bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model for Estimating Soil Water, Plant, and Atmospheric Interrelations: I. Description and Sensitivity
Authors: Nimah M. N. , Hanks R. J. 
Published: July 2010

AbstractA 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

AbstractA 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

AbstractA 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

AbstractAmino 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

AbstractSelenium (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

AbstractDisturbed 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

AbstractCarbon 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

AbstractA 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

AbstractThe 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

AbstractLayered 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

AbstractIn 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

AbstractIf 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

AbstractThe 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

AbstractAn 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

AbstractStudies 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

AbstractThis 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

AbstractAmorphous 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

AbstractA 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

AbstractAdsorption 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

AbstractBands 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

AbstractThe 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.