bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate Reduction to Ammonium in Anaerobic Soil
Authors: Buresh R. J. , Patrick W. H.
Published: July 2010

Knowledge regarding the pathway and soil conditions necessary for NO3‐ Conversion to NH4+ and organic N, a process which conserves soil N, is limited. The influence of rice straw (2.5 mg C/g soil), methanol (1.0 mg C/g soil), and glucose (1.0 mg C/g soil) on the fate of 100 µg/g 15N‐labelled NO3‐‐N was studied in Crowley silt loam. The fraction of the added NO3‐‐N in the NO3‐, N2, NH4+, and organic N forms was determined after 4‐day incubations under an Ar atmosphere at 30°C. In glucose‐amended soil 9 and 19% of the applied NO3‐‐N was recovered as NH4+‐N and organic N, respectively. A 1‐day preincubation with glucose (0.5 mg C/g soil) before the 4‐day incubation with added NO3‐ and glucose increased labelled NH4+‐N and organic N recovery to 36 and 34% of the added NO3‐‐N, respectively. The corresponding values for rice straw‐ and methanol‐treated soil and soil containing no added energy source were each less than 5%.

Nitrate‐N reduction to NH4+‐N increased to 20.5% after a 4‐day incubation when soil with no C amendment was incubated under Ar for 20 days before NO3‐ addition. The redox potential was −260 mV upon NO3‐ addition

Transformation of significant amounts of NO3‐ to NH4+ and organic N required intensely reduced soil conditions. The reaction was apparently not suppressed by NH4+. Evidence indicated that NO3‐ was reduced to NH4+ by a nonassimilatory pathway in which NO3‐ functioned as a terminal electron acceptor.
Effects of Heating on Some Changes in Soil Properties in Relation to an Ethiopian Land Management Practice
Authors: Sertsu Sahle M. , Sánchez Pedro A.
Published: July 2010

The physical, chemical, and mineralogical changes resulting from heating three soils up to 600° C for 48 hours were determined in the laboratory in an attempt to explain the effects of the “guie” (soil burning) practice common of Ethiopia. Heating to 200° C did not affect soil color, particle size distribution or clay mineralogy. Heating to 400 and 600° C changed colors to redder hues, the textures from clayey to sandy, produced the collapse of layer‐silicate clay minerals and probably fused clay particles into sand‐sized particles. Organic C started to decompose between 100 and 200° C and was essentially eliminated at 400° C. Total N decreased by half at 400 and 600° C. Ammonium nitrogen increased sharply at 200° C heating but decreased at higher temperatures. Soil pH values increased with heating temperature in acid soils but decreased in the alkaline soil up to 400° C. Changes in exchangeable Ca, Mg, K, Al, and available Fe, Mn, Cu, and Zn varied with soil properties. The most pronounced chemical change was a marked increase in available P in all soils when heated at 200° C or above. Although the different layers in the “guie” heaps are heated to different temperatures, the main beneficial effect of heating in the amorphous Ethiopian soils seems related to increases in available NH4+‐N and P at temperatures low enough to prevent drastic changes in particle size distribution or organic matter content.
Morphology of Discontinuous Phase Plinthite and Criteria for its Field Identification in the Southeastern United States
Authors: Daniels R. B. , Perkins H. F. , Hajek B. F. , Gamble E. E.
Published: July 2010

Plinthite is defined in Soil Taxonomy as an iron‐rich material that hardens on repeated wetting and drying, especially when exposed to the sun. Many morphologically similar materials rich in iron oxides do not harden on repeated wetting and drying and are misidentified as plinthite. We propose that the following field‐tested criteria be used to distinguish plinthite from similar materials that will not harden and from material that has already irreversibly hardened. Plinthite has a color range from 10R to the 7.5 YR hues. It occurs as discrete bodies > 2 mm that can be separated from the matrix. It is firm when moist and hard to very hard when dry, yet it can be broken in the hands. A moist body of plinthite withstands moderate rolling between the thumb and forefinger, and either moist or air dry it will not slake when submerged in water even with periodic gentle agitation.

Plinthite has platy and nodular forms. Platy plinthite bodies are red to yellowish red or strong brown about 1 cm thick and 2 to 4 cm long. They commmonly have a horizontal orientation. Nodular plinthite bodies have a similar color range but have an irregular to spherical shape. A horizon with about 10% platy plinthite will perch water. Horizons with nodular plinthite do not perch water, but the underlying reticulately mottled zone is a restrictive horizon that perches water. It is suggested that platy plinthite forms on level landscapes with a freely fluctuating water table. Nodular plinthite apparently forms on more sloping landscapes where lateral movement of water above a restrictive horizon is a contributing factor.
Size Distribution of Eroded Material From Simulated Rainfall: Effect Over a Range of Texture
Authors: Gabriels D. , Moldenhauer W. C.
Published: July 2010

Size distribution of eroded materials has implications in deposition mechanics and in carrying capacity for pollutant materials. Dispersed clay stays in suspension virtually as long as water is moving. This dispersed clay, especially the expanding lattice types, has a high carrying capacity for pollutant materials. The aggregated materials high in clay settle according to their size and density. Their carrying capacity for pollutants is assumed to be much greater than that of single‐grained materials of the same size. Studies of the carrying capacities of the various sizes and compositions of aggregates are in progress. The present study reports size distributions and composition of material detached by water drops and transported in shallow flow.

