bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation Hazard from Americium‐Beryllium Neutron Moisture Probes
Authors: Gee G. W. , Stiver J. F. , Borchert H. R.
Published: July 2010

Neutron fluxes from shielded neutron moisture probes need to be measured to evaluate total radiation exposure from these instruments. Theoretical considerations suggest that for 100 mCi Am‐Be neutron moisture probes the fast neutron flux can be relatively high and contribute significantly to the radiation exposure of probe operators.

Measured radiation dose levels at the surface of 100 mCl Am‐Be neutron probes manufactured by Troxler Laboratories were found to be as high as 37m Rem hours‐1 which exceeds reported levels by as much as 38 times. This is likely due to nonreporting of fast neutron fluxes. Conventional field use of these probes may present a radiation hazard to operators if the probe is hand carried for periods which exceed 3 hours/week. The probe should be transported to and from sites inside a wooden storage crate and be kept at least 1 m from personnel. To improve the radiation safety factor for on site use we recommend a hand cart to transport the probe.
Heat and Water Movement Under Surface Rocks in a Field Soil: I. Thermal Effects
Authors: Jury W. A. , Bellantuoni B.
Published: July 2010

Results of a field experiment designed to evaluate the effect of surface rocks on soil heat flow are presented. Temperature observations were made by thermocouples at 12 locations under and adjacent to rocks placed over bare soil. Continuous readings were taken for 24‐ and 48‐hour intervals using seven different kinds of rock cover, ranging from large granite slabs to gravel piles, during the time between December 1974 and August 1975.

Experimental results consistently showed a nonnegligible 24‐hour net horizontal heat flow toward the rock at both the 2.5 and 5.0 cm depth. Net vertical heat flow was always downward in the soil under the bare surface, but was observed to be either upward or downward in the soil under the rock cover depending on prior conditions. Because water vapor movement in moist soil is generally in the same direction as heat flow it was suggested that surface rock cover may be a mechanism for water collection in arid climates.

A simulation model was constructed to describe two‐dimensional heat flow in a uniform soil with a rectangular rock on the surface. Using the measured surface temperature as boundary values and a soil thermal conductivity corresponding to the mean daily soil surface temperature, the simulation model adequately reproduced the observed temperatures under and adjacent to the rock.
The Effect of pH, Salt Concentration, and Nature of Electrolytes on the Charge Characteristics of Brazilian Tropical Soils
Authors: Morais F. Ilton , Page A. L. , Lund L. J.
Published: July 2010

A study of the distribution of electric charges in the A and B horizons of some Oxisols, Ultisols, and Alfisols from Brazil was made by direct measurement of retention of ions in the presence of varying electrolyte concentrations. Soil samples were collected from the Amazonian Jungle and from the principal cocoa‐producing zone of the country, the southern part of Bahia State.

The electrochemical behavior of these soils was found to be similar to that of the constant potential systems in which the surface potential is determined by H+ and OH‐ ions in the equilibrium solution, hence charge distribution varied substantially with pH and electrolyte concentration. Direct measurement of adsorption of ions from solutions of MgSO4, K2SO4, KCl, and MgCl2 showed that the nature and valence of the counter‐ions also influenced the magnitude of the electric charges on the soil particles. The pH at the zero point of charge (ZPC) of the soils varied from 1.2 to 3.4 in the A horizons and from 4.0 to 6.1 in the B horizons. At or near their field pH the surface horizons were, in general, net negatively charged, while the subsurface horizons were either isoelectric or positively charged. This fact was found to be related to differences in organic matter contents of the horizons.
Relation of Nonexchangeable Potassium and Magnesium to Development in Some Midwestern Soils
Authors: Kovar J. A. , Riecken F. F.
Published: July 2010

The nonexchangeable (NEx) potassium and magnesium status of the <1µm clay and other properties of the thin loess over till soils of northwestern and eastern Iowa were investigated to better understand the genesis and morphology of these soils and to provide a firmer basis for classification of this recently delineated group of soils. These soils are compared with similar soils from Illinois and Ohio to evaluate the regional effects of parent materials, vegetation, and climate.

The Sac and associated soils from northwestern Iowa have a higher NEx K and Mg content, are less texturally developed, release more K with sodium tetraphenylboron, and have a higher illite content than the Dinsdale and associated soils from eastern Iowa. These differences are attributed to the less weathered condition of the northwestern Iowa soils, primarily because of the lower mean annual precipitation (MAP) in that area. These differences support the separation of the two groups of soils at the series level.

The loess‐derived upper sola of the forested Iowa soils have about the same NEx K and Mg contents, but more illite, and are less texturally developed than the upper loess portion of the forested Illinois and Ohio soil profiles. The lower‐till‐derived sola of the Iowa soils have a lower NEx K, NEx Mg, and illite content than the Illinois and Ohio soils. These differences in characteristics support the separation of the Iowa thin loess over till soils from the Illinois and Ohio thin loess over till soils at the series level.
Analysis of Soil Variability with Repetitive Aerial Photography
Authors: Milfred C. J. , Kiefer R. W.
Published: July 2010

Repetitive aerial photography can be used to help identify and evaluate variation within soil mapping units. An area of approximately 12 ha (30 acres) was photographed from a light plane with two 35‐mm cameras using color and color infrared film on 20 different dates from May through November 1969. This sequence of aerial photographs recorded changes in surface soil moisture patterns and documented a close correlation to patterns of differences in growth and maturation of corn (Zea mays L.) that were visible later on during the growing season.

