bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaf Fall and Forest Floor Characteristics in Loblolly Pine Plantations in the South Carolina Piedmont
Authors: Van Lear D. H. , Goebel N. B.
Published: July 2010

The seasonal pattern and quantity of leaf fall were studied in three unthinned loblolly pine (Pinus taeda L.) plantations in the South Carolina Piedmont. Peak period of leaf fall occurred from October through December. Although the plantations ranged in age from 15 to 32 years, total quantities of leaf fall (4,100–4,400 kg/ha) did not differ significantly. Nutrients stored in forest floor components in the youngest stand ranged from 171 kg/ha for N to 16 kg/ha for K. Approximately 16.3, 2.2, 4.4, 18.0, and 4.8 kg/ha of N, P, K, Ca, and Mg, respectively, were returned in annual leave fall. The forest floor has a differential ability to store nutrients. Concentrations of N and P increase as leaf litter decomposes, probably because of slow mineralization rates and rapid immobilization by microorganisms. Calcium, Mg, and K are more easily leached into the soil.
Sulfur‐coated Fertilizers for Sugarcane: II. Release Characteristics of Sulfur‐coated Urea and KCl
Authors: Snyder G. H. , Gascho G. J.
Published: July 2010

Nitrogen release from sulfur‐coated urea and K release from S‐coated KCl were examined by several techniques under field conditions in three south Florida sand soils in order to assist in the interpretation of plant response data and to provide insight into the use of three slow‐release fertilizer materials. Decreased thickness of S coating, higher temperatures and higher moisture generally favored nutrient release. However, considering the range of field conditions involved in the studies, variations in N and K release were comparatively small. Release was rapid during the first 6 months, averaging 70–80% of that applied, but was much slower thereafter.
Mineralogy and Chemistry of Manganese Oxides in Some Indiana Soils
Authors: Ross S. J. , Franzmeier D. P. , Roth C. B.
Published: July 2010

Manganese‐rich mottles and glaebules are common in many soils and their presence is taken as morphological evidence of a fluctuating water table. Manganese‐rich material from soils of the Aqualf, Psamment, Udalf, Udoll, and Udult suborders was chemically and mineralogically characterized in order to better understand the role of Mn in soil formation. Concentrations of Mn, Al, Fe, Ca, Mg, Ba, Li, K and Na were found to vary greatly in the Mn mineral from among the different horizons studied. The Mn compounds from the soils studied were largely amorphous to X‐ray due to poor crystallinity, fineness, or both. Todorokite was present in a calcareous horizon and birnessite was present in some acid horizons. The previously reported association of birnessite with alkaline soils was not found in this study. To differentiate the X‐ray pattern of birnessite from that of kaolinite, the sample was boiled in 5N NaOH to destroy the kaolinite. This treatment either crystallized birnessite from amorphous compounds or improved the crystallinity of a weakly crystalline mineral already present.
Calculating the Unsaturated Hydraulic Conductivity and Diffusivity
Authors: Whisler F. D.
Published: July 2010

The methods of R. D. Jackson and R. H. Brooks and A. T. Corey for calculating the unsaturated hydraulic conductivity from water content‐pressure head relationships are compared. The corresponding diffusivity relationships can also be evaluated either by a numerical differentiation of the water content‐pressure head curves plus the conductivity, or by direct calculation from the differentiation of the Brooks and Corey function. Both methods give approximately the same results for the hydraulic conductivity relationships. The diffusivity values calculated from the Brooks and Corey functions are lower than those calculated by the numerical method for a Grenada silt loam soil. Both diffusivity relationships give essentially the same β values for the W. R. Gardner and M. S. Mayhugh diffusivity‐water content function.
The Resistance of Intact Maize Roots to Water Flow
Authors: So H. B. , Aylmore L. A. G. , Quirk J. P.
Published: July 2010

Using a novel tensiometer‐potometer system the relationship between the root resistance to water flow of maize and the water potential of the root tissue has been examined. Over the range of water potentials used a linear relation has been observed in contrast to previous observations. Calculations using published data indicate that the rhizosphere resistance is of the same order of magnitude as the root resistance when the soil moisture potential of the rhizosphere is about −1 to −2 bars.
Computer Simulation of Phosphorus Movement Through Soils
Authors: Harter Robert D. , Foster Bennett B.
Published: July 2010

Although the movement of P through soil can be described by mathematical models, this approach has certain limitations in practical application, particularly when soil is used for waste water renovation. To circumvent the limitations of mathematical modeling, empirical adsorption equations can be obtained and utilized in computer simulation of phosphorus movement. In this way, the renovation lifetime of a soil can be estimated. This approach is not limited to P, and can be used for any potential ground‐water contaminate, whether inorganic or organic.
Comparison of Five Kinetic Models for Orthophosphate Reactions in Mineral Soils
Authors: Enfield Carl G. , Harlin Curtis C. , Bledsoe Bert E.
Published: July 2010

The kinetics of orthophosphate sorption with 25 mineral soils have been experimentally measured under laboratory conditions. The 25 mineral soils represent a wide range of physical and chemical properties. Regression analyses have been performed fitting the experimental data to five kinetic models. The five kinetic models include: a linearized first‐order sorption, a first‐order Freundlich sorption, an empirical function, a diffusion‐limited Langmuir sorption, and a diffusion‐limited Freundlich sorption. Mean correlation coefficients of 0.81, 0.83, 0.84, 0.86, and 0.88 were obtained for the models, respectively.
Influence of Soil pH on the Availability of Added Boron
Authors: Peterson L. A. , Newman R. C.
Published: July 2010

