bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Water Content on Electrical Conductivity of the Soil
Authors: Gupta S. C. , Hanks R. J.
Published: July 2010

Measurement of dynamic salinity and water content profiles under laboratory conditions were needed to test a model developed to characterize the simultaneous flow of water and salts in soils. Methods were needed for measuring salinity in place in a system where rapid water movement occurred. Because of the time lag in salinity sensors, other methods were considered for evaluating salinity.

The four‐probe system of measuring electrical conductivity of soil eliminates the time lag error, but introduces the problem of correcting the changes in conductivity caused by water content. Units were constructed and samples prepared to evaluate the influence of water content, and salt concentrations on the four‐probe conductivity (K4P). Two soils were studied. Regression equations developed to estimate saturation or 1:5 extract electrical conductivity from four‐probe conductivity and water content (π) gave correlation coefficients of 0.75 and 0.90, respectively. Correlations for individual soils were generally higher than the combined soils. The regression equation relating the ratio of K4P to four‐probe conductivity at saturation (K 4PS) with water content was 4K4P/K4PS = − 0.26 + 2.49π with a correlation coefficient of 0.88 for the combined soil data.
Solutions for Miscible Displacement of Soil Water with Time‐Dependent Velocity and Dispersion Coefficients
Authors: Warrick A. W. , Kichen J. H. , Thames J. L.
Published: July 2010

Miscible displacement processes with time‐varying velocity and dispersion coefficients are examined. Simplified solutions utilizing arbitrary initial conditions are presented and used to simulate step and slug inputs of solutes into soil during infiltration of water. The solutions are used in the analysis of experimental data, both for field infiltration with a slug of solute and for psychrometric measurements of salt fronts in a laboratory sand column. Experimental data obtained for solute movement was more accurately described using time‐increasing dispersion relationships than for constant values.
Characteristics of Phosphorus Adsorption by Some Nigerian Soils
Authors: Udo E. J. , Uzu F. O.
Published: July 2010

Tropical acid soils adsorb a large portion of phosphorus added to them. In order to study the characteristics of phosphorus adsorption in 10 Nigerian acid soils, 2 g of soil were equilibrated in 0.01M CaCl2 containing various amounts of phosphorus for 48 hours. The phosphorus disappearing from solution was taken as the amount adsorbed. The capacity to adsorb phosphorus varied among the soils, but in general the more strongly weathered soils from the eastern area adsorbed more phosphorus than those from western Nigeria. At low concentrations of phosphorus in the equilibrium solution, the adsorption could be satisfactorily described by Langmuir Isotherm equation. The adsorption was significantly correlated with sesquioxides and the exchangeable forms of Al and Fe as well as the clay content and pH. The citrate‐dithionite and the oxalate extractable oxides were of equal significance in the phosphorus adsorption, but the role of Al was more important than that of Fe.
Interacting Diffuse Layers in Mixed Mono‐Divalent Ionic Systems
Authors: Bresler Eshel
Published: July 2010

A numerical solution of the electric double‐layer problem, for the case of overlapping diffuse layers in mixed monovalent‐divalent ion systems, is used to obtain a series of graphs for various cation compositions in the external solution. In these graphs, the electric potential is expressed as a function of the surface charge density, the concentration of the two cations in the equilibrium solution, and the distance between platelets in various ionic mixtures. The graphs cover most of the situations usually encountered in soil systems, and are not sensitive to the valency of the anions present. They are used to estimate the electrostatic effect on cation exchange equilibria, swelling pressures, and electrokinetic phenomena in mixed‐ion clay systems. Application of these estimates to theoretical analyses and comparisons between theoretical models and experimental data are illustrated. Some of the examples used for this illustration are based on work previously published by others.
Effect of Phosphate Salts as Saturating Solutions in Cation‐Exchange Capacity Determinations
Authors: Schalscha E. B. , Pratt P. F. , Kinjo T. , Amar A J.
Published: July 2010

Cation‐exchange capacities with KCl or NaNO3 in volcanic ash soils varied from 6 to 18 meq/100 g whereas CEC with KH2PO4 or NaH2PO4 varied from 78 to 188. Cation‐exchange capacities with NaH2PO4 and NaNO3 were 28 and 6, respectively, for an alfisol and 12 and 2, respectively, for an oxisol. The ratios of CEC with H2PO4‐ as compared to Cl‐ or NO3‐ varied from about 4 to 30. The effect of the H2PO4‐ is explained as a result of neutralization of positive charge in the soil with a simultaneous release of negative charge.
Effect of Freeze‐Thaw Cycles on Aggregate Stability and Hydraulic Conductivity of Three Soil Aggregate Sizes
Authors: Benoit George R.
Published: July 2010

The study reported here was conducted to determine freeze‐thaw influences on the vertical hydraulic conductivity of soil. To accomplish this three soil aggregate sizes (0.0 to 0.8 mm, 0.8 to 1.2 mm, and 1.2 to 2.0 mm) were packed in aluminum cores, equilibrated at two water levels (maximum water‐holding capacity and 0.5 bar of pressure) and subjected to 20 freeze‐thaw cycles at two freezing temperatures (−4C and −18C). Hydraulic conductivity and aggregate stability were determined for all cores before and after the freeze‐thaw cycles.

Generally, water‐stable aggregate breakdown was statistically greater at maximum water holding content. The percentage of water‐stable aggregates in the 0.0‐ to 0.8 mm aggregate class increased by a factor of 1.26 from initial values after freezing and thawing at the 0.5 bar water level and −4C freezing temperatures.

