bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Membrane Pore Size on the Measurement of Water Tension in Bentonite Suspensions
Authors: Banin Amos , Davey Brian G. , Low Philip F. 
Published: July 2010

AbstractA pressure‐transducer tensiometer and a dynamic osmometer were used to measure water tensions and osmotic pressures, respectively, in clay‐water systems. The two methods of measurement produced the same results. Different membranes, having pore sizes ranging from 0.004µ to 0.8µ were used with the tensiometer. It was found that the measured water tension of a given system depended on the pore size of the membrane; as the pore size increased, the tension decreased. However, experience indicates that little or no turbidity appears in a solution when it is separated from a clay suspension by a membrane having pores as small as those of the present experiments. Therefore, the relationship between pore size and tension was not due to differences in membrane permeability to the clay particles. Nor was it due to differences in membrane permeability to dissolved solutes. Tests showed that no lasting tension developed when a NaCl solution or an extract of the clay were utilized in place of the clay suspensions. Two possible explanations were proposed, namely: (i) entrance of particles into the pores was all that was required to lower the reflection coefficient, and (ii) the gelation of the clay suspensions within the pores produced gels having particle densities and arrangements and, hence, permeabilities to dissolved solutes, that were dependent on the dimensions of these pores. It was pointed out that, regardless of the explanation, the existence of such a relationship between membrane pore size and measured water tension is noteworthy.
Theory and Application of Gas Chromatography in Soil Aeration Research
Authors: Tackett J. L. 
Published: July 2010

AbstractMethods for the gas chromatographic analysis of soil atmosphere samples as well as the construction details of two devices for obtaining the samples are presented. Typical column materials, arrangements and operating conditions are reviewed. A new approach to the dual analysis of oxygen and carbon dioxide on the same sample using a stream splitter instead of a dual column valve is presented. Advantages of the stream splitter arrangement over the dual column valve arrangement include better zero control, faster analysis, and the lack of valve switching necessary during an analysis.
Soil Organic Matter and Nitrogen Changes During 24 Years of Dryland Wheat Tillage and Cropping Practices
Authors: Unger Paul W. 
Published: July 2010

AbstractSoil organic matter and total nitrogen were determined after 24 years3 of growing dryland wheat (Triticum aestivum L.) under various tillage and cropping practices in the Southwestern Great Plains. The various tillage practices resulted in significant differences in soil organic matter content when a wheat‐fallow cropping system was used. Values were highest for delayed stubble‐mulch tillage. Differences in soil organic matter content due to tillage practices used were not significant where wheat was grown continuously, but values for continuous wheat were higher than those for wheat‐fallow for comparable tillage practices.Soil total N content was significantly affected by the tillage practice used for the wheat‐fallow, but not the continuous wheat cropping system. Values for continuous wheat were higher than those for wheat‐fallow for comparable tillage treatments. Soil organic matter was closely related to soil total N.
Lithium‐Calcium Exchange Equilibria in Soils and Clays
Authors: Bair F. L. , Pratt P. F. 
Published: July 2010

AbstractCation‐exchange equilibria at pH 7 were determined for a number of soils and clays using Li adsorption ratios (LAR) of 0.2 to 20 (mmoles/liter)½. Data for montmorillonite and montmorillonitic soils gave linear relationships between exchangeable Li ratio (ELR), or ratio of exchangeable Li to exchangeable Ca, and LAR; similar slopes were obtained in all cases. However, relationships between ELR and LAR for kaolinite and kaolinitic soils were all curvilinear with a relatively high adsorption affinity for Li at low Li concentrations, indicating that this high affinity for Li existed only in a small fraction of the cation‐exchange capacity of these materials. Drying in a Li‐saturated form increased the affinity of kaolinite for Li but had only a small effect on montmorillonite.
Velocity‐Gradient Relationships for Steady‐State Unsaturated Flow of Water in Nonswelling Artificial Soils
Authors: Olson T. C. , Swartzendruber D. 
Published: July 2010