Field investigation of soil profiles in the study area established the relationship of these patterns of surficial soil moisture and crop growth to variations in soil profile characteristics, especially depth of solum, thickness of silt mantle and soil drainage class. The yield of ear corn associated with delineated areas of crop and soil patterns ranged from 5,865 to 9,087 kg/ha. Differences in crop growth and yield were attributed to variations in the amount of available soil moisture, as influenced by soil profile characteristics and surface topography.
Sampling the Unsaturated Zone of Irrigated Lands for Reliable Estimates of Nitrate Concentrations
Authors: Rible J. M. , Nash P. A. , Pratt P. F. , Lund L. J.
Published: July 2010

Data from a study of 56 field sites were used to examine the variability of nitrate‐nitrogen concentrations in the unsaturated zone underneath the root zone. The specific data were nitrate‐nitrogen concentrations in soil water in samples taken at 0.9‐m intervals from the 4.5‐ to 11.9‐m depth from four holes per site. Analyses of variance of these data provided estimates of variances that were used to predict the depth sampling interval and the number of holes required for site means to be within confidence limits of 10, 20, and 30%. Calculations were based on sampling intervals of 0.9, 0.6, and 0.3 m providing 9, 13, and 26 samples per hole, respectively. Relationships developed between number of sites, number of holes required, sampling interval, and confidence limits were used to test selected sampling plans for degree of precision in comparison with the actual sampling procedure. A cost analysis of the field study indicated that it would cost three to four times more than the field study to use a sampling plan which would reasonably ensure that 75% of the sites' true means fall within 20% of the measured means at a confidence level of 95%.
A Method for Sectioning Saturated Soil Cores
Authors: Reddy K. R. , Patrick W. H.
Published: July 2010

A simple system for sectioning water‐saturated cores without prior freezing is described. The method described can be used for studying the distribution and movement of ions in soil or sediment cores prepared in the laboratory or obtained in undisturbed form from the field. The average coefficient of variation was 4.8% for the sectioning of the cores prepared in the laboratory and 10.5% for the sectioning of the cores obtained from the field.
Tile Drainage in Bedded Soil or a Draw
Authors: Powell Norris L. , Kirkham Don
Published: July 2010

The process of shaping flat land by plowing it into a series of ridges separated by parallel dead furrow is called bedding and the ridge‐furrow systems are called beds. The furrows are supposed to remove surface water from the ridges, but often do not. In this paper the amount of water that can be removed by tile if they are placed under the furrows is computed on the basis of Darcy's law and potential theory. In the analysis, water‐saturated, steady‐state conditions and a subsurface barrier on which the drain tile are laid are assumed. For a poorly drained prairie soil, the calculations show that tile (or plastic tubes, etc.) placed 0.35 m below the furrow bottoms and 30 m apart in beds of 2% slope will remove 5 mm of water/day, and that the bed furrows would have to remove an additional 4.52 mm/day to take care of an expected drainage coefficient of 9.52 mm/day. For general use, 28 depth and spacing geometries are analyzed and tabulated for amounts of flow to tile in the beds. For certain geometries, some of the recharge rainfall seeps in and out of the ridge slope before the water seeps down again into the soil. This in and out seepage occurs for small tile depths, and small tile sizes. Flow nets are presented. It is shown that the theory applies to the drainage of a draw.
Comparison of Drainage Equations for the Gravity Drainage of Stratified Profiles
Authors: Watson K. K. , Whisler F. D.
Published: July 2010

The output from a computer‐based numerical analysis of the gravity drainage of a sand profile through an underlying impeding layer is used as the data for testing the manner in which algebraic equations are capable of describing the stratified drainage process. The comparisons indicate that no single equation is satisfactory in describing the wide range of nonlinear behavior that occurs with eight cases analyzed. However, when specific coefficients determined from a least squares analysis are used in an equation of the Jackson and Whisler type satisfactory correspondence is achieved.
Effects of Liquid‐phase Electrical Conductivity, Water Content, and Surface Conductivity on Bulk Soil Electrical Conductivity
Authors: Rhoades J. D. , Raats P. A. C. , Prather R. J.
Published: July 2010

Recent research has demonstrated that field soil salinity can be inferred from four‐electrode soil electrical conductivity (ECa), if the soil profile is near “field capacity” and calibration curves, based on saturation extract salinity (ECe), are available. To extend the use of this field method to arbitrary water contents, we studied EC in the laboratory as a function of water content (θ) and in situ soil water conductivity (ECw). We collected undisturbed cores of four soil types (fsl, vfsl, l, cl) using Lucite column inserts, which were tapped for later insertion of electrodes. The cells were equilibrated with waters of a desired ECw and, using a pressure membrane apparatus, adjusted to a desired θ. Values of ECa were calculated for each ECw − θ equilibration from measured four‐electrode resistances and an appropriate cell constant. Our results indicated that over the θ‐range of practical concern, ECa = (transmission coefficient) × θ × ECw + surface conductivity. This relationship is derived using a simple capillary model, which assumes that liquid phase and surface conductivities (via exchangeable cations) behave as resistors in parallel.
Nitrogen, Phosphorus, and Potassium Utilization in the Plant‐soil System: An Analytical Model
Authors: Smith O. L.
Published: July 2010

