Three different steady infiltration rates corresponded with different channel morphology. One channel occurred per 200 cm2 of soil. The measured, dominant infiltration rate in a channel was used to calculate ponding time on and the associated water movement in the soil matrix after adding 2 cm of water. The latter was calculated with an existing simulation model for one‐dimensional infiltration in homogeneous soil using K‐θ and h‐θ data. Calculations of h indicated lack of soil saturation. This agreed only with in‐situ measurements when small tensiometer cups were used. Large cups intercepted water‐conducting macropores, erroneously suggesting saturation of the entire soil matrix. Addition of a 5‐cm thick layer of sand to the surface of infiltration made the macropores discontinuous and induced saturated conditions, as measured and simulated. Measurement of infiltration rates into individual macropores, rather than calculation of those rates, is recommended when macropore morphology is irregular.
Effects of Rate of Application and Time on Phosphorus Sorption by Soils
Authors: Ibrahim H. S. , Pratt P. F.
Published: July 2010

Several soils from southern California were treated with different rates of phosphorus (P) and then incubated in 0.01M CaCl2 to measure the effect of incubation time up to 84 d at 25°C. There were only small effects of incubation times beyond 3 d for low rates of P applications. At higher rates of application those soils that were deficient in P as indicated by the NaHCO3 test (< 10 µg P extracted/g) gave increased P sorption with increase in incubation time beyond 3 d. Those soils well supplied with available P reached equilibrium in 3 d. In those soils deficient in P, equilibrium was attained by the 42nd d of incubation.
Changes in Inorganic and Organic Soil Phosphorus Fractions Induced by Cultivation Practices and by Laboratory Incubations
Authors: Hedley M. J. , Stewart J. W. B. , Chauhan B. S.
Published: July 2010

Changes in inorganic and organic phosphorus (P) fractions resulting from 65 years of cropping in a wheat‐wheat‐fallow rotation were studied using a sequential extraction technique. Total P content of the cultivated soil was 29% lower than that of the adjacent permanent pasture; the major loss of P (74% of total P lost) was organic P and residual P. Of the total P lost, 22% was from the extractable organic P forms, whereas 52% originated from stable P.

Incubation studies were used to study seasonal P transformations during simulated fallow with and without residue incorporation and P fertilization. Nine monthly additions of cellulose (765 µg C · g−1 soil) with and without P (9 µg · g−1 soil) significantly altered levels of total extractable organic P and inorganic P in incubated soils. Evidence is provided for microbial activity playing a major role in redistributing P into different forms in the soil.
Geostatistical Analysis of Soil Chemical Properties of Large Land Areas. I. Semi‐variograms
Authors: Yost R. S. , Uehara G. , Fox R. L.
Published: July 2010

Soil properties are usually sampled on some grid or pattern which presumes to represent the unsampled neighborhood. Spatial dependence is a measure of the extent a soil sample represents the unsampled neighborhood. Geostatistics provides procedures to measure spatial dependence. Eighty pedons (Andepts) on the Island of Hawaii were sampled and spatial dependence was measured with semi‐variograms. Areas of soil with similar properties (zones of influence) were delineated by the “range” of the semi‐variogram. Areas of similarity were much greater for soil properties of the 0‐ to 15‐cm depth than of the 30‐ to 45‐cm depth. The ranges of the semi‐variograms for soil pH, Ca, Mg, K, Si, and P sorbed at 0.02 mg P/L were 32 to 42 km while the range of the variogram of rainfall had a similar value of 32 km. Semi‐variograms for Ca, Mg, K, and P based on 30 to 45‐cm‐depth samples demonstrated much greater variability and had smaller zones of influence (Ca, Mg, and K) or were extremely variable (P). Silicon in saturation extract, however, had the same zone of influence in the subsoil as in the topsoil. These results suggest that rainfall has imposed a degree of uniformity on the surface soil properties not apparent in the subsoil. Subsoil properties were highly variable, as might be expected, resulting from great variation over short distances in age and weathering of volcanic ash. The results suggest that soil chemical properties may be spatially dependent and that the spatial dependence in this example represents the imprint of soil‐forming processes and perhaps management. Zones of influence as delineated by semi‐variograms of soil properties may suggest groupings for soil management or soil classification.
Variations in Nitrate and Chloride Concentrations below Selected Agricultural Fields
Authors: Lund L. J.
Published: July 2010