The size distributions of aggregates and primary particles in the splashed, washed, and seal material at different times during a laboratory simulated rainfall were compared for different textured soils. The wash had more finer material than did the splash. The wash and splash material at equilibrium were not different from the original soil, while the seal of all soils had a larger silt content than the original soils. The silt loam soil had seals with about the same clay content as the original soil, while silty clay soils had seals with less clay than the original soils.

Of significance from this study is the low percentage of dispersed clay being eroded compared to the percent of clay in the original soil and that this percentage didn't change significantly with time. The most striking differences were between soils and these were influenced mainly by texture and aggregate condition of the original soils.
Effects of Nitrogen and Phosphorus Additions on Deciduous Litter Decomposition
Authors: Kelly J. M. , Henderson G. S.
Published: July 2010

Urea and concentrated superphosphate were applied to plots in a deciduous forest to examine their effects on decomposition of white oak leaves (Quercus alba L.) in litter bags and the associated populations of decomposer organisms. Urea applications decreased soil invertebrate populations by about 30% and caused a three‐ to four‐fold increase in bacterial populations while increasing decomposition rates by 1 and 3% at the 550 and 1,100 kg/ha N levels, respectively. Superphosphate additions caused bacterial populations to decrease by 30% at the highest addition rate and decreased decomposition by 4 and 6% at the 275 and 550 kg/ha P rates, respectively. Soil acidity changes following fertilizer additions appear to be primarily responsible for observed results although longer‐term changes in decomposition may be associated with changes in the nutrient status of the forest floor.
Adaptation of the Soxhlet Extractor for Pedologic Studies
Authors: Singleton G. A. , Lavkulich L. M.
Published: July 2010

The use of the soxhlet apparatus has had limited success in its application to pedogenic weathering studies. Modified designs of the original soxhlet eliminated problems of sample inundation, erosion, and leachate contamination. The modifications, which utilized extraction thimbles, were made either by reducing the height (A) or completely removing (B) the siphon tube. B‐modified extractors increased Ca extractability of a soil material from the original 50 ppm to 210 ppm compared to an increase to 125 ppm in the unmodified apparatus. Use of a CO2 atmosphere in modification A caused rapid change in reaction of the material from the initial pH 5.1 to 4.5 compared to pH 6.1 in unmodified units. The use of these modified soxhlets showed promise in simulating pedogenic processes.
Water and Salt Movement in Unsaturated Frozen Soil: Principles and Field Observations
Authors: Cary J. W. , Papendick R. I. , Campbell G. S.
Published: July 2010

Soil temperatures, electrical conductivities, and water redistribution were measured at four field sites during a 30‐day period in which the soil was never completely thawed. The soil on each site was a silt loam with varying aspects and vegetation covers. Both upward and downward flow of water and solutes were observed. Assuming that liquid water flow in frozen soil is analogous to unsaturated liquid flow in unfrozen soil, led to a simple equation that in general agreed with the field observations. The equation requires knowledge of the soil temperatures, the solute concentrations, and two constants that characterize the soil's water release curve and saturated hydraulic conductivity.

Infiltration and frost heaving are discussed with respect to this simple theory. Water in frozen soil flows from high to low temperatures and from high to low salt concentrations. Consequently, solutes in even very low salt soils are important in decreasing frost heave and increasing infiltration. The liquid flow is so closely coupled with temperature that heat flow must be considered simultaneously in any comprehensive analysis. This coupling, as expressed in the simple liquid flow equation, accounts for the effect of soil water content on frost heave rates and the effects of temperature on maximum heaving pressures.
A Drainage Model for a Reclaimed Surface Mine
Authors: Prunty Lyle , Kirkham Don
Published: July 2010

Stripmine reclamation for row‐crop production employing bench‐terraced geometry is under study and may become increasingly common. A simplified model of the postreclamation soil profile at the Iowa Coal Project Demonstration Mine No. I is created. The model is used to find the steady‐state water‐table shape if one tube drain per terrace is installed. Dupuit‐Forchheimer (D. F.) theory is used for the analyses. Water‐table curves are generated for a series of alternative drain‐tube locations. An analysis is made to find the best position for the drain tube. It is found that, for a recharge‐to‐soil‐conductivity ratio of 0.01 for terraces repeating at a 45.7‐m (150‐ft) interval, the best drain‐tube location is beneath the horizontal portion of the terrace 4.87 m (16 ft) from the toe of the backslope if the drain tubes are placed 2.44 m (8 ft) beneath the surface of soil underlaid by a barrier at 3.05 m (10 ft) depth. The horizontal portion of the bench terraces is 38.08 m (125 ft), and the vertical drop from one terrace to the next is 3.05 m (10 ft). A table of best drain locations is given for other drain depths and recharge rates. Previous work on D.F. theory for a uniformly sloped barrier is discussed briefly and compared with and contrasted to the present work for a barrier that parallels the bench‐terraced surface of the reclaimed surface mine.
Adsorption and Desorption of Sulfate and Charge Relationships in Allophanic Clays
Authors: Rajan S. S. S.
Published: July 2010

Sulfate adsorption by a synthetic and a natural allophane increased with increasing solution concentration. Initially both the materials had net positive charges. With the progressive adsorption of sulfate the positive charges were neutralized, followed by increases in the negative charges. Sulfate adsorption released OH‐ into the solution and linear relationships were obtained between the two parameters. Very little Si was released on sulfate adsorption. From the relationships between the various parameters studied it is proposed that on a net positive surface sulfate is adsorbed as a bidentate forming a six‐membered ring, displacing either two aquo or hydroxyl ligands. On a neutral or a negative surface sulfate is adsorbed as a monodentate displacing one aquo or one hydroxyl ligand and this makes the surface more negative.

