bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron and Silica in Water, Acid Ammonium Oxalate, and Dithionite Extracts of Some North Carolina Coastal Plain Soils
Authors: Gamble E. E. , Daniels R. B.
Published: July 2010

Sequential water, oxalate, and dithionite extracts of a Paleaquult and two Paleudults were analyzed for iron and silica. The ratio of oxalate iron to dithionite iron (active iron ratio) suggests that there is little accumulation of amorphous iron compounds in the Paleudults. It also suggests goethite may be the main iron oxide mineral. The active iron ration in the gray matrix of the Paleaquult shows that the common fine yellowish or brownish flecks and mottles contain a high proportion of amorphous iron compounds that have not aged sufficiently to become crystalline. Water table studies suggest these may be associated with the seasonal variations of water table depth. The silica extracted, especially by the dithionite, probably comes directly from the quartz sand and kaolinitic clay rather than from dissolution of iron compounds.
Effect of Probe Condition on Ultrasonic Dispersion of Soils by Probe‐Type Ultrasonic Vibrators
Authors: Genrich D. A. , Bremner J. M.
Published: July 2010

Pitting of the probe tip occurs when probe‐type ultrasonic vibrators are operated for approximately 10 hours. This reduces the output of ultrasonic energy from the probe and increases the vibration time required for dispersion of soils by ultrasonic vibration of soil‐water suspensions. The effect of pitting can be eliminated by polishing the probe tip with fine emery paper after every 30 min of probe operation. A simple method of checking the performance of probe‐type vibrators is described.
Spectrophotometric Determination of Soil Water Content
Authors: Bowers S. A. , Smith S. J.
Published: July 2010

The absorbance at 1.94µ by a soil‐methanol extract was used for measuring the soil water contents of three different textured soils. A linear relation between absorbance and soil water content was adequate for moisture determinations ranging from air dry to the moisture equivalent. For Quincy loamy sand and Barnes loam soils, calibration based only on laboratory standards was sufficient. For Houston Black clay, calibration against oven‐dry samples was necessary. Determination time was approximately 1 hour.
A Limiting Flux Condition in Infiltration into Heterogeneous Porous Media
Authors: Watson K. K. , Perrens S. J. , Whisler F. D.
Published: July 2010

Infiltration into a porous medium in which the hydraulic conductivity increases with depth is shown to approach at quite early times a limiting flux condition. This condition is defined by a pressure head profile in the saturated zone becoming tangential to the water entry value profile. Equations are presented enabling the values of the limiting flux (fl) and the elevation of the point of contact (zl) to be calculated in terms of the material properties and the boundary conditions. Below zl an unsaturated zone exists and wetting up in this zone continues under the condition of limiting flux. A method is presented whereby the pressure and water content profiles for this zone can be determined.
Nitrogen‐Fixing Activity in Upland and Flooded Rice Fields
Authors: Yoshida T. , Ancajas Rosabel R.
Published: July 2010

The acetylene reduction and 15N methods showed that under field conditions of rice (Oryza sativa L.) culture nitrogen fixation ranging from about 3 to 63 kg/ha occurred in soil, water, and the rice plant rhizosphere. The greatest fixation occurred in the rhizosphere and was more pronounced under flooded than under upland conditions. The nitrogen‐fixing activity in flooded soils increased after the panicle initiation stage of the rice plant. It was higher in the planted soil than in the unplanted soil.
Soil Enzymes in Relation to Old Field Succession: Amylase, Cellulase, Invertase, Dehydrogenase, and Urease
Authors: Pancholy Sunil K. , Rice Elroy L.
Published: July 2010

Amylase, cellulase, invertase, dehydrogenase, and urease activities in soil were determined every other month for a year in two old‐field successional stages and a climax stand in each of three vegetation types; tall grass prairie, post oak‐blackjack oak forest and oak‐pine forest. The activities of amylase, cellulase, and invertase were highest generally in the first successional stage, intermediate in the second stage, and lowest in the climax stand. On the other hand, dehydrogenase and urease activities were generally lowest in the first successional stage, intermediate in the second stage, and highest in the climax. These trends were observed in all three vegetation types throughout the year. No correlation was found between soil enzymatic activity and amount of organic matter or soil pH. The type of vegetation and thus the type of organic matter added to the soil during succession seem to be the chief determiners of the activity gradients of the enzymes under study.
Influence of Steam Treatment and Fumigation of Soil on Growth and Elemental Composition of Avocado Seedlings
Authors: Martin J. P. , Farmer W. J. , Ervin J. O.
Published: July 2010

Steam treatment or fumigation of Greenfield sandy loam and Fallbrook sandy loam with D‐D, chloropicrin, ethylene dibromide, propylene oxide, or carbon disulfide decreased P absorption by Mexicola avocado (Persea americana) seedlings subsequently grown in the soils. The P deficiency was corrected by applications of 135 to 540 ppm P to the soils. Fumigation with D‐D, chloropicrin, or ethylene dibromide caused halide injury on the older plant leaves. In general injury was more severe following D‐D or chloropicrin treatment than following ethylene dibromide fumigation. Tests with KCl and KBr, however, indicated that Br‐ was more toxic than Cl‐ to the seedlings. Phosphorus additions to the soil accentuated the halide injury and relative growth retardation related to halide excesses. Leaf Mn was increased up to 10 fold by steam treatment or fumigation with D‐D, chloropicrin, or carbon disulfide. Additions of P to the soil enhanced Mn absorption. Leaf Mn although attaining concentrations of > 1,000 ppm did not appear to be directly related to plant growth. The treatments exerted little effect on leaf Ca, Mg, K, Na, Cu, Zn, or Fe concentrations.
Ammonification and Nitrification of N as Influenced by Soil pH and Previous N Treatments
Authors: Dancer W. S. , Peterson L. A. , Chesters G.
Published: July 2010