Nitrate‐nitrogen (NO‐3‐N) and chloride (Cl‐) concentrations below four agricultural fields were determined to evaluate the validity of assuming that the nitrogen (N) cycling systems were at steady state for purposes of calculating N balances. Eight or nine sites in the fields in the Santa Maria Valley of California were sampled two or four times to determine the spatial and temporal variations in NO‐3‐N and Cl‐ concentrations in the unsaturated zone. Significant spatial variations were found within all fields with mean field concentrations of NO‐3‐N and Cl‐ ranging from 40 to 136 mg/L and 4.5 to 7.1 meq/L, respectively. Temporal variations were less dramatic. Nitrate‐nitrogen and Cl‐ concentrations did not change with time over the period of study below a field that had been cropped to artichokes (Cynara scolymus) for the previous 12 years. Differences did occur with time for the other fields. For two of the fields the changes in mean concentrations could be related to past management with decreasing NO‐3‐N concentrations reflecting periods of less N fertilization.
Theories and Tests of Electrical Conductivity in Soils
Authors: Bohn Hinrich L. , Ben‐Asher Jiftah , Tabbara Hadi S. , Marwan Mukhtar
Published: July 2010

The soil's specific electrical conductivity (ECa) is similar in principle to the EC of a pure solution, but the nonconducting soil air and solids cause complications. The ECa measured by four‐electrode Wenner arrays in laboratory and field experiments was linearly proportional to the product of the soluble salt concentration and the soil water content over a salinity range of 0 to 40 dS/m in the soil solution and 0.1 to 15 bar soil water suction. Theories of soil EC based on a conductivity cell and microscale conduction were compared to a macroscale theory and all explained the measured results equally well. Soil can be viewed as an intricate container for electrolyte solution, as a conductor having a tortuous path, or as many conduction paths of varying cross section and length. The macro model was extended to relate ECa to soil water potential, but ECa appears to be inherently dependent on both the soil moisture and salt contents.
Effect of pH on the Rate of Gaseous Products of Denitrification in a Silt Loam Soil
Authors: Koskinen W. C. , Keeney D. R.
Published: July 2010

To examine the effect of soil pH on the rate and products of denitrification, a silt loam soil (Typic Argiudoll) was used that had been collected from a field experiment maintained at various pH levels for 18 years. The soil pH ranged from 4.6 to 6.9 and was nearly uniform in organic C (1.15 ± 0.05%) and texture. Incubation was performed under He in all‐glass systems that were sealed throughout the incubation period. The soils were amended with 100 µg/g of NO‐3‐N before incubation. Denitrification products (N2O, NO, and N2) and CO2 were determined by gas chromatography using an ultrasonic detector.

It appears that the rate of organic C mineralization rather than pH controls the rate of denitrification in C‐limited systems. At 100 µg NO‐3‐N added per gram of soil, the overall rates of denitrification correlated with the rates of C mineralization (CO2 evolution) but were not consistently related to pH or to total organic C.

Soil pH did affect the products of denitrification. Nitrous oxide comprised 83% of the gaseous‐N products for pH 4.6 and 5.4 when 90% of the NO‐3 had been denitrified. The N2O was then rapidly reduced to N2. The highest amount of NO was observed at pH 4.6 and 5.4. At pH 6.0 the rate of production of N2O exceeded the rate of reduction only for the first 2 d of incubation. However, N2O was the dominant product until ∼83% of the NO‐3 had been denitrified. At pH 6.9, N2 was the dominant product after the 1st d of incubation.
Improved Corrective Fertilizer Recommendations Based on a Two‐Step Alternative Usage of Soil Tests: II. Recovery of Soil‐Equilibrated Potassium
Authors: McLean E. O. , Adams J. L. , Hartwig R. C.
Published: July 2010

The objective of these studies was to improve corrective fertilizer K recommendations using soil quicktest methodology which measures K‐fixation tendencies for individual soils. Actual amounts of fertilizer K required to reach a computed sufficiency level of NH4OAc‐exchangeable K were measured from the added K vs. exchangeable‐K relationship in 15 soils with a wide range in K‐fixation tendency. Using quicktest procedures, the new Mehlich extractant removed from the various K‐equilibrated soils the same amounts of K as did NH4OAc solution, which suggests the possibility that both K and P may be simultaneously equilibrated and extracted with one extractant. Regressions were computed between the actual and variously computed amounts of K to reach sufficiency level based on constant‐fraction recovery, quicktest‐measured recovery (one‐step), and curvilinear regression‐adjusted recovery (two‐step). The results indicate that the proposed quicktest methodology (2‐h K equilibration) combined with a second calibration step based on longer‐time K equilibration of representative soils makes possible a greatly improved recommendation for fertilizer K.
Calcic Horizon Distribution and Soil Classification in Selected Soils of the Texas Coast Prairie
Authors: Sobecki T. M. , Wilding L. P.
Published: July 2010

In the nearly level southeastern Texas Coast Prairie, extensive areas of Udolls with calcic horizons are intimately associated with noncalcareous Aqualfs. Transect and grid studies of 1‐ to 2‐ha plots and other field studies in the area indicate that soils with calcic horizons are confined to microtopographic highs. Aqualfs occupy irregular microdepressions only 0.5 m lower than microhighs. This soil pattern is found on coastal plain geomorphic surfaces of both the Beaumont and Montgomery Pleistocene geological formations, especially on distributary elements of deltaic origin.