A Plano silt loam (Typic Argiudoll) with five relatively constant pH levels (4.7, 5.3, 5.8, 6.3, 7.4) was used to study the influence of soil pH on the availability of added B. A greenhouse study was conducted using tall fescue (Festuca arundinacea Schreb. Cv. ‘Kentucky 31’) with five soil pH levels, and four rates of applied B essentially equivalent to 0, 5, 10, and 20 kg/ha, and five herbage harvests. Herbage yields of tall fescue were not affected by either soil pH or B treatments; however, tissue B concentrations ranged from 8 to 739 ppm for the five harvests. Boron uptake by tall fescue was relatively uniform for soil pH levels of 4.7, 5.3, 5.8, and 6.3 within each level of B availability. Recovery percentages of 30 to 50% of the added B by five cuttings of forage indicate a soil fixation of B. Highest recovery percentage was associated with the highest rate of added B. A 2.5‐fold drop in B uptake occurred at pH 7.4 as compared with the other soil pH levels indicating substantial fixation of B. Hot‐water‐soluble B content of the soil generally increased with an increase in pH and with added B. The soluble B test did not predict the low recovery of B at pH 7.4.
Surface Residue, Water Application, and Soil Texture Effects on Water Accumulation
Authors: Unger Paul W.
Published: July 2010

Surface residue rates and water application amounts affect evaporation from soil. These factors were evaluated for their effects on water accumulation in a clay loam and a fine sandy loam soil. Surface residue rates ranged from 0 to 12,000 kg/ha and water was added at 0.25, 0.5, 1.0, or 2.0 cm/addition. At low residue rates and water applications, little or no water accumulated in the soils. The amount of water that accumulated in the soils increased as surface residue rates and water applications increased. Results for the two soils were remarkably similar, apparently because the liquid and vapor flow characteristics for the two soils were similar at high water contents, even though their water retention characteristics differed markedly. The results of this laboratory study are discussed with regard to residue management practices for low (dryland) and high (irrigated) residue production systems of the Great Plains.
Solution of the One‐Dimensional Linear Moisture Flow Equation with Implicit Water Extraction Functions
Authors: Lomen D. O. , Warrick A. W.
Published: July 2010

Analytical solutions of the one‐dimensional steady‐state moisture flow equation are presented for several functions modeling soil water extraction. These functions depend directly on the matric flux potential and thus are implicit with depth. A constant surface flux was assumed. Graphs of the matric flux potential and cumulative uptake are given depicting the effect of model parameters and comparing different water extraction functions. The results are useful in obtaining a variety of water extraction distributions.
Influence of Salt and Alkali on Ionic Equilibria in Submerged Soils
Authors: Pasricha N. S. , Ponnamperuma F. N.
Published: July 2010

To clarify the effects of salt and alkali on Fe2+ and Mn2+ equilibria in submerged soils, Maahas clay (a Haplustalf) was amended with NaCl and NaHCO3 to give initial electrical conductivities of 5, 10, 20, and 25 mmhos/cm at 25°C and exchangeable Na percentages of 5, 10, 15, 20, and 25, respectively. The amended soils and an untreated control were kept submerged in 16‐liter pots in a greenhouse at 25–30°C. The soil solutions, drawn anoxically by gravity, were analyzed fortnightly for Eh, pH, CO2, and the major ions. As the salt level increased, pH decreased and the concentrations of all cations increased. As alkalinity increased, the concentrations of all cations except K+ and Na+ decreased. In spite of wide variations in pH, Eh, ionic strength, and the concentrations of Fe2+ and Mn2+ in the soil solutions, the values of the expressions, pE − pFe2+ + 3 pH, pE − 1.5 pFe2+ + 4 pH, pE + pH, and pH − 0.5 pMn2+ − 0.5 pCO2 were nearly equal to 17.9, 23.3, 7.3, and 4.1, respectively, indicating that even in the salt and alkali treated soils, the Fe(OH)3‐Fe2+ and Fe3(OH)8‐Fe2+ systems controlled the solubility of Fe2+ while the MnCO3‐H2O‐CO2 system regulated the solubility of Mn2+.
Phosphorous Sorption and Desorption Characteristics of Soil as Affected by Organic Residues
Authors: Singh B. B. , Jones J. P.
Published: July 2010

The influence of seven organic residues on sorption and desorption of P by a high P‐fixing soil was determined after 30, 75, and 150 days of incubation. After incubating for 30 days, all residues decreased the amount of P sorbed by the soil, resulting in higher equilibrium solution P levels. However, after incubating for either 75 or 150 days, the P content of the organic residues had a marked influence on sorption of added P and desorption of sorbed P. The critical value of P in organic residues which resulted in no tie‐up of soil P was 0.3%. Sawdust, wheat straw, and cornstalks which contained < 0.3% P decreased labile soil P and increased sorption by soil after incubating for 75 or 150 days. Alfalfa (Medicago sativa), barley (Hordeum vulgare), beans (Phaseolus vulgaris), and poultry manure that contained P in excess of 0.3% decreased sorption of P. The results suggest that P fertilizer rates estimated from sorption isotherms may need to be modified following addition of organic residues.
The Influence of Cation Exchange Capacity and Depth of Incorporation on Ammonia Volatilization from Ammonium Compounds Applied to Calcareous Soils
Authors: Fenn L. B. , Kissel D. E.
Published: July 2010