The desorption studies showed that aquo and hydroxyl ligands from the solution exchanged with the sulfate on the surface and, depending on the surface charge, a 1:1 or 1:2 stoichiometry apparently exists between the moles of sulfate desorbed and the ligands adsorbed. Irrespective of the initial concentration of sulfate on the clay surface the amount left on the surface after desorption was about the same.
Organic Carbon Determination by the Walkley‐Black and Dry Combustion Methods in Surface Soils and Andept Profiles from Costa Rica
Authors: Bornemisza E. , Constenla M. , Alvarado A. , Ortega E. J. , Vasquez A. J.
Published: July 2010

The efficiency of oxidation of organic C by the Walkley‐Black method was studied by comparing with determinations using dry combustion equipment and gravimetric determination for the evolved CO2. Fifty surface soils (0–30 cm) were studied, in groups of 10, each one belonging to one of the following taxonomic suborders: Fluvents, Andepts, Tropepts, Udults, and Ustults. Samples from 17 Andept profiles were also analysed to study changes of oxidation efficiency with depth.

The results for the surface samples indicated that the commonly used conversion factor was somewhat too small. It is recommended that 75% oxidation be used as the base for conversion to total C, as 86% of the studied samples deviated in < 2% from this value.

It was observed that the organic matter in the deeper horizons is more easily oxidized through the Walkley‐Black procedure, perhaps because plant residues are less abundant and there is an accumulation of fulvic acids. In some cases the oxidation is almost complete. This oxidation is rather variable and it was not correlated with the texture or pH of these soils. It is believed that the extent of oxidizability can allow conclusions on the relative age of horizons in Andept profiles and indicates the presence of buried horizons.
Decomposition and Stabilization of Ring‐14C‐Labeled Catechol in Soil
Authors: Martin J. P. , Haider K. , Linhares L. F.
Published: July 2010

Decomposition percentages for ring‐14C‐labeled catechol and coumaryl alcohol and anisic acid for comparison over a 12‐week incubation period at 1000 ppm in Greenfield sandy loam (pH 7.0) were 20, 50, and 75, respectively. When linked into model humic acid type polymers carbon losses were 10% for a catechol only polymer and 5 to 7% for polymers containing 17 additional phenolic units. In Chino loam (pH 5.6) losses of catechol carbons were about 28% at concentrations ranging from 1 to 10,000 ppm. In San Jacinto loam (pH 8.0) losses were 6% for the 1 ppm addition and 14% for concentrations of 10 to 10,000 ppm. When the soil was initially sterilized and reinoculated from 14 (1 ppm) to 50 (1,000 ppm) % of the C was evolved as CO2 from the acid soil and about 10% was lost from all concentrations in the alkaline soil. After 1 week only a trace to 12% of the added catechol could be recovered by soil extraction. Under sterile conditions 6 and 90%, respectively, could be extracted from the alkaline and acid soils. After 5 weeks a small amount of catechol was still present in the sterile acid and neutral soils and in addition 8 other phenolic compounds could be separated by TLC. About 50% of the catechol present in model humic acid reaction mixtures was recovered in polymer form when phenolase was used as a catalyst. Over 90% was recovered when peroxidase was used. The study indicates that the apparent high stability of catechol in soil is caused by a rapid polymerization into phenolic polymers or into existing soil phenolic polymers brought about by the action of existing phenolase enzymes in the soil, by phenolases associated with living organisms, and by autoxidation.
Direct Measurement of Denitrification Loss from Soils: II. Development and Application of Field Methods
Authors: Ryden J. C. , Lund L. J. , Letey J. , Focht D. D.
Published: July 2010

A method was developed for the direct measurement of denitrification N loss from field soils. The method was based on the observation that in the presence of acetylene (C2H2) concentrations of 0.1 to 5.0% (vol/vol) the sole product of denitrification in soils was nitrous oxide (N2O). Sustained C2H2 concentrations of approximately 0.4 to 1.6% were induced in the atmosphere of a field soil by supplying C2H2 through probes inserted into the soil to a depth of 1 m. The time required to establish these C2H2 concentrations ranged from 15 to 30 min. The concentrations could be maintained for at least 17 hours during which C2H2 was supplied at 2.8 liters/hour. Essentially, no increase in 30N2 concentration was detected under closed soil covers installed at C2H2‐treated field locations which had received 15N‐NO3. At locations without C2H2 treatment an average 30N2 enrichment of 14.2% relative to air was observed. Production of 15N‐labeled N2O and N2 at locations with and without C2H2 treatment was very similar, and essentially 100% of the 15N evolved at C2H2‐treated locations appeared as N2O. Direct measurements of N2O fluxes from an irrigated, fertilized Haploxeroll at locations with and without C2H2 treatment were made using a previously established method. Net denitrification N fluxes, measured as N2O flux from C2H2‐treated locations ranged from 0.5 to 80 g N/ha per hour. Peak N fluxes were between 30 and 80 g N/ha per hour and usually occurred 30 to 60 hours after irrigation had ceased. Total denitrification loss during 123 days was 51.2 kg N/ha with the total fertilizer application being 335 kg N/ha. Dinitrogen/nitrous oxide ratios, determined from the difference in N2O evolution at sites with and without C2H2 treatment, ranged from 0 to 1 during the first 12 to 24 hours of each denitrification cycle after which the ratio gradually increased to values of 10 to 20 towards the end of each cycle. The average value was between 5.6 and 7.4. The methodology provides a technique for direct monitoring of denitrification N loss in situ.
The Effect of Extractable Aluminum, Iron, and Silicon on Strength and Bonding of Fragipans of Northeastern Ohio
Authors: Hallmark C. T. , Smeck N. E.
Published: July 2010