Variation in depth to the calcic horizon in Mollisols ranges from 18 to 115 cm and results in complex soil patterns of Aeric Calciaquolls and Aquic Haplustolls in microhighs. Multitaxa map units are necessary to accurately map the soils in these landscapes. Local relief differential of <1 m within the study area is the key landform indicator of soil differences. A new category for Soil Taxonomy, Calciaquic Hapludolls, is proposed to accommodate soils currently placed as Haplustolls that have udic moisture regimes despite calcic horizons within 1.5 m of the soil surface.
Slope Angle‐Interrill Soil Loss Relationships for Slopes up to 50%
Authors: Singer Michael J. , Blackard John
Published: July 2010

Soil loss data were collected from 1.2‐m long by 0.6‐m wide plots under 76 mm/h simulated rainfall for two soils at slopes from 3 to 50%. Soil loss and soil loss ratio (soil loss at any slope ÷ soil loss at 9% slope) were related to the sine of slope angle in degrees. Second‐ and third‐degree polynomial equations fit the data best. An equation for the Hillgate soil showed that the soil loss ratio increased rapidly up to 35 to 40% slope and then became nearly constant. This may be partly due to the experimental conditions of short slope length but is realistic because at high slope angles there is less direct raindrop impact on the soil surface.

The equation for the Contra Costa soil loss ratio yielded a curve much below the Hillgate curve at slopes between 15 and 40%. These data suggest that soil properties and slope effects are not independent. The experimental conditions are not meant to be representative of field conditions but the data represent the effect of slope steepness on interrill erosion by raindrop impact and overland flow.
Soil Phosphorus and pH Influence the Growth of Mycorrhizal Sweetgum
Authors: Yawney William J. , Schultz Richard C. , Kormanik Paul P.
Published: July 2010

The response of sweetgum (Liquidambar styraciflua L.) seedlings grown either without or inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Gigaspora margarita ‘Becker’ and ‘Hall’ to 25, 50, and 100 ppm soil phosphorus (P) and adjusted soil pHs of 4.5, 5.5, 6.5, and 7.8 was observed during the first growing season. The best seedling growth for both VAM and noninoculated seedlings occurred at soil pH 4.5 and 100 ppm of soil P where mean heights and top dry weights averaged > 28 cm and 8 g, respectively. As soil pH increased, seedling growth decreased significantly and at pH 7.8 the seedlings averaged < 4 cm in height regardless of the soil P level or mycorrhizal condition. Seedling growth at all pH levels, except pH 7.8, decreased with decreasing soil P. Inoculated seedlings were significantly larger than noninoculated seedlings at 25 ppm soil P and pHs 4.5 and 5.5. Soil P, soil pH, and mycorrhizal condition significantly influenced nutrient levels in plant parts. Soil nutrient levels varied significantly with soil pH.
Clay Mineralogy in Relation to Landscape Instability in the Coast Range of Oregon
Authors: Istok J. D. , Harward M. E.
Published: July 2010

Field and laboratory data reported in this study indicate that the kind of mass movement and the mineralogy of the materials involved vary with the parent material. The clay fraction of debris avalanches is dominated primarily by nonexpanding layer silicates that have large particle sizes and small water‐holding capacities. Dehydrated halloysite, chloritic intergrade, and mica were the common minerals in those areas underlain by sandstones and siltstones of the Tyee Formation as well as the massive basalt flowrock of the Siletz River Volcanic Series. The clay fraction of soils derived from Tertiary sandstones of the Galice and Lookingglass Formations is dominated by chloritic intergrade, chlorite, mica, and kaolinite. Serpentine, chlorite, and mica were the soil clays associated with debris avalances on serpentinite of the Otter Point Formation. Expandable layer silicates, or those with high charge or water‐holding capacity, were not major constituents of debris avalanches although smectite and vermiculite commonly occurred in a thin layer of soil above the underlying bedrock.