The objective of this study was to determine the influence of soil cation exchange capacity (CEC) and depth of incorporation on NH3‐N volatilization from NH4+‐N compounds applied to calcareous soil. This study was conducted in the laboratory on soils with a wide range of CEC. An increasing CEC resulted in decreasing NH3 losses. Ammonium sulfate produced higher soil pH values and NH3 losses than did NH4NO3. The pH of the soil decreased with increasing NH4NO3 application rates. With NH4NO3, percent NH3‐N losses decreased with increasing application rate; however, with (NH4)2SO4, percent NH3‐N losses increased as the application rates increased.

Incorporation of the NH4+‐compounds into the soil reduced NH3 losses. Increasing depths of NH4+‐incorporation resulted in reduced NH3 loss. Losses decreased as the CEC of soil increased. The effectiveness of soil depth in reducing NH3 loss was associated with soil water content. Decreasing the soil water increased the effectiveness of soil incorporation for reducing NH3 losses.

Two regression equations were developed to describe NH3 losses with respect to CEC, soil pH, time, NH4+‐N application rate and temperature. Correlation coefficients were 0.86 and 0.81 for (NH4)2SO4 and NH4NO3 systems, respectively.
A Markovian Stochastic Basis for the Transport of Water Through Unsaturated Soil
Authors: Bhattacharya R. N. , Gupta Vijay K. , Sposito Garrison
Published: July 2010

The differential equation that describes the isothermal, isohaline transport of water through a homogeneous, isotropic, unsaturated soil is shown to result from a fundamental stochastic hypothesis: that the trajectory of a water molecule is a nonhomogeneous Markov process characterized by space‐ and time‐dependent coefficients of drift and diffusion. The demonstration makes possible a new theoretical interpretation of the water diffusivity and the hydraulic conductivity at the molecular level and results in a derivation of the Buckingham‐Darcy flux law that does not rely directly on experiment.
Ammonia Volatilization from Surface Applications of Ammonium Compounds on Calcareous Soils: V. Soil Water Content and Method of Nitrogen Application
Authors: Fenn L. B. , Escarzaga R.
Published: July 2010

Ammonia‐nitrogen losses from soils were dependent on the existence of sufficient water for solubilization of the applied NH4‐compounds. Laboratory data revealed that NH3 volatilization from (NH4)2SO4 was greatly reduced on soils with 55% water at 12, 22 and 30°C as compared to soils with 30% water. Ammonia‐nitrogen losses were the highest at all temperatures and nitrogen applicatin rates when soils contained 13 to 30% soil water. Dry NH4‐chemicals did not dissolve in soils with 0 and 8% soil water, therefore, little NH3 was lost. Application of a concentrated (NH4)2SO4 solution to soils with 8% water resulted in near maximum NH3 loss. This same solution, when applied to the surface of an oven dry soil, resulted in lower losses. Application of NH4NO3 to soils with 55 water resulted in lower NH3 losses when compared to soils with 8 to 30% water. Soils with 0% water retained essentially all applied NH4+‐N whether applied in dry or concentrated liquid form.

Apparent nitrogen recovery with barley (Hordeum vulgare L., cv. Griggs) in a greenhouse experiment corresponded well to nonvolatilized NH4+ determined in the laboratory. All nitrogen compounds were on the soil surface 7 days before application of irrigation water. Nitrogen uptake by barley was greatest when the material was applied as a dry salt to the surface of an air dry soil, intermediate when added as a dry salt to the surface of a recently saturated soil, and lowest when added as a solution to the surface of an air dry soil. Urea, urea + NH4H2PO4, and NH4NO3 were exceptions. These compounds resulted in equal plant nitrogen absorption whether applied as a dry salt or as an aqueous solution to the surface of an air dry soil. Plant absorption of nitrogen from soil with these same N‐compounds, however, was greatest when applied to the surface of a soil saturated with water.
Nutritional Problems of Pinus taeda L. (Loblolly Pine) Growing on Pocosin Soil
Authors: MacCarthy R. , Davey C. B.
Published: July 2010

Apart from drainage considerations, the main factors militating against good growth on most pocosin soils are a deficiency of available P and a high exchange acidity of the soil. Liming and fertilization with P both increased the height growth of loblolly pine. Combination applications of lime and P produced the greatest height increases. The results of chemical analyses of foliage and soil explain the large differences in growth of loblolly pine on treated and control plots. Significant linear correlations were found between the height of loblolly pine and available P in the soil and between tree height and the content of P in loblolly pine and Lyonia foliage. Critical values were established for P in the soil, loblolly pine needles, and Lyonia foliage as guides for P fertilization. The critical level of P in Lyonia foliage establishes predictor values of growth equal to those produced by the critical levels of P in loblolly pine needles, thus providing an indicator species in the absence of the pine.
Radial Movement of Saturated Zone Under Constant Flux: Theory and Application to the Determination of Soil‐water Diffusivity
Authors: Sawhney B. L. , Parlange J. ‐Y.
Published: July 2010

A two‐dimensional similarity solution yields the soil‐water diffusivity of an unsaturated soil when the soil water content is measured as a function of the distance from the source. When ponding occurs, the positions of the saturated and unsaturated fronts are related to the diffusivity. If the diffusivity can be described with two parameters, it can be predicted from the position of the two fronts alone without measuring the moisture profile.