An intermediate‐resolution analytical model of nitrogen, phosphorus, and potassium utilization in the plant‐soil system was developed and tested. Starting from specified natural or artificial sources in the soil, element transport to root absorption surfaces was modeled in terms of diffusion, mass flow, and soil buffering mechanisms. Element uptake was described by carrier theory formalism, and assimilation was based on four premises about the roles of N, P, K, and photosynthate in cell chemistry. There were three main objectives of the model. The first was to predict the first‐order interactive growth response of particular plant species to any combination of these macronutrients supplied in the soil medium. Species parameters required by the model include root absorption rate and certain cell chemistry reaction rates. The second objective was to make the model sufficiently general to describe a broad range of species. It was built upon common denominator principles of physiology condensed from available experimental data on corn (Zea mays L.), bean (Phaseolus vulgaris), pine (Pinus elliottii Var. elliottii), etc. In this generic sense it is a measure of what plants have in common. The third objective was to use the model to test several well‐known theories of plant growth.

The model was validated against reported experiments on ryegrass (Lolium perenne L.), oat (Avena sativa), a legume (Stylosanthes humilis), and rutabaga (Brassica napobrassica, Mill.), in which dry matter yield was measured as a function of factorial application of N, P, and K to the soil. The model shows that much of the deficient, optimal, toxic, and interactive response of plants to N, P, and K can be explained in terms of strong linear response of cell chemistry to low nutrient concentrations and inhibition by N, P, and K at high nutrient concentrations. Applying the model in a test of plant response to suboptimal nutrient concentrations, the model strongly confirms the Liebig Law of the Minimum and refutes the opposing multi‐limiting‐element Baule Product Law. The model also shows that the Liebig theory of linear growth response to nutrient concentration and the opposing, nonlinear Mitscherlich Law of Diminishing Return are not necessarily in disagreement, but rather may apply to different parts of the nutrient concentration range. And the model confirms that the effects on growth of nitrogen, phosphorus, and potassium levels are more often additive on the reciprocal scale than on either the logarithmic or untransformed scales.
Water Use and Productivity of Wheat under Five Irrigation Treatments
Authors: Ehlig C. F. , LeMert R. D.
Published: July 2010

Water use and yield of wheat (Triticum aestivum L. em. Thell, cultivar Bluebird 2) were compared under five irrigation treatments using wheat planted in a silty clay loam soil in December and harvested in May. Water was applied at five rates from 11% more to 23% less than evapotranspiration (ET) from a weighing lysimeter planted to the same crop. Equal quantities of water per irrigation were applied at 76 mm in the pre‐emergence and the first postemergence irrigations and 102 mm in later irrigations. For a 102‐mm application, an irrigation was scheduled whenever cumulative ET from the lysimeter reached 91, 102, 112, 122, and 132 mm of water, since the last scheduled irrigation for the treatments. Total amounts of 485 to 688 mm of water were applied in five to seven irrigations. Soil water content to 1.5 m decreased progressively with water applications below ET. The soil water content was determined gravimetrically before each irrigation and water use determined from differences in soil water content between irrigations plus the amount of applied water. Seasonal water use decreased progressively from 677 to 540 mm as irrigation frequency decreased, although water use in all treatments was similar for the first 120 days.

Yields decreased as water applications decreased, except between the treatments equal to ET and at 10% below ET. At the three driest treatments yield decreased proportionately with water use, indicating that water use efficiency was not increased by restricting water use below ET from adequately watered wheat. A relationship between grain yield (Y), in g/m2, and water use (X), in mm water, was characterized by the expression: Y = −9548 + 46.42X − 0.06866X2 + 0.00003390X3 (r = 0.98). Seed weight was unaffected by irrigation treatment. Cumulative total dry weight was similar on all treatments for the first 120 days. Plants headed 7 to 10 days earlier and matured 5 or 6 days earlier on the driest treatment than on the wettest treatments. Earlier maturity could have accounted for most of the differences in water use and total dry matter between treatments, although water stress was also important in the driest treatment. Plants produced more heads on the drier than on the wetter treatments and were shorter on the driest treatment. Data on the salt balance of the soil profile were inconclusive. The significance of these data to irrigation scheduling is discussed.
Surface Soil Moisture within a Watershed—Variations, Factors Influencing, and Relationship to Surface Runoff
Authors: Henninger D. L. , Petersen G. W. , Engman E. T.
Published: July 2010