The clay fraction of samples from sites undergoing failure by creep and slump consisted primarily of smectite. Smectite, chloritic intergrade, dehydrated and hydrated halloysite, and mica were the minerals commonly associated with soil creep and slump on slopes underlain by siltstones of the Tyee Formation. Montmorillonite was the major constituent of a large rotational slump at the contact between the Nye Mudstone and the sandstones of the Astoria Formation. Smectite, chlorite, and serpentine were identified in sites underlain by serpentinite of the Otter Point Formation.

The mineralogy of soils involved in earthflow consisted predominantly of hydrated and dehydrated halloysite, amorphous material, and chloritic intergrade. No difference in mineralogy could be detected between sites underlain by siltstones of the Tyee and Nestucca Formations and tuffaceous siltstones and tuff of the Siletz River Volcanic Series. Surface samples were more poorly crystallized than samples taken at lower horizons. Electron micrographs reveal an abundance of amorphous gels and “coatings” on the surface of mineral grains. The abundance of “pores” may account for the fluid behavior of these materials during failure.
Approximate Soil Water Movement by Kinematic Characteristics
Authors: Smith Roger E.
Published: July 2010

Using the Richard's equation in the Fokker‐Planck nonlinear diffusion form, unsaturated soil water flow may be treated as a diffusion‐convection wave process. If ∂θ/∂z is assumed a function of θ alone, the unsaturated flow equation may be solved by the method of characteristics, and when ∂θ/∂z becomes sufficiently small, the Peclet number is assumed large enough to treat unsaturated flow kinematically. Changes in θ with depth in the soil profile are treated as waves, moving downward. Advancing and receding “waves” are treated differently in the approximate analytical technique described here, with advancing wetting fronts described by kinematic “shocks.” The method is compared to the complete solution to Richard's equation for a complex rain pattern and found to predict well the location of deeper moving fronts and also general θ patterns. The kinematic method is also shown to apply to root water extraction zones and to layered soil situations.
Chemical Denitrification of Nitrite in Frozen Soils
Authors: Christianson C. B. , Cho C. M.
Published: July 2010

The effect of low temperature on chemodenitrification of nitrite in several Manitoba soils was investigated using highly enriched N‐15 and a mass spectrometric technique, which distinguished between N2 formed via a chemical reaction and that formed via the biological reduction of NO‐2. When a slightly acid soil (pH 6.4) was incubated with NO‐2 concentrations ranging from 25 to 300 µg N/g, the chemical N2 production rate was approximately first order with respect to initial NO‐2 concentration. When the soil was incubated with NO‐2 under different temperatures (+20 to −20°C), the rate of chemical N2 production was found to decrease with decreasing temperature up to −1.8°C. Lowering the temperature to −3.5°C resulted in the rate of N2 production greater than the value observed at 20°C on each concentration. Further decrease in temperature resulted in a gradual decrease in the rate. Similar trends were found with two other slightly acidic soils. The enhancement in the rate of chemodenitrificatoin upon freezing of moist soil was believed to be due to freeze concentration of NO‐2 into an unfrozen layer of soil water near soil colloids. Such an increase in NO‐2 concentration in solution resulted in the rate of denitrification.
Isolation and Identification of Amino Sugars in Soil
Authors: Stevenson F. J.
Published: July 2010

Chromatographic analysis of amino sugars in soil hydrolysates revealed the occurrence of a wide variety of compounds that gave color reactions typical of amino sugars when analyzed with the classical Elson‐Morgan and indole‐HCl colorimetric methods. The presence in soil of up to 11 amino sugars in addition to glucosamine and galactosamine was indicated. Mannosamine and muramic acid were positively identified and provisional identifications were made for gulosamine and fucosamine. Considerable variation was observed in amino sugar distribution patterns for soils of diverse types. The distribution of amino sugars in a humic acid preparation was similar to that of the original soil. A soil polysaccharide contained amino sugars.
Nitrification Inhibition by Nitrapyrin and Etridiazol in Soils Amended with Sewage Sludge Compost
Authors: McClung G. , Wolf D. C. , Foss J. E.
Published: July 2010