Freezing and thawing caused the greatest decrease in vertical hydraulic conductivity of those cores with large aggregates and high water content subjected to the −18C freezing temperature. Freezing and thawing of cores at 0.5‐bar water content generally increased hydraulic conductivity. An exponential relationship seems to exist between the change in the ratio of final to initial hydraulic conductivity and the soil water content at freezing. Drainage of soil water from surface horizons could induce freeze‐thaw improvement of the soil's vertical hydraulic conductivity.
Chloride Movement in Undisturbed Swelling Clay Soil
Authors: Kissel D. E. , Ritchie J. T. , Burnett Earl
Published: July 2010

Relatively large, continuous soil pores were important pathways of downward Cl‐ movement in saturated, swelling clay soils. Using water‐soluble fluorescein as a tracer for downward water and Cl‐ movement in field basins, distinct small areas of the soil contained fluorescein, whereas nearby areas contained no visible fluorescein after Cl‐ and fluorescein was ponded at the surface for 1.5 days. Chloride contents in the areas containing fluorescein were considerably higher than in nearby areas. Breakthrough curves of a large saturated core of undisturbed swelling clay soil indicated that Cl‐ was moving quite rapidly through large connected pores. In the undisturbed swelling clay soil, the volume of soil water not containing Cl‐ was about 60%; when the disturbed soil was repacked to the same density this value decreased to 40%.

More of the original soil solution was eluted from long undisturbed cores than from short undisturbed cores of the same diameter before Cl‐ appeared in the effluent. Apparently the longer core wall blocked more connected flow paths which were not vertical.
Mobility of Polyphosphates in Soil
Authors: Hashimoto Isao , Lehr James R.
Published: July 2010

Ammonium ortho‐, pyro‐, tripoly‐, tetrapoly‐, and long‐chain polyphosphates and cyclic ammonium tri‐ and tetrametaphosphates were surface applied to soil columns. After 1, 2, and 4 weeks the soil columns were sliced into 1‐mm sections and examined for the distribution of P along the columns. Each soil section was analyzed for total and orthophosphate P in both the water‐soluble and the immobilized (NaOH‐extractable) fractions. The general features of the distribution patterns usually were established by the first week, after which soluble P moved much more slowly and the amount of immobilized P increased slowly. The total distance of movement and the distribution patterns of water‐soluble P were similar for all the phosphates tested, but the polyphosphates differend markedly in the degree of immobilization of P and differed significantly in the positions of maximum retention of P in the soil columns. These positions of maximum retention had no apparent relation to the degree of condensation of the polyphosphates.
Interactions with Soil Lipase Activation and Inhibition
Authors: Pancholy Sunil K. , Lynd J. Q.
Published: July 2010

Soil lipase interactions of Psammetic paleustalf, Eufaula loamy sand, were determined with a fluorometric assay of enzymatic cleavage converting nonfluorescent 4‐methyl umbelliferone butyrate (4‐MUB) to the highly fluorescent 4‐methyl umbelliferone (4‐MU). Soil lipase activity accelerated with manipulation of base cation levels. Combination effectiveness as reaction activators at 2.0M × 10‐4 was Ca + Mg + Na or K or Na + K > Ca + Mg > Ca > Mg > Na or K. Highly significant competitive lipase inhibition was induced with 0.1M Cu2+ > S2‐ > EDTA at MUB substrate levels of 12.5 to 75.0 × 10‐4M. Iron3+ noncompetitive inhibition was near constant.
X‐Ray Diffraction, Electron Microscopy, Electrophoretic Mobility, and pH of some Stable Smectite‐Protein Complexes
Authors: Harter Robert D. , Stotzky G.
Published: July 2010

X‐ray diffractometry, electron microscopy, electrophoretic mobility, and pH measurements have been used in an attempt to understand the mechanisms involved in the formation of stable clay‐protein complexes. Pepsin was apparently adsorbed to positive edge sites on the smectite, and all other proteins were adsorbed on planar surfaces. Casein, chymotrypsin, lysozyme, and ovomucoid intercalated the H and Na‐smectites, and catalase may have intercalated the H‐smectite. All proteins, except catalase, appeared to intercalate the clays when the weight ratio of protein‐to‐clay exceeded about 1:5. Catalase did not appear to intercalate the Ca, Al, La, or Th‐smectites, even though the ratio of adsorbed protein‐to‐clay exceeded 1:5. The electrophoretic mobility of the H, Na, and Th‐smectites became less negative upon adsorption of proteins, indicating a physical or chemical covering of the negative clay surface charge and a flocculation of the complex. When protein was adsorbed by Ca, Al, and La‐smectites they either showed little change or increased in electrophoretic mobility, indicating a tendency for clay tactoids to be broken. The pH of all protein‐clay complexes tended to approach neutrality. In the acid clays (H, Al, and Th‐smectite), especially, this indicated a cation exchange reaction, since the exchanged inorganic ions would be subsequently removed from the clay.
A Multichannel Syringe Pump for Steady State Flow in Soil Columns
Authors: Wierenga P. J. , Black R. J. , Manz P.
Published: July 2010