The effect of soil pH on rates of ammonification and nitrification was studied. Soil samples which ranged in pH from 4.7 to 6.6 from an established lime and N fertility experiment were used. Soil pH values in the lime plots have been relatively constant for several years. Soil pH did not affect rates of ammonification appreciably; however it had a significant effect on nitrification rates. Length of the delay period (t′) was increased and rate of NO3‐ accumulation (Km) decreased with a decrease in soil pH. Previous field N treatments increased the length of t′ at low pH and decreased t′ and Km at high pH. Nitrification rates and production of NO3‐ were similar for soil pH values of 5.3, 6.0, 6.3, and 6.6 with a different pattern at pH 4.7.
Soil Changes Caused by Erosion Control Treatments on a Salt Desert Area
Authors: Wein Ross W. , West Neil E.
Published: July 2010

Soil samples taken in the environs of gully plugs and contour furrows installed in shale‐derived saline‐sodic soils showed that the physical and chemical characteristics differed from the control profile. Physical measurements of moisture holding capacity, bulk density, and infiltration, varied because of fine clay deposition in the catchment basins of these structures and because of the mechanical disturbance of the shale during gully plug and furrow construction.

Electrical conductivity and sodium measurements differed from the normal profile due to leaching since construction. The movement of salts was related to the rainfall received rather than to the season. These edaphic changes would have a profound effect on the establishment, development, and growth of introduced species seeded on the treatments.
Comparison of Zinc Sulfate and Zine EDTA as Zine Fertilizer Sources
Authors: Boawn Louis C.
Published: July 2010

Field experiments were performed to compare the agronomic effectiveness of a chelate Zn source (ZnEDTA) with that of an inorganic Zn source (ZnSO4 · H2O). Effectiveness was determined on the basis of Zn in bean plans (Phaseolus vulgaris L.) at the 4‐compound‐leaf stage and at early bloom, and Zn in corn plants (Zea mays L.) just before tasseling. Comparisons were made using three methods of Zn fertilizer application: (i) broadcast and plowed down, (ii) banded prior to planting, and (iii) broadcast and leached with sprinkler irrigation. The latter method was intended to approximate application of Zn by injection into sprinkler‐applied irrigation water.

Where the Zn sources were broadcast and plowed down, 1 unit of Zn applied as the chelate was equivalent to approximately 2 to 2.5 units applied in sulfate form. The effectiveness ratio appeared to be slightly greater, at least 2.5, when Zn was banded prior to planting. Where the Zn sources were broadcast and leached in with sprinkler irrigation, increasing rates of ZnSO4 had no effect on the amount of Zn in bean plants. In contrast, ZnEDTA was a highly effective source of Zn when applied in this manner.
Effect of Endogone Mycorrhiza on Phosphorus Uptake by Soybeans from Inorganic Phosphates
Authors: Ross J. P. , Gilliam J. W.
Published: July 2010

Seed yields of soybean (Glycine max L. Merr) mycorrhizal with Endogone were compared to yields from nonmycorrhizal plants in a P‐deficient soil fertilized with various phosphate sources. Mycorrhizal outyielded nonmycorrhizal plants by 79, 530, 0, and 56% when fertilized with Al, Fe, rock, or monocalcium phosphate, respectively. Yields from mycorrhizal plants fertilized with Fe phosphate were ⅙ and ⅕ those fertilized with monocalcium or Al phosphate, respectively.

In a selective phosphate depletion experiment, mycorrhizal and nonmycorrhizal soybeans were grown in soil from Ap horizon of a Norfolk sandy loam with dilute acid extractable P contents of 70 to 162 ppm. Aluminum, Fe, Ca, and reductant soluble phosphates were determined in soil samples taken at planting and 10 and 23 weeks later. Soil planted to mycorrhizal soybean contained 5 and 8 µg of Al P/g of soil less than soil from nonmycorrhizal plots at the last two sampling dates, respectively. Mycorrhizal soybean plot soil contained 2.4 µg Fe P/g of soil less than nonmycorrhizal soil 23 weeks after planting. No differences were detected in Ca or reductant soluble phosphate fractions.

The increased P absorption by mycorrhizal soybean plants grown under P stress is principally from those phosphate sources most available under nonmycorrhizal conditions.
The Effect of Ammonium and Urea Phosphates With and Without a Nitrification Inhibitor on Growth and Nutrient Uptake of Wheat
Authors: Spratt E. D.
Published: July 2010

Five fertilizers, monoammonium orthophosphate (MAP), ammonium polyphosphate (APP), triammonium pyrophosphate (TAPP), urea orthophosphate (UOP), and urea polyphosphate (UPP) were compared in the field and growth chamber using wheat (Triticum aestivum L.) as the test crop. They were tested with and without the nitrification inhibitor 2‐chloro‐6‐(trichloromethyl)‐pyridine (N‐Serve).