Nitrification inhibitors, which have been used to reduce fertilizer N losses from soils, may have potential for use with organic soil amendments such as sewage sludge compost. Effects of two nitrification inhibitors, nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] and etridiazol [5‐ethoxy‐3‐(trichloromethyl)‐1,2,4‐thiadiazole] on nitrification were investigated in laboratory studies with Beltsville silt loam (Typic Fragiudult), Hagerstown silty clay loam (Typic Hapludalf), and Pocomoke loamy sand (Typic Umbraquult). The soils were amended with sewage sludge compost at rates of 0.0, 44.6, and 89.2 g/kg and incubated at 25°C, and at compost rates of 0.0 and 89.2 g/kg and incubated at 15°C. In all soil‐compost combinations at either temperature, there were no significant differences between nitrapyrin and etridiazol as measured by NH4‐N or NO3‐N concentrations in the soils. At least 83% inhibition of nitrification was observed in all soil‐compost combinations following 18 weeks of incuhation at 25°C with the highest inhibitor rate of 50 µg/g. After 9 weeks of incubation at 15°C, > 76% inhibition of nitrification was observed in all soil‐compost combinations with the highest inhibitor rate of 10 µg/g. Generally NO3‐N production decreased with increased inhibitor concentration and with decreased compost rate.
NCSOIL, A Model of Nitrogen and Carbon Transformations in Soil: Description, Calibration, and Behavior
Authors: Molina J. A. E. , Clapp C. E. , Shaffer M. J. , Chichester F. W. , Larson W. E.
Published: July 2010

NCSOIL is a submodel of a larger program NTRM (nitrogen‐tillage‐residue management). NCSOIL computes short‐term dynamics of carbon and nitrogen organics, ammonium, and nitrate which result from the processes of residue decomposition, mineralization, immobilization, nitrification, and denitrification. Both total and isotopic nitrogen are considered. NCSOIL is built on the concept of catenary sequence of heterogenous substrates. The active soil organic phase is divided in two pools which are dynamic, defined by their kinetic rate constants and their position in the model structure. Residues are defined in terms of their chemical or morphological nature. A double feedback loop in the carbon flow adjusts the rate of residue decomposition and the efficiency factor to the availability of inorganic nitrogen. NCSOIL was calibrated with, and its behavior contrasted against published and unpublished data from an experiment reported by Chichester et al. in Soil Science (see p. 455, vol. 120): “Relative Mineralization Rates of Indigenous and Recently Incorporated 15‐N labeled Nitrogen.” Experimental results of the Chichester et al. experiment were discussed in view of computer‐simulated flow rates and substrate concentrations.
Effects of Heating on Soil Chemical Properties and Growth and Nutrient Composition of Corn and Millet
Authors: Kitur B. K. , Frye W. W.
Published: July 2010

Heating or burning has a wide variety of effects on soils, the magnitude of which is determined largely by the temperature to which the soil is heated and on soil properties. In parts of Africa, the practice is used on soils in the field to improve crop production. The objective of this study was to determine the effect of heating Alfisol and Mollisol soil materials on their chemical properties and on the early growth and nutrient composition of corn (Zea mays L.) and millet (Setaria italica) grown in the greenhouse. Heating the soils to 110°C decreased pH, but the pH increased when the soils were heated to 200 or 250°C. Organic matter and extractable Mg decreased while extractable NH+4 and Mn and electrical conductivity (EC) increased greatly with heating. The effects on soil‐test P and K and extractable Ca were small and variable, but the soils were already higb in these elements. Increases in extractable NH+4 and Mn, EC, and pH probably came from both the destruction of soil organic matter and release from inorganic compounds in the soils. Heating soils to 110°C resulted in greater growth of both corn and millet, but heat treatments of 200 and 250°C suppressed growth. The increase in the growth of corn and millet was attributed primarily to moderate increases in extractable NH+4 at 110°C. The suppression of growth with heat treatments of 200 and 250°C was thought to be due largely to excessive amounts of NH+4. Extensive work on NH+4 shows that certain levels of this form of N may be toxic to plants. Heating of soil was shown to be both heneficial and detrimental to the growth of plants. Crops may benefit from nutrients released when soils are heated, provided the amounts are not excessive. The detrimental effects observed in this study would not usually be noticeable under field practice, because only a small proportion of the soil volume is heated.
Relative Effectiveness of Tillage and Natural Forces in Alleviating Wheel‐Induced Soil Compaction
Authors: Voorhees W. B.
Published: July 2010

Wheel‐induced soil compaction can have detrimental consequences in reduced tillage systems if off‐season weathering forces are not very effective in ameliorating a compacted soil. Field studies were conducted on a Nicollet silty clay loam (Aquic Hapludoll) in Minnesota on plots with a history of controlled wheel traffic. After 5 years of autumn tillage, the plots were split, with one‐half of each plot moldboard plowed or reduced tilled (chisel plow or tandem disk) and the other one‐half remaining untilled over the winter period. Bulk density, penetrometer resistance, soil water content, aggregate size, and clod density were measured to assess the relative effect of natural forces and tillage on amelioration of wheel track‐compacted soil. Moldboard plowing in the autumn effectively ameliorated compaction of the bulk tilled layer. Reduced forms of tillage such as chisel plow or tandem disk were only slightly more effective than natural weathering forces which reduced penetrometer resistance by 20 to 50%, but had little effect on bulk density. The structure of individual soil aggregates and clods was not changed much by either tillage or natural weathering. Thus, a no‐till system may result in higher bulk density, aggregate density, and penetrometer resistance because of incomplete amelioration of compacted soil by natural forces during the winter season. Potential consequences include seedbed preparation problems, uneven germination, lower hydraulic conductivity, and undesirable early root growth environment.
Modeling Infiltration into Crusted Soils by the Green—Ampt Approach
Authors: Ahuja L. R.
Published: July 2010

