bluuebunny/crossref_metadata_2025 huggingface dataset:
Glycerol Vapor Adsorption on Clay Minerals and Montmorillonitic Soil Clays
Authors: Moore D. E. , Dixon J. B.
Published: July 2010

Adsorption isotherms of glycerol were obtained for clay fractions of montmorillonite, vermiculite, kaolinite, and eight soil clays at 80C in an evacuated system. The weight of glycerol required for monolayer formation was determined by application of the BET equation to adsorption data. Montmorillonite samples gave BET monolayer values from 211 to 230 mg glycerol/g of montmorillonite which is in the theoretical range. Monolayer values calculated for soil montmorillonites from BET monolayer values and corrected for impurities were 209 to 239 mg glycerol/g of montmorillonite in < 0.08µ soil clays. The surface area values estimated from these soil montmorillonite monolayer values range from 738 m2/g to 844 m2/g. Vermiculite gave BET monolayer values of 40 mg and 96 mg/g of clay for 2 to 0.2µ and 0.2 to 0.08µ samples, respectively. This method appears to effectively measure the sorption surface of montmorillonite and indicates lower sorption surface of vermiculite than is suggested by its structural similarity to montmorillonite. Glycerol monolayer values indicate only modest reduction of particle size in < 0.08µ compared to 0.2 to 0.08µ montmorillonite from soil clays and Wyoming bentonite. The success of glycerol adsorption on clays, in spite of a very low vapor pressure, suggests that more volatile polar organic molecules might effectively be studied by adsorption on clay surfaces.
The Influence of Soil Water Matric Potential on the Strength Properties of Unsaturated Soil
Authors: Williams John , Shaykewich C. F.
Published: July 2010

A study was made of the contribution that matric potential makes to effective stress and therefore the strength properties of two unsaturated soils. From an evaluation of the effective stress parameters C' and ø', and the unconfined strength, the shear strength, effective stress, and the χ factor were estimated as a function of soil water matric potential over the range −0.59 to −15.1 bars.

The strength properties of a Gretna clay increased rapidly with decreasing matric potential. In a Wellwood loam, however, the strength properties remained relatively constant over the range −0.59 to −15.1 bars.

The influence of matric potential on the strength properties of an unsaturated soil can be described in terms of the contribution that matric potential makes to the effective stress operating in the soil system. A measure of the proportion of the matric potential operative in the effective stress is given by the χ factor which is related to the degree of saturation. Therefore, the influence that matric potential has on the strength of an unsaturated soil is related to the moisture retention properties of the soil.

The implications arising from the contribution that matric potential makes to the strength properties of an unsaturated soil are briefly discussed in terms of soil‐plant relations.
Adsorption of Polysaccharides by Montmorillonite
Authors: Parfitt R. L. , Greenland D. J.
Published: July 2010

Amylose and a dextran of MW 2 million were adsorbed by montmorillonite. However, two dextrans of lower MW did not adsorb on montmorillonite. It is suggested that entropy changes arising from changes in configuration of the macromolecules and the association of water molecules with clay and polymer control the adsorption behavior of uncharged polysaccharides. Poly (galacturonic acid) was adsorbed by aluminum montmorillonite but showed negative adsorption on sodium montmorillonite. The uronic acid components of a soil polysaccharide were adsorbed by montmorillonite if aluminum ions or hydroxy aluminum species were present on the clay; neutral sugar components were adsorbed irrespective of the exchangeable cations present or the pH.
Laboratory Determination of Leachable Soil Boron
Authors: Rhoades J. D. , Ingvalson R. D. , Hatcher J. T.
Published: July 2010

Laboratory methods are presented for determining the amounts of boron that must be leached from soils to reduce their soluble boron concentrations to nontoxic levels. One method consists of an extraction of a soil sample with a 0.01M mannitol −0.01M CaCl2 solution. The second method consists of dialysis of a soil sample against a boron‐specific resin in the presence of 0.01M CaCl2 solution. Some of the soils studied were observed to “regenerate” toxic levels of soluble boron following reclamation.
Denitrification by Isolated Soil Bacteria Under Various Environmental Conditions
Authors: Bollag J.‐M. , Orcutt Mary Lou , Bollag Brigitte
Published: July 2010

Nitrate reducing microorganisms were isolated from soil and their denitrifying properties were compared under various environmental conditions. The isolated denitrifiers cultured in a liquid medium under anaerobic conditions responded differently to changing pH, temperature, nitrate or nitrite concentration. Unfavorable growth conditions led to the accumulation of nitrite. Various combinations of the selected bacteria revealed that interactions occur among the microbes during growth in relation to their denitrifying activity. Variation among bacterial species and specific environmental conditions resulted in different denitrifying characteristics; therefore, generalizations cannot be made regarding microbial denitrification in soil for possible applied uses.
Mulch Rates Required for Erosion Control on Steep Slopes
Authors: Meyer L. D. , Wischmeier W. H. , Foster G. R.
Published: July 2010

The erosion‐reducing effectiveness of six rates of straw mulch was tested on slopes averaging 15%. Mulch rates of only 0.56 and 1.12 metric tons/ha reduced soil losses to less than one–third of those from unmulched areas during a series of intense simulated rainstorms. A 2.24‐metric tons/ha rate decreased soil loss to only 18% of that from no mulch, and the 4.48‐ and 8.96‐metric tons/ha rates reduced it to less than 5%.

