bluuebunny/crossref_metadata_2025 huggingface dataset:
Description of Soils Having Disturbed or Discontinuous Horizons
Authors: Fisher R. F. , Miller R. J.
Published: July 2010

The highly disturbed and discontinuous horizons of many podzolic soils make them difficult to describe, classify, and identify in the field. A method of differentiating such soils was used on three map units in Southern Ontario. The method required some modification because it failed to use discontinuity as a variable. The use of a disturbance index and a discontinuity index in describing soil series and map units with highly disturbed and/or discontinuous horizons is suggested.
Importance of Prereducing Selenium(VI) to Selenium(IV) and Decomposing Organic Matter in Soil Extracts Prior to Determination of Selenium Using Hydride Generation
Authors: Workman S. M. , Soltanpour P. N.
Published: July 2010

Hydride generation techniques using NaBH4 are widely used for the determination of Se in aqueous solutions. In soil extracts, Se(IV) is the only form of Se reduced to SeH2 by NaBH4. Se(VI) must be prereduced to Se(IV) to be measured. Organic constituents of soil extracts also appear to inhibit hydride production. A pretreatment procedure overcoming these problems is presented, and a simple hydride generator is described.
Chloride Movement in Undisturbed Soil Columns
Authors: Tyler D. D. , Thomas G. W.
Published: July 2010

Chloride movement was studied in soil columns taken from three Kentucky alluvial soils—Karnak, Huntington, and Bruno. The soils ranged from silty clay loam to sandy loam in texture and from well structured to unstructured. Columns were taken by driving a 15‐cm diameter heating duct into the soil to a depth of 30 cm and then digging out around the column to remove it. These columns were mounted on blocks of candle wax and leached under 1.5 cm of Hg tension. A 25‐ml “slug” of KCl was applied to each column and followed by deionized water at a rate just slow enough to prevent ponding on the soil surface. The maximum effluent concentration of Cl appeared far ahead of 1 pore volume in both Huntington and Karnak soils, which have well‐defined structure, and at 1 pore volume in the Bruno sl which is not structured. The results emphasize the channeling of water in soils with well‐defined structure.
The Importance of Cr Horizons in Soil Classification and Interpretations
Authors: Lietzke D. A. , Weber R. S.
Published: July 2010

Paralithic boundaries and underlying Cr horizons have been observed in numerous soils on an extensive variety of sedimentary rocks both flat lying and steeply dipping in the Appalachian region of Virginia and in every type of igenous and metamorphic rock that is common to the Southeastern United States Piedmont and Blue Ridge geological provinces. In addition, the very dense basal till that underlies soils formed in glacial materials also appears to qualify for a Cr horizon. Cr horizons profoundly affect water movement and root penetration. The depth to Cr horizon and its thickness in a soil is especially important in interpreting soil properties for septic tank drainfields where water movement is crucial. A paralithic boundary (the top of the Cr horizon) is usually difficult to detect with barrel auger observations. Paralithic boundaries may be located by the presence of root mats, clay plugged zones, or other evidence of reduced permeability in soils with and without argillic horizons. The Cr horizon lying just below the paralithic boundary does not have any evidence of soil fauna activity that produced pores and tunnels. Soil pits are much more useful in observing and evaluating these particular soil features. Soil scientists can learn to locate a paralithic boundary with barrel augers by changes in moisture content, increased shearing resistance, and increased coarse fragments content. A Cr horizon at < 1.8‐m depth in a soil has an important place in Soil Taxonomy since its presence determines the depth at which base status is evaluated for placement at the order or great group levels.

A Cr horizon should be diagnostic at the subgroup level when it occurs at depths of 50 to 100 cm, at the series level when it occurs between depths of 100 and 125 cm, and at the phase level when it occurs between depths of 125 and 180 cm.
The Quantitative Assay of Minerals for Fe2+ and Fe3+ Using 1,10‐Phenanthroline: I. Sources of Variability
Authors: Stucki J. W. , Anderson W. L.
Published: July 2010

Factors affecting the reliability of results using 1,10‐phenanthroline (phen) in the quantitative assay of minerals for Fe2+ and total Fe were studied. The greatest source of variability was the photochemical reduction of ferric‐phen species during Fe2+ analyses. It is believed that oxo‐bridged dinuclear complexes of Fe2+ and phen are formed in the mineral digests, which then are susceptible to photochemical reduction by wavelengths < 400–500 nm. The rate of photoreduction of a solution obtained by digesting oxidized nontronite was sufficient to increase the predicted Fe2+ content of the clay from about 0 to 2.45% by simply leaving the sample for 1 hour in normal fluorescent light in the laboratory; and for partially reduced nontronite, from 3.25 to 4.68%. The rates of increase for the two clays were 0.0024 and 0.0014 absorbance units/min, respectively. Interferences due to this phenomenon were eliminated when samples were kept in the dark or under subdued red light. Other factors that adversely influence the accuracy and precision of the standard curve included (i) the amount of 48% HF used to digest the sample; (ii) addition of chemical reducing agents such as hydroxylamine hydrochloride and hydroquinone; (iii) the order in which phen is added relative to other reagents; (iv) pH; and (v) the length of time allowed for color development if phen is added only to the final dilution.
Hydraulic Properties of Fullerton Cherty Silt Loam
Authors: Luxmoore R. J. , Grizzard T. , Patterson M. R.
Published: July 2010