Pyrophosphate, oxalate, and HCl‐acetylacetone extractions for Al, Fe, and Si were made on five soils with fragipans (Aeric Fragiaqualfs and an Aquic Fragiudalf) and two soils without fragipans (Aeric Ochraqualfs) from Ohio to evaluate the role of amorphous components in effecting bonding between soil particles of fragipans. The distribution of Al extractable in HCl‐acetylacetone was found to coincide with the position of the fragipan and correlated positively at the 0.01 level with rupture strengths which are indicative of fragipan development. Rupture strengths of soil disks from fragipans were shown to decrease following treatment with HCl‐acetylacetone as compared to water treatment alone confirming the removal of a bonding phase in the fragipan by HCl‐acetylacetone. Although a number of features of fragipans are inherited from the parent material, evidence suggests precipitation of an amorphous phase at contact points between soil particles which imparts strength and brittleness observed in fragipans.
Soil Changes Resulting From Long‐term Management Practices in Western Nigeria
Authors: Aina P. O.
Published: July 2010

Two soils at the University of Ife (Nigeria) research farm were evaluated for their physical and chemical properties under long‐term pasture, bush fallow, and arable cultivation that involved three tillage techniques and two fertility levels. The cultivated plots were adjacent to the fallow plots, which were at least 1/2 ha in size. Differences in soil properties between fallow and cultivated soils were considered to be due to soil changes resulting from continuous cropping.

The percentage of water stable aggregates (> 2.36 mm) in the 0‐ to 15‐cm soil depth was highest and more stable under fallow than under bush. Stability values were 95 and 80%, respectively, under grass and bush. About 76% and 80% of these aggregates were destroyed after 5 years of continuous cropping, and 88% after 10 years. Aggregate stability of the cultivated soils ranged from one‐fifth to one‐third those of fallow soils. The average bulk densities were 1.24 and 1.52 g/cm3 for fallow and cultivated soils, respectively, while the reductions in porosity and saturated hydraulic conductivity were more than proportionate to the increases in bulk density of the cultivated soils. The fallow soils were about four‐times higher in organic matter than the cultivated soils, which had an average organic matter content of 0.8%. The fallow soils were also higher in nitrate‐nitrogen, exchangeable bases, and CEC than the cultivated soils.

Soil deterioration in decreasing order was: Plow‐disk‐harrow > plow > no‐tilage. Fertilizer treatments had no efect on soil deterioration after 10 years of continuous cropping.
A Rupture Technique to Determine Fragipan Strength
Authors: Hallmark C. T. , Smeck N. E.
Published: July 2010

A method is presented to evaluate the strength of fragipans based upon the rupture of 1.2 cm thick disks cut from air dry soil cores. Rupture values abruptly increase in the fragipan as compared to overlying horizons and decrease with depth in the lower B3 and C horizons. Rupture strength measurements may prove valuable in objectively assessing fragipan development and its subsequent influence on water movement and root penetration.
The Mitigating Effect of Residual Fertilizer Copper on the Decomposition of an Organic Soil in Situ
Authors: Mathur S. P. , Hamilton H. A. , Levesque M. P.
Published: July 2010

The recently reported inhibitory effect of Cu on the in vitro decomposition of some organic soils was examined under field conditions.

The 2‐ha field studied has been cultivated for 45 years Within this field, the extent of humification, and pH vary little among the 114 sites examined. Since Cu was applied for the last 15 years almost exclusively to a distinct area along the short axis of the field, total and extractable Cu contents were found to decrease twofold from this band to the remainder of the field. Evolution of CO2 from 15 sites on this field was found to carry 16 to 52 g of C from each square meter of soil surface in a period of 40 days in summer. Carbon loss from this field did not correlate significantly with soil moisture or ash contents. The rate of CO2 evolution, however, significantly (1% level) negatively correlated with both the total and extractable Cu contents. Acid phosphatase activity also fell sharply as Cu content increased. The possibility of using Cu (<100 kg/ha) for mitigating the subsidence of some organic soils is discussed.
Calculation of Saturated Hydraulic Conductivity of Some Pedal Clay Soils Using Micromorphometric Data
Authors: Bouma J. , Jongerius A. , Schoonderbeek D.
Published: July 2010

The saturated hydraulic conductivity (Ksat) was calculated for undisturbed freeze‐dried samples of seven clay soils, by using micromorphometric Quantimet data. Voids were characterized in terms of quantity (number and length), type and directly measured size. Methylene blue was used to indicate flow patterns. A statistical planar and tubular void‐interaction model was used to estimate sizes of “necks” in the flow system, which were assumed to determine Ksat. Measured Ksat values were within the calculated Ksat range, when relatively large, vertically continuous tubular voids were not present. Very small variations of the width of planar “necks” had a strong effect on the magnitude of Ksat. Soil which was moist when sampled had larger planar “necks” and higher Ksat values than soil which had been in wet condition for several months. This difference was attributed to the effects of soil swelling. In general, volumetric percentages of active (stained) voids (estimated by % surface area) were <1. This illustrates the basic difficulty of estimating Ksat in clay soils by methods which use relative volumes of voids.
Nitrate Leaching in a Sludge‐Treated Forest Soil
Authors: Sidle R. C. , Kardos L. T.
Published: July 2010