The study deals with infiltration of water through a stable surface crust, wherein the water content at the crust‐soil interface increases with time for a long period, and remains below the saturated value. An approximate Green‐Ampt‐type formulation derived from a physical basis, containing a time‐dependent capillary drive term and a profile shape factor, is evaluated by comparisons to a similarity solution and a finite‐difference numerical solution of the problem. The exact nature of the derived Green‐Ampt formulation is established for early to intermediate stages for certain reasonable conditions. Calculations of cumulative infiltration with time made by the above approach, with the profile shape factor set equal to unity, were within tolerable error from the numerical solution results for one soil and a set of experimental data for another. A previously reported piecewise application of the conventional form of the Green‐Ampt equation is also developed to enable its use from time zero, as an independent predictive method. This method, which includes some implicit correction for the profile shape, gave slightly better calculations of the cumulative infiltration. The above simple methods should also be applicable to related unsaturated flow problems, such as infiltration through a transient crust‐seal resistance and into a layered soil having a fine material overlying a coarse material.
Fixation Kinetics in Potassium‐Aluminum‐Orthophosphate Systems
Authors: Kim Y. K. , Gurney E. L. , Hatfield J. D.
Published: July 2010

The rate of removal of phosphate and potassium from solution was studied by contacting an aluminum‐impregnated, cation exchange resin with solutions of monopotassium phosphate in concentrations of 0.05 to 0.25M and with atomic ratios Al:P from 0.25 to 4.0. The removal of both K and P from solution followed first‐order reaction models for all experimental conditions, the K being removed faster than the P. The rate constants for K and P removal increased as the ratio Al:P increased, but were affected to a lesser extent by the initial concentration of KH2PO4. The concentration of Al with time agreed with a consecutive first‐order reaction model involving cation exchange and precipitation. The rate constants for each experimental condition were evaluated by nonlinear regression analysis, and the reaction model represents the data well. The precipitate (prepared in 0.25 or 1M KH2PO4 solution) was identified as potassium aluminum taranakite by chemical and x‐ray analysis. The phosphate retained in the resin was negligibly small and perhaps was occluded in the beads. Phosphate was removed from solution by the precipitation of taranakite. The taranakite precipitation rate constant, k4, varied directly with the atomic ratio Al:P and inversely with the initial KH2PO4 concentration, Co, by the correlation k4 = 1.09 (Al:P)1.066 (Co)‐0.401.
Determination of Inorganic Sulfate in Foliage with Barium Chloranilate
Authors: Richter D. D. , Johnson D. W.
Published: July 2010

Foliage samples were extracted in 0.01M HCl at room temperature and extracts analyzed indirectly for sulfate (SO2‐4) with a barium chloranilate procedure. The method was tested with foliage of coniferous and deciduous tree species, and sulfate recovery was comparable to that obtained by hydriodic acid reduction. Similar amounts of sulfate were recovered from foliage by both acid and salt extractions, and it was concluded that foliar sulfate in the species tested was inorganic and did not include appreciable amounts of hydrolyzable organic sulfates. The barium chloranilate procedure requires equipment available to most soil and plant analysis laboratories and can be readily applied in evaluating sulfur nutrition in plant‐soil systems.
Simulation of Landsat Multispectral Scanner Response of Soils using Laboratory Reflectance Measurements
Authors: Thompson D. R. , Pitts D. E. , Henderson K. E.
Published: July 2010

Laboratory soil reflectance measurements from surface soil samples representing 246 soil series within 39 of the 48 contiguous states of the USA were used to simulate Landsat MSS (multispectral scanner) digital counts for two atmospheric conditions. The resulting Landsat MSS digital counts were within the range of values for soils seen in Landsat data. The importance of accounting for the soil background in various spectral vegetation indexes is demonstrated. Spectral curve forms for different soils are shown to be generally separable within greenness and brightness vector space for the various reflectance values and simulated Landsat MSS values and atmospheres. Organic matter content could be stratified into 0 to 2 and > 2% with > 80% accuracy. The ability to convert reflectance data from controlled experiments to simulated Landsat MSS digital counts will allow researchers to account for the effect of the soil on crop‐spectral relationships, conduct sensitivity analyses of the effect of soil on spectral models, and to develop a better understanding of the relationship of spectral and physical‐chemical properties of soils and advance the application of remote sensing for soil survey and classification.
A Method for Maintaining Constant Soil Moisture Availability for Potted Plants
Authors: Schwaegerle Kent E.
Published: July 2010