A multichannel syringe pump3 was designed for maintaining a constant rate of outflow over long periods of time. Low flow rates are obtained by using a timer‐control which causes the pump to make one cycle per set time interval. The pump is not pulse free, but for many studies requiring steady state water movement in soil columns this is not considered too great a disadvantage. Measured over a 10‐day period at a rate of outflow of 173 ml/day, the mean day‐to‐day variation was less than 0.2 ml/day.
The Chemistry and Phytotoxicity of Arsenic in Soils: II. Effects of Time and Phosphorus
Authors: Woolson E. A. , Axley J. H. , Kearney P. C.
Published: July 2010

Arsenate from sodium arsenate changes to less soluble compounds in soils with time. To study these changes, the arsenic soluble in 1N NH4Cl, 0.5N NH4F, 0.1N NaOH, and 0.5N H2SO4 solutions was determined. These dissolved arsenates were designated as WS‐As (water soluble), Al‐As, Fe‐As, or Ca‐As, respectively. The percent of WS‐As present was proportional to As added and inversely proportional to time, and to the Fe and Al content. Fe‐As was the predominant form of As in Hagerstown silty clay loam while Al‐As predominated in Lakeland loamy sand. Growth of corn (Zea mays) increased with increase in time of As incubation in the soil before planting.

Arsenic phytotoxicity and As in the plant were altered by P additions. Arsenic residues in the Lakeland soil became more phytotoxic, while residues in the Hagerstown soil became less phytotoxic with P additions. This plant response was related to the availability of As and P in these soils. Leaching with 0.05M KH2PO4 removed 77% of the total As from a contaminated Dunkirk fine sand. The distribution of the forms of As in this soil changed during leaching.
Water Movement and Caliche Formation in Layered Arid and Semiarid Soils
Authors: Stuart D. M. , Dixon R. M.
Published: July 2010

In soils, downward water movement is restricted when finetextured materials are underlain by sand or gravel layers. Water accumulates in arid and semiarid soils at the interface of the fine‐ and coarse‐textured materials and may rarely enter the coarse‐textured materials. Calcium carbonate, silica, and other salts are deposited at or near the top of the sand or gravel layers as water is removed by evapotranspiration. With time, silica, calcium carbonates, and other salts become cemented or indurated, forming calcareous crusts at these interfaces. The sands and gravels are not wet uniformly when water does enter, because it enters relatively small areas. Calcareous concentrations may form in these small, wetted areas and may be seen as calcareous cemented columns surrounded by noncal careous sands or gravels.
Horizontal Infiltration of Water in Soils: A Theoretical Interpretation of Recent Experiments
Authors: Parlange Jean‐Yves
Published: July 2010

A general theory of water movement is used to describe the horizontal infiltration of water when the diffusivity increases exponentially with moisture content. The results can be expressed in simple analytical form and are in excellent agreement with experimental observations. The results confirm that the theory is accurate because water diffusivity varies with water content.
Factors Affecting the Formation of Quasi‐Crystals of Montmorillonite
Authors: Greene R. S. B. , Posner A. M. , Quirk J. P.
Published: July 2010

Light scattering techniques and the development of flow birefringence by suspensions have been used to follow the rearrangement of elementary silicate sheets of Ca‐montmorillonite to form quasi‐crystals.

Shaking transforms Ca‐montmorillonite particles in a 0.25M CaCl2 suspension from loose, fluffy floccs into stable, compact particles >2.0µ in lateral extent and as much as 20 to 30 layers thick, known as quasi‐crystals. Quasi‐crystals of similar lateral extent but only four layers thick took longer to form at low electrolyte levels, <10‐3M CaCl2, in which more extensive double layers are present. Dialysis of Ca‐montmorillonite suspensions also produced quasi‐crystals, which are intermediate in thickness between those formed by the above two preparations.

The stability of quasi‐crystals was demonstrated by the fact that high energy ultrasonic radiation was required to disrupt their structure.

Sodium montmorillonite suspensions subjected to similar conditions of mechanical agitation and dialysis failed to form quasi‐crystals, the only form of aggregation being into unstable floccs.
Unsteady Two‐Dimensional Flow of Water in Unsaturated Soils Above An Impervious Barrier
Authors: Selim H. M. , Kirkham Don
Published: July 2010

The unsteady two‐dimensional, water flow equation for unsaturated soils is solved by use of a finite difference approximation and an alternating‐direction implicit (ADI) method. The two‐dimensional flow medium is a homogeneous soil with an impervious barrier at some depth from the soil surface and having equally spaced trenches. The bottom of the trenches are wetted at time zero and are kept at a constant 0.50 cm3/cm3 water content, the initial soil water content of the flow medium is 0.20 cm3/cm3. Water movement from the walls of the trenches and the soil surface is neglected. Computer results of the water content with time at all locations in the flow medium are obtained for physical data from an Ida silt loam soil for two geometries. For trenches at 120 cm spacing, 30 cm deep, and 30 cm wide, the wetting front reaches a depth of 30 cm in 35 min, and reaches the soil surface in 140 min. For trenches at 60 cm spacing, 15 cm deep, and 15 cm wide, the wetting front reaches a depth of 30 cm in 45 min, and reaches the soil surface in 30 min. The ADI method proves valuable for use with a modern computer to solve unsteady two‐dimensional flow problems.
Diurnal Soil‐Water Evaporation: Time‐Depth‐Flux Patterns
Authors: Jackson R. D. , Kimball B. A. , Reginato R. J. , Nakayama F. S.
Published: July 2010