Anaerobically digested liquid sludge was applied during two separate periods to plots in a mixed hardwood forest. High treatment plots received 26.96 metric tons/ha total solids and 3,034 kg/ha N loadings during the two applications, and low treatment plots received approximately half these loadings. Percolate samples collected at the 15‐cm depth contained a maximum of 290 mg/liter NO3‐‐N in the high treatment and 194 mg/liter NO3‐‐N in the low treatment. Maximum monthly levels of NO3‐‐N in percolate sampled at the 120‐cm depth lagged 6 months behind peak levels at the 15‐cm depth. Calculated average active transmitting soil porosity (Pact), based on field water budget data over this 6‐month period, ranged from 15 to 22%. A CSMP computer simulation model based on a solution to the convection diffusion equation estimated the average Pact to be 15%. Since these data indicate that 27 to 50% of the pores may be stagnant, this suggests that soluble NO3‐‐N was being channeled through interconnected macropores in the soil profile.
Comparative Effectiveness of Fourteen Solutions for Extracting Arsenic from Four Western New York Soils
Authors: Johnston Steven E. , Barnard Walther M.
Published: July 2010

Four western New York soils differing in soil type and land use were subjected to (i) extraction of As by 14 solutions for soil‐solvent mixtures shaken for 1, 3, 7, and 18 hours; (ii) a sequential extraction with solvents designed to identify water soluble‐As (Ws‐As) and As associated with Al (Al‐As), Fe (Fe‐As), and Ca (Ca‐As); and (iii) a hot HNO3‐H2SO4 digestion to determine “total” As. Arsenic was determined by atomic absorption spectrophotometry employing arsine generation.

In each soil sample the sequential extraction demonstrated that Fe‐As >> Ca‐As > Al‐As > Ws‐As; the total amount removed by the sequential extraction was only 34 to 41% of the total As in three low As (15.0 to 16.4 µg/g As) soil samples and 98% in a lead arsenate‐sprayed orchard sample containing 52.1 µg/g As.

Deionized distilled water, 1N NH4Cl, and 0.5M solutions of CH3COONH4 (“NH4Ac”), NH4NO3, and (NH4)2CO3 generally removed < 0.1 µg/g As from the soils. For the more effective solvents, the amount of As extracted increased with shaking time but an 18‐hour shake never exceeded 80% of that extracted sequentially for any sample. The relative effectiveness of the basic solutions in removing As was in the order of 0.5M NH4F ≈ 0.5M NaHCO3 < 0.5M (NH4)2CO3 < 0.5M Na2CO3 < 0.1M NaOH; for acid solutions the order was 0.05N HCl + 0.025N H2SO4 ≈ 0.5M HCl < 0.5M KH2PO4 < 0.5N H2SO4.

Arsenic extraction data obtained in this study are consistent with the view that P and As react similarly in solutions containing acetate, sulfate, fluoride, bicarbonate, hydroxide, and hydrogen ions.
Water‐Dispersible Soil Organic‐Mineral Particles: I. Carbon and Nitrogen Distribution
Authors: Young J. L. , Spycher G.
Published: July 2010

Water‐dispersible particles from six epipedons and one Bh horizon representing six different soil orders were separated into sand, silt, and clay particles, and the clay‐organic particles were further fractionated by density. Organic C and N concentrations were lowest in sand, intermediate in silt, and highest in clay, but exceptions to this trend were observed and accounted for. Light clay‐size, organo‐mineral particles had (i) high levels of sorbed organic C; (ii) wide C/N ratios; and (iii) low amounts of alkali‐extractable C. The reverse was true for heavy clay‐size particles. A continuum of particle compositions existed between the density extremes which differ for different soils. The heterogeneity of clay‐size particles can be explained in terms of their position within the soil fabric: Light particles evolve at the surfaces of (micro‐) aggregates and are exposed to the soil biosphere, whereas heavy particles occupy intra‐aggregate space shielded from the soil biosphere.
A Simple Textural Index for Assessing Chemical Weathering in Soils
Authors: Torrent Jose , Nettleton W. D.
Published: July 2010

Chemical weathering affects the particle size distribution of soils, but little use has been made of this fact other than the inferences of increased chemical weathering generally made from increase in clay content. We postulated a simple model for assessing chemical weathering from particle size distribution. In the model, we assumed that a rind tends to peel‐off a mineral when the mineral is under attack by an advancing weathering front parallel to its surface. Using the model, we calculated theoretical particle size variations of some loessial soils. The calculations, as expected, showed that fine fractions (< 50 µm) are much more affected by chemical weathering than are coarse fractions (> 50 µm). We concluded from this that silt fractions may be used for assessing chemical weathering, but if they must be used for assessing uniformity of parent material, they should be used advisedly.