Soil hydraulic properties at eight depths in a Fullerton cherty silt loam (a clayey, kaolinitic, thermic Typic Paleudult) profile were derived from measurements of water content with a calibrated neutron probe and of matric potential with tensiometers during drainage of a flooded 2‐ by 2‐ by 3‐m deep soil plot. Soil cores taken from the field plot were used for laboratory determinations of the retention properties. The field retention data were generally unsatisfactory, indicating significant differences in the response times and spatial resolution of the tensiometers and neutron probe. The tensiometers did not provide reliable hydraulic gradient data during drainage. Hydraulic conductivity was calculated by the instantaneous profile method and by three simple field methods, assuming a unit hydraulic gradient in all methods. There were greater differences in hydraulic characteristics between two profiles 1 m apart than there were between the alternative methods of calculation. Maximum hydraulic conductivity calculated by the instantaneous profile method for the well‐aggregated B horizons had values up to 58 and 177 cm per day at two positions in the soil plot.
Physical and Chemical Characteristics of Pre‐mine Soils and Post‐mine Soil Mixtures in Illinois
Authors: Snarski R. R. , Fehrenbacher J. B. , Jansen I. J.
Published: July 2010

The chemical, physical, and mineralogical properties of Sable and Darmstadt soils were studied to determine the value of solum and subsolum material as mediums for plant growth. Sable silty clay loam from western Illinois has nearly ideal physical and chemical properties for plant growth, while the more weathered Darmstadt silt loam from southern Illinois has unfavorable chemical and physical properties that limit plant growth.

The suitability of various soils and subsurface overburden mixtures were determined by measuring and defining the chemical and physical properties that have a potential for enhancing or limiting plant growth. The B2 horizon material from the Darmstadt soil has the least favorable properties. The top 3‐m mix (topsoil included) and 3‐m mix (topsoil not included) have similar properties and appear to be the most favorable materials for use in constructing a post‐mine soil. The range of chemical and physical properties in the Sable mixtures are not as great as in the Darmstadt mixtures. The top 3‐m mix, 6‐m mix (exclusive of the A horizon), and calcareous loess mix from the Sable soil all have similar chemical and physical properties.

Incorporation of the A horizon into the 3 m below the A horizon of both Sable and Darmstadt soils only slightly enhances the chemical and physical properties of the mixtures.

Comparison of tested and calculated soil values indicate that most chemical and textural properties of a solum and subsolum mixture can be predicted prior to mining. The pH of a mixture can also be predicted by using an equilibration technique.
Tillage Effects on Wheat and Sunflower Grown in Rotation
Authors: Unger Paul W.
Published: July 2010

Methods of fallowing commonly used in the Southern Great Plains are relatively ineffective for increasing soil water contents, and subsequent crop yields on a total area basis are less with fallow than with continuous cropping. Consequently, improved cropping practices are needed that increase soil water storage during fallow or that decrease the total time devoted to fallow in a cropping sequence. The objective of this study was to determine the effects of disk, sweep, limited‐, and no‐tillage on soil water storage and yields of dryland sunflower (Helianthus annuus L.) and irrigated wheat (Triticum aestivum L.) when grown in rotation. The tillage treatments were applied during the 10‐month fallow period between harvest of irrigated wheat and planting of dryland sunflower. Wheat was planted immediately after sunflower harvest. Average gains in soil water content during fallow ranged from 3.8 cm with disk tillage to 7.2 cm with no‐tillage. These differences were statistically significant, but subsequent sunflower seed yields, which averaged 1.26, 1.24, 1.24, and 1.38 metric tons/ha with disk, sweep, limited‐, and no‐tillage treatments, respectively, were not significantly different. Grain yield of wheat planted after sunflower averaged 4.17 metric tons/ha. There were no significant residual effects of the tillage treatments on wheat yields. For 1977 and 1978, wheat yields in this study (excluding limited‐tillage) averaged 3.40 metric tons/ha compared with 2.22 metric tons/ha in an irrigated wheat‐fallow‐dryland grain sorghum [Sorghum bicolor (L.) Moench] study with the same tillage treatments. The wheat‐sunflower rotation resulted in more timely planting and higher yields of wheat than the wheat‐sorghum rotation. The wheat‐sunflower rotation allows timely planting of wheat and sunflower, provides for two crops in 2 years, and thus should increase total yields as compared with systems involving an extra fallow period.
Effects of Fertilization and Vesicular‐Arbuscular Mycorrhizal Inoculation on Growth of Hardwood Seedlings
Authors: Schultz Richard C. , Kormanik Paul P. , Bryan William C.
Published: July 2010

Eight hardwood species were grown in fumigated soil without vesicular‐arbuscular mycorrhizae (VAM) or in soil infested with a mixture of Glomus mosseae and Glomus etunicatus. Three fertilizer treatments of 140, 560, and 1,120 kg/ha of 10‐10‐10 fertilizer were established in combination with the two mycorrhizal treatments. Ten equal applications of NH4NO3, totaling 1,680 kg/ha, were added to all the treatment plots during the growing season. For six of the eight species, the VAM seedlings showed greater height and diameter growth and dry weight production than nonmycorrhizal seedlings. Sugar maple (Acer saccharum Marsh.) and walnut (Juglans nigra L.) displayed no height growth differences. Only boxelder (Acer negundo L.), of the inoculated seedlings, consistently responded to increases in fertilizer level. Nonmycorrhizal seedlings generally showed increased growth with increased fertilizer applications. The growth of the nonmycorrhizal seedlings at the higher fertilizer levels was not sufficient to produce plantable seedlings for artificial regeneration. A difference in host preference for the Glomus spp. symbionts is suggested by the large difference in infection between species. Infection values varied from a high of about 80% for sycamore (Platanus occidentalis L.), green ash (Fraxinus pennsylvanica Marsh.), and boxelder to a low of 40% for sugar maple and sweetgum. The growth data suggest that high quality seedling stock of most of these hardwood tree species can be obtained in nurseries as long as cultural practices in the nursery encourage VAM development.
Sand Grain Micromorphology and Soil Age
Authors: White Kenneth L.
Published: July 2010