Runoff velocity for the 0.56‐metric tons/ha rate was one‐half that for no mulch, but heavier rates decreased velocity only slightly more. The reduced velocity due to mulching accounted for much of the resulting decrease in soil erosion.

Although the small mulch rates greatly reduced erosion, more mulch was required to fully control erosion than was required on the less‐steep, more permeable soil conditions tested in earlier studies.
Measurement of Attenuation of 137Cs and 241Am Gamma Rays for Soil Density and Water Content Determinations
Authors: Corey J. C. , Peterson S. F. , Wakat M. A.
Published: July 2010

Soil density and water content can be determined concurrently by measuring the attenuation of two different gamma energies. A dual source containing 241Am and 137Cs was shown to be suitable for these measurements. Multichannel pulse‐height analyzers were evaluated to determine their accuracy under experimental conditions for simultaneous measurements of soil density and water content. NaI(Tl) and Ge(Li) detectors were also evaluated. The measurements were made with a collimated beam, 1 cm in diameter, of 662‐keV gamma rays and 59.6‐keV gamma rays from a source containing 70 mCi of 137Cs and 29 mCi of 241Am. Measured mass attenuation coefficients were 0.08565, 0.07803, and 0.07887 cm2/g for cesium gamma rays and 0.20493, 0.27100, and 0.33480 cm2/g for americium gamma rays with water, Cecil, and Houston Black soil, respectively. The higher resolution of the Ge(Li) detector and a 4096‐channel pulse‐height analyzer had no significant advantage with peaks as widely separated as 662 keV and 59.6 keV. A NaI(Tl) detector and a 400‐channel pulse‐height analyzer were satisfactory. With the multichannel pulse‐height analyzer, it was simpler to adjust the area under the americium peak for the Compton contribution from the cesium radiation than with a single channel pulse‐height analyzer. Water content and density changes in both a swelling and nonswelling soil illustrate the utility of the system.
Measuring Soil Matric Potential in situ by Sensing Heat Dissipation within a Porous Body: II. Experimental Results
Authors: Phene C. J. , Rawlins S. L. , Hoffman G. J.
Published: July 2010

A sensor described previously to measure the matric potential of soil water in situ was tested in soil‐plant systems. Experiments were performed in the laboratory in a controlled environment and in the field. In the field, temperatures obtained by the sensor were used to predict optimum time for measurement to avoid error caused by diurnal temperature drift in the soil. The error caused by temperature drift was eliminated completely by using two matched diode sensors and taking a temperature difference measurement.

The accuracy of the matric potential sensor proved to be as good as or better than that of other techniques used to measure matric potential. Sensors with high sensitivity in the 0 to −2 bar matric potential range had an accuracy of ±0.2 bar. The accuracy decreased progressively to ±1 bar at a matric potential of −10 bars.
Toxic Metals in Acid Soil: I. Estimation of Plant‐Available Aluminum
Authors: Hoyt Paul B. , Nyborg Marvin
Published: July 2010

Exchangeable Al and 0.01M CaCl2‐soluble Al were measured in 40 acid surface soils by Clark's procedure for corrected lime potential and exchangeable cations, and by a modified procedure which was developed here. In the modified procedure, 0.01M CaCl2‐soluble Al was extracted by using 16 hr of shaking instead of 5 days, and exchangeable Al was extracted with 1N KCl for 2 min instead of with 2N NaCl for 16 hr. Good agreement was given with the theoretical relationship between corrected lime potential and percent base saturation of the permanent charge sites by both the original and modified procedures. Aluminum extracted by the two procedures and also that extracted by three other methods were then assessed for their availability to plants grown on the soils in a greenhouse study.

Criteria of plant‐available Al were the yield responses to liming by barley (Hordeum vulgare L.), turnip rape (Brassica campestris L.), and alfalfa (Medicago sativa L.), and the Al concentration in alfalfa grown on the unlimed soils. Exchangeable Al and 0.01M CaCl2‐soluble Al measured by Clark's and the modified procedures were all closely correlated with the criteria of Al availability. Aluminum extracted by 1N NH4OAc (pH 4.8), 1N NH4OAc (pH 3), or 0.002N HCl methods were not so closely correlated with the criteria.

The use of extractable soil Al for the diagnosis of the need for liming is discussed.
Sorption of Inorganic Phosphate by Lake Sediments
Authors: Shukla S. S. , Syers J. K. , Williams J. D. H. , Armstrong D. E. , Harris R. F.
Published: July 2010

Twenty‐five sediments from nine soft‐water and five hard‐water Wisconsin lakes sorbed between 20 and 100% of the inorganic P added at a level of 830 µg P/g oven‐dried sediment and between 14 and 99% of that added at a level of 6,700 µg P/g oven‐dried sediment. Noncalcareous sediments usually sorbed more added P than calcareous sediments. P sorption fended to be inversely related to the CaCO3 content of the calcareous sediments. Treatment with oxalate destroyed or virtually eliminated the ability of noncalcareous sediments to sorb added P and greatly reduced that of the calcareous sediments. Oxalate extracted widely varying amounts of Fe (3 to 131 mmoles/100 g) and Al (6 to 26 mmoles/100 g) from the noncalcareous sediments; an appreciable proportion of the total Fe in the noncalcareous sediments was oxalate‐extractable. One noncalcareous sediment, high in oxalate‐extractable Fe, sorbed over 80% of inorganic P added at a level of 16,700 µg P/g oven‐dried sediment. With one exception, two treatments with citrate‐dithionite‐bicarbonate or one oxalate extraction had similar effects on the P‐sorption capacity and released comparable amounts of Fe, suggesting that the extractable Fe is derived from an amorphous iron oxide complex. The proportion of added P sorbed was closely related to the amount of oxalate Fe and to the levels of native total inorganic P in the sediments. It is postulated that a gel complex of hydrated Fe oxide which contains small amounts of Al2O3, Si(OH)4, and organic matter, is the major P‐sorbing component of sediments.
Incorporation of 15N‐Tagged Mineral Nitrogen into Stable Forms of Soil Organic Nitrogen
Authors: Legg J. O. , Chichester F. W. , Stanford G. , DeMar W. H.
Published: July 2010