We applied our model to 161 loessial soils of the Mississippi Valley, all having udic or aquic moisture regimes. We used the fine‐silt/total‐silt ratio trend for the upper part of the solum as a weathering index. The index correlates with mean annual temperature (r = 0.70) which in humid regions is assumed to be the main factor involved in the chemical weathering of soils. Although our index is not universally applicable, it may help in comparing the weathering status of soils developed on similar parent materials.
Irrigation Water Conservation Using Wide‐spaced Furrows
Authors: Stone J. F. , Garton J. E. , Webb B. B. , Reeves H. E. , Keflemariam J.
Published: July 2010

Furrow irrigation studies comparing water applications to narrow and wide‐spaced furrows were conducted on three crops at thee locations in Oklahoma over eight growing seasons. Wide‐spaced‐furrow irrigation usually required about half the water of narrow spacing. In 9 of 11 studies, no yield reductions were noted. In the seasons where yield reductions were noted, the atmospheric evaporative demand was high. A simple test was devised to indicate if a season in progress shows high atmospheric demand. The evaporative demand test involves measurement of rainfall and daily wind movement. Using standard National Weather Service instruments, daily average of rain > 1.6 mm between 15 July and 31 Aug. combined with daily wind movement < 155 km in August caused no yield reduction in wide‐spaced‐furrow irrigation. Wind was measured at the standard height of a “Class A” evaporation pan (51 cm). Conservation of water from wide‐spaced‐furrow irrigation should be possible on medium to fine textured soils in many semiarid regions of the world.
Carbon Cycling During Sewage Sludge Decomposition in Soils
Authors: Terry R. E. , Nelson D. W. , Sommers L. E.
Published: July 2010

The objectives of this study were to determine the extent and kinetics of sludge decomposition in soil, to evaluate the effects of sludge addition on microbial degradation of soil organic matter, and to determine the distribution of residual sludge organic C in soil organic matter fractions. Synthetic sewage sludge was prepared by anaerobically digesting a mixture of 14C‐labelled Candida utilis cells and inorganic salts. The prepared sludge had a composition which was similar to that of many anaerobically‐digested municipal sludges. Synthetic sludge was added to soils and 14CO3 activity and CO2 production were measured periodically during 336 days of incubation. At the end of incubation, the distribution of residual 14C in soil organic matter fractions was determined. Sludge decomposition was rapid during the first 28 days of incubation and then decreased to a slower, nearly constant rate for the remainder of the period. At the end of 336 days of incubation, 46% of synthetic sludge organic 14C was evolved as CO2. In comparison, 26 to 42% of added organic C was apparently evolved as CO2 from soils treated with municipal sludges and incubated for 130 days. These findings suggest that a fraction of anaerobically‐digested sludge was readily decompossible when added to an aerobic soil; however, the major portion of sludge organic matter (55 to 80%) was resistant to decomposition. There was a linear relationship between cumulative 14CO2 evolution and the log of incubation time. From this relationship the turnover time of synthetic sludge in soil was calculated to range from 343 to 890 years. Decomposition of sludge in soil increased the degradation of native soil organic matter by approximately 100% over a period of 336 days. At the end of 168 days of incubation, 62% of the residual sludge organic 14C added in sludge was recovered from soils as humic and fulvic acids.
Soil‐Landscape Relationships of the Tidal Marshes of Maryland
Authors: Darmody R. G. , Foss J. E.
Published: July 2010

A study was conducted to investigate and model the soil‐landscape relationships represented in the 87,000 ha of tidal marsh in Maryland. Models are presented for three physiographic marsh landscapes: Coastal, Estuarine, and Submerged Upland. Coastal marshes, about 8% of the total marsh area, have formed in the lagoons behind coastal barrier islands. The associated soils are primarily Sulfaquents and Sulfihemists. Estuarine marshes, 38% of the total, have formed from recent accumulation of sediments in stream channels and estuarine meanders. The majority of the associated soils are Sulfaquents, Sulfihemists, and Hydraquents. Submerged Upland marshes are the most extensive, covering an estimated 54% of the total. These marshes have formed as a result of the inundation of low‐lying uplands by rising sea level. It appears that the soils were formerly Aquults and, because of submergence, they have become Histic Halaqualfs (proposed) and Sulfihemists.
Physical, Chemical, and Mineralogical Characteristics of Soils from Volcanic Ash in Northern Idaho: I. Morphology and Genesis
Authors: Fosberg M. A. , Falen A. L. , Jones J. P. , Singh B. B.
Published: July 2010

Mission soils, coarse‐silty, mixed, frigid Andic Fragiochrepts, are representative of volcanic ash soils found extensively in northern Idaho, northeastern Washington, and northwestern Montana. They have developed under a western hemlock (Tusuga heterophylla) habitat type with 740 mm of precipitation, > 8°C mean summer soil temperature and 7.5°C mean annual soil temperature (weather data, Univ. of Idaho. Res. Stn., Sandpoint). The B2ir or cambic horizons have developed from volcanic ash and the underlying IIA'&B' and IIB'2x horizons have fragipans developed in glacial outwash sediments. Horizons from volcanic ash have higher values of estimated allophane, organic C, extractable Fe, Al, and Mn, exchangeable H, 1/3‐ and 15‐bar moisture, and CEC than do underlying horizons. Bulk densities range from 0.80 to 0.90 in volcanic ash horizons compared with 1.41 to 1.65 for glacial sediments. X‐ray patterns show little indication of crystalline minerals in the ash‐related horizons. Concretions have greater contents of Mn and Fe whereas Al remains relatively constant in relation to the total soil. Development of a B2ir, without an Al horizon under the O horizon, is characteristic of soils associated with these climatic and vegetational zones. Diagnostic properties make the cambic gradational to a spodic horizon.
Influence of Weed Growth and Tillage Interval During Fallow on Water Storage, Soil Nitrates, and Yield
Authors: Lavake D. E. , Wiese A. F.
Published: July 2010

In an effort to minimize tillage operations and production costs five sweep tillage intervals were evaluated for 7 years during the two 11‐month fallow periods in a winter wheat (Triticum aestivum L. ‘Tascosa’)‐sorghum (Sorghum bicolor (L.) Moench) cropping sequence. The tillage intervals ranged from very short or once every 2 weeks to as long as 24 days after weed emergence. Their effect on soil water storage, soil NO3‐N level and crop yield were determined on Pullman clay loam in the Southern Great Plains.