In both the field and growth chamber tests, the use of the nitrification inhibitor, to maintain greater levels of ammonium‐N in the soil, with the ammonium and urea phosphates increased the percent P and P‐uptake of vegetative wheat plants prior to heading significantly above the levels obtained without the nitrification inhibitor. However, the increased uptake of P during early stages of growth did not affect the yield of grain significantly.

Ammonium polyphosphates (APP and TAPP) and urea phosphates (UOP and UPP) were more effective fertilizers than MAP in both the field and growth chamber. In the field, wheat receiving ammonium polyphosphates and urea phosphates sustained its dry matter production and P‐uptake after heading (adding 23% of their dry matter and 22% of their P‐uptake between heading and harvest) while wheat with MAP added little to its total dry matter or P‐uptake after heading.

Using phosphate fertilizers increased P levels in wheat and depressed Ca, Mn, and Zn concentrations in the herbage. In the case of Zn, TAPP showed less depressive effect on concentration than MAP; the Zn levels were 13.2, 15.7, and 25.9 ppm for MAP, TAPP, and no P, respectively.
Local Soil‐Landscape Relationships in Western Iowa: I. Distributions of Selected Chemical and Physical Properties
Authors: Huddleston J. H. , Riecken F. F.
Published: July 2010

A single, open‐system hillslope was studied in detail to determine the extent to which pedologic processes and geologic processes act both separately and jointly to produce modern characteristics of contiguous soils in the soil‐landscape system. Sixteen soil cores were taken at equal spacings between the hillslope summit and the water way center. Each core was described and subdivided into nineteen 10‐cm samples, which were then analyzed for percent carbonates, total phosphorus, free iron, and particle size distribution. The carbonate distribution demonstrates the geologic effects of landscape evoluation, which beveled calcareous, deoxidized loess, and left a thin leached sediment above the erosion surface. Both carbonate and free‐iron distributions indicate the effects of the processes of dissolution of carbonates and iron, local translocation, and reprecipitation in nodules. The distribution of geometric mean particle size shows the geological effects of loess stratification during deposition and the exposure of these strata during landscape evolution. Total phosphorus and clay distributions illustrate the effect of pedological redistribution. They also illustrate the effect of pedological redistribution. They also illustrate the interaction between the pedological process of vertical redistribution and the geological process of surface modification by landscape evolution.
The Relationship Between Rainfall Frequency and Amount to the Formation and Profile Distribution of Clay Particles
Authors: Goddard T. M. , Runge E. C. A. , Ray B. W.
Published: July 2010

For Typic Argiudolls in Illinois the amount of pedogenic clay particles formed, over that inherited from the calcareous Peoria loess, seems to be controlled by rainfall frequency. The amount of solution leaching through the soil, as inferred from the amount of rainfall, was not related to the amount of pedogenic clay particles formed. This finding may help explain why the clay minerals found in the argillic horizon of some soils are not in the clay mineral stability field predicted by dilute solution chemistry.

The distribution of clay within the soil profile is related to the amount and distribution of rainfall (leachable water), depth of leaching, and natural drainage class.
A Simple System for Controlling Redox Potential and pH in Soil Suspensions
Authors: Patrick W. H. , Williams B. G. , Moraghan J. T.
Published: July 2010

A simple system, utilizing laboratory pH meters and suitable meter relays, is described for controlling the redox potential and pH of flooded soils.
Phosphate Sorption by Soils Evaluated by the Langmuir Adsorption Equation
Authors: Syers J. K. , Browman M. G. , Smillie G. W. , Corey R. B.
Published: July 2010

The sorption of added inorganic phosphate (P) by three soils which varied appreciably in their ability to sorb P was evaluated using the Langmuir adsorption equation. When the sorption data were plotted according to the conventional Langmuir equation, two linear relationships were obtained, indicating the presence of two populations of sites which have a widely differing affinity for P. Previous workers have obtained a single linear Langmuir relationship over the same equilibrium P concentration range (up to 14 µg/ml). The sites in part I (straight line corresponding to lower equilibrium P concentrations) had a very much higher (between 33 and 91 times) binding energy constant (K1), determined by regression analysis, than those in part II (straight line corresponding to higher equilibrium P concentrations). Between 40 and 52% of the total adsorption maxima was sorbed by sites in part I. A plot of the sorption data according to a rearranged form (Eadie‐Hofstee plot) of the Langmuir equation gave a curve which could not be resolved satisfactorily into two straight‐line components, suggesting the existence of three populations of sites. The rearranged form of the Langmuir equation was found to be preferable for evaluating P sorption at low equilibrium P concentrations. Predictions, based on the addition of high levels of added P, of the interrelationships between sorbed P and equilibrium P concentrations typical of the soil solution and soil‐water systems, such as runoff, may be in error because of the failure to consider the existence of sites with appreciably higher K1 values than those which sustain relatively high concentrations of inorganic P in solution.
Effect of Soluble and Exchangeable Aluminum on Pseudomonas stutzeri
Authors: Zwarun A. A. , Thomas G. W.
Published: July 2010

The test organism, Pseudomonas stutzeri, behaved as a typical cation exchanger having a CEC of 340 meq/100 g organism (oven dry wt). Increasing the acidity from pH 6.6 to 4.5 greatly reduced the number of surviving cells suspended for 3 hours in an acetate buffer. Although addition of 1 ppm soluble Al to the buffer produced no further reduction in survival, addition of 10 ppm soluble Al did significantly reduce the survival rate. Addition of 80 ppm soluble Al to the buffer proved to be lethal to the organism.