Four experiments with a fine sandy loam at two different flow rates were performed to determine the diffusivity from the position of the two fronts. The moisture profile was then predicted from the measured diffusivity. The predictions are in good agreement with the observations.
Calcium and Strontium Absorption by Corn Roots in the Presence of Chelates
Authors: Malzer G. L. , Barber S. A.
Published: July 2010

While chelates have been shown to increase the flux of metal cations into roots, the mechanism has been subject to question. The objective of this research was to characterize the action of chelates on metal cation absorption. Calcium and Sr rather than micronutrient metals were used because some plant roots do not discriminate in their absorption, hence, relative flux of Ca vs. Sr could be used to evaluate uptake mechanisms. The chelates used were: EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (hydroxethylenediaminetriacetic acid). Flux into corn (Zea mays L.) roots was determined by monitoring Ca, Sr, and chelate depletion from solution with time. Double labeling of Ca and Sr with 45Ca and 85Sr was used. Ligand concentrations were measured using Cd titration, 14C‐labeling, and UV‐absorption measurements of Cu‐ligand complexes.

Calcium and Sr were removed from solution more rapidly than the chelate. Only 11 to 16% of the chelating ligand was absorbed over a 5‐day period whereas 90% or more of each of Ca and Sr was absorbed. The Ca/Sr ratio of uptake indicated that some of the Ca and Sr was absorbed directly from the chelate. However, where Ca2+ was maintained by continual addition, chelated Ca appeared relatively unavailable to the plant.
Rapid Determination of Unsaturated Hydraulic Conductivity in Tilled and Untilled Loess Soil
Authors: Ehlers W.
Published: July 2010

A rapid method recently developed for determining moisture diffusivity and unsaturated hydraulic conductivity in undisturbed soil cores was employed to calculate the hydraulic functions of the upper layers of tilled and untilled loess soil. The results obtained with the new method compare well with results obtained by a field method. Diffusivity functions as influenced by tillage and depth were significantly different. Conductivities were highest in the 20–30‐cm layer of untilled soil and were lowest in the same layer of tilled soil. The number of replicates necessary to evaluate the hydraulic functions with arbitrarily specified precision was calculated. For the soil under study, five to nine samples are needed, when upper and lower limits of the 95% confidence interval of diffusity means are defined not to be different more than by a factor of three.
Simultaneous Transport of Nitrate and Gaseous Denitrification Products in Soil
Authors: Rolston D. E. , Marino M. A.
Published: July 2010

A pulse of NO3‐ fertilizer tagged with 15N was applied to 100 cm long Yolo loam (Typic Xerorthents) topsoil and subsoil columns maintained uniformly unsaturated at soil‐water pressure heads between −20 and −140 cm of water at soil‐water fluxes between 1.0 and 0.1 cm day‐1. Nitrate, molecular nitrogen, and nitrous oxide from the applied fertilizer were measured as a function of soil depth and time until the NO3‐ pulse eluted from the column. An analytical solution describing the transport and transformation of NO3‐ was used to determine values for the first‐order denitrification rate constants within the columns. A numerical solution of the coupled equations for transport and transformation of NO3‐ and diffusion of the gaseous denitrification products was compared with measured N2 and N2O concentration profiles within columns. The gaseous concentration profiles were very much dependent upon values of the denitrification rate constant and the soil gaseous diffusion coefficient. Values of the soil gaseous diffusion coefficient, more than an order of magnitude smaller than those values measured in the upper part of the column, were required to approximately fit the numerical solution to the measured gas concentration profiles.
Effect of Pore Water Pressure on Sand Splash
Authors: Sloneker L. L. , Olson T. C. , Moldenhauer W. C.
Published: July 2010

We studied the effect of pore‐water pressure and particle‐size distributions on the amount of sand splash and on the instantaneous pressure changes within a packed sand core caused by single water drops falling on the surface. Both splash amounts and pore‐water pressure changes were affected by particle size, pore‐water pressure before drop impact, and by the direction of approach to the pore‐water pressure equilibrium. Pore‐water pressure increases from falling water drops were generally greater when equilibrium pressures were approached directly than when they were approached from minimum pressure. Sand splash was also generally greater when equilibrium pressure was approached directly.
Impact of Deicing Salts upon the Endomycorrhizae of Roadside Sugar Maples
Authors: Guttay A. J. R.
Published: July 2010

To evaluate the effects of deicing salts upon the endomycorrhizae of sugar maples (Acer saccharum Marsh.) root, soil, and leaf samples were examined from 44 roadside trees in Connecticut. Progressively greater dieback was significantly correlated with a decrease in endomycorrhizae, an increased depth to viable roots, and increased Na and chloride in roots and in the soil of the rhizosphere. Salt damage on sugar maple is attributed to a progressive root destruction as annual salt applications continue and an increasing top dieback as the diminishing root system is unable to sustain the top.
Relative Movement of Bromide and Nitrate in Soils under Three Irrigation Systems
Authors: Onken Arthur B. , Wendt C. W. , Hargrove R. S. , Wilke O. C.
Published: July 2010