Surface soil moisture was measured within the upper 15 cm using neutron‐scattering equipment on six soil series within a 57.8‐ha Pennsylvania watershed during the 19 May to 11 Nov. 1971 period. Surface soil moisture was responsive to individual storm events, showed discernible seasonal trends, and displayed larger fluctuations at higher moisture levels than at lower moisture levels. An analysis of variance showed that well‐drained soils had significantly different surface soil moisture levels than the more poorly drained soils and could be grouped into a hydrologic unit distinct from the more poorly drained soils. Surface soil moisture measurements along parallel transects approximately perpendicular to the slope contours showed high surface soil moisture contents proximal to the stream indicating that these areas contribute more to surface runoff in a shorter period of time than areas distant from the stream channel. Multiple regression equations using pan evaporation and surface soil moisture for each soil series were used to show the relative importance of the internal soil drainage class in predicting surface runoff.
Simulation of Profile Water Storage as Related to Soil Hydraulic Properties
Authors: Hillel Daniel , van Bavel C. H. M.
Published: July 2010

A previously published numerical model of soil‐water dynamics was used to simulate the separate and combined processes of infiltration, drainage, and evaporation, as determined by hydraulic properties.

Three hypothetical soils were compared: sand, loam, and clay. Typical soil moisture characteristic functions were assigned to each, and the respective hydraulic conductivity functions were calculated. Uniform profiles of these soils were then subjected to various sequences of rainstorms and dry periods. The sandy soil provided the least evaporation and the most rapid downward flow. This resulted in the most effective storage under a relatively dry regime. The situation was reversed in the case of the clay soil, which stored the most water under a relatively wet regime, while the loam exhibited intermediate behavior. Some consequences of this pattern affecting arid zone ecology are discussed.
Cation‐Exchange Capacity of Acid Soils Using Aluminum Chloride and Barium Chloride‐Triethanolamine
Authors: Alexander E. B.
Published: July 2010

Base saturation is such an important criterion for classifying soils in the U.S. Soil Taxonomy that a procedure has been developed for scantily equipped field laboratories. Exchange acidity and cation‐exchange capacity (CEC) are determined in sequence with the same samples. The procedure involves (i) displacement of exchangeable hydrogen and Al with BaCl2‐triethanolamine solution and back‐titration with HCl to determine the exchange acidity, (ii) saturation with Al from AlCl3 solution, (iii) removal of excess Al with water, (iv) displacement of Al with BaCl2‐triethanolamine solution and back‐titration with HCl to determine the exchange capacity, and (v) estimation of basic cations by the difference between the CEC and the exchange acidity. This is an extension of a well‐established procedure for determining exchange acidity. The CEC results compare closely with the sums of cations for acid subsoils, but are low for Al horizons with much organic matter.
Soil Elastic Constants: II. Application to Analysis of Soil Cracking
Authors: Briones A. A. , Uehara G.
Published: July 2010

Soil briquets from a Vertisol and two Oxisols, equilibrated over a range of 15 to 936 bar water tension were subjected to a constant rate of strain. The trend in measured flexure and stress at rupture was adequately predicted by theory, but the measured values differed from calculated values by a large factor. The breaking stress or modulus of rupture followed the same trend as the ratio of the material's surface tension to a parameter which measures pre‐existing, microcracks. Elastic constants were necessary, but not sufficient to accurately predict cracking. The precursor to cracking appears to be prefailure microcrack formation which determines the manner of soil cracking.
Model of Salt Flow in Soil with a Source‐sink Term
Authors: Melamed D. , Hanks R. J. , Willardson L. S.
Published: July 2010

Irrigation management practices require a knowledge of the salinity in the root zone. Models which simulate the simultaneous movement of water and soils, but ignore the buffering property of the soil fall to predict the root zone salinity distribution in many field situations. The present work develops a model that takes into consideration source and sink processes and tests it under laboratory and field situations.

In determining a “source‐sink” term to be included in the model, it was assumed that precipitation and dissolution were the most important source processes and that the rate of the processes was a function of the surrounding concentration.

The parameters for the “sink‐source” term for soil columns were determined from effluent data, and were found suitable for predicting the salinity of the entire soil column. Under field conditions, individual parameters for each layer were needed for good prediction.
A Technique to Index Soil Pores and Aggregates Larger than 20 Micrometers
Authors: Wilkins D. E. , Buchele W. F. , Lovely W. G.
Published: July 2010

A laboratory technique was developed to measure soil pore size, soil aggregate size, and orientation of soil pores and soil aggregates. The technique consisted of fixing soil samples with a fluorescent polyester resin, sectioning the soil samples, and taking a photograph under black light. The black light provides sharp contrast between pores and soil aggregates. The photographs were scanned with a Flying Spot Particle Analyzer (FSPA). From the FSPA scanning information, means, and variances of soil aggregate size, soil pore size, and apparent soil porosity were calculated. This technique is limited to nonswelling soils with pore and aggregate intercepts > 20 µm.
Historical Highlights in Soil Genesis, Morphology, and Classification
Authors: Cline M. G.
Published: July 2010

Although E. W. Hilgard and G. N. Coffey pioneered, it remained for C. F. Marbut to integrate concepts in a comprehensive model of soil that found acceptance in America. Establishment of the Soil Survey by the controversial Milton Whitney created a major instrument for progress in the subject matter of Division S‐V. The Soil Survey responded to the philosophies of Marbut and survived a bitter controversy during the early years of the USDA Soil Conservation Service.