A method was developed to reduce labor time in experiments in which soil moisture is to be periodically adjusted by observed changes in pot weight. In an experiment involving 420 pots of Phlox species, a pair of modified balances was used daily to fill pots with water automatically to a precise weight. To achieve six different levels of soil moisture availability six weights of equal volume were placed in the pots. Pots displayed daily changes in soil moisture of 0.9 to 2.3%. Daily watering of all pots required only 75 to 90 min. This system proved effective for analysis of plant growth response to different soil moisture levels in experiments where statistical considerations demand large sample sizes.
Furrow and Trickle Irrigation: Effects On Soil Oxygen and Ethylene and Tomato Yield
Authors: Meek B. D. , Ehlig C. F. , Stolzy L. H. , Graham L. E.
Published: July 2010

This study was conducted to determine whether low soil oxygen levels or high soil ethylene reduce tomato (Lycopersicon esculentum) yield in clay soil, when high temperatures are combined with trickle or furrow irrigation. Treatments were daily or weekly trickle irrigations (100 or 120% of pan evaporation) and furrow irrigations (5‐ or 10‐d intervals). Soil oxygen and ethylene levels and soil matric potentials were measured at the 20‐ and 40‐cm depths immediately before and during part of the fruiting cycle. Daily trickle irrigations (100 or 120% of pan evaporation) resulted in oxygen levels of 3 to 6% and matric potentials of 0 to −7 kPa. Furrow irrigation or weekly trickle irrigations resulted in oxygen levels that were about double the values measured for the daily trickle irrigation, and in soil matric potentials of −1 to −60 kPa. Irrigation frequency or rate did not have a significant effect on yield of tomatoes. Soil ethylene levels were low for all treatments (< 1 ppm). Because of higher oxygen level, weekly trickle or furrow irrigation would be preferable to daily trickle irrigation when oxygen may be limiting or when the crop grown is oxygen sensitive.
A Method for Estimating the Standard Free Energy of Formation of Borate Minerals
Authors: Mattigod S. V.
Published: July 2010

An empirical method has been developed to estimate the standard free energy of formation (ΔGof,298) values for hydrated borate minerals. The method is completely general, and the only parameter used in the computation is the number of born atoms in the polyanion unit of a mineral. The standard free energy of formation values estimated by this method are within ± 10 kJ of the experimental data obtained from the literature. This method has fewer limitations than the structural method of Bassett.
The Influence of a Microalgal Conditioner on Selected Washington Soils: An Empirical Study
Authors: Metting Blaine , Rayburn William R.
Published: July 2010

Chemical and physical analyses of four Columbia Basin soils were used to evaluate the effects of repeated annual inoculation with the mass cultured microalgal soil conditioner Chlamydomonas mexicana ‘Lewin’. Carbohydrate concentrations were consistently, though not significantly, greater in both the surface 10 mm and in the upper 300 mm of treated portions of a Quincy loamy fine sand, a Quincy loamy sand, and a Warden silt loam compared to untreated portions from the same soil mapping units. Treated soil samples from the two Quincy soils contained from 0.12 to 0.40 g/kg more carbohydrate than did untreated samples, while differences of about 1.0 g/kg of soil were measured in the Warden silt loam. Using locations as replicates, increases in water retention from treatments were significant (0.05% level), ranging from 2 to nearly 5% above untreated soils. Wet sieving of 0.92‐ to 1.68‐mm natural aggregates showed striking differences (significant at 0.1% level) between treated and untreated samples of the three soils. Stability in water was increased from 54.4 to 76.1% for the Quincy loamy fine sand, from 44.5 to 63.4% for the Quincy loamy sand, and from 82.1 to 86.1% for the Warden silt loam. Disruption of natural 0.92‐ to 1.68‐mm aggregates by rotary dry sieving was significantly different (0.05% level) between algal‐treated and untreated samples. Disruption to particles < 0.42 mm was 75.1 and 87.2% of treated and untreated samples, respectively, of Quincy loamy fine sand. Corresponding values for the Quincy loamy sand were 81.3 and 97.6%, and for the Warden silt loam, 60.9 and 78.8%. Moisture is implicated as the factor most likely controlling growth and polysaccharide production by the microalgal inoculum from the fact that differences in these chemical and physical properties could not be measured between treated and untreated samples from a dryland Ritzville silt loam.
Effect of Slope on Water Balance Under Center‐Pivot Irrigation
Authors: Hanna A. Y. , Harlan P. W. , Lewis D. T.
Published: July 2010