Transformation of 15N‐tagged mineral N into organic forms was accelerated by growing a series of oat crops (Avena sativa L.) in the greenhouse, with each crop growing to sufficient maturity for the seed to be used for the next crop. The plant material was returned to the soil, except for triplicate pots which were removed for analysis at each cropping period. Availability ratios (fraction of plant N that is 15N divided by the fraction of soil N that is initially 15N for each cropping period) declined from an initial value of 10.4 for the Chester surface soil to approximately 2 after 11 crops.

During long‐term mineralization tests with soil samples taken after two, five, and eight cropping periods, availability ratios were also stable, or soon became stable, at approximately 2. When similar soil samples were extracted after autoclaving in 0.01M CaCl2 or subjected to acid hydrolysis, however, the “extractability ratios” approached unity. It is hypothesized that about half of the indigenous N in the Chester soil is biologically unavailable because of inaccessibility to microorganisms of organic N compounds or complexes incorporated within microaggregates.
Recovery of Residual Nitrogen by Corn (Zea mays L.) from Various Soil Depths as Measured by 15N Tracer Techniques
Authors: Gass W. B. , Peterson G. A. , Hauck R. D. , Olson R. A.
Published: July 2010

A tracer technique was used to evaluate crop recovery of residual inorganic nitrogen from several soil depths. 15N‐labeled nitrate was placed at depths of 9, 60, 120, and 180 cm in field plots planted to corn (Zea mays L.) and containing 409, 468, and 582 kg inorganic N/ha in the 180‐cm profile. Flag leaf samples were collected at three growth stages and their 15N and total N contents determined.

At early silk stage, no labeled nitrate was extracted from soil at depths below 120 cm, regardless of residual N level. Nitrate was absorbed at the blister stage from a depth of 180 cm in soil containing the lowest amount of residual N. In soil at the highest level of residual N, little labeled nitrate was recovered at any growth stage at depths below 120 cm. At harvest, more 15N derived from the upper soil profile was found in the stover, while the grain contained considerable 15N obtained from the middle and lower profiles, presumably related to the later period of uptake.
Release of Herbicides from Clay Minerals as a Function of Water Content: I. Kaolinite
Authors: Don Scott H. , Lutz J. F.
Published: July 2010

The influence of water content on the release of six herbicides from kaolinite was studied. Kaolinite suspensions were treated with 14C‐labeled herbicides at rates of 1 and 4 µg/g (based on dry weight of clay). Extracts of the soil solution were obtained at successively increased increments of pressure from 0.3 to 15 bars, using the pressure membrane extractor. The following determinations were made: (i) volume of extract for each pressure‐increment; (ii) concentration of herbicide in the extract, as measured by liquid scintillation; (iii) amount of herbicide remaining, as calculated by difference; and (iv) pH of the extract.

The results show that for all herbicides used, except simazine, the concentration in the extracts decreased with increasing pressure increments. The decreases were greatest with diuron and chlorpropham. Simazine concentration was from two to three times greater in the high than in the low‐pressure extracts. High concentrations in low‐pressure extracts suggest that plant availability is high and that movement with water could be a problem with high rainfall under field conditions. Fluometuron and 2,4‐D were negatively adsorbed; the others were positively adsorbed. The order of release in terms of total recovery of herbicide applied at the 1‐ppm rate was: fluometuron > 2,4‐D > atrazine > chlorpropham > simazine > diuron. The order was the same for the 4‐ppm rate except that 2,4‐D was greater than fluometuron. The total recovery of the herbicides in the extracts ranged from 12.0% for diuron to 92.1 for fluometuron.
Effect of Soluble and Exchangeable Aluminum on a Soil Bacillus
Authors: Zwarun A. A. , Bloomfield B. J. , Thomas G. W.
Published: July 2010

The test organism, a Bacillus species isolated from soil, behaved as a typical cation exchanger having a CEC of 95 meq/100‐g organism (oven‐dry weight). Increasing acidity from pH 6.6 to 4.5 greatly reduced the number of surviving cells suspended for 3 hours in an acetate buffer. Addition of soluble aluminum up to 80 ppm produced no further detrimental effect upon the organism, even though the cell walls of the organism were saturated with aluminum. Exchangeable aluminum in the form of Al‐saturated Wyoming bentonite decreased the number of surviving cells as compared with a Ca‐ saturated Wyoming bentonite. Addition of soluble Al to the Al‐clay suspension did not result in any interaction. Upon incubation with the clay suspensions, the organism changed its gram‐staining characteristic. Clay particles in all treatments were adsorbed by the cells producing organism‐clay aggregates.
Extraction of Anions and Cations from Recent Volcanic Ash
Authors: Bornemisza Elemer
Published: July 2010