The micromorphology of quartz grains (0.5 to 1.0 mm) from three soils developed in granitic alluvium were studied using scanning electron microscopy. The soils are located on riverine terraces in southern California. The soils have been dated as 22,000, 44,000, and 63,000 years before present (YBP). The grains are dominated by solution/precipitation features. The samples from the A horizons are quite similar. Grains from the lower B horizons display an increasing complexity of features with advancing age. The C horizons from the older terrace yield the most diagenetically altered grain surfaces. Age in fact, appears to have greater significance than change in soil texture or water holding capacity.
Infiltration of Fungal and Bacterial Propagules into Soil
Authors: Wilkinson H. T. , Miller R. D. , Millar R. L.
Published: July 2010

Phytophthora megasperma zoospores and cysts and Serratia marcescens cells were infiltered during the establishment of a gradient of matric potential in horizontally positioned columns of soil. Tensiometers placed in the soil columns were used to record matric potentials (in situ). In columns wetted a distance of 65 cm, zoospores moved 35 cm behind the wetting front in sand, 44 cm in sandy clay loam, 48 cm in loam, and failed to move in silt loam soil. In the sand, sandy clay loam, and loam soils, matric potentials of −14.5, −18.4, and −16.2 mbars, respectively, were calculated for soil at the boundary between infested and noninfested soils. Zoospore cysts moved one‐half the distance zoospores did in each soil, respectively. The matric potentials associated with their boundary were −13.2, −13.4, and −12.0 mbars. Serratia marcescens cells were recovered close behind the wetting front in the first three soils but 48 cm behind in the silt loam. The matric potential 48 cm behind the wetting front was −33.5 mbars. Attempts were made to develop a predictive model for infiltration of biological propagules based on propagule size and soil moisture characteristic curves. Results indicated that infiltration of propagules occurred after soil pores with radii considerably larger than a priori estimates of the limiting pore radii were filled with water.
Ionic Activity Product of Calcium Carbonate Precipitated from Soil Solutions of Different Degrees of Supersaturation
Authors: Levy Rachel
Published: July 2010

Calcium carbonate (CaCO3) was precipitated by equilibrating samples of calcareous soil and noncalcareous soil with a dilute sodium bicarbonate solution at two soil‐to‐solution ratios. Different degrees of supersaturation of the soil solutions prior to precipitation were thus achieved by releasing variable amounts of exchangeable calcium (Ca). Six sequential equilibrations were performed on each soil at each soil‐to‐solution ratio. Both Ca and magnesium (Mg) were released from exchange sites during equilibration, but mainly calcium carbonate precipitated. Precipitation in the soil extracts actually occurred if the degree of saturation after precipitation was lower than the degree of saturation prior to precipitation. The logs of the lonic activity product of calcium carbonate, pIAPc, of the noncalcareous soil were 7.57 and 7.83, and of the calcareous soil, 7.78 and 7.86, at the 1:1 and 1:10 soil‐to‐solution ratios, respectively. These pIAPc values were within experimental error of those obtained from undersaturation at a 1:1 soil‐to‐water ratio (Levy, 1981). The same pIAPc values were obtained regardless of the path by which equilibrium was approached, apparently because the same inhibitors were present in each case.
Nutrient Diagnosis in Corn Grown on Hydric Dystrandepts: I. Optimum Tissue Nutrient Concentrations
Authors: Escano C. R. , Jones C. A. , Uehara G.
Published: July 2010

The Benchmark Soils Project is an internationally based research project testing the hypothesis that agricultural technology can be transferred from one location in the tropics to another in soils of the same family. Environmental conditions and maize hybrids used in the tropics differ from those in temperature and subtropical regions. These factors can Influence the “adequate range” or “critical” tissue nutrient concentrations at which acceptable crop growth is obtained. The use of incorrect criteria for diagnosis of nutrient deficiencies from plant tissue analyses could result in inaccurate fertilizer recommendations. The objectives of this study were to evaluate several methods of determining adequate ranges and critical earleaf concentrations for a single maize hybrid grown on Hydric Dystrandepts in Hawaii and to compare the results with published data for other locations.

Four methods of determining the optimum ranges of tissue nutrient concentrations were compared using data from eight N × P and seven CaCO3 × P fertilizer experiments. Optimum concentrations or ranges were calculated as follows: (A) the range of nutrient concentrations associated with the highest 5% of all plot grain yields; (B) the range of nutrient concentrations within one standard deviation of the mean concentration of the highest 15% of all plot yields; (C) the nutrient concentration at 95% of the maximum yield; and (D) the nutrient concentration which, when used as the critical concentration, resulted in the highest percentage of correct diagnoses of nutrient deficiencies. Methods (A) and (B) were used to determine optimum concentrations and ranges of N, P, K, Ca, Mg, S, Al, Mn, Fe, Cu, and Zn. Methods (C) and (D) were used for N and P only.