Delaying tillage for 17 and 24 days after weed emergence reduced available soil water in the top 120 cm of soil.

Average NOa‐N content in the top 120 cm of soil decreased from over 185 kg/ha with sweep tillage at 2‐week intervals to 56 kg/ha when sweep tillage was delayed until 24 days after weed emergence.

Average wheat yields were not reduced when sweep tillage was performed 17 days after weed emergence, however they were reduced when tillage was delayed until 24 days after weed emergence. Average sorghum yields were not reduced when tillage was delayed 10 days after weed emergence. Delaying tillage to 17 days after weed emergence cut sorghum yield. Most farmers till about 4 to 10 days after weed emergence. Delaying tillage as much as possible as indicated in this trial will eliminate on or two tillage operations in an 11‐month fallow period.
Correlation of Soil Plasticity with Amorphous Clay Constituents
Authors: McNabb D. H.
Published: July 2010

The percentage of amorphous constituents removed from the clay size fraction of western Oregon soils by kinetic dissolution was significantly correlated with soil plasticity. Soil plasticity was identified by the plasticity angle which was defined by the angle, relative to the ‘A’ line intercept, where the Atterberg limits of air‐dried soil occurred on the Casagrande plasticity chart. An exponential correlation between the plasticity angle and the sum of the amorphous Al2O3 and SiO2 was more significant than between the plasticity angle and the sum of the amorphous Al2O3, SiO2, and Fe2O3 (r2 = 0.88** and 0.76**, respectively).

The Atterberg limits of the soil were not directly correlated with the percentage of amorphous constituents.
A Critical Evaluation of the Extension of Zero Point of Charge (ZPC) Theory to Soil Systems
Authors: Parker J. C. , Zelazny L. W. , Sampath S. , Harris W. G.
Published: July 2010

The points of zero salt effect (PZSE) of surface and subsurface horizons of soils ranging from an Hapludoll to a Paleudult were obtained from batch titrations in CaCl2 solutions with and without prior Ca saturation and in NaCl solutions following Na saturation. PZSE's of Na‐saturated samples equilibrated for 1 hour were generally between pH 2 and 3, while those of Na‐ or Ca‐saturated samples or unwashed samples equilibrated for 2 days were generally between 3 and 4. The effect of equilibration time was attributed to gradual sample decomposition accompanied by conversion of Na‐saturated soil to an Al‐Na‐system.

Points of zero net charge (PZNC) were evaluated by measurement of Ca and Cl adsorption at various pH levels. No net charge reversal from negative to positive was found to occur above pH 2.0. This discrepancy between PZSE and PZNC was attributed to specific adsorption of cations, H+ exchange with counterions associated with permanent charge sites and other reactions of H+ or OH‐ which did not result in a change in surface charge. From 30–90% of the H+ or OH‐ lost from solution during titration did not create an equivalent change in surface charge. Exchange reactions and reaction of H+ with Al and Fe in various forms are implicated in this regard. It is suggested that the use of potentiometric titrations for the estimation of electrochemical properties of soils regarded with considerable caution.
Origin of the Effects of Citrate, Tartrate, and Acetate on Phosphate Sorption by Soils and Synthetic Gels
Authors: Earl K. D. , Syers J. K. , McLaughlin J. R.
Published: July 2010

The ability of two contrasting soils and synthetic Fe and Al gels to sorb inorganic phosphate (P) in the presence of three commonly‐occurring organic anions was evaluated using sorption isotherms. At 10−3M, citrate was markedly effective in reducing P sorption (50% reduction), tartrate was only moderately effective (20% reduction), whereas acetate had little or no effect (1% reduction) at a final solution P concentration of 0.20 mmole/liter for the four sorbents. A close linear relationship was established between the reduction in P sorption and the amounts of (Fe + Al), Fe, or Al removed from the Fe‐rich soil, Fe gel, or Al gel, respectively, by varying concentrations of citrate and tartrate. At 10−1 M, citrate and tartrate removed 91% of the Fe and 88% of the Al from the Fe and Al gel, respectively, reducing P sorption by 89 and 88%. At equivalent anion concentrations, however, tartrate was sorbed to a greater extent than citrate, resulting in a larger reduction in P sorption by this anion for a given amount of (Fe + Al) or Fe removed from the two soils and Fe gel. The curvilinear relationship obtained between the reduction in P sorption and the amount of (Fe + Al) removed from an Al‐rich soil resulted from the removal, at low organic anion concentrations, of a readily‐extractable form of Al which had little effect on P sorption. A similar finding was obtained for Al gel. The reduction in P sorption observed in the presence of citrate resulted primarily from the elimination of a significant proportion of P‐sorbing sites rather than from the competitive specific sorption of citrate. In contrast, tartrate reduced P sorption through a combined dissolution‐competitive sorption effect. Although 10−1M acetate had little effect on P sorption, a high proportion was sorbed by the sorbents, indicating that the sorption mechanism or site of binding of acetate differs from that of P.
Metal Ion Binding and Exchange with Hydrogen Ions in Acid‐Washed Peat
Authors: Bloom P. R. , McBride M. B.
Published: July 2010