Division S‐5 originated as an association of soil survey workers in 1920. The association gradually broadened its scope from primary concern with soil survey affairs to include most elements of soil science. In 1936 it merged with the Soils Section of ASA as the Soil Science Society of America, with its Division S‐V responsible for the subject matter of the original association.

The approaches to soil morphology, genesis, and classification have been dominated by requirements of the soil survey. From largely qualitative concepts, the work has progressed to the quantitative approaches characterized by the Soil Survey Manual of 1951 and Soil Taxonomy of 1975. Increased awareness of geomorphic history has made age a much more important element in concepts of genesis. The quantitative limits of Soil Taxonomy have focused attention on the heterogeneity of mapping units. The greatly increased amount of data and modern data processing methods promise major opportunities for advances in soil genesis and soil interpretation.
Modeling Nitrate Movement and Dissipation in Fertilized Soils
Authors: Saxton K. E. , Schuman G. E. , Burwell R. E.
Published: July 2010

It is important to know the fate of nitrogen (N) fertilizers to ensure crop production and avoid pollution, but frequent measurement of soil N is difficult. Therefore, we developed a digital model to calculate the occurrence, movement, and dissipation of nitrate‐nitrogen (NO3‐N) within the soil profile of fertilized agricultural lands. Daily NO3‐N amounts and distributions within a 1.8‐m soil profile were calculated by representing the major processes influencing NO3‐N for the entire year. Daily soil moisture amounts and movement were predicted by a previously developed soil moisture‐evapotranspiration model.

Profiles of NO3‐N measured periodically on two research watersheds in western Iowa, one normally fertilized (168 kg/ha per year) and the other excessively fertilized (448 kg/ha per year) with N were used for model verification. The daily calculations for the fertilized cornfields (Zea mays L.) with moderately permeable soils included NO3‐N movement, dissipation, and profile leaching. The predicted NO3‐N profiles closely represented those measured.
Mass Transfer Studies in Sorbing Porous Media: II. Experimental Evaluation with Tritium (3H2O)
Authors: van Genuchten M. Th. , Wierenga P. J.
Published: July 2010

A comparison is made between observed tritium effluent concentration distributions and those calculated with a previously published analytical solution for the movement of chemicals through unsaturated, aggregated sorbing media. In the analytical model the liquid phase of the soil is divided into mobile and immobile regions, with transfer between the two regions diffusion controlled. Effluent data obtained from several displacements of tritium through 30‐cm long columns of Glendale clay loam were used to determine the different parameters in the analytical solution by curve fitting. The data indicate some adsorption or isotopic exchange of tritium during its flow through the soil columns. The amount of immobile water increases with decreasing flow velocity and increasing aggregate size, and varies between 6 and 45% of the total volume of water in the columns. The analytical solution provides an excellent description of the experimental effluent data, and shows that tailing can be explained satisfactorily by diffusional exchange of tritium between mobile and immobile regions of the soil.
A Comparison of Numerical Simulation Models For One‐Dimensional Infiltration
Authors: Haverkamp R. , Vauclin M. , Touma J. , Wierenga P. J. , Vachaud G.
Published: July 2010

Six models, employing different ways of discretization of the nonlinear infiltration equation were compared in terms of execution time, accuracy, and programming considerations. All models yielded excellent agreement with water content profiles measured at various times in a sand column. The two explicit models, the θ‐based CSMP model and the h‐based explicit model, used between 5 and 10 times more computer time than the implicit models. Results obtained with the two models which used the Kirchhoff integral transformation were no better than those obtained with the two h‐based implicit models. The implicit schemes with implicit, or explicit evaluation of the hydraulic conductivity and water capacity functions appear to have the widest range of applicability for predicting water movement in soil with both saturated and nonsaturated regions. Excellent agreement was obtained between water content distributions, infiltration rates, and cumulative infiltration volumes calculated with the implicit finite difference model and Philip's quasi‐analytical solution.
Kinetics of Pyro‐ and Tripolyphosphate Hydrolyses in the Presence of Corn and Soybean Roots as Determined by NMR Spectroscopy
Authors: Subbarao Y. V. , Ellis R. , Paulsen G. M. , Paukstelis J. V.
Published: July 2010

Kinetics of pyro‐ and tripolyphosphate hydrolyses by corn (Zea mays L. var. ‘NK P × 50 A’) and soybean (Glycine max L. Merv. var. ‘Cutler 71’) roots were studied using a split‐root technique to supply nutrients and to prevent precipitation reactions between phosphate sources and other nutrients. Phosphate species were determined by nuclear magnetic resonance (NMR) spectroscopy after freeze drying to concentrate the sample. A chelating agent eliminated interference by ions in sample solutions.