Time‐depth patterns of soil water flux in the 0‐ to 9‐cm zone of a bare field soil are presented for four 24‐hour periods at 3, 7, 16, and 37 days after irrigation. On day 3, the flux at 0 cm (evaporation) dominated the flux patterns for all depths. As the soil dried, this flux decreased and those at the greater depths gradually became dominant. On all 16 days of measurement, downward flux was observed below 1 to 3 cm during several hours between sunrise and early afternoon. Only one period of downward flux was observed for day 3; whereas, 2 to 4 periods were noted for subsequent days. The data demonstrate the dynamic nature of soil water flux in the surface zone of a field soil subjected to diurnally varying environmental conditions.
Use of Indigenous Soil‐Rubidium Absorbed by Cotton Plants in Determining Labile Soil‐Potassium Pool Sizes
Authors: Hafez A. A. R. , Stout P. R.
Published: July 2010

The rubidium/potassium (Rb/K) ratios of natural soils and of most soil‐grown plants are higher than Rb/K ratios of many available fertilizer‐grade potassium salts as revealed by analyses of 24 samples of commercial K‐fertilizers. Low‐Rb K‐fertilizers of 0.02 mmoles Rb/mole K or lower may offer practicable means for field scale tracing of fertilizer‐K absorbed by crop plants when growing under normal management regimes. Whenever K‐fertilization results in lower Rb/K ratios appearing in fertilized plants, this dilution or “reversed‐tagging” of indigenous soil‐Rb with low Rb‐containing K‐fertilizers permits determinations of pool‐sizes of labile soil‐K. Four different soils were compared for NH4OAc extractable‐K, HNO3 extractable‐K, and the pool‐size of labile‐K as determined from Rb/K ratios of K‐fertilized cotton plants (Gossupium hirsutum L.). A large pool size of labile‐K does not necessarily mean that the K supplying power of a soil is large. The Rb/K ratios can also be used to calculate relative amounts of absorbed plant‐K originating from the indigenous soil‐pool vs. the plant‐K derived from a K‐fertilizer.
Weathering of Biotite in Soils of a Humid Tropical Climate
Authors: Ojanuga A. G.
Published: July 2010

The weathering of biotite in soils formed in saprolites derived from granite and gneiss was studied. The soils occurred in the Southwestern Upland of Nigeria which is characterized by a humid tropical climate.

Vermiculite and montmorillonite are the usual products of biotite weathering in well‐drained temperature soils, whereas kaolinite appears to be the dominant product in the well‐drained, moderately acidic, tropical soils studied. The formation of kaolinitic pseudomorphs represented a stage in the kaolinization of biotite in the soils. A mechanism for the kaolinization of biotite has been suggested.
Dissolved Aluminum in Acid Sulfate Soils and in Acid Mine Waters
Authors: van Breemen N.
Published: July 2010

Analytical data on water samples from acid sulfate soils and acid mine spoils indicate that the upper limit of dissolved Al is regulated by a basic aluminum sulfate with the stoichiometric composition AlOHSO4. The observed solubility relationship, pAl + pOH + pSO4 = 17.23, can be useful in defining environmental conditions in terms of pH and dissolved sulfate for the occurrence of Al concentrations toxic to plants.
Liming as Related to Solubility of P and Plant Growth in an Acid Tropical Soil
Authors: Amarasiri S. L. , Olsen S. R.
Published: July 2010

The reactions between soil and fertilizer P at six levels of liming were investigated on an acid tropical soil. An acidic soil of pH 3.8 was limed to pH 7.0 in stages. Four levels of phosphorus were added to the soils.

For any level of phosphorus, liming decreased soluble P and labile P until the pH reached about 6.5. The phosphate potentials did not lie consistently on known solubility isotherms, but the potentials approached hydroxyapatite at pH values between 6.9 and 7.0. A labile pool of P appeared to govern mainly the concentration of P in the soil solution. Limed soil had a higher maximum adsorption capacity for phosphorus than the unlimed soil. Adsorption of P by the freshly precipitated Fe and Al hydroxides apparently caused the greater inactivation of added phosphorus in the limed soils.

Rye (Secale cereale L.) and millet (Setaria italica L.) were grown in the greenhouse at six levels of lime and four levels of phosphorus. The yields and percent P of rye were significantly increased by P without lime, but the response to added P was greater in the presence of lime. Lime with added P caused larger differences in yield and percent P of millet than in rye. Liming increased the yields of millet with added P until a pH of about 5 to 6 was reached, but further additions of lime decreased the yields. The percent P of millet increased with the initial applications of lime, but further additions resulted in a slight decrease of percent P. Plants were healthier and their root system better developed on the limed soil, which probably caused a higher percent P in the tops.
Uniformity of Limestone Mixing in Acid Subsoil as a Factor in Cotton Root Penetration
Authors: Pearson Robert W. , Childs Joel , Lund Zane F.
Published: July 2010

Cotton (Gossypium hirsutum L.) root growth response to different degrees of mixing limestone in strongly‐acid subsoil was determined, using both short‐term radicle elongation and full‐growth‐cycle root extension as criteria. The roots displayed no chemotropic response to limed pathways in the acid subsoil. Roots grew best when the entire subsoil mass was mixed with limestone. However, when applied at an adequate rate, even poorly‐mixed limestone increased rooting depth at least twofold. Both radicle elongation rate and final root pattern were closely related to percentage of total subsoil mass limed in the incompletely mixed treatments, even when the neutralized soil zones averaged as much as 7.6 cm apart.
Mulch and Tillage Relationships in Corn Culture
Authors: Van Doren D. M. , Triplett G. B.
Published: July 2010

Relative effects of soil mulch cover and various tillage practices on corn (Zea mays L.) yield were studied as functions of previous crop and rainfall on a typic fragiudalf soil. Residues (mulch from previous crops of corn or tall fescue) were removed from the soil prior to tillage, manipulated according to action of the tillage implements, or replaced on the soil surface after tillage. Eight tillage treatments consisted of all possible combinations of moldboard plowing, disking, and post emergence cultivation.