Except for N, Mg, and S, the optimum ranges calculated by methods (A) and (B) were similar and were within previously reported sufficiency ranges for malze (Zea mays L.). For N, Mg, and S, high maize grain yields were found at concentrations slightly lower than those previously reported. The optimum concentrations of N and P obtained by methods (C) and (D) were similar and fell well within published ranges.

In seven N × P experiments, highly significant positive correlations were found between both tissue N and P concentrations and grain yield. Likewise, the concentrations of tissue K, S, Cu, and Zn were often positively correlated with tissue N and P concentrations and with grain yield. Only Mn had a consistent negative correlation with grain yield and earleaf N concentration.
Coating of Calcium Carbonate on Gypsum Particle Surfaces
Authors: Keren R. , Kauschansky P.
Published: July 2010

The coating of calcium carbonate on gypsum particle surfaces was examined by electron microprobe technique. The gypsum‐carbonate interaction was studied in two systems: (i) gypsum‐sodium carbonate and (ii) gypsum‐calcareous soil. In both systems, the calcium carbonate was precipitated on the gypsum particle surfaces, forming a coating layer.
Elimination of Aerobic Degradation During Characterization of Pesticide Adsorption—Desorption in Soil
Authors: Koskinen W. C. , Cheng H. H.
Published: July 2010

Two methods for elimination of aerobic pesticide degradation during characterization of pesticide adsorption‐desorption in soil were compared, using 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) as the test compound. Steam sterilization of soil significantly decreased 2,4,5‐T adsorption by soil, and degradation of 2,4,5‐T became noticeable after three days of desorption. Conducting the adsorption‐desorption process under a nitrogen atmosphere resulted in little change in 2,4,5‐T adsorption characteristics and negligible degradation even after six days of desorption.
Electromagnetic Determination of Soil Water Content Using TDR: II. Evaluation of Installation and Configuration of Parallel Transmission Lines
Authors: Topp G. C. , Davis J. L. , Annan A. P.
Published: July 2010

Time‐domain reflectometry (TDR) applied to parallel transmission lines in soil was used to measure the soil water contents during infiltration, drainage, evaporation, and rising water table conditions in a 1.05‐m column of silt loam soil in the laboratory. Three types of installation and several types of transmission lines were evaluated. Comparisons of volumetric water content from gravimetric samples and from TDR showed differences were always <0.03 cm3cm−3. Trends of the TDR values with time showed that these differences likely resulted from soil density variations. Neither the installation method nor the design of the rods of the transmission line affected the water content values, provided there was good electrical contact with the soil. Transmission lines with discontinuities gave an effective and efficient measure of the soil water‐content profile.
Constant‐Flux Infiltration from a Hemispherical Cavity
Authors: Clothier B. E. , Scotter D. R.
Published: July 2010

Existing theories of Raats, Parlange, and Warrick describing constant‐flux absorption and infiltration from hemispherical cavities are reviewed. A simple theory for absorption is derived, using the flux‐concentration relation of Philip. Three‐dimensional infiltration experiments are described that were used to test these theories. The results showed that infiltration at 360 ml/h into a 4‐mm‐radius hemispherical cavity in a repacked fine sand was described quite well by the simple absorption theory for the first 100 min. Beyond this time, at this flux, the effects of gravity became evident, as expected from a comparison of the matric and gravitational potential gradients. The nonlinear, steady‐state infiltration theory of Raats gave reasonable estimates of the water content profiles behind the wet front. The linearised (constant diffusivity) theory of Warrick was of no value in this context. The success of the Raats theory adds some credence to the use in trickle irrigation design of the Wooding's theory which describes infiltration from a circular pond on the basis of the same assumptions.
The Apparent Solubility of Calcium Carbonate in Soils
Authors: Suarez D. L. , Rhoades J. D.
Published: July 2010

Soils in the laboratory were reacted with agricultural drainage‐ and distilled waters at various carbon dioxide (CO2) levels. The soil water solutions yielded different ion activity product (IAP) values than that of calcite, depending on experimental technique and whether calcite “equilibrium” is approached from supersaturation or undersaturation. Sample storage conditions affected IAP values as did partial pressure of CO2 and soil/water ratio. With sufficient reaction time all soil waters became supersaturated with respect to calcite—but to different degrees. The only calcium carbonate (CaCO3) phase detected in these soils was low Mg calcite. Calcium carbonate particles isolated from the soils gave IAP values expected for calcite (10−8.45 to 10−8.49). The calcite supersaturation in soil appears to be due to the presence of silicates in the soil more soluble than calcite, and is not the result of unstable CaCO3 phases. It thus appears inappropriate to try to determine the solubility of soil CaCO3 by reacting soil containing CaCO3 and water in the laboratory. Since soil‐ and drainage waters are not in equilibrium with calcite (or any other CaCO3 phase), calcite solubility is inappropriate for arid land soil‐water models. It is likely that the kinetic factors controlling soil solution composition under field conditions are not simulated by conventional types of laboratory experiments.
Gypsum Dissolution and Sodic Soil Reclamation as Affected by Water Flow Velocity
Authors: Keren R. , O'Connor G. A.
Published: July 2010