Titration and electron spin resonance (ESR) studies of metal ion adsorption processes on acid peat were used to investigate metal‐proton exchange. Localization of ions at carboxylate sites is suggested but the data indicate that chelation mechanisms or sites of greatly different acid strength need not be involved. The peat is observed to behave very much like synthetic cross‐linked polycarboxylic acids in terms of metal ion adsorption. Most of the divalent ions adsorbed at acid pH appear to maintain a hydration sphere while the strongly immobilized Cu2+ ion coordinates directly with functional oxygens of the peat.
Growth and Nutrient Relations of a Grass‐Legume Mixture on Sodic Coal‐Mine Spoil as Affected by Some Amendments
Authors: Safaya N. M. , Wali M. K.
Published: July 2010

Laboratory and growth chamber investigations were conducted to study the effects of fertilizers, gypsum, H2SO4, and leonardite (oxidized lignite) on the growth and nutrient relations of a mixed crop of thickspike wheatgrass [Agropyron dasystachyum (Hook.) Scribn.] and yellow sweetclover [Melilotus officinalis (L.) Lam.] on a calcareous sodic coal‐mine spoil. Application of NPK increased the dry matter yield of the two species by 10 and 37 times, respectively. However, sweetclover required P only but wheatgrass yields almost doubled when N was included with P. Inclusion of Zn with NPK decreased the growth of sweetclover, and reduced Mn uptake in both species. Zinc, Mn, Cu, and Fe concentrations in the plants decreased variously with fertilizer applications. P‐fertilization decreased the concentration of K in wheatgrass but not in sweetclover.

The two species exhibited differential growth response to leonardite, which was correlated with K+/Na+ ratios in the plants and their Ca‐uptake efficiency. Leonardite increased Na concentration in wheatgrass (Ca‐inefficient) and decreased its growth, but caused a reverse effect on sweetclover (Ca‐efficient). It also decreased K and Zn in wheatgrass, and Cu and Fe in sweetclover. Gypsum tended to alleviate the effects of leonardite on wheatgrass, and increased Zn and Mn content in NPK‐supplied plants. The extractability of applied P was higher from leonardite treated spoil. Sulfuric acid proved more effective than gypsum in releasing Na from the exchange sites in the spoil. Moreover, H2SO4 improved the P status of plants, and increased the yield of wheatgrass to the same extent as did the application of 75 µg P/g spoil from H3PO4 source.
Estimation of Amorphous Material, 1:1 Type Layer Silicates, and Gibbsite Dissolved in Hot Alkali Treatment of Soil Clay
Authors: Calvert C. S. , Weed S. B. , Buol S. W.
Published: July 2010

Differential thermal analysis (DTA) is combined with selective dissolution (hot 0.5N alkali solution) to provide a quantitative estimate of amorphous inorganic material in deferrated soil clays consisting predominantly of 1:1 type layer silicate minerals, gibbsite, and amorphous material. Data from DTA are used to estimate gibbsite and 1:1 type layer silicate minerals in the original and alkali‐treated clay. Correction is then made to the weight loss due to alkali treatment to estimate amorphous inorganic material solubilized in boiling 0.5N NaOH or KOH. Qualitative support for conclusions reached is provided by x‐ray diffraction and infrared spectroscopic studies of the original and treated samples.
High Gradient Magnetic Separation of Iron Oxides and other Magnetic Minerals from Soil Clays
Authors: Schulze D. G. , Dixon J. B.
Published: July 2010

A filter of ferromagnetic stainless steel wool, placed in a strong magnetic field, provides the magnetic field gradients necessary to trap weakly magnetic clay size particles from a flowing suspension.

Of the total dithionite‐citrate‐bicarbonate extractable Fe2O3 in the 2–0.2 µm size fraction of six soils, 70 to 94% was recovered in the magnetic fraction which consisted of 1.6 to 27.7% free Fe2O3 by weight. For the <0.2 µm size fraction, 11 to 40% of the total free Fe2O3 in the size fraction was recovered in the magnetic fraction which contained 2.8 to 53.1% free Fe2O3 by weight. Larger particles are captured more efficiently because of their greater overall magnetic attraction. Goethite, hematite, lepidocrocite, and anatase are concentrated in the magnetic fraction, while quartz is concentrated in the tailings. Chlorite is effectively concentrated in the magnetic fraction. Although mica, vermiculite, and smectite are often found in both the tailings and the magnetic fraction, vermiculite and mica appear to be more concentrated in the magnetic fraction. The concentration effect on kaolinite appears to be dependent on the particle size and rate of flow through the magnetic filter.
Flux‐Controlled Sorptivity Measurements to Determine Soil Hydraulic Property Functions
Authors: Dirksen C.
Published: July 2010

Using a new method, the hydraulic diffusivity and conductivity functions D[θ] and K[h] can be determined over most of their range in about 4 hours. This method uses a series of fast and simple, one‐dimensional adsorption measurements for which the cumulative volumes of absorption are controlled proportional to the square root of time with syringes driven by cames. Each combination of motor speed, can size, and syringe size represents an imposed sorptivity for which the water content and/or pressure head at the interface must be measured after they become steady. Steady values are normally reached after only a few minutes. Pressure heads can be recorded during the absorption runs, and at the end a soil sample for gravimetric water content determination can be obtained in about 15 sec. Hydraulic diffusivity and conductivity functions derived from measured sorptivity functions were obtained for a variety of undisturbed and hand‐packed soil columns. They all showed excellent agreement with independent data. The flux‐controlled boundary resulted in uniform wetting almost every time, whereas previously used potential‐controlled boundary conditions often caused nonuniform wetting, which prevented accurate evaluation of sorptivities. The speed, range, and accuracy of this improved version of the sorptivity method compare favorably with other available methods. The method is suitable for routine and large scale use.