Bromide has desirable characteristics as an indicator of nitrate movement in soils, although it has not been tested under field conditions. We studied its field applicability by growing sweet corn (Zea mays L.) on plots to which a mixture of sodium nitrate and sodium bromide were band applied. Irrigation was accomplished by either furrow, sprinkler or subirrigation. Nitrate and Br‐ moved together in the soil profile, but the concentrations of NO3‐‐N and Br‐ were quantitatively unrelated. The lack of a quantitative relationship was probably due to (i) NO3‐‐N was the sum of that already present, that from mineralization of organic matter, plus that applied while bromide came only from that applied, and (ii) NO3‐‐N from all three of these sources and Br‐ were removed from the soil at different rates by the growing crop.
Historical Highlights in American Soil Physics, 1776–1976
Authors: Gardner Walter H.
Published: July 2010

Although there was some practice of soil physics in the first century of the nation's existence, soil physics as an identifiable discipline had its beginning in this country at the start of its second hundred years, with the most rapid growth coming in the early part of the 20th century. Particle size distribution and soil structure have been major themes in the development of the science, but these have been gradually replaced by water. Increasing attention has been given to the effect of physical properties on plant growth. Development and acceptance of theoretical concepts regarding water flow and retention in soils were enhanced by the development of instruments of measurement in the 1920's and 1930's. Modern needs appear to be for development of more comprehensive mathematical models of plant growth which may be used to help identify areas of needed research in soil physics.
Historical Developments in Soil Chemistry: Ion Exchange
Authors: Thomas G. W.
Published: July 2010

The early development of ideas on cation exchange from 1850 to 1900 is described. From 1900 to the present, the coverage has been divided as the work has concentrated on soil acidity, alkali soils, and classical cation exchange studies. The discovery of crystallinity in soil clays and the rediscovery of the importance of noncrystalline oxides adsorbed on crystalline clay minerals as sources of pH‐dependent acidity and anion exchange are reviewed. Some of the more important contributions made in understanding ion exchange in soils are covered in some detail. Other contributions are mentioned. It is concluded that despite the progress made, our understanding is still far from complete.
Laterally Confined, Steady Flows of Water from Sources and to Sinks in Unsaturated Soils
Authors: Raats P. A. C.
Published: July 2010

Laterally confined, steady flows from line and point sources at arbitrary distance below the soil surface and to line and point sinks at arbitrary distance above an impermeable base are analyzed on the basis of the assumption that the hydraulic conductivity is an exponential function of the pressure head. The results include expressions describing the flow pattern, the distribution of the components of the flux, and the distributions of matric flux potential, pressure head, water content, and total head. The horizontal variations are described by trigonometric functions in problems involving line sources and sinks, and by Bessel functions in problems involving point sources and sinks. The regions below and above the sources and sinks are treated separately, subject, of course, to matching along the interface between the two regions. The vertical variations are described by exponential dampings, and surface and base reflections. For the flows to sinks, with each flow pattern there is associated an infinite variety of distributions of the matric flux potential etc., corresponding to different suctions applied at the sinks. Some problems involving partial supply by sources and interception by sinks are also treated.

The application of water along lines and at points is of interest in connection with furrow, subsurface, and drip irrigation. The removal of water along lines and at points is of interest in connection with uptake of water by plant roots and a variety of devices used to extract water and measure fluxes in the laboratory and in the field.
Immobilization of Fertilizer Nitrate Applied to a Swelling Clay Soil in the Field
Authors: Kissel D. E. , Smith S. J. , Hargrove W. L. , Dillow D. W.
Published: July 2010

Low recoveries of N fertilizer by crops on Houston Black clay prompted this investigation. Our objectives were to determine how much fertilizer nitrate can be biologically immobilized under field conditions when fertilization exceeds crop requirements and to determine when immobilization occurs during the growing season. Calcium nitrate tagged with 9.6 atom % 15N was applied to field microplots at 328 kg N/ha and grain sorghum (Sorghum bicolor L.) was planted in rows across each microplot. The various components of the N balance were measured by sampling microplots at different times during the season.

Only 2.1 kg N/ha was immobilized during the first 47 days after fertilization and planting. The rate of immobilization increased rapidly during the next 60 days and an additional 60 kg N/ha was immobilized. This increase was apparently in response to an increase in soil temperature above 22°C.

About 91% of the fertilizer N was recovered, indicating that no more than 9% was denitrified, in spite of ample water that was received as rain or irrigation water during the study. A net immobilization (an increase in soil organic N relative to an unfertilized plot) of 53 to 73 kg N/ha was measured on the fertilized plot. This net immobilization suggests that the organic N content of swelling clay soils that have historically been subjected to exhaustive cropping may increase slowly and gradually reach a higher equilibrium level due to N fertilizer use.
Soil Acidity from Long‐term Use of Nitrogen Fertilizer and Its Relationship to Recovery of the Nitrogen
Authors: Jolley Von D. , Pierre W. H.
Published: July 2010

Two N‐rate experiments in which corn (Zea mays L.) had been grown continuously for 15 and 17 years were used: (i) to study quantitatively the amounts of acidity that had been developed at different levels of N fertilization and (ii) to determine to what extent the acidity produced can be explained and predicted from the amounts of N recovered in the crops and in the soil as NO3‐N and organic N. The measured acidity was compared with the acidity calculated from N recovery, and both were expressed as percentages of the theoretical (potential) acidity developed from nitrification.