The dissolution rate of gypsum fragments in aqueous solutions was studied for Ca‐soil‐gypsum mixtures at two gypsum contents and four soil water velocities. Equations were derived to estimate the dissolution rate coefficient of gypsum fragments at different soil water velocities for a given surface area of gypsum. The soil water velocity controls both the time in which an elemental volume of water is moving in the soil‐gypsum layer and the dissolution rate coefficient. Increasing the soil water velocity increased the dissolution rate coefficient but decreased the contact time between an elemental volume of water and a unit of surface area of the gypsum fragments; the net effect is that increasing the water velocity decreases the gypsum dissolution rate. The effect of contact time on gypsum dissolution rate is much greater at the higher soil water velocity range than at the lower range. The soil water velocity also has a significant effect on sodic soil reclamation. The slower the soil water velocity, the higher the efficiency of replacing Na+ by Ca2+. The probable reasons for these findings are discussed.
Nitrate Reduction in Spartina Alterniflora Marsh Soil
Authors: Smith C. J. , DeLaune R. D. , Patrick W. H.
Published: July 2010

The transformation of nitrate (NO‐3) was investigated in flooded Louisiana Gulf Coast salt marsh soll. Nitrate formed in the aerobic zone of the soil is readily reduced in the deeper anoxic zone by dissimilatory and/or assimilatory processes. The experiments were conducted in soil cores 15 cm in diameter by 12 to 15 cm in depth. 15N‐labelled NO‐3 at 0.6 g N m−2 was administered in either a single injection into the floodwater or in repeated small injections below the sediment‐water interface. For the single application experiment, 14% of the 15N remained in the system; 4% NH+4‐N and 10% organic N. This implies dissimilatory reduction, with NO‐3 being reduced to NH+4 prior to formation of organic N. Fifty separate applications increased the recovery of 15N in the NH+4‐N and organic N pool to 52%. The latter procedure more nearly reproduces the low steady‐state concentration of NO‐3 observed in salt marsh soil; the increased recovery suggests that the internal inorganic‐N cycling in these soils may be more efficient than previously reported.
Flow of Kaolinite and Sewage Suspensions in Sand and Sand‐Silt: II. Hydraulic Conductivity Reduction
Authors: Swartzendruber D. , Uebler R. L.
Published: July 2010

The reduction in satiated (near‐saturated) hydraulic conductivity of fine quartz sand and sand‐silt (95% fine quartz sand and 5% quartz silt) for the flow of stable water suspensions of kaolinite clay and sewage solids was investigated in vertical flow columns. An equation was derived theoretically in which hydraulic conductivity is expressed as an exponential function of the cumulative volume of suspension inflow, and that contains a characterizing constant, termed the clogging coefficient, which is zero when water alone is the flow liquid. The equation was verified by experimental measurements. For a given suspension, the clogging coefficient was larger for sand‐silt than for sand, and of a given porous medium was larger for kaolinite suspension than for sewage suspension, but was not significantly affected by the initial water content (air‐dry or satiated) of the porous medium. The clogging coefficient offers promise as a criterion for the design of land‐application sewage systems and as a parameter for describing soil crusting caused by the infiltration of muddy water.
Predicting Loblolly Pine Growth Response from N Fertilizer, using Soil‐N Availability Indices
Authors: Lea Russ , Ballard Russ
Published: July 2010

Mineralizable nitrogen (N) fractions extracted from surface soil by 2N KCl, anaerobic or aerobic laboratory incubation, autoclaving, and dilute acid were not significantly correlated to five‐year volume growth response to N fertilization, site index, or N levels of foliage or litterfall. Site index was significantly and directly correlated to foliar N concentrations and inversely correlated to the surface soil C/N ratio. The amounts of N extracted by anaerobic and aerobic laboratory incubations could be significantly predicted, using total soil N and soil acidity.
Residual Value of Lime and Leaching of Calcium in a Kaolinitic Ultisol in the High Rainfall Tropics
Authors: Friesen D. K. , Juo A. S. R. , Miller M. H.
Published: July 2010

A long‐term experiment was conducted on a highly acidic (pH 4.6), coarse‐textured Ultisol (Typic Paleudult; loamy, siliceous, isohyperthermic) in the high rainfall region of southeastern Nigeria in order to evaluate the requirement for and residual value of lime [Ca(OH)2] to a continuous crop rotation, and to determine the fate of applied Ca in the soil profile. The initial lime rates used were 0, 0.5, 1, 2, and 4 t of Ca(OH)2 per hectare. Maize (Zea mays) was planted in the first season and cowpea (Vigna unguiculata) in the second season under a no‐tillage, stubble conservation system.

Results from the six‐year experiment indicate that relatively low rates of lime are adequate to sustain yields in a continuous maize‐cowpea rotation system. Liming at a rate of 0.5 t/ha maintained maize yield near maximum for 2 years after application. Sustained maize yields for 5 years or more were possible with a lime rate of 2 t/ha. The critical level of exchangeable Al required for 90% maximum yield of maize was about 35%. Cowpeas performed well and showed strong tolerance to soil acidity when planted as a late second‐season crop after maize without additional fertilizer application. The critical level of exchangeable Al ranged from 25 to 55% depending upon rate of chemical fertilizer as well as cowpea variety used.

Leaching losses of Ca from the surface soil during the first 3 years were <0.5 t/ha of Ca(OH)2‐equivalents in the 0‐ to 2‐t/ha treatments. But an equivalent of 1.6 t/ha of lime was leached from the surface soil of the 4‐t/ha treatment suggesting that the mobility of Ca in this soil is a consequence of the hydrolysis of the pH‐dependent charge in the presence of acidifying nitrogeneous fertilizer.