AbstractThe relationship between flow velocity and hydraulic gradient was studied for steady‐state unsaturated flow of water in horizontal columns of two nonswelling porous media, one a mixture of sand, ground silica, and kaolinite, and the other a mixture of sand and ground silica only. The flowing water contained 0.1% phenol to inhibit bacteria. Soil‐moisture tension was measured with three tensiometers positioned within the soil column. Gradients at different velocities could be determined at a single location. Tension changes were always from low to high, to eliminate hysteresis effects. This required the use of a graphical analysis to calculate corresponding values of velocity and gradient at a given constant tension.In general, essential proportionality between flow velocity and tension gradient at given tension was found for both materials. Very slight greater‐than‐proportional tendencies were present in the sand‐silica‐kaolinite mixture, but were not consistently related to tension. In the sand‐silica mixture a less‐than‐proportional flow response was observed at low and intermediate tensions, but became proportional as the tension increased. Minimal pore‐volume saturations achieved were 0.74 for the sand‐silica‐kaolinite, and 0.65 for the sand‐silica.
Theoretical Analysis of Two‐Dimensional, Transient Flow of Water in Unsaturated and Partly Unsaturated Soils
Authors: Rubin J. 
Published: July 2010

AbstractThe Darcian flow‐equation for two‐dimensional, transient transfer of water in rectangular, unsaturated or partly unsaturated soil slabs was solved numerically with the aid of alternating‐directions, implicit difference methods. Two alternative processes were considered: predominantly horizontal infiltration and ditch‐drainage. The results obtained for the horizontal infiltration process indicate that it involves upward flow‐components which are due, primarily, to a gravity‐induced variation in hydraulic conductivity along the inflow face. These components may materially affect the course of infiltration, especially during its earlier stages. The drainage case results demonstrate that transient water flow within the unsaturated zone and the outflow from the seepage zone may significantly affect the progress of water‐table descent and the total outflow rates.
Influence of Water Flux and Porous Material on the Movement of Selected Herbicides
Authors: Davidson J. M. , Rieck C. E. , Santelmann P. W. 
Published: July 2010

AbstractThe rate at which two substituted urea herbicides move through a water‐saturated glass bead and uniformly packed soil column depends upon the water flux or average pore velocity. A 200‐ml slug of 0.01N CaSO4 solution containing either fluometuron (3‐(m‐trifluoromethylphenyl)‐1,1‐dimethylurea) or diuron (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea) was introduced at one end of a 30‐cm long column at a specific flux and the herbicide displaced through a column with 0.01N CaSO4 at the same water flux. Effluent samples collected every 5‐ml show fluometuron and the chloride ion to mix in a similar manner at the two fluxes studied. Experimental and calculated effluent concentration distributions did not agree when fluometuron was retained by the porous material.
Nitrate Uptake and Reduction as Affected by Calcium and Potassium
Authors: Minotti P. L. , Williams Doris Craig , Jackson W. A. 
Published: July 2010

AbstractNitrate uptake patterns by nitrogen‐depleted wheat seedlings (Triticum vulgare var. Atlas 66) exhibited an initial lag phase which was lessened, but not completely overcome, by presence of solution Ca. Maintenance of a more rapid subsequent rate of nitrate uptake, which developed after the initial lag phase, depended upon presence of solution K. The rapid phase was enhanced when both Ca and K were present and was curtailed by shoot excision and by Ca deficiency. Sizeably larger amounts of nitrate were recovered in the shoots after 24 hours in KNO3 as compared to Ca(NO3)2, and with the former salt, smaller proportions of the absorbed nitrate were reduced. The data suggest a beneficial influence of Ca both on initial nitrate uptake by root tissue and on transport to shoots while a continual K supply was apparently beneficial in nitrate transport.
Nitrate‐Stimulated Uptake and Transport of Strontium and Other Cations
Authors: Jackson W. A. , Williams Doris Craig 
Published: July 2010

AbstractSupplying nitrate to N‐depleted wheat seedlings (Triticum vulgare, var. Atlas 66) stimulated the uptake of both divalent (Sr, Mn, and Mg) and monovalent (Cs, Na, K) cations. Rapid nitrate uptake, and the lower ambient acidity resulting from it, appeared to be partially responsible for the increase in cation uptake. Nevertheless, pretreatments with nitrate exerted some stimulation in Sr and Cs uptake, indicating an additional action of nitrate after it had entered the tissues. Pretreatment with nitrate, as well as its presence during the Sr uptake period, increased transport of Sr to the shoots more than total uptake. Transport to shoots of previously absorbed Sr was enhanced by subsequent nitrate treatments, the amount transported being significantly greater with nitrate salts of Ca, Mg, and Na than with K or NH4.
Factors Important in the Calculation of Hydraulic Conductivity
Authors: Kunze R. J. , Uehara G. , Graham K. 
Published: July 2010