Mulch cover produced three times as great a yield effect as any other single variable, with the effect (kg/ha) = 36.2M − 0.00218 MS, where M is percent of the soil surface covered with mulch and S is yield in kg/ha of the plowed plus cultivated treatment. Tillage variables increased yield in order of cultivation > plow > disk, and results are expressed in terms of mulch cover required to produce an equal yield effect. Most tillage and mulch effects were additive.

The major reason for mulch and tillage effects on corn yield is assumed to be their influence on soil water content. Possible extrapolation of these results to other soils and climates is discussed.
Water Vapor Movement Through Mulches Under Field Conditions
Authors: Kimball B. A.
Published: July 2010

The loss of water vapor through 0.5‐, 1‐, and 2‐cm depths of water repellent mulches was measured under field conditions with lysimeters. Concurrent measurements were made of wind velocities, air vapor pressures, and temperatures at the soil‐mulch interfaces. Mulches used included 0.5‐, 1‐, and 2‐mm glass beads and 1‐mm glass bead aggregates.

By assuming that the relative humidity of the soil air at the soil‐mulch interface was essentially 100%, effective diffusion coefficients for field conditions were calculated. The average effective diffusion coefficient for afternoon periods was 1.26 times greater than the molecular diffusion coefficient. An error analysis revealed that the value could have been as low as 0.90 or as high as 1.63, but these values would have been realized only if the effects of several possible systematic errors were completely additive.

Little correlattion was found between wind velocity and effective diffusion coefficient. However, the generally low range in wind velocities observed and the smoothing required for the reduction of the lysimeter data may have prevented detection of such a correlation.
Water Transport Through Plant Tissues in the Presence of a Diffusable Solute
Authors: Molz Fred J. , Hornberger George M.
Published: July 2010

Because water transport through soils and plants are closely related and interdependent phenomena, it is logical to attempt to develop a quantitative description of water flow in the plant portion of the soil‐plant‐atmosphere continuum comparable to that which exists for the soil portion. The present paper utilizes the theory of nonequilibrium thermodynamics to develop a quantitative description of water transport through aggregations of plant cells containing both permeating and nonpermeating solutes in aqueous solution. Application of the theory results in two linear, coupled, partial differential equations with a water potential‐related term and the diffusable solute concentration as dependent variables. As the permeability of the diffusable solute approaches zero, the system of equations reduces to a single equation first derived by Philip (1958d), wherein the dependent variable is water potential. Using the Crank‐Nicolson method, the one‐dimensional forms of the equations are solved numerically for the case of a fully turgid tissue placed in a solution of diffusable solute at time zero. The solution shows that the resulting transport process is entirely different from the classical case in which the cell membranes are permeable to water only.
The Partial Molal Volumes of Several Ionic Forms of Montmorillonite in Dilute Suspensions
Authors: Miller Raymond J. , Schepers J. , Hassett J. , Brown D. S.
Published: July 2010

A high precision magnetic float densitometer was used to determine the density of dilute aqueous NaCl solutions. The method of intercepts was then used to calculate the partial molal volume of the water and the NaCl salt. These values compared favorably with those in the literature.

Using the above methods, the molal volumes of dilute suspensions of Na+, Li+, K+, and Al3+‐montmorillonite were determined. The partial molal volumes of the homoionic saturated clays were corrected for the exchangeable cations using the additive principle. From these values an apparent density for the four clays was determined. The calculated values are consistent with literature values for dilute suspensions. The data indicates that there are clay‐water‐ion interactions such that the partial molal volume of the clay is greater than expected and the apparent density is less. These differences depend on the exchangeable cation and suggest that the clayion associated water is different than normal water.
Adsorption of Picloram (4‐Amino‐3,5,6‐Trichloropicolinic Acid) on Panoche, Ephrata, and Palouse Soils: A Thermodynamic Approach to the Adsorption Mechanism
Authors: Biggar J. W. , Cheung M. W.
Published: July 2010

The adsorption of picloram (4‐amino‐3,5,6‐trichloropicolinic acid) was studied on Panoche clay loam (at pH 4.2 and 1.2), Ephrata sandy loam, and Palouse silty loam. The adsorption processes could be described by the Freundlich equation with Freundlich constants, K, 1/n, and percentage of adsorption at 25C: respectively, 0.210, 0.92, and 3–5.6% for Panoche at pH 4.2; 2.5, 0.93, and 30% for Panoche at pH 1.2; 0.172, 0.99, and 1.9–3.6% for Ephrata; and 1.74, 0.92, and 26–33% for Palouse. Also evaluated were the standard free energy, entropy, and enthalpy associated with the adsorption processes. The values of ΔG° (kcal/mol), ΔS° (cal/mol per degree), and ΔH° (kcal/mol) were: respectively, −1.2±0.1, −14±2, and −5.3±0.6 for Panoche at pH 4.2; −2.98±0.05, −59±2, and −20±1 for Panoche at pH 1.2; −1.80±0.06, −24±3, and −9±1 for Ephrata; and −3.11±0.05, −3.3±1.5, and −4.1±0.4 for Palouse. Thermodynamic parameters were useful in assigning adsorption mechanisms to the four picloram‐adsorbent‐water systems.
Chemical and Physical Processes that Affect Atrazine and Distribution in Soil Systems
Authors: Swanson Roger A. , Dutt Gordon R.
Published: July 2010