Exchangeable‐Al saturation in all subsoil layers of all treatments 3 years after liming exceeded 40% and soil pH (H2O) was <4.3 indicating that lime was leached as neutral Ca salts and had little effect in ameliorating subsoil acidity. Soil profile analysis after 3 years showed that nearly all Ca applied may be found within the 90‐cm depth. However, recycling of the leached Ca from the subsoil would require deep‐rooting species tolerant to high Al levels.
The Effect of Sodium Carbonates' Presence on the Soil Extract's Chemical Composition
Authors: Nadler Arie , Magaritz Mordeckai
Published: July 2010

It is shown experimentally that some sodic soils contain difficult‐to‐detect Na carbonate minerals which affect the chemical compositions of their aqueous extracts. Upon extraction with water, a portion of the dissolved HCO‐3 reacts with Ca2+ initially present in the soil (in a solid phase or occupying exchange sites) and is immediately precipitated as CaCO3. This phenomenon reduces extract pH and alkalinity (by precipitation of CaCO3 and release of CO2 gas) which obscures the initial presence of alkalinity.
Storage of Nitrous Oxide on Molecular Sieves
Authors: Duxbury J. M. , Voghel S.
Published: July 2010

A procedure was developed for storing the N2O in 50‐mL air samples on activated molecular‐sieve type 5A in 60‐mL serum bottles. The procedure was equally effective for N2O concentrations of 1 and 10 µL · L−1 and storage times up to 6 weeks. Blank values for sieves stored 3 to 5 months after activation ranged from about 0.04 ± 0.002 to 0.05 ± 0.005 µL · L−1. Allowing freshly activated sieves to cool in air before capping the bottles increased blank values and variability to unacceptable levels. Nitrous oxide fluxes from soil > 10 g N · ha−1 · d−1 could be reliably determined when the storage procedure was used in conjunction with a chamber method for N2O flux measurement.
A Technique for Rapid Removal of Gypsum from Soil Samples
Authors: Rivers E. D. , Hallmark C. T. , West L. T. , Drees L. R.
Published: July 2010

Removal of gypsum from soil samples is necessary to disperse soils for particle‐size analysis or clay separation for mineralogical study. A technique utilizing the heating of gypsiferous soil overnight at 105°C is presented. The heat treatment converts gypsum to bassanite which is more soluble than the gypsum and the disruption of the gypsum upon dehydration also yields bassanite particles which can easily be crushed to provide a greater surface area. Subsequently, the time required to remove gypsum from soil by dialysis is reduced by >50%. Heating the samples did not change the clay mineralogy or the cation exchange capacity, but did result in slightly higher total and fine clays and slightly lower sand contents.
Nonsymbiotic Nitrogen Fixation in an Oak‐Hickory Forest Following Long‐Term Prescribed Burning
Authors: Vance E. D. , Henderson G. S. , Blevins D. G.
Published: July 2010

Seasonal rates of nonsymbiotic nitrogen fixation in the surface soil of oak‐hickory forest plots exposed to 30 years of annual and periodic (4‐year) prescribed burning were estimated using an in‐situ acetylene reduction procedure. Fixation rates were low, averaging 0.1 kg·ha−1·year−1 for all soil cores assayed in April, August, and October 1980 and April 1981 with approximately 11% of samples displaying activity. Burning treatments had no influence on fixation rates or proportion of samples displaying activity. Highest rates were found in autumn with an average rate for active samples of 2.2 kg·ha−1·year−1. Higher autumn fixation rates may be related to higher quantities of high energy foliar leachates which could induce a significant seasonal peak on sites demonstrating higher rates of fixation.
Effects of Knifed Vs. Broadcast Fertilizer Placement on Yield and Nutrient Uptake by Tall Fescue
Authors: Lamond R. E. , Moyer J. L.
Published: July 2010

Field studies were conducted from 1979 to 1981 to evaluate two fertilizer application techniques for established tall fescue (Festuca arundinacea Schreb.). Fertilizer solutions were formulated from urea‐ammonium nitrate solution (UAN, 28‐0‐0) and potassium tripolyphosphate (0‐11‐21) or ammonium polyphosphate (10‐15‐0) and potassium chloride (0‐0‐50) to supply various rates of N, P, and K. These fertilizer solutions were either surface‐broadcast through flat fan‐spray nozzles or injected (knifed) 15 to 20 cm deep behind shanks on 38‐cm spacings. The knifed method could be called a subsurface band application that places the fertilizer directly in the root zone.

In Experiment I, N was applied at 56, 112, and 168 kg per ha with or without 20 kg of P/ha and 37 kg K/ha. In Experiment II, rates were 13, 112, and 168 kg N/ha; 0 and 20 kg P/ha; and 0 and 37 kg K/ha. All experiments were conducted on Parsons silt loam soils (Mollic Albaqualf, fine, mixed, thermic) that tested low to medium in available P and K. Total yields and N concentrations of forage generally increased with N rates up to 168 kg N/ha. Phosphorus fertilization increased forage yields, P concentrations, and P uptake. Forage yields were not significantly increased by K fertilization, but on low‐K soil, adding K tended to increase yields when N and P were supplied. Fertilization with K increased forage K concentrations, but had little influence on other forage constituents. Knifed fertilization was superior to broadcast applications of fertilizer and significantly increased forage yields, N content, N uptake, K uptake, and sometimes K concentrations and P uptake. The superiority of the knifed application was due mainly to better N utilization.
Behavior of Bromacil and Napropamide in Soils: I. Adsorption and Degradation
Authors: Gerstl Z. , Yaron B.
Published: July 2010