The effects of slope on soil water storage and other water balance components under center‐pivot irrigation were studied in Gage County, Nebraska. Soil water, surface runoff, precipitation, and irrigation were measured for soils of low infiltration on slopes of 2, 4, and 8% under corn (Zea mays L.). Evapotranspiration was calculated. Soil water content (0‐ to 137‐cm depth) during the growing season was higher in soils on 8% slopes than in soils on slopes of 2 and 4%. Runoff from all slopes was not associated with sprinkler irrigation in the crop production system studied. As slope increased, surface runoff caused by rain increased, and internal drainage beyond the 137‐cm depth decreased at approximately the same rate. The overall water depletion during the growing season was not significantly affected by slope.
Origin of Red Clay over Dolomite in the Loess‐Covered Wisconsin Driftless Uplands
Authors: Frolking T. A. , Jackson M. L. , Knox J. C.
Published: July 2010

Red clays associated with Prairie du Chien and Sinnipee (Galena) dolomites and loess were studied stratigraphically and geomorphically at 10 locations. The clay content (< 2 µm, 82 ± 9.1%; < 0.2 µm, 70 ± 10.4%, n = 15) relative to the overlying loess (< 2 µm, 28 ± 4.4%; < 0.2 µm, 16 ± 4.9, n = 4) and the dolomite insolubles (< 2 µm, 47 ± 11%; < 0.2 µm, 34 ± 9.6%, n = 7) indicate fine clay enrichment. Smectite‐rich oriented clay coatings on dolomite sands suggest illuviation. Undisturbed chertlines from dolomite through red clay bodies necessitate a volume‐for‐volume replacement. Periglacial activity during the Wisconsinan frequently produced loess (i), over a mixed zone of loess and red clay (ii), over in‐situ red clay (iii), and dolomite (iv). For the 1‐to 10µm quartz; euhedral grains indicated by x‐ray diffraction I(100)/(101) = 0.23, 0.54, 1.02, 0.70, respectively; nine trace element contents = 2.15 ± 0.40, 1.61 ± 0.18, 0.78 ± 0.10 relative to dolomite (1.0); and oxygen isotopes expressed as δ18O = 18.6, 19.7, 26.9, 26.4%. The values for the mixed zone (ii) fall between those for the loess (i) and insitu red clay (iii). Optical data for the morphology of the fine sand fractions (50–250 µm) were corroborative. The silt and sand of in‐situ red clay (protected in karst depressions and by chert lag gravels) are from the dolomite.
Mineralogy and Acidity of an Inland Acid Sulfate Soil of Texas
Authors: Carson C. D. , Dixon J. B.
Published: July 2010

The Aubrey soil occurs in the East Cross Timbers Region of north‐central Texas. It has developed in an acid clayey shale of the Lewisville member of the Woodbine geologic formation of Upper Cretaceous age. Jarosite [KFe3(OH)6(SO4)2] occurs in localized concentrations in the lower horizons. Selected particles form the C horizon were 87.6% jarosite and served as a reference mineral for the soil. Jarosite content of the B3 and C horizons was 1.6 to 6.7% and was detectable by thermal and x‐ray diffraction analyses of the whole soil. Scanning electron microscope examination indicated that the jarosite occurred as cubes and octahedra. These isometric forms suggest jarosite formation from pyrite present in the parent material. Smectite and kaolinite are the major clay constituents and they are both more poorly crystalline in the major A and B horizons than in the lower three horizons. The pH in water ranges from 5.0 in the upper B horizon at the 8‐cm depth to 4.0 in the C horizon to the 152‐cm depth. Exchangeable and nonexchangeable acidity increase with depth into the C horizon. The Aubrey soil has developed an accumulation of free Fe oxides above the jarosite zone, which is characteristic of an acid sulfate soil.
Distribution of Silica, Sesquioxides, and Clay in Quebec Podzolic Soils and Their Effects on Subsoil Cementation
Authors: De Kimpe C. R. , Laverdiere M. R. , Dejou J.
Published: July 2010

Three soil profiles containing two types of brittle horizons were extracted using citrate‐hicarbonate‐dithionite (CBD), a modified CBD, and NaOH procedures. The modified CBD method with a low soil‐solution ratio was the most effective extractant for Fe, Al, and, especially, Si. Increases in extractable Si could be associated with the presence of a fragipan‐duripan intergrade horizon, but a similar relationship was not observed with a well‐expressed fragipan.