Hydrolyses of pyro‐ and tripolyphosphates at substrate concentrations of 75 ppm P followed zero‐order kinetics. Pyro‐ and tripolyphosphates were hydrolyzed faster by corn roots than by soybean roots under the conditions studied. The zero‐order rate constant for hydrolysis of pyrophosphate was 4.36 × 10−2 mmoles hour−1 in the presence of corn roots and 1.38 × 10−2 mmoles hour−1 in the presence of soybean roots. During tripolyphosphate hydrolyses by corn and soybean roots, tripolyphosphate concentration decreased linearly and orthophosphate concentration increased linearly; pyrophosphate hydrolyzed faster than tripolyphosphate. Rate constants for hydrolysis of tripolyphosphate were 2.50 × 10−2 mmoles hour−1 and 5.42 × 10−3 mmoles hour−1 by corn and soybean roots, respectively.
Ammonia Volatilization from Surface Applications of Ammonium Compounds to Calcareous Soils: VI. Effects of Initial Soil Water Content and Quantity of Applied Water
Authors: Fenn L. B. , Escarzaga R.
Published: July 2010

Ammonia losses from (NH4)2SO4 (AS) and NH4NO3 (AN) applied to the surface of initially wet and initially dry soils, when followed by irrigation, were generally greater from the initially wet soils, especially when water application rates were < 2.5 cm. The greatest NH3 loss occurred at the lowest water addition and the least loss at the highest water addition. The addition of 20.3 cm of water to a Harkey silty clay loam did not reduce NH3 loss below that found with the addition of 5.1 cm of water. Ammonium was moved deeper into the soil by water in the initially wet soil than into the initially dry soil.

Approximately a twofold increase in NH3 loss was observed following the application of AS and AN to the soil through irrigation water compared with NH3 loss following broadcast fertilizer application and subsequent irrigation. Again, initial soil water content influenced total NH3 loss with greater loss occurring from initially wet soil.

A direct relationship was found between the loss of water and NH3 in sand. This relationship was not changed by placing a barrier to capillary water and N movement in the soil profile. The barrier greatly reduced absolute NH3 and H2O losses but did not influence the ratio of NH3 to H2O loss.
Characterization of Yield and Economic Loss from Nonuniform Fertilizer Distribution Using Computer Simulation
Authors: Sorensen R. C. , Wiese R. A.
Published: July 2010

A simple computer program has been developed to predict yield losses from uneven broadcast fertilizer distribution on the basis of distribution pattern, yield response curve, fertilizer rate, soil test rating and amount of fertilizer swath overlap.

Losses were serious only on soils classed “very low” in nutrient supply. Losses for a highly responsive crop are less than for a less responsive crop. Overlapping succeeding swaths may improve the appearance of a field, but has a small effect on yield loss unless the amount of overlap is > 50%. Visually evident streaks in plant growth patterns may not necessarily indicate high yield loss.
Water and Salt Flow Through Compacted Clays: I. Permeability of Compacted Illite and Montmorillonite
Authors: Rolfe P. F. , Aylmore L. A. G.
Published: July 2010

Studies have been made of the pressure‐induced flow of the chloride solutions of various monovalent, divalent and trivalent cations, at various concentrations, through compressed Wyoming bentonite and Willalooka illite cores.

The majority of the measurements were carried out on the Willalooka illite core and its permeability has been shown to depend markedly on the nature and concentration of the cations present, with three‐ to fourfold variations being observed in some instances. At the lower electrolyte concentrations permeability increases in the order Na < Ca < Ba < La < Cs at a given concentration. In addition the permeability increases linearly with flow pressure to an extent ranging from some 15% for the Na systems to 97% for the 3.0M LaCl3 system over the pressure range examined.

The contributions to the permeability changes arising from mechanical expansion of the flow cell, particle rearrangements and the electroviscous effect have been shown to be quite inadequate to account for the major changes observed. It is suggested that the most significant effects arise as a result of the influence of cationic size, charge, and concentration on the viscosity of the several layers of coerced water which form adjacent to the clay surfaces. Coercion of water may arise partly through its association with the exchangeable cations adsorbed on the surface or forming diffuse double layers, but mainly from the preferred or unique water structure developed in proximity to the clay surface. In particular increasing concentrations of Cs, Ca and La cations appear to cause a pronounced breakdown in water structure within the pores.
An Alkaline Oxidation Method for Determination of Total Phosphorus in Soils
Authors: Dick W. A. , Tabatabai M. A.
Published: July 2010

A simple and precise method for determination of total phosphorus in soils and lake sediments is described. A mixture of soil and sodium hypobromite solution is boiled to dryness in a sand bath (260–280°C), and the total amount of orthophosphate is extracted with 1N H2SO4 and determined colorimetrically by the molybdenum blue method. Analysis of a group of diverse soil, lake sediment, and sewage sludge samples indicated that the proposed method and the HClO4 digestion method give essentially the same total P values. With 10 soils, the average results by the proposed NaOBr oxidation method were 1% higher than those obtained by the HC1O4 digestion method and 4% lower than those obtained by the Na2CO3 fusion method. A comparison of methods used for colorimetric determination of the orthophosphate extracted indicated that the results by the recently developed method by Dick and Tabatabai agree closely with those obtained by the method of Murphy and Riley. Digestion of samples with sodium hypobromite solution and colorimetric determination of the extracted P by the method of Murphy and Riley permits rapid analysis of a large number of samples at one time.
Determining Cation Exchange Capacity: A New Procedure for Calcareous and Gypsiferous Soils
Authors: Polemio Mario , Rhoades J. D.
Published: July 2010