The adsorption and degradation of napropamide [2‐(α‐naphthoxy)‐N,‐N‐diethyl propionamide] and bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil) was studied in a number of Israeli soils with various properties. The adsorption of napropamide by soils was moderate, with Kd (adsorption coefficients) values ranging from 0.27 to 2.96 mL/g. Bromacil was adsorbed only slightly with Kd values of 0.03 to 0.39 mL/g. Adsorption was only slightly correlated with the soil clay content but was highly correlated with soil organic matter content, giving KOC (the adsorption per unit weight of organic carbon) values of 34 and 336 mL/g organic carbon for bromacil and napropamide, respectively. Use of the aqueous solubility of the compounds to predict adsorption gave values with considerable error in comparison with those measured, but by using the octanol/water partition coefficient (KOW) predictions were improved considerably. Degradation was studied at several moisture contents, temperatures, and initial concentrations. For the soils studied temperature and moisture content affected degradation more than did soil type or initial concentration. Degradation fit first‐order kinetics, with half lives of 17 to 1,643 d for napropamide and 14 to 1,494 d for bromacil.
Acid Tolerance of Rhizobium Trifolii in Culture Media
Authors: Thornton Frank C. , Davey C. B.
Published: July 2010

Tolerance to acidity (pH 4.2 to 4.6), low P (1 to 6 µM) and high Al (15 to 40 µM) for 100 strains of Rhizobium trifolii was assessed in liquid culture media in the laboratory. Response to acidity and Al varied among strains as evidenced by lower maximum cell densities and reduced growth rates, most preceded by a lag phase. Tolerance to acidity did not imply tolerance to Al in all cases. Strains were capable of tolerating higher levels of Al if acidity were reduced. Limitations in rhizobial growth due to low P concentrations were not as severe a stress as high acidity or high Al concentration.
The DTPA‐Extractable Iron, Manganese, Copper, and Zinc from Neutral and Calcareous Soils Dried Under Different Conditions
Authors: Leggett G. E. , Argyle D. P.
Published: July 2010

DTPA (diethylenetriaminepentaacetic acid)‐extractable Fe, Mn, Cu, and Zn were determined on several neutral and calcareous soils dried at various temperatures. Extractable Fe increased linearly over the drying temperature range 22 to 100°C, whereas Mn increased in an irregular manner. Values for Cu and Zn changed only slightly over this temperature range. Extractability of all four elements increased when field‐moist samples were air dried; Fe by a factor of 2 to 3, and Mn, Cu, and Zn by a factor of about 1.3 to 1.5. The increases in extractable Fe and Mn appear to result from separate temperature and dehydration effects and are only partially reversible with rehydration and moist incubation. The results of this study indicate that sample handling be standardized for calibration and routine tests before DTPA‐extractable Fe and Mn can be used as reliable diagnostic tests for these elements. Close control of drying conditions for Zn and Cu analysis may be desirable but is not as critical as for Fe and Mn.
Structure of a Tilled Soil as Influenced by Tillage, Wheat Cropping, and Rainfall
Authors: Dexter A. R. , Radke J. K. , Hewitt J. S.
Published: July 2010

Tillage with a tined cultivator (scarifier) and a rotary cultivator was done on Urrbrae fine sandy loam in South Australia. One‐half of the plots were kept bare, while the other one‐half were cropped with wheat (Triticum aestivum L.). Soil macrostructure (voids and aggregates > 0.5 mm) was observed on sections sawed from blocks of the tilled soil which had been impregnated with epoxy resin. Macrostructure was quantified statistically along linear transects on the sections at 0.25, 0.5, and 0.75 of the depth of tillage at the time of tillage and on three subsequent dates when there had been 10, 135, and 395 mm of natural rainfall, respectively. Soil structures are compared and differences between them are presented. Initial differences in soil structure between the tillage treatments had largely disappeared by the second sampling date. Differences in structure due to the presence of the wheat crop were not significant until the final sampling date when the crop was at 0.66 of its final height. Multiple regression equations are presented for the soil macrostructure parameters as functions of cumulative rainfall after tillage and depth in the tilled soil layer.
A Constant‐Potential Soil Water Sampler
Authors: Riekerk H. , Morris L. A.
Published: July 2010

A porous cup soil water sampler which uses a separate hanging water column to create a partial vacuum for collection of soil water is described. The reliability of porous cup lysimeters combined with a simple contant‐potential vacuum supply make the installation suitable for soil water monitoring at remote locations.
The Soil Water Diffusivity Near Saturation
Authors: Clothier B. E. , Wooding R. A.
Published: July 2010

Many laboratory porous materials are considered to have a zone of tension‐saturation in their water retentivity curve near saturation. This implies that the soil water diffusivity, D, is infinite in such a region. Here three new methods of measuring the diffusivity near saturation are presented. Experiments were carried out on a fine sand and all methods found D to be finite, yet large, having a value of approximately 1 to 2 × 10−3 m2 s−1. Since the near‐saturated conductivity of the sand is of the order 10−5 m s−1 this implies that the water retentivity curve near saturation has a finite but large slope of order 102 m. This was compatible with the measured retentivity data. The theory of one‐dimensional absorption implies that the slope of the Boltzmann variable with respect to volumetric water content near saturation equals twice D divided by the sorptivity. The slope calculated this way was compatible with that found in absorption experiments.
The Effect of Exchangeable Cations on Soil Mineral Weathering
Authors: Frenkel H. , Amrhein C. , Jurinak J. J.
Published: July 2010