Water extracts of ash from Mt. Arenal, Costa Rica's most recently active volcano, contained up to 32 ppm Ca, 3.3 ppm Mg, 4 ppm K, 4 ppm Na, and 0.4 ppm Mn. No phosphates were extracted by water, but sulfates reached 35 ppm and silicates 1.6 ppm in the extracts. The sample farthest away from the volcano gave extracts of lowest Ca and Mg content. The pH of diluted NaOH suspension of ash decreased on standing by up to 1.5 pH units.
Characterization of Inorganic Phosphate in Noncalcareous Lake Sediments
Authors: Williams J. D. H. , Syers J. K. , Armstrong D. E. , Harris R. F.
Published: July 2010

Inorganic P added with 0.5M NH4F to noncalcareous sediments was recovered in the NH4F and succeeding 0.1N NaOH extractions. Values of NH4F‐P, corrected on the basis of the recovery of P added with the NH4F reagent, underestimated the total amount of inorganic P capable of interacting with NH4F, but by less than the corresponding uncorrected values. The amounts of inorganic P extracted by 0.5M NH4F followed by 0.1N NaOH, by citrate‐dithionite‐bicarbonate, and by 0.3N NaOH were very similar, the means of the three quantities varying by only 11 ppm. Oxalate‐extractable inorganic P exceeded these quantities by an average of 250 ppm but exceeded the sum of NH4F‐P, 1st NaOH‐P, and reductant‐soluble P by an average of 60 ppm, the difference in the latter comparison being ascribed to the partial or complete dissolution of apatite by the oxalate reagent. Although NH4F‐Al was moderately well correlated with oxalate‐Al (r = 0.70) neither variable was related to NH4F‐P. The very high correlations between NH4F‐P, 1st NaOH‐P, and reductant‐soluble P, on the one hand, and between these three fractions and oxalate‐ and citrate‐dithionite‐bicarbonate‐extractable Fe, on the other, indicate a common origin for the inorganic P in the three fractions as part of a short range order Fe‐rich complex. Apatite was low in all sediments.
Decomposition of Urea Phosphate in Soils
Authors: Bremner J. M. , Douglas L. A.
Published: July 2010

Studies of the decomposition of urea phosphate (NH2CO‐NH2 · H3PO4) in soils showed that the phosphoric acid in this compound retards enzymatic hydrolysis of the urea by soil urease and reduces gaseous loss of urea N as ammonia. When soils treated with urea and urea phosphate were incubated at 20C for 14 days, the percentage loss of urea N as ammonia was 4.6–61.1% (average, 21.2%) for the soils treated with urea, but was only 0.1–1.1% (average, 0.7%) for the soils treated with urea phosphate. The studies reported support the conclusion from previous work that urea phosphate has significant potential advantages over urea as a fertilizer.
Changes in DTPA‐Extractable Zinc, Iron, Manganese, and Copper in Soils Following Fertilization
Authors: Follett R. H. , Lindsay W. L.
Published: July 2010

Eleven soils were fertilized with Zn, Fe, Mn, and Cu and examined periodically with the DTPA micronutrient soil test. The study continued for 14 weeks while the soils were cropped in the greenhouse first with oats (Avena sativa) and then with corn (Zea mays). During this period fertilizer Cu declined to 61%, Zn to 44%, and Mn to 14% of their initial values. Only 20% of the Fe added as FeSO4 · 7H2O remained extractable after 1 week. With chelated Fe as FeEDDHA, 70% was extractable at 7 weeks and 26% at 14 weeks. The results are in general agreement with reported residual response from these fertilizers and suggest that the DTPA soil test may be useful for monitoring the availability of micronutrient cations in fertilized as well as unfertilized soils.
Soil Profile Gravel Layers: I. Effect on Water Storage, Distribution, and Evaporation
Authors: Unger Paul W.
Published: July 2010

Soil water distribution and evaporation following water application were affected by a gravel layer placed on or 5, 15, or 25 cm below the soil surface. Soil above gravel retained more water than soil at similar depths in uniform columns. Evaporation from soil with gravel on the surface or at 5 cm was slower than from the check, while evaporation from soil with gravel at 15 or 25 cm generally was more rapid than from the check.

The water content of soil near the surface of field plots was markedly influenced by rainfall or duration of rain‐free periods. For the entire soil mass sampled, gravel on or at 5 cm below the surface increased the water content of plots as compared with both the check plots and treatments with gravel at 15 or 25 cm during periods of relatively frequent precipitation (spring and early summer). All treatments, however, permitted considerable water losses during extended dry periods (late summer, fall, and winter).
Triammonium Pyrophosphate as a Source of Phosphorus for Plants
Authors: Hughes J. D. , Hashimoto Isao
Published: July 2010

When ammonium ortho‐ and pyrophosphates were applied to mixtures of sand and a soil mineral (kaolinite, montmorillonite, or gibbsite), both the uptake of P by plants and the immobilization of the P were affected more by the soil mineral than by any other factor. Pyrophosphate was hydrolyzed to orthophosphate during incubation more rapidly in the presence than in the absence of a soil inoculum. The results tend to support the hypothesis that plants utilize orthophosphate more readily than pyrophosphate. Although the reactions of pyrophosphate with soil minerals differ markedly from those of orthophosphate, the two forms of phosphate were immobilized by the soil minerals to about the same extent, and differences between the two forms disappeared as hydrolysis and immobilization proceeded. The P uptake was in the order control (no mineral) > kaolinite > montmorillonite > gibbsite, in agreement with the extent of reaction of the applied phosphate with these minerals.
A Simple Statistical Procedure for Partitioning Soil Test Correlation Data Into Two Classes
Authors: Cate Robert B. , Nelson Larry A.
Published: July 2010