AbstractThe calculation of hydraulic conductivity by a modified Millington‐Quirk method with a matching factor gave conductivity values closely approximating experimentally measured values. The technique requires knowledge of the moisture characteristic and the saturated conductivity. A number of factors that affect the calculated values and improve the computational results were investigated. Calculated conductivity values decreased with an increasing number of pressure classes at low moisture contents. For all soils tested the calculated conductivities were less than the experimental values at the terminal point of the moisture characteristic. This discrepancy was partially corrected by a small change in the Millington‐Quirk equation, by extending the moisture characteristics to higher suction values, and by reducing the number of pressure classes to approximately 10. A matching factor, the ratio of measured over calculated saturated conductivity, was found necessary for obtaining the best fit of calculated and measured data. Two conductivity functions calculated separately from each moisture characteristic forming a hysteresis loop, converged as the hysteresis loop was translated to higher tensions. All computations were done by computer.
Soil‐Water Diffusivity Values Based Upon Time Dependent Soil‐Water Content Distributions
Authors: Cassel D. K. , Warrick A. W. , Nielsen D. R. , Biggar J. W. 
Published: July 2010

AbstractA laboratory method based upon time dependent soil‐water content distributions is presented for calculating isothermal soilwater diffusivity values for soils at 5 to 15 volume percent water. The redistribution of water within sealed soil columns was monitored by gamma‐radiation attenuation at approximately 100 to 1,000 hour intervals over a period exceeding 3 months. Diffusivity values from numerical integration of the diffusion equation were obtained easily and compared favorably with those of previous investigators.
Rhizo‐Deposition of Organic Debris in Soil
Authors: Shamoot Saad , McDonald Lain , Bartholomew W. V. 
Published: July 2010

AbstractDeposition of organic debris from or associated with plant roots during periods of active growth (Rhizo‐deposition) was measured by the use of carbon‐14. The measurements were made by growing plants from the seedling stage to near maturity in an atmosphere containing carbon‐14, harvesting the tops and roots and determining the tracer C residual in the soil. The magnitudes of rhizo‐deposition were directly related to the extent of root growth and ranged from 25 to 49 g residual organic debris for each 100 grains of harvested roots.
Inhibition of Nitrification in Bladen Grassland Soil
Authors: Brar S. S. , Giddens Joel 
Published: July 2010

AbstractLow nitrification in Bladen grassland soil was not improved by extraction of possible toxic substances. Liming improved nitrification after a delay period. Addition of nitrifiers to a limed soil resulted in good nitrification. Nitrifiers developed in Bladen soil gave better nitrification in Bladen than nitrifiers from Cecil. The acid Bladen soils were very high in extractable aluminum. It was concluded that acidity and the resulting low population of nitrifiers was the cause of low nitrification in Bladen sod soil.
Zn‐Dust Distillation and Fusion of a Soil Humic and Fulvic Acid
Authors: Hansen E. H. , Schnitzer M. 
Published: July 2010

AbstractA humic and a fulvic acid extracted from a Podzol Bh horizon were subjected to Zn‐dust distillation and fusion. The reaction products were first purified by vacuum‐sublimation and then separated by a combination of preparative thin‐layer chromatography on silica gel and on cellulose. Identification of each fraction was performed by ultraviolet spectroscopy and spectrophotofluorometry. The main products were polysubstituted naphthalene, substituted phenanthrene, and substituted and unsubstituted anthracene, pyrene and perylene. In addition, small amounts of the following polycyclic hydrocarbons were also identified: fluoranthene, 1,2‐benzofluorene, 2,3‐benzofluorene, 1,2‐benanthracene, 1,2‐benzopyrene, 3,4‐benzopyrene and naphtho‐(2′,3′:1,2)‐pyrene. Semi‐quantitative yields for individual polycyclic hydrocarbons were estimated. Our results point to the occurrence in the “nuclei” of soil humic compounds of significant amounts of polycyclic aromatic ring structures or structures yielding such systems under the experimental conditions employed.
Response of Several Corn Hybrids to Level of Water‐Soluble Zine in Fertilizers
Authors: Giordano P. M. , Mortvedt J. J. 
Published: July 2010