Suspensions of Ca‐bentonite, Al‐bentonite, and Al‐bentonite in conjunction with 1 ppm soluble Al did not affect the organism's survival rate. However, Al‐bentonite in conjunction with 10 ppm soluble Al significantly reduced the organism's survival rate. Aluminum‐bentonite in conjunction with 100 ppm soluble Al was lethal to the organism.

The toxic effects of Al on P. stutzeri were approximately exponential.
Spectral Reflectance of Selected Pennsylvania Soils
Authors: Mathews H. L. , Cunningham R. L. , Petersen G. W.
Published: July 2010

Spectral reflectance curves of selected soil characterization samples and standard clay minerals were studied over the wavelength interval 0.5 to 2.6µm. Results reported include reflectance data from three Hagerstown profiles and the Ap horizons of a Berks, Penn, and Ellery profile. Hagerstown soils are developed from limestone while the Berks, Penn, and Ellery are developed from shale, sandstone, and glacial deposits, respectively. Spectral curves for standard clay mineral samples of nontronite, kaolinite, and illite are also included.

Spectral reflectance data indicate that clay type and the amount of organic matter, free iron oxides and silt influence the intensity of energy reflected by soils in the 0.5 to 2.6µm range. High contents of organic matter and free iron oxides reduced reflectance intensity in the 0.5‐to‐1.2µm range while clay type influenced curve shape and intensity over the entire range studied. For the Hagerstown profiles silt is highly correlated with percent reflectance in the 0.8‐to‐2.5µm range.
The Nature of K‐Feldspars of Selected Soils in the Canadian Prairies
Authors: Somasiri S. , Huang P. M.
Published: July 2010

The nature of K‐feldspars of four soils developed from glacial till deposits and lacustrine sediments in Saskatchewan, Canada was studied. The K‐feldspars from the size fractions 20‐2,000µ were concentrated by heavy liquid separation at a specific gravity of 2.59. X‐ray diffraction analysis was used to identify orthoclase and microcline, to estimate the proportion of orthoclase to microcline, and to determine the obliquity of microcline. The K‐feldspars in the size fractions 50 to 2,000µ of certain soils were further studied by optical microscope and electron microprobe methods.

The proportion of orthoclase to microcline increased with decrease in particle size. In the comparable size fractions of the soils developed from the glacial till deposits, the proportion of orthoclase to microcline increased from north to south in the region under study. The proportion of orthoclase to microcline was higher in the Orthic Black soil developed from the lacustrine sediments than in the Orthic Black soil developed from glacial till deposits. The data obtained show the bearings of soil parent material on the relative abundance of orthoclase to microcline. The obliquity values range from 0.81 to 0.89, indicating a high degree of exsolution. The presence of perthite, as revealed by X‐ray data, optical microscope, and electron microprobe studies, further elucidate the nature of exsolution.
Formation of Mica in Surface Horizons of Dryland Soils
Authors: Nettleton W. D. , Nelson R. E. , Flach K. W.
Published: July 2010

A mineral with a 10Å X‐ray spacing is the dominant clay mineral in the surface horizon of many dryland soils in which vermiculite or vermiculite‐biotite is dominant in subjacent horizons. The mineral occurs in soils with aridic, torric, xeric, and ustic moisture regimes. To study its genesis we separated weathered mica flakes from soils developed in granitic‐textured rocks. The mineral has a refractive index of 1.64 to 1.65 and an exchange capacity of 24.7 to 44.0 meq/100 g. Its chemical composition shows that, except for its K content, it is as weathered as the vermiculite or vermiculite‐biotite of subjacent horizons. It has fixed NH4+ (5.4 – 8.0 meq/100 g) as well as K+. Together K+ and NH4+ amount to more than half of its total charge. Most of its charge comes from the tetrahedral sheet, and its tetrahedral charge is less than that of weathered mica flakes in B and C horizons. Since the weathered mica flakes in these soils contain relatively large amounts of K, small additions of K+ or NH4+ released by plant decay will collapse the minerals to 10Å. The process reduces the loss of K+ through leaching and may supply important amounts of N in soils that contain little organic matter.
Model for Estimating Soil Water, Plant, and Atmospheric Interrelations: I. Description and Sensitivity
Authors: Nimah M. N. , Hanks R. J.
Published: July 2010

A model and its numerical solution were developed to predict water content profiles, evapotranspiration, water flow from or to the water table, root extraction, and root water potential under transient field conditions. Soil properties needed are hydraulic conductivity and soil water potential as functions of water content. Plant properties needed are rooting depth and limiting root water potential. Climatic properties needed are potential evaporation and potential transpiration.

The model predicted significant changes in root extraction, evapotranspiration, and drainage due to the variations in pressure head‐water content relations and root depth. Variations in the limiting root water potential had a small influence on estimated evapotranspiration, drainage, and root extraction.
Model for Estimating Soil Water, Plant, and Atmospheric Interrelations: II. Field Test of Model
Authors: Nimah M. N. , Hanks R. J.
Published: July 2010

A mathematical model was developed to predict water content profiles, evapotranspiration, water flow from or to the water table, root extraction, and root water potential at the surface under transient conditions.