No significant increases in acidity were found in either soil below a depth of 30 cm. With amounts of applied N that produced near‐maximum yields, soil nitrate accumulation was small, and the measured acidity (CaCO3 requirement) was < 30% of the theoretical or potential. When excessive amounts of N were applied, however, relatively large amounts of NO3‐N were found in the profile, and nearly 50% of the theoretical acidity was developed. The calculated CaCO3 requirements from N recovery at near‐maximum yields tended to be smaller than that measured in the soil. This difference in the Galva soil profile was accounted for in part by a decrease in acidity between 30 and 45 cm, probably caused by nitrate absorption and by denitrification in these layers. With excessive N applications, the CaCO3 requirements calculated from N recovery were in very close agreement to that measured, averaging 48% and 47% of the theoretical, respectively.

Because the acidity calculated from N recovery essentially accounted for the acidity actually found and because the corresponding N recovery was only 68% (Table 6), the 32% of the N unaccounted for evidently was lost without an equivalent amount of base. Thus, the deficit in the acidity found provides corroborative evidence to the N‐recovery data that a substantial amount of the N applied in fertilizer was lost from the soils without an equivalent amount of base. Under the conditions of these experiments, this loss probably was through denitrification.
Profile Accumulation of Fertilizer‐Derived Nitrate and Total Nitrogen Recovery in Two Long‐term Nitrogen‐rate Experiments with Corn
Authors: Jolley Von D. , Pierre W. H.
Published: July 2010

Two long‐term N‐rate experiments with corn (Zea mays L.) which had been conducted in northwestern Iowa on the Moody and Galva silty clay loam soils for 17 and 15 years, respectively, were studied to determine the recovery of applied N (i) as NO3‐N at various soil depths, (ii) as organic or fixed N, and (iii) as N removed in the harvested corn grain. The annual N rates applied as NH4NO3 were 0, 56, 112, and 168 kg N/ha on the Moody soil and 0, 90, and 134 kg N/ha on the Galva soil. Nitrogen recovery in the fertilized plots was determined by subtracting the amounts for the unfertilized treatment from those for the fertilized treatments.

The maximum amount of N recovered as nitrate in the profiles was 1,307 kg/ha in the Moody soil as contrasted to only 231 kg/ha in the Galva soil. The maximum depth of accumulation, however, was between 1.2 and 1.5 m in both soils, and there was no indication of nitrate leaching below about 2.4 to 2.7 m in either soil.

The percentage of N recovered as nitrate with increasing N applications increased from 18% to 48% in the Moody experiment compared with only 7% to 12% in the Galva; conversely, the percentage N recovery in the grain decreased from 38% to 11% for the Moody, and from 40% to 28% in the Galva, with the increasing N applications.

At rates of N required to obtain maximum yield in the Moody and Galva soils, the percentage N recoveries in the grain were similar, 38% and 40%, respectively. Likewise, the percentage recoveries were 18% and 7% as NO3‐N, 18% and 22% as organic N, and 74% and 68% total, respectively. Thus, at maximum yields, the percentage of the applied N not accounted for was 26% and 32% of that applied to Moody and Galva soils, respectively. At the highest rate of application (168 and 134 kg/ha, respectively) the losses increased to 37% and 46% for the respective soils. The unaccounted for N is considered to have been lost largely through denitrification. These data emphasize (i) the close relationship that exists between efficient N utilization and possible nitrate pollution, and (ii) the importance of establishing and applying rates of N no greater than required to obtain maximum yield.
Effects of Irrigation Management on the Quality of Irrigation Return Flow in Ashley Valley, Utah
Authors: Bliesner Ron D. , Hanks R. J. , King L. G. , Willardson L. S.
Published: July 2010

The relationship between leaching fractions obtained under field conditions and soil water salinity profiles on nature alfalfa was studied by applying three qualities of water at three leaching fractions to areas of an alfalfa field (Medicago sativa L.) having three depths to water table. The electrical conductivity of the irrigation water and of the soil solution extract at various depths was measured for each irrigation. ET measurements from several lysimeters located in the field were used to determine depths of irrigation water to apply. A sprinkler irrigation system was used for application of the irrigation water to the plots, and the depth applied was determined by measuring the depth of water caught in cans placed in a sample plot during each irrigation.