Most soil test laboratories divide soil test results into two or more classes for the purpose of making fertilizer recommendations. This is usually done for the practical reason that it reduces the number of different recommendations necessary. However, the basis for defining the different classes (e.g., Very Low, Low, Medium, etc.) is often subjective or arbitrary. This paper explains a simple, yet statistically sound, method for setting the class limits. The procedure is to split the data into two groups, using successive tentative critical levels to ascertain that particular critical level which will maximize overall predictive ability (R2), with the means of the two groups (classes) as the predictor values. The paper presents an actual example, using data believed typical of this kind of problem. Several continuous correlation models were also fitted to the same data. None gave as high an R2 as a single Low‐High split defined by the suggested procedure. Similar results have been obtained with a majority of 200 sets of soil test correlation data, indicating that the new procedure may be widely applicable.
Steady Infiltration from Point Sources, Cavities, and Basins
Authors: Raats P. A. C.
Published: July 2010

Steady infiltration from buried point sources and surface point sources is analyzed. The partial differential equations for the matric flux potential and the Stokes' stream function associated with axially symmetric flows are derived. The discussion is based on the assumption that the hydraulic conductivity is an exponential function of the pressure head. Explicit expressions for the matric flux potential, the Stokes' stream function, the flux, the pressure head, and the total head are obtained. Some features of the solutions for buried point sources, surface point sources, and gravity‐free flows are compared. Related upward flows for which the soil becomes saturated everywhere are discussed briefly.
Nitrate Adsorption: III. Desorption Movement and Distribution in Andepts
Authors: Kinjo T. , Pratt P. F. , Page A. L.
Published: July 2010

A peak of NO3‐ accumulation occurred in the 1‐ to 2‐cm depth of an 11‐cm soil column when 0.2 meq of KNO3 was applied in sufficient solution (16 ml) to fill the pore space in a column of air‐dry San Gregorio soil. Practically no NO3‐ was found below the 4‐cm depth. The greater portion of the NO3‐ applied was displaced from the soil column by the addition of 3 pore volumes of water. The anion distribution coefficient obtained from a column of San Gregorio soil was 2.2 ml/g and was similar to that obtained from a batch‐type method when the soil was in equilibrium with the same concentration of NO3‐. The rate of NO3‐ desorption was described by a first‐order reaction equation. The effect of adding SO42‐ and NO3‐ in the same column was to increase the rate of movement of NO3‐. Sulfate movement was much slower than that of NO3‐.
Montmorillonite Equilibria and the Weathering Environment
Authors: Kittrick J. A.
Published: July 2010

Stability equations were derived for Belle Fourche and Aberdeen montmorillonites. Both the composition of structural ions and the cation exchange capacity (CEC) were considered to be essential features of montmorillonite stability. However, montmorillonite stability was considered to be independent of the solution activity of exchangeable ions.

Simultaneous solution of the stability equations for Belle Fourche and Aberdeen montmorillonites indicated the two minerals could be at equilibrium with one another, but only under solution conditions quite different from those of their original stability determinations. The two montmorillonites (with hematite to control pH — 1/3pFe3+, kaolinite to control H4SiO4 activity, and a constant high Mg2+ activity) were then equilibrated from both low pH (undersaturation) and from high pH (supersaturation). The agreement between experimental and predicted equilibria was well within the experimental error of the original montmorillonite stability determinations. The good agreement between calculated and experimental equilibria under solution conditions far different from those employed for the original stability determinations (about 4 pH units higher, for example) confirms the accuracy of the original stability determinations.

Agreement between predicted and experimental equilibria also supports the view that structural ions such as Mg2+, Fe3+, Al3+, and Si4+, as well as the CEC, are essential features of the montmorillonite structure. The relationship between montmorillonite stability and the activities of constituent ions in solution permits the construction of several diagrams showing the variation in stability of Belle Fourche and Aberdeen montmorillonites with change in composition of the soil solution. From these diagrams, it is concluded that the various montmorillonite compositions encountered in nature are primarily a reflection of diverse solution environments rather than a chance incorporation of ions during the crystal growth process.
Capacity of Desert Algal Crusts to Fix Atmospheric Nitrogen
Authors: Macgregor A. N. , Johnson D. E.
Published: July 2010

Approximately 4% of the soil surface of an area of desert grassland in the Sonoran Desert of southern Arizona possessed algal‐crust formations. Samples of dry intact algal crusts were examined for nitrogen fixation by the acetylene‐ethylene method. Three hours after being moistened, algal crusts produced detectable levels of ethylene. Premoistened algal crusts were capable of producing ethylene equivalent to 0.7 µg of N/cm2 of algal crust per hour. On the basis of these findings, 1 ha of desert grassland may receive a nitrogen input of 3 to 4 g of N/hour (0.3 mg to 0.4 mg N/m2 per hr) following a rainfall.
Water and Solute Movement in Svea Loam for Two Water Management Regimes
Authors: Cassel D. K.
Published: July 2010