The kinetics of dissolution of soil minerals as a function of the ionic composition of the exchange phase were studied using a calcareous soil and a noncalcareous soil. It was concluded that mineral dissolution occurred as a two‐step reaction when an exchanger phase is present. The initial fast reaction was completed in < 1 h and was linearly related to the amount of exchangeable sodium. The second slower reaction was independent of the exchangeable cation but dependent on the total mineral surface (soil‐to‐water ratio) available for weathering. The kinetics of dissolution for the second reaction was diffusion controlled.
A Mathematical Model of Soil Erosion and Deposition Processes: II. Application to Data from an Arid‐Zone Catchment
Authors: Rose C. W. , Williams J. R. , Sander G. C. , Barry D. A.
Published: July 2010

Mathematical theory for soil erosion and deposition processes on a plane land element was applied to data on runoff and sediment concentration as a function of time for nine runoff events from a small (1.3 ha) arid watershed in Arizona. Sediment concentration (and therefore sediment flux) vs. time measured at the exit to the watershed could be matched by the theory using particular values of two physically defined parameters. These two parameters are essentially the detachability of soil to rainfall, and the efficiency of sediment entrainment by overland flow. The first parameter had greatest effects on sediment concentration early in any runoff event, and the second parameter dominated later concentrations, thus allowing almost independent assessment of both parameters. The variation in soil detachability with mean depth of overland flow derived from the field data bore similarities to controlled laboratory observations.
A Simplified Model for Solute Movement Through Soils
Authors: Amoozegar‐Fard A. , Warrick A. W. , Fuller W. H.
Published: July 2010

Solute movement through soil can be described by a variety of mathematical models whose unknown parameters (often three or more) must be estimated accurately and efficiently. In many cases, the movement of an ion can be described by a breakthrough curve at a given depth. Such a curve resulting from a step input of solute is often of sigmoidal shape. In this paper, an error function model that fits such a breakthrough curve is presented with two unknown parameters. The parameters can be estimated explicitly by a small calculator. Although chosen by least square differences, the parameters can be interpreted on the basis of sound physical principles.
Effect of Soluble Species Released from Soil Sources on the Composition of Soil and Drainage Solutions
Authors: Levy Rachel , Shainberg I. , Mazouz Rachel , Eisenberg Henrietta
Published: July 2010

Two soils differing in the amounts of calcium and magnesium released during dissolution of soil minerals, cation exchange capacity (CEC), lime content, and water‐holding capacity were irrigated under the same conditions with four synthetic waters. Two of the waters contained only chloride, and the other two contained both chloride and bicarbonate anions. Sodium adsorption ratios of the two chloride and two bicarbonate waters were either 10 or 20. Following every 10 wetting and drying cycles the two soils were leached with about 10% excess water. Five such leachates were collected and analyzed. Soil analysis was performed after 20 and 40 irrigation cycles. A significant difference was found between the chemical composition of the drainage and soil solutions of the two soils. To evaluate this diversity, the law of mass conservation was used to calculate the amount of calcium and magnesium released by dissolution in the absence and presence of carbonate precipitation. Two assumptions were used in these calculations: (i) during irrigation with the chloride waters no precipitation of carbonates occurred, and (ii) during irrigation with the bicarbonate waters no dissolution took place. These assumptions proved valid only for the soil that released small amounts of salt by dissolution. The two soils released almost equal amounts of calcium and magnesium from exchange sites, although there was a significant difference in CEC. It was concluded that the primary source that induced the differences in chemical composition of the drainage and soil solutions was the amount of calcium and magnesium released by mineral dissolution.
Multifactor Kinetics of Phosphate Reactions with Minerals in Acid Soils: II. Experimental Curve Fitting
Authors: Lin Chenfang , Motto H. L. , Douglas L. A. , Busscher W. J.
Published: July 2010

A kinetic model of phosphate reactions with minerals in acidic soils was used to simulate experimental results obtained under a variety of conditions based on three factors—solution pH, solution concentration, and mineral specific surface area. Three minerals with different reactivity (kaolinite, gibbsite, goethite) were studied to check the adaptability of the model and show the effect of mineral properties on reaction with phosphate. The experimental data as well as the kinetic models showed that high pH values, low concentrations of the phosphorus in the reacting solution, and small specific surface area will reduce retention of phosphate. Any other change of the three factors increases the retention capability. The model shows its flexibility in simulating phosphate reactions with different minerals. The results show promise for the miltifactor approximation of phosphate reactions with soil minerals in acid to neutral soils.
pH‐Dependent Boron Adsorption by Montmorillonite Hydroxy‐Aluminum Complexes
Authors: Keren R. , Gast R. G.
Published: July 2010

Boron adsorption by hydroxy aluminum and by hydroxy aluminum montmorillonite complexes was determined as a function of pH and boron concentration in solution. Data from both experiments were compared with results computed according to the fitted adsorption coefficient. The agreement between calculated values and experimental results indicates that the phenomenological equation suggested by Keren et al. (1981) can be used in a modified form to predict boron adsorption on hydroxy aluminum as a function of both the boron concentration and the pH. Boron adsorption by both the physical and chemical mixtures (hydroxy aluminum and montmorillonite) was greater than by montmorillonite alone, with the physical mixture adsorbing the largest amount of boron.