The model was field tested in 1970 and 1971. With alfalfa (Medicago sativa L.) as the crop, predicted and computed water content‐depth profiles show best agreement 48 hours after any water addition. The poorest agreement for all crops tested was right after irrigation.

The computed cumulative upward water flow from the water table was 4.80 cm as compared to 0.0 cm measured for the whole 1971 season of 116 days.
Using Infiltrations of Heptane and Water into Soil Columns to Determine Soil‐Water Contact Angles
Authors: Bahrani B. , Mansell R. S. , Hammond L. C.
Published: July 2010

A horizontal infiltration procedure using two liquids, water and η‐heptane, has been presented for determining wetting soil‐water contact angles in columns of water‐repellent soil. The method can be used to measure contact angles less than, equal to, or greater than 90° and requires minimal reaction time between water and soil during experimental measurements. This technique was applied to two columns of water‐repellent Pomello fine sand for six cycles of wetting, leaching, and drying. Wetting contact angles decreased from 101° initially to 91° after the six cycles.
Amino Acid Distribution in Forest Humus Layers in British Columbia
Authors: Lowe L. E.
Published: July 2010

Amino acid distribution was studied in hydrolysates from L, F, and H horizons at seven sites under different vegetation. Hydrolysis in an autoclave for 6 hours was found comparable to a 24‐hour hydrolysis under reflux, but was more rapid and convenient and gave better precision in estimates of individual amino acid levels.

Amino acid distribution was generally similar to that reported for mineral soils, but with increasing decomposition (L→F→H), the proportions of glutamic acid, proline, and leucine decreased relative to glycine. Increasing decomposition was also associated with increasing hexosamine levels.

Amino acid‐N content of horizon samples ranged from 0.07% to 0.95%, with L horizons under deciduous cover showing higher levels than corresponding horizons of coniferous or sphagnum sites. Basic amino acid‐N accounted for 19 to 27% of total amino acid‐N, and showed no consistent change with increasing degree of decomposition.
Effect of Fertilizer Anions on the Solubility of Native and Applied Selenium in Soil
Authors: Cary E. E. , Gissel‐Nielsen G.
Published: July 2010

Selenium (Se) was added to the Madras sandy loam as K2SeO3 at rates of 0.02 and 0.5 ppm Se and as K2SeO4 at a rate of 0.02 ppm Se. Both Se sources were labeled with 75Se. Combinations of nitrate, phosphate, and sulfate were added to the selenized Madras sl and to unselenized Madras sl and Dalton sil to determine what effect these fertilizer anions have on the solubility of applied and native Se as measured by extraction of Se with 0.01M CaCl2. When selenate was added to the Madras sl, about 25% was fixed within 1.5 hours. After 73 days of equilibration with the soil, over 50% of the added 75Se could be extracted with 0.01M CaCl2. After an initial decrease during the first few hours, the specific activity of the CaCl2 extracts remained nearly constant. Phosphate added with selenate had no effect on the extractability of 75Se with 0.01M CaCl2, but nitrate and sulfate slightly increased the amount of 75Se extracted with 0.01M CaCl2. Selenite reacted more completely with the soil than selenate during the same time. After 1.5 hours, only 9% to 17% of the 75Se was extracted with 0.01M CaCl2. After 73 days of soil contact about 3% of the 75Se added as selenite was extracted with CaCl2. The specific activity of the soil extracts was still decreasing after 73 days. The addition of phosphate with selenite increased the absolute amount of Se in the CaCl2 extracts slightly. Nitrate and sulfate had no effect on the extraction of selenite‐75Se with CaCl2 solution.
Relative Detachability of Soil Particles by Simulated Rainfall
Authors: Farmer Eugene E.
Published: July 2010

Disturbed surface soil masses of two coarse‐grained granitic soils and a single fine‐textured clay soil were subjected to simulated rainfall. The relative detachability of 11 soil‐size fractions was determined by comparing the proportion of a given size fraction in the pretreatment soil mass with the proportion of that size fraction in the splashed soil.

Tests were conducted under two levels of rainfall intensity, three degrees of slope steepness, and in the presence or absence of overland flow. Effects of rainfall intensity and slope steepness were small. Overland flow had a pronounced effect on particle detachment resulting from raindrop impact.

Without overland flow, soil particle sizes in the range of 110–1,450 µm were most susceptible to detachment by raindrop impact. With overland flow, the susceptible size range was 219–2,034 µm.
Carbon Dioxide Evolution from the Floor of an Oak‐Hickory Forest
Authors: Garrett H. E. , Cox G. S.
Published: July 2010

Carbon dioxide evolution from the floor of an oak‐hickory (Quercus sp.) (Carya sp.) forest was studied. The influence of soil temperature, soil moisture, and position on a west‐facing slope was evaluated on a seasonal basis. Highest evolution rates were observed during the summer and declined in the order of fall, spring, and winter. Maximum summer rates were 1.20 g/m2 per hour while maximum winter rates were 0.18 g/m2 per hour. Temperature was found to have its greatest limiting effect during the winter and spring while moisture was most limiting during the fall. Release of CO2 at the lower slope position was 20% greater on a mean annual basis than at the middle and upper slope positions. Most of the CO2 evolved from the forest floor is considered to be contributed by root respiration and associated microorganisms.
Anion Exclusion and Coupling Effects in Nonsteady Transport Through Unsaturated Soils: I. Theory
Authors: Bresler Eshel
Published: July 2010