A new, two‐step procedure is presented for determining the cation exchange capacity (CEC) of calcareous and gypsiferous soils. The method eliminates most of the errors inherent in conventional methods. The cation exchange sites are saturated with sodium by four successive “equilibrations” of the soil (4–5 g) with 33‐ml increments of a pH 8.2, 60% ethanol solution of 0.4N NaO Ac − 0.1N NaCl (saturating solution). The saturated sample then is extracted with three 33‐ml increments of 1.0N, pH 7 magnesium nitrate. Total sodium (Nat) and chloride (Clt) are subsequently determined in the extracted solution. Chloride (Clt) is determined so that the soluble sodium (Nasol), from the excess saturating solution carried over from the saturation step to the extraction step, may be deducted from the total sodium (Nat) to obtain exchangeable sodium (Naexch), which is equivalent to the CEC. Thus, CEC = Naexch = (Nat − Nasol) = Nat − [Clt(Na/Cl)saturating solution] where (Na/Cl)saturating solution is the ratio of Na to Cl in the saturating solution.
Short‐term Replenishment of Soil Solution Phosphorus
Authors: Peaslee D. E. , Ballaux J. C.
Published: July 2010

Depletion of soil solution P from zones around plant roots indicates that diffusive flux of P from the soil solution to the plant root is inadequate to keep pace with removal by plant roots. Consequently, the concentration and/or concentration gradients of solution P maintained under conditions of repeated removal over time are an important soil property that is a factor in determining the quantity of P diffusing to root surfaces. This study was conducted to determine the P release characteristics of five soils differing in P retention properties and pretreated with quantities of P equivalent to their sorption maxima.

Five‐gram samples were sequentially extracted with 3.5‐ml aliquots of 10−3N CaCl2 for 350, 15‐min cycles. Quantities of extracted P were 15 to 30% of the added P. Concentrations maintained during repeated extractions revealed three distinct phases of release presumably associated with different forms of soil P. Release persisted through approximately 25, 125, and 150 extraction cycles for the initial, intermediate, and final phases, respectively. For different soils, concentrations of P ranged from 0.5 to 1.1 µg/ml in initial phases and 0.02 to 0.08 µg/ml in final release phases. Though pretreatment of soils with P was based on retention properties, relative extractability and concentrations in solution during release phases appeared to be a characteristic of each soil. During the intermediate release phase, P concentration was very high and decreased rapidly for one soil, was moderately high and stable for another soil, and was very low and hardly discernible from the final phase for a third soil.
Observed and Predicted Rates of Phosphorus Diffusion in Soils of Varying Bulk Density and Water Content
Authors: Hira G. S. , Singh N. T.
Published: July 2010

The self‐diffusion coefficient of phosphorus (D) was measured at bulk densities of 1.25, 1.45, 1.60 and 1.75 g/cm3 and at three levels of soil water content in Choa sandy loam and Haibowal silty clay loam. The tortuosity factor was calculated from the self‐diffusion coefficient of 36Cl. Appropriate values of the adsorption isotherm and the tortuosity factor were used to predict P diffusion coefficient in both soils.

The tortuosity factor increased with increase in soil bulk density and increase in water content from 7 to 18% in the Choa soil and 14 to 25% in the Haibowal soil. As bulk density increased from 1.25 to 1.60 g/cm3, the observed diffusion coefficient values averaged over all water contents, increased from 0.05 × 10−10 to 0.31 × 10−10 and 2.13 × 10−10 to 5.07 × 10−10 cm2/sec in Choa and Haibowal soils, respectively. Further increase in bulk density to 1.75 g/cm3 decreased the diffusion coefficient. At high bulk density changes in water content affected the self‐diffusion coefficient of P in both soils to a greater extent than at low bulk density. The phosphate ion‐soil particle interaction was minimum at a soil bulk density of 1.60 g/cm3.
Techniques for Determining Root Length Infected by Vesicular‐arbuscular Mycorrhizae
Authors: Ambler J. R. , Young J. L.
Published: July 2010

Techniques were adapted and combined to estimate root lengths and total root length with vesicular‐arbuscular (VA) mycorrhizal infection. Steps include separating roots quantitatively from known volumes of soil, cutting roots into short segments to allow subsampling and mounting, clearing tissue in 10% KOH, staining fungi with trypan blue, subsampling root segments suspended in glycerol by using a syringe, spreading root segments in a counting/observation chamber (made easily from 80 × 100 mm lantern‐slide cover glasses), and line‐intersection counting of segments during microscopic examination. Root lengths with and without fungal infection are calculated from the counts. Root hairs, tips, branching, diameters, cell outlines, and condition of the cortex and stele are microscopically visible in the cleared, stained roots. Consequently, the method offers potential for quantifying several important root characteristics. Data collected from roots of Festuca arundinacea Schreb. are presented as an example.
Stabilization of Calcium by Surface Charge Variation in an Oxisol
Authors: Munns D. N. , Fox R. L.
Published: July 2010

In the surface layer of a Ca‐deficient, fine‐textured Hawaiian Oxisol, concentrations of Ca in solution were poised against tendencies to increase with liming in the pH‐range 5–6, and to decrease with dilution in the range of water content 0.35 to 2.0. Effects of lime and water content on the distribution of Ca between solid phase and solution were shown to be quantitatively consistent with effects of pH and ionic strength on exchange capacity.