The electrical conductivity of the irrigation waters applied averaged 0.98 mmhos/cm, 2.22 mmhos/cm, and 2.80 mmhos/cm for the season. Leaching fractions for the low leaching treatment of each water quality averaged 0.003. The other leaching treatments ranged from 0.082 to 0.343. Assuming an inert soil with no precipitation or dissolving of salts, there should have been increases in average soil profile salinity ranging from 1.81 mmhos/cm to 5.45 mmhos/cm during the season depending on the treatment. The largest increase measured on any treatment was 0.32 mmhos/cm. Some treatments actually caused a decrease in salinity where an increase was expected. For the condition of this study it appears that soil profile salinity is relatively insensitive to leaching fraction for short periods of time (1 or 2 years). This is attributed to the high relative concentrations of calcium and sulfate in the irrigation water and soil solution. Bearing these factors in mind, it appears that the quantity of salt removed in the drainage water varies directly with the quantity of drainage water since the concentration is relatively constant.
The Effect of Potassium Fertilization and/or Irrigation on Elemental Leaching in a Red Pine Plantation
Authors: Marion G. M. , Leaf A. L.
Published: July 2010

On a glacial outwash plain in the Adirondack Mountains of New York, a K fertilizer‐irrigation study on elemental leaching in red pine (Pinus resinosa Ait.) was initiated in 1966. Elemental leaching was monitored for 3 years using tension plate lysimeters. Significant leaching of K fertilizer occurred during the initial year of treatment. Despite the high mobility of K in the coarse‐textured soils of the study area, K soil leachate concentrations remained high for the 3 years of the study. The previously reported long‐term response to K fertilization on these K deficient sites may be due, at least in part, to the persistence of K in the soil surface. Potassium fertilization increased leaching of Ca, Mg, and Na. Irrigation increased the mobility of fertilizer K and may have increased elemental leaching of P. With the exception of Ca, elemental leaching losses from untreated plots were small relative to soil stores.
Evaluation of Theoretically Predicted Thermal Conductivities of Soils under Field and Laboratory Conditions
Authors: Hadas A.
Published: July 2010

In the literature one finds claims that the Philip‐deVries model of heat and moisture transfer fails to predict the amounts of water moved by vapor transfer.

In the work reported here an attempt was made to check and verify the predictive capabilities of the deVries, Philip and deVries models for vapor transfer by evaluating the latent heat transfer carried by vapor rather than to account for vapor flow from the usually performed total moisture balance.

It was found that the deVries model predicts quite accurately the transfer of heat by vapor under steady state conditions, but underestimates it under nonsteady state conditions.

The possibility that the assumed diffusive vapor transport should be corrected by including “enhancement factors” so as to incorporate local thermal gradients and mass movement induced vapor transfer, not accounted by the present model is brought up and the nature of the enhancement factors and the implications to field conditions are discussed.
Evaporation and Salt Movement in Soils in the Presence of Water Table
Authors: Hassan F. A. , Ghaibeh A. Sh.
Published: July 2010

Evaporation from homogeneous and stratified columns, in the presence of shallow water table, at steady state, was examined. Soils from Syria and Egypt were used. Their hydraulic conductivity‐moisture tension curves were determined and fitted to smooth curves represented by Gardner's empirical formula. Solutions obtained by Gardner for the steady flow equations were modified for the boundary conditions of the top and bottom layers then reduced to a dimensionless form with two variables, the relative flux density, and the relative tension at the interface. The resulting equations were used to calculate the evaporation rates. Salt profiles near the surface, at different evaporation rates, were also studied.

In case of homogeneous soil columns the calculated values gave close estimates of the measured evaporation rates. However, the ratio of the calculated to measured rates was 1.3 to 1.6 for stratified columns.

The salt profiles in the top dry layer indicated the polyphasic nature of water movement in this zone. The observed increase in the dispersion coefficient with the solution velocity was more pronounced in soils of wider range of pore size.
Miscible Displacement of Nitrate and Chloride under Field Conditions
Authors: Misra C. , Mishra B. K.
Published: July 2010

In an attempt to develop the capability for predicting the reduction loss of NO3‐N during leaching of nitrate fertilizers in an Oxisol field profile, a 2‐cm pulse of Ca(NO3)2 solution containing 304 ppm of NO3‐N was displaced through a 300‐cm by 300‐cm field plot saturated with water down to the depth of 55 cm. On the following day an identical pulse of NH4Cl solution containing 795 ppm of Cl was leached through the same plot. The results were analyzed by means of a convective diffusion type transport equation that incorporated an irreversible first‐order sink term. The agreement between the observed and the theoretical breakthrough curves allowed the determination of the first‐order reduction rate constant for NO3‐N as 0.1 hour−1 at an average soil temperature of 34°C. Under these conditions, the recovery of added NO3‐N in the leachate was 70% whereas that of Cl was 100%, approximately, when the two pulses moved past the 55‐cm soil depth. The apparent diffusion coefficients for NO3‐N and Cl were velocity dependent and ranged between 41 cm2 hour−1 to 80 cm2 hour−1, corresponding to the pore velocity range of 11.5 cm hour−1 to 17 cm hour−1. Although the present model was reasonably successful in predicting transport of ions undergoing microbial transformation in a natural soil, a more appropriate treatment should consider ion movement in stagnant and mobile phases in the soil pores in view of greater precision in working out the kinetics of biodegradable solutes.
The Critical Zn2+ Concentration for Corn and the Nonabsorption of Chelated Zinc
Authors: Halvorson A. D. , Lindsay W. L.
Published: July 2010

Corn (Zea mays) was grown in nutrient solutions of pH 5.2 and 7.5 with EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) as chelating agents. At pH 5.2, corn plants were healthy and fully green, but at pH 7.5, the nutrient solutions with DTPA produced severely stunted, Zn‐deficient plants. Spraying the foliage with Zn or increasing the level of ZnSO4 added to the nutrient solution prevented Zn deficiency.