Soil water and soil solute movement were investigated in a sub‐humid environment over a 3‐month period for two water regimes. Ammonium nitrate and KCl were broadcast on duplicate 3.7‐m square plots. Each plot was irrigated with 6 to 10 cm of water at 7‐ to 14‐day intervals. One plot was covered to prevent exchange of water at the soil surface (covered plot) while the second remained bare and was thus subjected to the prevailing environmental conditions. Soil water flux and unsaturated hydraulic conductivity values were calculated using soil water pressure and water content data from the covered plot. Analyses of soil solution collected from 30‐, 61‐, 91‐, 122‐, and 152‐cm depths for NO3‐N and Cl revealed that, for the environmental conditions encountered (35 cm pan evaporation and 15 cm rainfall), downward movement of ions was nearly 1.5 times greater for the covered compared with the bare plot. The solute did not move with the soil water in a one to one relationship for either plot.
General Theorem on Steady Infiltration from Surface Sources, With Application to Point and Line Sources
Authors: Philip J. R.
Published: July 2010

A general theorem is established that enables the solution of the quasilinearized steady infiltration equation for any distribution of surface sources to be found immediately from the corresponding (mathematically simpler) solution for buried sources. It is introduced through the special cases of the surface line and point sources. The first of these solutions is new and the present derivation of the second is much simpler and more direct than that available hitherto. These solutions hold also for steady infiltration from suitably‐shaped furrows and basins. Corollary to the general theorem, relations of the same type hold between the horizontal flux density components. Both the theorems and the special results apply also to processes such as diffusion in a uniform convective flow and sedimentation under gravity and Brownian motion.
Influence of Soil Treatment on Persistence of Six Chlorinated Hydrocarbon Insecticides in the Field
Authors: Guenzi W. D. , Beard W. E. , Viets F. G.
Published: July 2010

An experiment was designed to compare the rate of disappearance of dieldrin, endrin, heptachlor, lindane, DDD, and DDT from flooded and nonflooded soils. Chopped alfalfa (Medicago sativa L.) (0.25% in the top 10 cm of soil) was added to half of the plots. The nonflooded treatment was subdivided into a soil mixing treatment (surface 8 cm of soil mixed every 2 weeks) and a nonmixing treatment. Holes were dug in the field and plastic containers (43 cm in diameter and 53 cm in depth) were placed in the holes and filled with soil to a depth of 48 cm so that the soil surface inside the container was level with the surrounding soil. Pesticides were incorporated into the surface 10 cm of soil. In the nonflooded soil, neither soil mixing nor added alfalfa enhanced the loss of dieldrin, endrin, DDD, or DDT from the top 8 cm of soil during a 22‐week period. Under the same conditions, the concentrations of lindane and heptachlor decreased with time, and more pesticide was lost from the soil receiving the mixing treatment than from the nonmixed soil. Lindane, heptachlor, endrin, and DDT were susceptible to degradation in the flooded soils. The order of degradation for the degradable insecticides was heptachlor > DDT > lindane > endrin.
The Chemistry and Phytotoxicity of Arsenic in Soils: I. Contaminated Field Soils
Authors: Woolson E. A. , Axley J. H. , Kearney P. C.
Published: July 2010

Arsenic (As) residues on 58 surface soil samples taken from soils with a history of As application averaged 165 ppm As, while nearby soils not treated averaged 13 ppm As. Most of the residual As was found as Fe‐As (0.1N NaOH extractable) by a modified soil P procedure. Water‐soluble As (1N NH4Cl extractable) was detected in soils from two states. Other forms, Al‐ and Ca‐As (0.5N NH4F and 0.5N H2SO4 extractable As, respectively), may predominate if the amount of “reactive” Al or Ca is high and reactive Fe is low. Bioassay of the contaminated and uncontaminated soils showed a correlation of 0.74 between growth reduction and total As and 0.82 with a summation of As fractions. Plants were tolerant to large As applications (670 ppm As) to soils which were high in reactive (1N NaOH extractable) Al.
Calcium Fluoride Formation During Extraction of Calcareous Soils with Fluoride: I. Implications to Inorganic P Fractionation Schemes
Authors: Syers J. K. , Smillie G. W. , Williams J. D. H.
Published: July 2010

Added inorganic P sorbed during 0.5M NH4F extraction of calcite or aragonite was recovered in subsequent citrate‐dithionite‐bicarbonate (CDB) and HCl extractions of the Williams et al. (1967) inorganic P fractionation scheme. The sorbed P was shown to be associated with CaF2 formed by the replacement of CaCO3 during the NH4F extraction. Similar results were obtained for soils which contained calcite but no P fertilizer reaction products. Thus, the amounts of non‐occluded Al‐ and Fe‐bound P (NH4F‐ and NaOH‐extractable) were underestimated whereas reductant‐soluble P (CDB‐extractable) was overestimated and acid‐extractable Ca‐P frequently overestimated. In contrast, magnesite, dolomite, and a dolomitic soil sorbed only a low proportion of added P during NH4F extraction. A modified fractionation procedure, developed for calcareous soils, omitted the NH4F extraction and involved sequential extraction with (i) NaOH to remove nonoccluded Fe‐ plus Al‐bound P, (ii) NaCl and citratebicarbonate (CB) to remove P sorbed by carbonates during the preceding NaOH extraction, (iii) CDB to remove occluded P (reductant‐soluble P), and (iv) HCl to remove Ca‐bound P. Phosphorus added with the NaOH reagent to carbonate minerals and calcareous soils was recovered during the NaOH, NaCl, and CB extractions, enabling differentiation of nonoccluded Fe‐ plus Al‐bound P from occluded P. The procedure also permitted a more meaningful separation of nonoccluded Fe‐ plus Al‐bound P and Ca‐bound P, particularly in calcareous soils which contained P fertilizer reaction products.
Adsorption of Ametryne and Atrazine on an Oxisol, Montmorillonite, and Charcoal in Relation to pH and Solubility Effects
Authors: Yamane V. K. , Green R. E.
Published: July 2010