Interactions studied included adsorption and desorption of atrazine by Ca2+, Mg2+, and Na+ saturated soil material and the effect of chloride salts of the above cations on solubility of crystalline atrazine. It was found that adsorption isotherms follow the Freundlich equation. The desorption isotherm had the same shape as the adsorption isotherm but followed a different path back to the starting point. This hysteresis effect encountered indicates that adsorption and desorption of atrazine are irreversible reactions. The desorption isotherm was also found to fit the Freundlich equation where the exponential desorption coefficient was equal to the exponential adsorption coefficient divided by 2.3.

The effect of exchangeable cations was found to be within experimental error, and the solubility of crystalline atrazine was found to be exponentially related to the ionic strength of the solution. Using the equation developed, a computerized model for predicting atrazine distribution and movement in soil systems was prepared. Predicted breakthrough and elution curves were in agreement with those found for effluents from soil columns. It was concluded that the skewed nature of the experimental curve was primarily due to differences in the adsorption and desorption of atrazine.
Self‐Diffusion Coefficients of Selected Herbicides in Water and Estimates of Their Transmission Factors in Soil
Authors: Scott H. D. , Phillips R. E.
Published: July 2010

Self‐diffusion coefficients of selected herbicides were measured in aqueous solution by the capillary tube method. The diffusion coefficients were approximately 0.6 × 10‐5 cm2/sec at 23C and were not particularly related to the configuration of the herbicide molecule. Values calculated for the transmission factors of these herbicides differed with the more mobile compounds being associated with the higher values.
Controlled Instantaneous Application of Free Water to a Porous Surface
Authors: Swartzendruber D. , Asseed M. S.
Published: July 2010

Instantaneous application of free water to a porous‐medium surface is achieved essentially by a device in which the central feature is a plastic plate perforated with small holes. The pressure head of the water can be controlled at a preselected value between 0 and 1 cm. Water enters the porous mdium at essentially zero external flow resistance, while volume and time of entry can be measured accurately. No lateral flow of free water occurs, thus eliminating the disturbing effects of such flow on the porous‐medium surface.
Measurement of Hydraulic Conductivity By Means of Steady, Spherically Symmetric Flows
Authors: Dirksen C.
Published: July 2010

The dependence of hydraulic conductivity upon pressure head can be determined from a series of steady, spherically symmetric flows: at any point the hydraulic conductivity is equal to the rate of change of the steady flux per unit solid angle with respect to the pressure head of that point, divided by its radial distance from the center of the water source. This method is very attractive for in‐situ measurements in the field since it requires only one controlled boundary condition, but does not require one‐dimensional flow. Experimental procedures are described and some results given. Hydraulic conductivity values derived from the pressure head in the source cavity itself were the same as those derived from tensiometer measurements near the source. A range of hydraulic conductivity values can be obtained faster with a series of different, steady pressure heads in the source cavity, rather than by measurements on a series of tensiometers located at several distances from the source.

Gravity tends to distort the spherical symmetry of the flow. An analytical solution for steady flow from a point source, for a soil with an exponential dependence of the hydraulic conductivity upon the pressure head, indicates that for most soils the effect of gravity near the cavity is small enough to obtain satisfactory hydraulic conductivity values. Gravity has no effect on the pressure head distribution directly below the cavity, suggesting that this is a preferred location for tensiometers. Actually, the analytical solution obtains the hydraulic conductivity in an exact manner for any position. The radius of the cavity should be kept as small as possible.
Solute Movement Through Disturbed and Undisturbed Soil Cores
Authors: Cassel D. K. , Krueger T. H. , Schroer F. W. , Norum E. B.
Published: July 2010

Displacement of nitrate and 36Cl through disturbed (reconstituted horizon by horizon) and undisturbed soil profiles of Aberdeen loam and Beotia loam representing strong and moderate soil structure, respectively, were investigated. Each soil core was 30 cm in diameter and at least 80 cm high. Mean water content θ̄ of the undisturbed soil profile was greater and mean bulk density D̄b less than the corresponding values for the disturbed cores for each soil. For example, disturbance increased θ̄ by 0.07 cm3/cm3 for Beotia with a 0.01 g/cm3 decrease in D̄b; disturbing Aberdeen decreased D̄b from 1.47 to 1.30 g/cm3 but increased θ̄ only 0.03 cm3/cm3. The disturbed soils required greater throughout volume of distilled water to displace the solutes and had smaller dispersion coefficients (D) than the undisturbed soils although not even a twofold difference in D was found. For a given effluent sample, relative nitrate concentration was consistently greater than relative 36Cl concentration due to nitrification occurring within both the disturbed and undisturbed soil profiles during the 24‐week period.
Buffer Intensities and Equilibrium pH of Minerals and Soils: I. The Contribution of Minerals and Aqueous Carbonate to pH Buffering
Authors: van Breemen N. , Wielemaker W. G.
Published: July 2010