AbstractFertilizers varying in level of H2O‐soluble Zn were prepared by combining fine ZnO and ZnSO4 in various proportions and pressure‐granulating the powders with ammonium nitrate, monoammonium phosphate, or ammonium polyphosphate. Forage yields and uptake of Zn by corn (Zea mays L.) grown on a P‐ and Zn‐deficient soil in the greenhouse increased with the level of H2O‐soluble Zn in these macronutrient fertilizers. Additional crop response was slight to fertilizers with levels of H2O‐soluble Zn in excess of about 50% but this varied, depending upon the macronutrient carriers. However, the amounts of Zn extracted after cropping from untreated soils and soils initially receiving 12 mg of Zn per 3 kg of soil in a highly H2O‐soluble form were comparable.In a second experiment differential response of several corn hybrids to amount of P and Zn and level of Zn solubility in the fertilizers suggests that the test variety might influence the interpretation of the results from fertilizer evaluation studies. No relationship was found between P/Zn ratios in the corn forage and the seed. The P/Zn ratios in corn forage were not related to the response of corn to applied Zn.
Interlayer Forces in Montmorillonite and Vermiculite
Authors: Kittrick J. A. 
Published: July 2010

AbstractOriented X‐ray spacings for vermiculite and montmorillonite were obtained as the sample temperature was changed at a constant rate. Temperatures at which an abrupt change in (001) spacing took place indicated the relative ease of expansion or contraction for a series of interlayer ions. From such temperatures, the difference between contracting and expanding forces was found to be dependent upon interlayer ion charge, distance, and hydration energy, indicating essentially a strong‐force balance (ion‐water, ion‐clay) for both vermiculite and montmorillonite.Transition temperatures for hydration were lower than the corresponding dehydration temperatures, where small interlayer ions were involved. After removal of a water layer, the layer silicate contracted. Stronger hydrating forces at lower temperatures were required to reexpand the layer silicate prior to sorption of a corresponding water layer. Where the size of the interlayer ion approached that of the water molecule, preventing contraction during dehydration, the hysteresis was eliminated.Temperatures at which comparable interlayers of water molecules were removed were higher for vermiculite than for montmorillonite, for Li, Na, Mg, Ca, Sr, and Ba ion saturations. A semi‐quantitative consideration of the strong‐force model indicates the presence of an expanding force in addition to hydration of interlayer ions, and one that is much stronger in vermiculite than in montmorillonite. Hydration of the negative charge sites meets these requirements, but does not explain ion fixation by vermiculite. Hydration of negative charge sites is indicated by plateau formation in the curves, by ion hydration theory and by swelling theory of ion‐exchange resins.
Plant Uptake and Chemical Extractions for Evaluating Potassium Release Characteristics of Soils
Authors: Conyers E. S. , McLean E. O. 
Published: July 2010

AbstractFive soils were treated with K at rates of 269, 134, and 0 kg/ha and were diluted 6:4, 3:7, and 1:9 with sand. Potassium was extracted from samples of the soils and soil‐sand mixtures by various methods. The treated soils were then sequentially cropped in a growth chamber to German millet (Setaria italica stramineofructa) (one cutting) and alfalfa (Medicago sativa) (four cuttings). After cropping, K was again extracted from samples of the soils and mixtures.The soils differed greatly in amounts of K released to the plants and to the various extracting solutions. Amounts of K removed by NH4OAc, HNO3, HCl, and NaBPh4 from soils prior to cropping generally correlated better with amounts of K uptake than did amounts of K removed by other extractants. When all soils, K additions, and soil dilutions were combined, energy of exchange (ΔF) values were poorly correlated with K uptake because of greater than proportional release of K in soil‐sand mixtures. Both the plants and chemical extractants removed more K from soil‐sand mixtures than that calculated on the basis of proportions of the soil in the mixtures. Cropping considerably reduced the amounts of exchangeable and boiling HNO3 releasable K and caused ΔF values to become more negative.
Rate of Cation Exchange on Clay Minerals as Determined by Specific‐Ion Electrode Techniques
Authors: Malcolm R. L. , Kennedy V. C. 
Published: July 2010