Adsorption of ametryne exceeded that of atrazine on soil and montmorillonite at both low and high pH. Ametryne (pKa ≅ 4.0) showed a greater increase in adsorption with decrease in pH than atrazine (pKa = 1.68). Addition of charcoal to soil masked the effect of soil pH on ametryne adsorption. Adsorption of ametryne on charcoal decreased at the low pH values conducive to ametryne protonation, demonstrating the effect of pH on triazine‐water affinity in the absence of specific triazine‐adsorbent interactions which are responsive to triazine protonation. Adsorption isotherms were adjusted by use of “relative solution concentrations” to examine the influence of pH and temperature on the relative affinities of water and adsorbent for triazine herbicides. A wetting agent used in the commercial ametryne product had no effect on the adsorption of ametryne.
Ecology of Nematodes in Clarion‐Webster Toposequences Associated With Glycine Max (L.) Merrill
Authors: Nyhan J. W. , Frederick L. R. , Norton D. C.
Published: July 2010

Toposequence variations in soil and plant properties were characterized and related to nematode populations associated with soybeans. The smallest populations of Aphelenchus avenae, Helicotylenchus pseudo‐robustus, Tylenchorhynchus nudus, Tylenchus spp., and non‐stylet‐bearing nematodes occurred at the toeslope position within the toposequences. Increases in soil pH, soluble salts, percentages of the soil pores filled with water, soil moisture relative to field capacity, silt plus clay, and soil organic matter within the toposequences were associated with decreases in nematode populations, plant top weight, and the concentrations of nitrogen, potassium, and barium in the plant tops. Factor analysis of the data revealed that 67–73% of the total site‐sampling period variance could be accounted for by soil structure, root activity, soil fertility, dry matter production, and nematode factors. However, nematode populations were more closely correlated with plant variables than with soil variables at each toposequence.
Recovery of 15N‐Labeled Fertilizers in Field Experiments
Authors: Westerman R. L. , Kurtz L. T. , Hauck R. D.
Published: July 2010

Urea and oxamide, each labeled with 15N, were compared as fertilizers in two field experiments in adjacent locations in successive years with ‘Sudax SX11’ Sorghum‐sudan hybrid (Sorghum sudanense) as the test crop. Four cuttings were harvested during the first experiment and three during the second. Patterns of uptake of fertilizer N were in accord with the characteristics of the two carriers. In the first harvests in both experiments the amounts of N taken up from urea were markedly greater than from oxamide; but by the third harvests, yield responses and N uptake from oxamide were greater than from urea. Total recoveries of fertilizer N from the two carriers during the entire growing season were similar as greater recoveries of urea‐N in the early summer were compensated for by greater recoveries of oxamide‐N in the late summer.

Of the N added in urea in the first experiment, 51% was recovered in the crops and 28% was still in the soil (0–25cm) at the end of the growing season. Corresponding figures for oxamide were 52% in the crops and 31% in the soil. In the second experiment, when fertilizer applications and planting operations were delayed until more favorable growing weather, 93% and 99% of the urea‐ and oxamide‐N, respectively, were estimated as recovered in the crops, and measurements of the amounts of fertilizer remaining in the soil were not attempted.
Residual Effects of 15N‐Labeled Fertilizers in a Field Study
Authors: Westerman R. L. , Kurtz L. T.
Published: July 2010

Residual effects of two 15N‐labeled N fertilizers, urea and oxamide, were compared during the second cropping season after they had been applied at rates of 0, 56, 112, and 168 kg N/ha. ‘Sudax SX11’ sorghum‐sudan grass hybrid (Sorghum sudanense) was grown and harvested three times during this second cropping season while the residual effects were being measured.

Fertilizer N removed in plant tops during this second year of cropping contained 13–18% of the residual fertilizer N in the soil at the end of the first season and was equal to 4–6% of that applied originally in the fertilizers. At the end of the second cropping season, 22 and 26% of the initial applications of N in urea and oxamide, respectively, remained in the soil. The effect of carriers on these amounts of residual fertilizer N was not significant. The removals in crops during the second season plus those amounts remaining in the soil at the end of the second season were essentially equal to the residual fertilizer N which had been in the soil at the end of the first season. Thus, no evidence was found for loss of residual N by leaching, denitrification, or other processes during the second cropping season. Since removals of N in crops were considerably greater than the additions in fertilizers, it is hypothesized that nearly all inorganic fertilizer N was taken out of the soil and most of the residual fertilizer N was in relatively stable organic forms. Conditions for these experiments had been selected to conserve N, and as a consequence the deficits of fertilizer N reported here may be expected to be smaller than might occur under other practices.
Anomalies and Sampling Variation in Forest Soil Water Measurement by the Neutron Method
Authors: Sartz Richard S.
Published: July 2010

Sampling errors were determined for neutron meter measurements of soil water content in a heterogeneous forest soil. Water content variance at individual 30‐cm depths on uncut plots increased with depth at a high water content but was uniform at a low water content. The variation was greater at a low than at a high water content on uncut plots, but was about equal on cut plots. Water content changes over a period of time were more variable than water content at a single point in time. Coefficients of variation for individual depths ranged up to 76% for uncut plots and up to 137% for cut plots. Coefficients of variation for total profile storage were a little lower for change in water content than for total water content on uncut plots, but the relationship was reversed on cut plots. Soil depth differences contributed substantially to the variance of total storage changes, but variable soil depth must be considered in sampling schemes designed to determine total water use under different cover conditions.
Effects of Hydroxyl‐Containing Organics on the Strength‐Energy Characteristics of Montmorillonite
Authors: Dowdy R. H.
Published: July 2010