A simulation model for the simultaneous transport of anions and water is developed, taking into account physico‐chemical interaction between the solutes and the soil matrix. The effects of convection, ionic diffusion, mechanical dispersion, anion exclusion (negative adsorption), and coupling phenomena are considered jointly. The dependence of the osmotic efficiency coefficient and anion exclusion on soil water content and solution concentration are estimated from diffuse double‐layer theory and hydrodynamic considerations. These estimates compare favorably with available data on clays and soils. The non‐steady flow equations are solved by a numerical approach that eliminates numerical dispersion. Based on an infiltration experiment which is characterized by relatively high water contents and rapid flow, data showed that osmotic gradients are of minor importance. A slight anion exclusion brought about some improvement in the comparison between the theoretical and experimental data.
Water Recharge in a Soil with Shrinkage Cracks
Authors: Blake G. , Schlichting E. , Zimmermann U.
Published: July 2010

The purpose of this study was to observe flow of water from the soil surface into a relatively dry Pelosol characterized by fine shrinkage cracks between peds. In this soil, for example, a coefficient of linear expansion of 0.115 was measured in peds of the Bva horizon between oven dryness and the 0.3‐bar percentage.

After a prolonged period in which evapotranspiration exceeded rainfall, 200‐µCi of tritium were added with 100 liters of water to a plot 1.4 by 1.4‐m. Replicated soil samples were taken after 24‐hours and again 14‐days later.

Had tritiated water replaced older water, as may be considered normal in granulated soil, it would have remained in the surface 15 or 20 cm of the profile. In fact it was not confined to surface layers, about half being found below the 20‐cm depth. Small amounts were found to the 100‐cm sampling depth.

Water content measurements indicated that the 50‐mm applied tritium water did not wet the surface layers to the 0.3‐bar percentage. Water additions of 765‐mm applied to an adjoining plot over a period of 1 month showed gradual accumulation in the surface horizons of the profile rather than wetting to “field capacity” in layers that proceed with time from the soil surface downward.

These results both of tritium and water flow are interpreted to indicate that water flowed down fine cracks in A and B horizons as free water, some of it soaking into the ped walls, or running into the C horizon. This was confirmed by measurements of the tritium concentration on crack walls. It was found to be significantly higher on ped surfaces in the Bva horizon than in soil taken from within the peds.
Vertical Infiltration into a Layered Soil
Authors: Aylor Donald E. , Parlange Jean‐Yves
Published: July 2010

Layered soils are often encountered in nature, and the analysis of water movement in such soils is difficult and relies on detailed numerical computations. We present here an analytical model which describes the soil moisture profiles for vertical infiltration into a layered soil (a fine textured layer over a coarser layer). For the case of constant imposed flux of water at the surface, we consider the effect of an initial soil moisture content that increases with depth which causes a steepening of the moisture profile; and we also consider the effect of the discontinuity in soil texture at the interface which causes an accumulation of water above the interface in the fine textured soil. Our technique is easy to apply and gives results which are in good agreement with experiment and substantially better than those obtained by a recent computer simulation.
Propagation of Sinusoidal Solute Density Oscillations in the Mobile and Stagnant Phases of a Soil
Authors: Raats P. A. C.
Published: July 2010

In order to account for the structure of a soil, a solute may be considered to be divided between a mobile phase and a stagnant phase. The mobile phase may correspond to the solution in a system of large pores and is assumed to move at a uniform, constant velocity in a certain direction. The stagnant phase may correspond to the solution in a system of small pores. The distribution and exchange of solute between the mobile and stagnant phases is assumed to be described by the ratio of the capacities of the two phases to store solute and a finite response time. The propagation of a sinusoidal solute density oscillation is analyzed in terms of its absorption coefficient, phase shift factor, and speed. The model shows clearly that the solute tends to bypass the stagnant phase. The results suggest several methods for measuring the parameters describing the interaction between the soil and the solute, and are of interest with regard to leaching of fertilizers and organic chemicals applied at the soil surface.
Unstable Wetting Fronts in Uniform and Nonuniform Soils
Authors: Raats P. A. C.
Published: July 2010

If the velocity of a plane wetting front increases with depth of penetration, then the front will be unstable, i.e., then a small perturbation of an initially plane front will tend to grow. On the basis of a simple hydraulic model due to Green and Ampt, criteria for instability are derived. It is found that decreases of depth of ponding and of capillary pressure head at the wetting front, increases with depth of the hydraulic conductivity and the initial water content, and compression of soil air ahead of the wetting front all have the effect of enhancing instability of the wetting front. The capillary pressure head at the wetting front is proportional to the surface tension and the cosine of the angle of contact of the water‐air‐soil interface and inversely proportional to the radius of curvature of the air‐water interface, which in turn is proportional to the mean size of the soil particles. The analysis is at first restricted to uniform soils and later extended to nonuniform soils. Criteria for instability of flows in layered soils and soils with crusts are included as special cases.
Rate and Mechanism of Na‐Montmorillonite Hydrolysis in Suspensions
Authors: Shainberg I.
Published: July 2010