Thermodynamic equilibrium considerations are used to calculate pH buffer intensities for a number of aqueous systems involving 16 common soil and rock minerals (viz. gibbsite, kaolinite, allophane, hematite, limonitic iron oxide, quartz, amorphous silica, calcite, siderite, hydrated magnetite + amorphous Fe(OH)3, microcline, albite, anorthite, Mg‐montmorillonite, two illites, and Mg‐chlorite), gaseous CO2 and 26 dissolved species. The calculation of buffer intensities is outlined for simple oxides and carbonates (analytical evaluation) and for silicate minerals during congruent and incongruent dissolution (graphical differentiation). Silicate minerals, carbonates and gibbsite provide strong buffering upon addition of strong acid under slightly alkaline to slightly acid conditions. Carbon dioxide at constant partial pressure is far more effective than any of the minerals considered in counteracting the effect of an increase in alkalinity.
Buffer Intensities and Equilibrium pH of Minerals and Soils: II. Theoretical and Actual pH of Minerals and Soils
Authors: van Breemen N. , Wielemaker W. G.
Published: July 2010

Equilibrium pH values of different clay minerals, oxides and carbonates at pCO2 = 10‐2 atm. are between 4.5 and 8, i.e., in the range typical for most soils. The agreement between the calculated pH and the abrasion pH for most minerals is reasonable. The pH of a number of soils can be explained by partial equilibrium between the soil solution and kaolinite, allophane, gibbsite, montmorillonite or calcite. For illite the agreement is less satisfactory. The effects of reducing conditions and the possible role of pH buffering by organic matter are discussed briefly. Application of the phase rule indicates that the specific mineral assemblage of acid sulfate soils provides a nearly ideal pH‐stat, i.e., addition of moderate amounts of sulfuric acid or lime hardly affects the pH.
Kinetics of the Phosphate Interaction with Calcite
Authors: Griffin R. A. , Jurinak J. J.
Published: July 2010

The kinetics of the phosphate interaction with calcite were studied. The results showed that the reaction did not proceed in the absence of the calcite surface. The kinetics of interaction could be described by two simultaneous reactions. The first reaction was second‐order and was ascribed to the adsorption of phosphate on the calcite surface. The second reaction was first‐order and was considered to be associated with the surface arrangement of phosphate clusters into calcium phosphate heteronuclei.

Solubility criteria were used to show that at low phosphate concentrations the ultimate calcium phosphate surface mineral formed was hydroxylapatite.

Desorption kinetics were studied by using an anion exchange resin technique. The desorption process could be described as two simultaneous first‐order reactions. The desorption mechanism was postulated to correspond to the dissolution of a surface nucleated calcium phosphate mineral, with the second reaction step being the desorption of phosphate from the calcite surface sites.

The rate constants for adsorption and desorption were determined at four temperatures between 0C and 40C. The rate constants were used to compute the activation energies of adsorption and desorption. In addition, the thermodynamic parameters for the enthalpy of activation (ΔH†), the entropy of activation (ΔS†), and the free energy of activation (ΔG†), for both the adsorption and desorption processes were computed and discussed.
Nitrogen Mineralization‐Water Relations in Soils
Authors: Stanford George , Epstein Eliot
Published: July 2010

The relationships between soil N mineralization, soil water content, and matric suction were studied with nine soils of widely differing chemical and physical properties. Highest N mineralization rates occurred between matric suctions of ⅓ to 0.1 bar, in which range 80 to 90% of the total pore space was filled with water. In the range from optimum soil water content (⅓ to 0.1 bar) to 15 bars, a near‐linear relation generally existed between amounts of mineral N accumulated and soil water contents (percent of oven‐dry soil). With increasing dryness, N mineralization continued to decline. Water levels above optimum often reduced mineral N accumulations, presumably because of denitrification.

Upon expressing the values for N mineralization (Y) and soil water content (X) for each soil on a relative basis with respect to maximum N mineralized (Y = 100) and associated optimum soil water content (X = 100), the regression of Y on X did not differ among soils. Regression coefficients for common (based on covariance) and total regressions, respectively, were 1.07 and 1.02. Corresponding Y‐intercepts were −2 and −4. A reasonable approximation of the relationships is expressed by Y = X. Possible application of the findings in predicting N mineralization under fluctuating soil water conditions is discussed.
Slash Pine Biomass Response to Site Preparation and Soil Properties
Authors: McKee W. H. , Shoulders Eugene
Published: July 2010

Of slash pine (Pinus elliottii Engelm. var. elliottii) plantations on an imperfectly drained soil in Louisiana, those on elevated beds developed about one‐third more aboveground tree biomass by age 8 years than did those on flat‐disked or unprepared sites (51 metric tons/ha as compared with 34 and 39). Bedding increased average depth to free water and average redox potential of the surface soil during winter and reduced the percent of organic matter in the 0–10‐cm layer. Independently of site treatments, total aboveground biomass and the amounts of N, P, Ca, and Mg it contained varied directly with average depth to the water table and soil redox potential during winter. Phosphorus content of the biomass was weakly, if at all, associated with these indicators of root aeration. Results indicate that root environment during winter profoundly influences early growth of slash pine and utilization of nutrients.
A Simplified Determination of Reductant‐Soluble Phosphate in Soil Phosphate Fractionation Schemes
Authors: Weaver R. M.
Published: July 2010