A concentration of 10−10.6 M Zn2+ was sufficient to prevent Zn deficiency with corn. Even at 105 times this concentration, chelated Zn was not absorbed by the roots. Equilibrium relationships of chelating agents in hydroponic solutions were extremely helpful in interpreting the results of this study.

The findings reported herein support the hypothesis that Zn2+ is the form of Zn absorbed by plant roots. Furthermore, plants can obtain adequate Zn from a nutrient media when Zn2+ is maintained at approximately 10−10.6 M. This concentration is nearly 4,000 times lower than the 10−7 M reported by Carroll and Loneragan. The hypothesis proposed herein is that chelation aids in the transport and movement of metal ions to plant roots, but only Zn2+ is absorbed.
Effect of a Saline and Alkaline Ground Water on Soil Genesis in Semiarid Southern Iran
Authors: Abtahi Ali
Published: July 2010

The Marvedasht and Korbal soil series, developed in the Marvedasht area under similar climatic, vegetation, and parent material conditions, but with different topography and depths to saline ground water, were investigated. Marked differences in the morphological, physical, chemical, and mineralogical properties of soil appear to be due to variations in topography and the depth of saline and alkaline ground water.

In this toposequence, soils with salic horizons (Salorthid) have formed on the flood plain with shallow ground water and soils with natric horizon (Natrixeralf) on the low terrace with deep ground water.

Both soils are calcareous throughout. Exchangeable sodium which is the major cause of clay dispersion and migration is only effective whenever the excess salts have been leached.

X‐ray analyses indicate this toposequence has a clear difference in relative occurrence of attapulgite and smectite clay minerals. The attapulgite is replaced by smectite in the drier climatic zones.
Variation in Physical Properties and Mineral Composition of Thin Loess Deposits in the Swift Current Area of Saskatchewan
Authors: Souster W. E. , St. Arnaud R. J. , Huang P. M.
Published: July 2010

The nature and distribution of thin loessial deposits occurring on the Swift Current Plateau in southwestern Saskatchewan were studied. Results of physical and mineralogical investigations confirm the eolian origin of the material and support the separation of these loessial soils from adjacent lacustrine soils for mapping purposes.

A definite thinning trend is apparent along a southeasterly transect across the area. The particle‐size distribution of the material is very similar to typical loess and the phi median diameter of individual samples increases progressively with increasing distance from the source.

Mineralogical analyses provide evidence of a sorting action during deposition of loess which is controlled by particle shape. Quartz and potassium feldspars, both 3‐dimensional tektosilicates, remain constant in very fine sand and silt fractions across the loess transect. In contrast, a marked concentration of platy micaceous minerals occurs in coarser fractions and their depletion is noted in finer fractions with transport distance. This sorting serves to explain previously anomalous trends in total K contents of size fractions as a function of distance reported for loessial deposits by other workers.
Dissolution Rates of Phosphate Rocks
Authors: Chien S. H.
Published: July 2010

The activity concept of phosphate‐rock solubility was tested kinetically with three phosphate rocks covering a wide range of solubility. Two approaches were used: a single extraction solution of low solid/solution ratio (0.2 g/500 ml) and successive extractions at a high ratio (5 g/500 ml). The solution used was 1N NH4OAc (pH 4.8). The results showed that the phosphate rocks differed in their solubility and each rock apparently contained two fractions which differed in solubility. The rate constant was found to depend on the degree of carbonate substitution for phosphate in apatite structure and the solid/solution ratio used.
A Modified Mercury Tensiometer
Authors: Savvides Loucas , Ayers Robert S. , Ashkar Mahmoud
Published: July 2010

The present paper introduces a modified type of Hg tensiometer. The manometer in this tensiometer uses the usual principal as for other Hg manometers. However, the main difference is that the Hg manometer is contained within the tensiometer body itself. A relatively small volume of Hg is used and the small mercury reservoir can be filled or emptied rather easily. Once the reservoir is filled, the mercury can usually be safely left for the lifetime of the tensiometer. Tensiometers of the proposed design have been handled successfully for scheduling irrigation on shallow soils by unskilled farmers in Cyprus for the last 4 years.
Experimental Test of the Langevin Equation as a Model for Water Flow Through Unsaturated Soil
Authors: Sposito Garrison , Sullivan Patrick J. , Gupta Vijay K.
Published: July 2010

In this paper the parameters that appear in the Langevin Equation, a molecular model for the flow of water through soil, are expressed as functions of the hydraulic conductivity, the water diffusivity, and the soil water matric potential. Since the parameters must have values lying within certain ranges in order that the Langevin Equation and the Markovian hypothesis on water flow that comes from it be applicable, it is possible to test the equation and the hypothesis experimentally. The results for 15 different soils show that the equation and the Markovian hypothesis are consistent with soil water data for homogeneous, unsaturated soils throughout the normal field range of water content.
Hydrolysis and Decomposition of Calcium Montmorillonite
Authors: Frenkel Haim , Suarez Donald L.
Published: July 2010

The extent to which exchangeable calcium hydrolysis occurs during the preparation of homoionic calcium montmorillonite clay and the rate of the reaction in distilled water at various supension concentrations and levels of CO2 was determined at 25°C. The rate and extent of hydrolysis was found to be comparable to that reported for sodium montmorillonite and increased with CO2 concentration. CEC was appreciably reduced during washing of residual salts while preparing calcium montmorillonite. The mechanism of hydrolysis is discussed.