AbstractA cationic electrode (used as a potassium specific‐ion electrode and a sodium specific‐ion electrode were used to measure rates of cation exchange on clay minerals. The Ba‐K exchange rates for kaolinite, illite, and montmorillonite were rapid with >75% exchange being measured within 3 sec. Because this time interval represents response time of the specific‐ion electrode, the Ba‐K exchange on these clay minerals occurs at a faster rate than this and may be an instantaneous process. Ba‐K exchange on vermiculitic materials was characterized by both a rapid and a slow rate of exchange. A major part of the Ba‐K exchange in silt‐ and clay‐size vermiculite was found to be diffusion controlled.Ca‐K, Mg‐K, Ca‐Na, and Mg‐Na exchange rates were rapid for all vermiculites and other clay minerals used in the experiment. Only Poole vermiculite exhibited two rates of Ba‐Na exchange similar to those shown by all vermiculites during Ba‐K exchange. Ba‐Na exchange rates on all vermiculites except Poole were rapid.
Influence of Soil Moisture Tension on Nitrate Accumulation in Soils
Authors: Sabey Burns R. 
Published: July 2010

AbstractThe influence of soil moisture tension on NO‐3‐N accumulation was studied in limed, silt loam, loessial derived soils to which a non‐limiting source of NH+4‐N was added. This was done by saturating the soils in an NH+4 solution, then subjecting the samples to 0, 0.1, 0.33, 1, 5, and 15 bars of soil moisture tension in conventional positive pressure equipment, and incubating the samples in a saturated atmosphere for varying intervals, to characterize the NO‐3‐N accumulation curve with time. The maximum slope of the line gave an estimate of the KM value or maximum rate of NO‐3‐N accumulation in ppm/day. The KM values in all soils were greatest at 0.1 bar tension, with KM values decreasing as soil moisture tension increased or decreased. The relative rates of NO‐3‐N accumulation, RM values or moisture rate indexes, varied much less than KM values among soils. The mean RM values at 0.1, 0.33, 1, 5, and 15 bars tension were 1.0, 0.71, 0.53, 0.29, and 0.13, respectively. The moisture rate index curve can be used to estimate the amount of NO‐3‐N accumulation in soils similar to those used in this study at all soil moisture tensions between 0.1 and 15 bars if the rate of NO‐3‐N accumulation is known at any one tension within the above range. The moisture rate index curve of this study and the temperature rate index curve of a previous paper are used in the previously proposed equation, N = KFRK(t − tFrt), to estimate NO‐3‐N accumulation in soils under varying conditions of temperature and soil moisture tension.
Effects of Soil Physical Properties, Rainfall Characteristics, and Wind Velocity on Clod Disintegration by Simulated Rainfall
Authors: Lyles Leon , Disrud L. A. , Woodruff N. P. 
Published: July 2010

AbstractThe effects of clod size and density, rainfall intensity and duration, and wind velocity on clod disintegration by simulated rainfall were studied in a laboratory wind tunnel‐raintower facility. Significant interactions (including those of higher order) were found among the variables studied. Clod bulk density had a minor effect on disintegration. For a specific clod size and wind velocity, 10‐min rains at 5.61 cm/hour were about as destructive as 90‐min rains at 1.60 cm/hour, even though the total volume of rainfall was 2.5 times larger in the latter case.Wind‐driven rain was very effective in clod disintegration. Up to 66% more soil was lost from clods exposed to 13.4‐m/sec winds than from those exposed to no wind for the same rain intensity, duration of exposure, and clod size. Mean drop size striking the clods probably increases with wind velocity and would account for some of the wind effects. Small clods were more susceptible to disintegration by raindrop impact than large clods. Multiple regression analyses indicate about 80 and 89% of the soil detachment variance was accounted for by linear and curvilinear procedures respectively.
Lindane Diffusion in Soils: II. Water Content, Bulk Density, and Temperature Effects
Authors: Ehlers Wilfried , Farmer W. J. , Spencer W. F. , Letey J. 
Published: July 2010

AbstractThe diffusion of lindane in Gila silt loam is strongly influenced by soil water content, bulk density, and temperature. The diffusion coefficient is nearly zero in soil of 1% water content. With an increase to 3% water content, which is equivalent to two layers of water between the montmorillonite clay plates, water is able to displace the lindane from the adsorbing surface so that the diffusion coefficient becomes maximal. A small additional increase in water content reduces the diffusion coefficient to about one‐half of the maximal value. This value then remains constant with increasing water content up to saturation. Decreasing bulk density or increasing temperature raises the diffusion coefficient. The influence of bulk density and temperature on diffusion is in good agreement with theoretical calculations.