The electrical conductivities of the Na‐montmorillonite suspensions at various NaCl concentrations and two temperatures as a function of time were recorded. The conductivities of the suspensions were found to increase with time indicating that the suspensions were not stable. The rate of the spontaneous decomposition was found to increase with the clay concentration in the suspension and with the temperature. When the electrical conductivities were plotted against the square root of time, a straight line was obtained. These findings suggest that the mechanism of the reaction consists of two elementary consecutive reactions: the first is a rapid exchange reaction between adsorbed Na and H+ ions in solution and the second reaction is a first‐order transformation of H‐clay to Al‐clay.
An Improved Method for the Enumeration of Denitrifying Bacteria
Authors: Focht D. D. , Joseph H.
Published: July 2010

An improved method for enumerating denitrifying bacteria from soil by use of the most‐probable‐number method is outlined. Difco nitrate broth was used, and culture tubes near the dilutions to extinction were analyzed for the disappearance of nitrate‐nitrite. The distinction between denitrifying and nondenitrifying bacteria was clearly defined and thus minimized visual subjective errors. Earlier methods which assumed that a pH increase was due solely to denitrification were shown to be ambiguous by comparison between culture tubes for nitratenitrite disappearance; 1 out of every 4 tubes compared gave an erroneous reading for dentirification. The distribution of denitrifying bacteria within two different soil profiles showed a definite logarithmic decrease in numbers with depth.
Michaelis Constants of Urease in Soils and Soil Fractions
Authors: Tabatabai M. A.
Published: July 2010

Studies to determine the Michaelis constant (Km value) for urease activity in Iowa surface soils showed that the value obtained for the activity of this enzyme was different for different soils. When the method used to determine Km did not involve shaking of the soil‐substrate mixtures, the Km value for urease activity ranged from 1.3 × 10‐3M to 7.0 × 10‐3M. Shaking the soil‐substrate mixtures during incubation decreased the Km value obtained, and statistical analysis showed that this value was significantly correlated with organic C and total N. There was no significant correlation, however, between Km value of the urease activity and other soil properties studied (pH, percentage clay, percentage silt, percentage sand). The maximum enzyme reaction velocity (Vmax value) for urease activity in soils was markedly different for different soils and always increased when the soil‐substrate mixtures were shaken during incubation. The Vmax values obtained from static and shaking incubation techniques were significantly correlated with organic C, total N, and clay content.

Results reported show that the Km value of urease in soils is similar to that of urease in soil fractions and is nearly two orders of magnitude lower than the previously reported Km value for this enzyme in soils.
Effect of Tractor Traffic, Surface Mulch, and Seedbed Configuration on Soil Properties
Authors: Koshi P. T. , Fryrear D. W.
Published: July 2010

This study was conducted to determine the effects of three seedbed configurations, four mulch rates, and tractor traffic confinement on soil properties that affect soil‐water relations of a sandy soil with cotton as a test crop. The lack of water limits crop production on dryland sandy soils in the Southern High Plains.

Undisturbed soil cores were taken from the 0‐ to 7.5‐, 7.5‐ to 15‐, and 22.5‐ to 30‐cm depths in the trafficked and nontrafficked interrows and crop rows of the flat, ridge, and furrow treatments. Surface mulch rates of 0, 5.6, 11.2, and 22.4 tons/ha of cotton‐bur mulch were applied annually after seedbed preparation to each split plot. Tractor traffic was confined to the same path each year using cotton (Gossypium hirsutum L.) as a test crop.

Mulching at rates > 11.2 tons/ha reduced the bulk density, increased hydraulic conductivity, air porosity, total porosity, and organic matter content even in the trafficked interrows. Hydraulic conductivity of the crop rows increased eight‐fold with heavy mulch applications. Hydraulic conductivity increased three‐fold, bulk density was reduced, and air porosity increased as a result of controlling tractor traffic even without mulch.
Amorphous Coatings on Mineral Surfaces
Authors: Jones R. C. , Uehara G.
Published: July 2010

Amorphous coatings on mineral surfaces too thin to be resolved by most electron microscopes were detected bridging particles suspended over holes in the supporting substrates. The coatings are gel‐like in appearance, may flow when wet, shrink and become porous when heated, cement primary particles into large masses, and exhibit a coat‐of‐paint effect with curved solid‐air interfaces. Amorphous gel coatings were found in alumino‐silicate systems, in high aluminum soils, and on quartz surfaces.
Solution and Adsorbed Fluometuron Concentration Distribution in a Water‐Saturated Soil: Experimental and Predicted Evaluation
Authors: Hornsby A. G. , Davidson J. M.
Published: July 2010

A technique is described for measuring the solution and adsorbed phases of fluometeron in water‐saturated soil columns. The data reveal that at an average pore‐water velocity of 5.5 cm/hour, the solution and adsorbed phases of fluometuron are not in equilibrium, whereas, at the 0.59 cm/hour velocity they were in equilibrium. The kinetic rate equations for adsorption and desorption were not significantly better than the equilibrium model when describing the fast displacement of fluometuron through soils. The desorption distribution coefficient (θkA′/ρkD′) was found to be a function of the maximum amount of herbicide adsorbed prior to desorption. The experimental data were reasonably well described by the mathematical model.
The Interaction of Phosphate with Calcite
Authors: Griffin R. A. , Jurinak J. J.
Published: July 2010

Adsorption isotherms of phosphate on calcite were shown to be described by a two‐region Langmuir isotherm equation, i.e., the plot showed two distinct linear portions. The break in the slope of the Langmuir plot was found, on a solubility diagram of the calcium phosphates, to correspond closely to the division between octocalcium phosphate and hydroxylapatite.