The effect of polyvinyl alcohols and glucose on the tensile strength and tensile strain energy (rupture energy) of montmorillonite was studied by utilizing direct tensile strain of oriented clay films. Polyvinyl alcohol (PVA) dramatically increased the tensile strength of homoionically saturated montmorillonite in the following order: Na ≥ Ca >> Al. The intermediate molecular weight PVA8 (70,000–80,000 MW) increased strength significantly more than did the lower molecular weight PVA9 (14,000 MW). The strength of Na clay increased from 120 to 560 kg cm‐2 with the addition of 30 g PVA8/100 g clay. Increases in strength were also noted at lower rates of polymer applications; 0.5 g PVA8/100 g clay doubled the strength of Ca clay. Glucose did not change the strength characteristics of montmorpillonite. The data suggest that long, linear, uncharged, polyhydroxylic polymers, such as PVA, are very effective in bridging clay domains. The tensile strain energy required to rupture montmorillonite increased with added PVA in a pattern similar to tensile strength increases.
Rate and Extent of Inorganic Phosphate Exchange in Lake Sediments
Authors: Li W. C. , Armstrong D. E. , Williams J. D. H. , Harris R. F. , Syers J. K.
Published: July 2010

The exchangeability of sediment inorganic P was investigated by adding carrier‐free 32P inorganic phosphate to steady‐state lake sediment‐water systems and measuring the rate and extent of 32P incorporation into the sediment phase. The effects of sediment properties (calcareous and noncalcareous), oxygen status, and addition of inorganic P on exchangeability were evaluated. Exchangeable P comprised from 19 to 43% of the total native inorganic P of the sediments investigated. Although inorganic P was released into solution in anaerobic systems due to reduction of iron from the ferric to the ferrous state, the total pool of exchangeable P (sediment phase plus in solution) was not greatly altered. Sorbed added inorganic P (equilibrated 2 weeks) showed approximately the same degree of exchangeability as native inorganic P in noncalcareous sediments but was more exchangeable in calcareous sediments. Exchangeable P exhibited exchange rates which were resolved into three separate first‐order reactions by a graphical procedure. A major portion of exchangeable native sediment P (45 to 87%) participated in the rapid exchange reaction characterized by an exchange rate constant ranging from 7.4 to 46 hours‐1. These results show that a large pool of sediment inorganic P has a high potential for interaction with the overlying lake water and for biological assimilation.
Anion Adsorption in Ferruginous Tropical Soils
Authors: Mekaru T. , Uehara G.
Published: July 2010

The difference in pH of a soil suspension prepared with 1N KCl and with water was used to determine net charge of colloids with constant potential type surface. The quantity (pHKCl‐pHH2O) called delta pH had a positive, zero, or negative value corresponding to the net surface charge. Negative and positive adsorption of chloride or nitrate ions were measured in soil suspensions with negative and positive delta pH, respectively. Increasing the nitrate ion concentration increased sulfate adsorption in suspensions with negative delta pH values. Negative adsorption of nitrate and chloride ions was measured when sulfate ions were added to a soil colloidal suspension which was initially net positively charged. This supports the present belief that specifically adsorbed anions render a surface more negative by displacing the zero point of charge to lower pH values. This was substantiated by a measured increase in CEC from an initial value of 26 meq/100 g in a phosphated soil. Each millimole of adsorbed phosphate increased CEC by 0.8 meq.
Steady Infiltration from Sources at Arbitrary Depth
Authors: Raats P. A. C.
Published: July 2010

This discussion of steady infiltration is based on the assumption that the hydraulic conductivity is an exponential function of the pressure head. The solution for infiltration from a single point source at arbitrary depth is presented. On the basis of this solution, J. R. Philip's superposition theorem for surface sources is generalized to an arbitrary distribution of sources at arbitrary depths. General expressions for the pressure head, the total head, and the components of the flux are also given.
Further Evidence for the Inability of the Kjeldahl Total Nitrogen Method to Fully Measure Indigenous Fixed Ammonium Nitrogen in Subsoils
Authors: Meints Vernon W. , Peterson Gary A.
Published: July 2010

Three methods of Kjeldahl total N determinations in soils were compared. Method 1 involved a pretreatment of the soil with a HF‐acid mixture and resulted in higher N values than methods 2 or 3 which involved a long period of digestion and a modification of a Gunning method, respectively. Differences in total N values obtained by the three methods were greatest for subsoils. The inability of methods 2 and 3 to measure all of the indigenous fixed NH4+‐N resulted in low N values and erroneously high C:N ratios in the subsoil.
Observed and Calculated Distribution of Lindane in Soil Columns as Influenced by Water Movement
Authors: Huggenberger F. , Letey J. , Farmer W. J.
Published: July 2010

Observed and calculated distributions of lindane in soil columns of infiltration experiments were compared. Three mineral soils with different organic matter contents and particle size distributions were used in the study. The adsorption coefficient (K′) and rate of adsorption (α) were determined in independent experiments. As predicted by the theory, application of a greater amount of lindane to the soil surface increased the concentration of lindane but did not influence the depth of penetration. Under leaching conditions, the depth of water penetration divided by K was a good estimate of the observed depth of maximum concentration of lindane. The theory failed in general to predict the shape of the distribution curve of lindane.