A simplified and more rapid procedure for the determination of reductant‐soluble phosphorus (P) was developed by a modification of the Murphy and Riley (1962) ascorbic acid method. The procedure which eliminated the interference of sodium dithionite by air‐oxidation and that of sodium citrate by addition of ammonium molybdate, was suitable for the determination of 0.1 to 0.7 µg P/ml in the presence of up to 3000 µg Fe/ml and 4.0 µg Si/ml.
Effect of Varying the On‐Off Time of Rainfall Simulator Nozzles on Surface Sealing and Intake Rate
Authors: Sloneker L. L. , Moldenhauer W. C.
Published: July 2010

Many erosion studies have been conducted using water drops formed by sprinkler irrigation nozzles. Rainfall intensity is controlled by varying the on‐off time. This study shows that after a certain point, the energy to initiate runoff is increased as the nozzle off time is increased. Water intake rate is increased as application rate is increased even though runoff is taking place.
Effect of Monosilicic Acid on Hydrolytic Reactions of Aluminum
Authors: Luciuk G. M. , Huang P. M.
Published: July 2010

The mechanisms and products of hydrolytic reactions of Al ions as influenced by Si(OH)4 were studied under the experimental parameters of degere of hydrolysis of Al (OH/Al molar ratios,) Si/Al molar ratios, Al concentrations of 1.39 × 10‐3M and 1.39 × 10‐4M, and time.

As the degree of hydrolysis of Al increased, the amounts of Si along with Al initially precipitated and removed from the solution phase by ultrafiltration consistently increased. The coprecipitation data, infrared evidence, and stoichiometric considerations of Si(OH)4 removal and proton release strongly indicate that the predominant coprecipitation of Si(OH)4 with hydroxy‐Al ions is the condensation reaction involving the hydroxyl groups in hydroxy‐Al ions. At the OH/Al molar ratios of 1 and 2 and in the absence of Si(OH)4, precipitation of Al continued with aging; whereas at the Si/Al molar ratios of 0.5 and 1, the reaction products were metastable, and there was formation of a significant portion of nonextractable Al which was not removed by ultrafiltration.

In the absence of Si(OH)4, the product was crystalline Al(OH)3 even at the OH/Al molar ratio of 1. Materials amorphous to X‐ray and electron diffraction were the only products at Si/Al molar ratios of 0.5 and 1, OH/Al molar ratios of 2 and 3, and both initial Al concentrations even after prolonged aging. Decreasing degree of hydrolysis of Al resulted in a distinct decrease in particle size for crystalline products, and in a decrease in the extent of aggregation for amorphous products. The thermal stability and Si/Al ratio of the reaction products were influenced by the Si/Al molar ratio of solution and the period of aging. The presence of Si(OH)4 in solutions also resulted in a decreased Cl inclusion in the reaction products.

The results clearly show that the presence of Si(OH)4 affects the hydrolytic reactions of Al at all degrees of hydrolysis of Al. This knowledge is of basic significance for a further understanding of pedogenic processes, and the fate of certain nutrients and environmental pollutants.
Adsorption of Fenuron and Monuron (Substituted Ureas) by Two Montmorillonite Clays
Authors: Van Bladel R. , Moreale A.
Published: July 2010

The effect of the type of clay mineral, exchangeable cation, temperature, and electrolyte concentration on the adsorption of two substituted ureas was investigated.

The adsorption was greater on a Bentonite than on a Camp Berteau montmorillonite, possibly because the lattice charge in the former originates from tetrahedral and octahedral layers whereas in the latter only from octahedral layers. The adsorption increased with the polarizing power of the exchangeable cation. Normal adsorption isotherms were exothermic but when the temperature effect on solubility was accounted for, the adsorption reaction tended to be more and more temperature independent as the electronegativity of the exchangeable cation increased. Relative thermodynamic data suggest that the favorable contribution to the adsorption energy arises mainly from enthalpy changes.

The effect of salt concentration was almost negligible up to 1.0N and for a given electrolyte good agreement was obtained between the heat of solution of the herbicide and its adsorption.
Anion Adsorption by Allophanic Tropical Soils: I. Chloride Adsorption
Authors: Gebhardt H. , Coleman N. T.
Published: July 2010

The adsorption of Cl by Andepts from Mexico, Colombia, and Hawaii was measured in solutions of HCl, HCl + NaCl, and AlCl3. Chloride adsorption varied from 0‐8 meq/100 g at pH 6 to as much as 32 meq/100 g at pH 3.8. At given pH, adsorption was concentration‐dependent in a manner consistent with the Langmuir adsorption equation. For a B‐horizon sample from San Gregorio, Mexico, the Cl adsorption maxima, in meq/100 g, were 7.4 at pH 6; 10.7 at pH 4.8; 13.4 at pH 4.4; 17.3 at pH 4.2; and 31.6 at pH < 4. The average a from the Langmuir equation was 0.04 liter/meq. Adsorbed Cl was removed by leaching with water, and was exchanged by NO3.

Chloride adsorption from HCl or HCl‐NaCl was accompanied by the consumption of protons; adsorption from AlCl3 resulted in the hydrolysis and precipitation of Al. Protons consumed or Al hydrolyzed exceeded Cl adsorbed by amounts corresponding closely to the effective CEC. The results suggest that protons are adsorbed to produce positively charged sites, which bind Cl nonspecifically.

Chloride adsorption capacity can be conveniently measured by shaking soil with AlCl3 solution and measuring Cl uptake. Chloride capacities of soils and clay minerals, determined by the AlCl3 procedure, were, in meq/100 g, 7–30 for Dystrandepts; 16–18 for Hydrandepts; 2–4 for acid soils containing crystalline clay and oxide minerals; 4 for kaolinite; zero for montmorillonite and illite.