The adsorption data were also found to be described by the BET equation. The monolayer capacity computed from the BET equation was found to correspond closely with the adsorption maximum computed from the initial solpes of the Langmuir plots. Comparison of monolayer capacities with the total surface area of the calcite indicated that only approximately 5% of the total surface was covered with phosphate ions.

The differential isosteric heat of adsorption, was computed from the adsorption data. A plot of as a function of phosphate sorbed revealed a discontinuity at the region 1 boundary of the adsorption data.

Kinetics of phosphate reaction with calcite were found to be consistent with heterogeneous nucleation theory and are discussed in terms of the previous adsorption data.

It was concluded that the interaction of phosphate with the calcite surface could be described as a heterogeneous nucleation process.
Effect of Stover Mulch on Soil Temperature, Corn Root Weight, and Phosphorus Fertilizer Uptake
Authors: Onderdonk J. J. , Ketcheson J. W.
Published: July 2010

Bands of corn stover placed on soil in different positions relative to corn (Zea mays L.) rows decreased soil temperature at a 10‐cm depth 2.5C for maxima, doubled the proportion of root growth in the surface 5 cm of soil, and tripled fertilizer uptake from a surface‐applied band of 32P‐labeled phosphorus fertilizer. The greatest increase in uptake occurred with the band of stover on both sides of the row. Total root growth to a depth of 15 cm was not greater with stover than without it.

The increase in uptake was credited to the relatively greater root growth near the surface, which in turn was believed due to the temperature depression and a tendency for a more horizontal direction of root growth. While a more favorable soil moisture level, as found under mulch, would be necessary for root growth and proliferation, it was not considered initially responsible for directing roots closer to the soil surface.
Sulfur Fractions and Carbon, Nitrogen, and Sulfur Relationships in Grassland, Forest, and Associated Transitional Soils
Authors: Bettany J. R. , Stewart J. W. B. , Halstead E. H.
Published: July 2010

The amounts of total S, organic N, organic C, and HI‐reducible‐S obtained from Ap layers of 54 soils collected from five major soil zones in Saskatchewan varied considerably with location within any one zone. However, the mean C/S, N/S ratios and the percentage of total S as HI‐reducible S of the soil organic matter showed similar and consistent trends. The C/N/S ratios ranged from 58:6.4:1 in the arid Chernozemic Brown soils to 129:10.6:1 in the leached Grey Wooded soils. The percentage of total S as HI‐reducible was approximately 50% in the Chernozemic soils in contrast to 36% in the Grey Wooded soils.
Soil Property Changes Associated with Crop Residue Management in a Wheat‐Fallow Rotation
Authors: Black A. L.
Published: July 2010

Wheat (Triticum aestivum L.) straw‐mulch rates of 0, 1,680, 3,360, and 6,730 kg/ha were established in the spring on fallow in alternate spring wheat‐fallow blocks in three replications on a Dooley sandy loam. Subplot fertilizer treatments applied before seeding were as follows: None (check), P, N, and N‐P. Both N and P were applied at a rate of 34 kg/ha; N was applied each crop year, and P was applied initially and every other crop year thereafter. Fertilizer and surface residue remaining after fallow were incorporated at seeding time with a tandem disk. Initially and after four crop‐fallow cycles, selected soil depths were sampled and various chemical and physical soil properties were determined.

As residue levels increased, soil organic matter, N, C, and C/N ratio increased significantly in the 0‐ to 7.6‐ and 7.6‐ to 15‐cm soil depths after four crop‐fallow cycles; no changes occurred below 15 cm. Following 1 year of fallow, NaHCO3‐soluble P in the 0‐ to 15‐cm soil depth increased as residue levels increased, independent of P fertilization. Soils obtained during fallow from the 0‐ to 15‐cm soil depth in each field subplot in 1970 were subjected to an 8‐week incubation period with added N rates of 0, 20, and 60 ppm in three replications. Total soil NO3‐N accumulation increased significantly as residue levels increased, regardless of N rate applied before incubation. However, residue levels had the greatest positive effect on NO3‐N accumulation when N was added both in the field and before incubation. Regardless of field fertilizer treatments, exchangeable K increased, Ca decreased, and Mg and Na were not influenced significantly by residue treatments in the 0‐ to 7.6‐cm soil depth after four crop‐fallow cycles. The nonerodible soil fraction (>0.84 mm) increased progressively in the 0‐ to 5‐cm soil depth as residue levels increased. Each 1,100 kg/ha of straw incorporated during the period reduced the erodible soil fraction about 8%. Bulk density of the 0‐ to 7.6‐cm soil depth decreased significantly as residue levels increased.

Changes in the chemical and physical soil properties measured were proportionate to the quantity of crop residue added over time. The data obtained provide information about the longtime influence of crop residue management systems on some chemical and physical soil properties.