Relationships between soil pH, cation exchange capacity, and dissolved Ca were determined in soil samples taken from a field‐liming trial. Effects of ionic strength on exchange capacity were determined by summation of adsorbed metal cations after equilibration of soil samples in different salt solutions. Effects of water content on cations in solution were determined by analysis of solutions centrifugally extracted at various water contents.

The results help explain why Ca‐deficiency may sometimes be corrected better by neutral Ca salts than by lime and why saturation‐extract Ca may approximate soil‐solution Ca adequately for diagnostic purposes.
The Solubilities of Carbonates and Phosphates in Calcareous Soil Suspensions
Authors: Marion G. M. , Babcock K. L.
Published: July 2010

Previously reported discrepancies between measured soil carbonate and phosphate activity products and the solubility products of pure crystalline minerals may, in part, be attributable to the incomplete characterization of ion‐pairs in solution.

Up to 50% of the soluble PO4 and significant amounts of Ca, Mg, and SO4 were present as ion‐pairs. Ignoring ion‐pairs resulted in significant differences in calculated activity products for both carbonates and phosphates.

One soil was undersaturated and two were supersaturated with respect to calcite. Calcite was the only carbonate mineral identified by X‐ray diffraction measurements. Calcium carbonate activity products were highly correlated to Mg activities. Magnesium‐calcite apparently controlled the solubility of soil carbonate. The soil phosphate activity products fell between the solubility products of octacalcium phosphate and hydroxyapatite. The phosphate solubility data were compatible with, but not proof of, the presence of calcium phosphate minerals in soils.
Basicity of Exchangeable Aluminum, Formation of Gibbsite, and Composition of the Exchange Acidity in the Presence of Exchangers
Authors: Veith J. A.
Published: July 2010

Montmorillonite, vermiculite, and a sulfonic resin were treated with different concentrations of Al(OH)BCl3‐B with the basicity B ranging from 0 to 2.2. The Al exchanged by vermiculite and the resin was always the nonbasic Al3+, independent of B and the amounts of Al(OH)BCl3‐B added. The Al exchanged by montmorillonite was Al3+ when exchanged from Al(OH)BCa0.5B‐montmorillonite containing 32 mmoles Al/100 meq CEC and became basic when large amounts of Al(OH)BCl3‐B had been added before the exchange reaction. In contrast to vermiculite and the resin, the montmorillonite adsorbed preferentially relatively large OH‐Al polymers and, therefore, accumulated much more Al in the interlayers than vermiculite and resin which excluded large OH‐Al polymers because of their smaller d spacings and/or high charge densities. When more OH‐Al accumulated in the interlayers of montmorillonite, the Al was adsorbed less strongly, and relatively large amounts of basic Al became exchangeable. It was shown also that an Al3+‐saturated vermiculite is much more unstable than an Al3+‐montmorillonite. These results are employed to discuss the widely‐observed formation of gibbsite when smectite reacts with basic Al. Finally, the exchange acidity from an Al‐saturated exchanger was shown to consist of both Al3+ and H+. The protons come from (i) the hydrolysis of exchanged Al3+ which, in turn, can be readsorbed as OH‐Al; (ii) from the hydrolysis of adsorbed Al; and (iii) by the exchange of H+ from permanent charges. The latter portion mechanism provides an amount of exchangeable acidity that, if it exists, is relatively small.
Absence of Local Equilibrium During Ammonium Transport in a Soil Column
Authors: Ardakani M. S. , McLaren A. D.
Published: July 2010

Adsorption of NH4+ from a stationary solution phase by a Hanford soil approached an equilibrium state exponentially after about 30 min. By contrast, a local equilibrium did not exist between NH4+ in a moving solution phase and soil in a column while a 75‐ppm NH4+‐N solution was delivered at a constant flow rate for 26 days. Local equilibrium, however, was established when the downward solution flow was stopped by setting the column horizontally 1 hour before sampling. Thus, the generality of the assumption of instantaneous equilibrium for cations in moving soil solutions is questioned.
Interactive Effect of Salinity and Phosphorus on Sesame
Authors: Cerda Antonio , Bingham F. T. , Hoffman G. J.
Published: July 2010

A solution culture experiment was conducted with a short‐season sesame [Sesamum indicum L. (Selection 333)] to observe interactive effects of osmotic potential (−0.4, −1.4, −2.4, and −4.4 bars NaCl added to a complete nutrient solution), and P concentration (0.5, 5, 25, and 50 mg P/liter) on water relations, mineral nutrition, and yield characteristics. Salinity reduced yields linearly with a 50% decrease in pod yield at an osmotic potential of approximately −2.7 bars. Increasing P concentrations increased yields only at low salinity levels; at higher salinity levels, yields decreased progressively as P increased. Salt tolerance was reduced by the higher P additions.

A multiple regression equation for pod yield as a function of salinity and P in combination was developed (R2 = 0.76). Leaf water potential at the early flowering stage decreased with pod yield as salinity and P concentrations increased. Leaf NO3 concentrations decreased as salinity increased.