bluuebunny/crossref_metadata_2025 huggingface dataset:
Amidase Activity in Soils: I. Method of Assay
Authors: Frankenberger W. T. , Tabatabai M. A.
Published: July 2010

Amidase [acylamide amidohydrolase, EC (Enzyme Commission) 3.5.1.4] is the enzyme that catalyzes the hydrolysis of amides and produces the corresponding carboxylic acid and ammonia. The detection of this enzyme in soils is reported, and a simple, sensitive, and precise method to assay amidase is described. The method involves determination by steam distillation of the NH4+ produced by amidase activity when soil is incubated with buffered (0.1M THAM, pH 8.5) amide solution and toluene at 37°C. The amide compounds studied included formamide, acetamide, and propionamide. The procedure developed gives quantitative recovery of NH4‐N added to soils and does not cause chemical hydrolysis of the substrates. Results showed that this soil enzyme has its optimum activity at buffer pH 8.5 and is inactivated at temperatures above 60°C. By varying the substrate concentration it was found that the initial velocity of the amidase reaction is optimum at 0.05M substrate. The initial rates of NH4‐N released obeyed zero‐order kinetics. Steam sterilization destroyed, and formaldehyde, sodium fluoride, and sodium arsenite inhibited, amidase activity in soils. Assay of amidase activity in the absence of toluene indicated that acetamide and propionamide may induce the synthesis of this enzyme by soil microorganisms.
Changes in Solution of Forest Soils with Waterlogging and Three Levels of Base Saturation
Authors: McKee William H.
Published: July 2010

Waterlogging and subsequent reduction significantly increased soil pH, except at high base saturation levels, for three Coastal Plain A horizon forest soils. When soils had high base levels, solution levels of Ca usually increased with soil reduction; Mg, Fe, and Mn levels increased with or without increase in base saturation. The effect of ion pairing was more proounced at low base saturation and on more weakly‐charged colloid soils. The sharp increase in cation levels in the soil solution, caused by waterlogging and the influence of bicarbonate pairing, emphasizes the importance of the soil reduction in determining levels of nutrients available to trees on seasonally waterlogged soils.
Nonionic Surfactant Effects on Adsorption and Degradation of 2,4‐D
Authors: Amonette J. , O'Connor G. A.
Published: July 2010

The effects of three nonionic surfactants on 2,4‐D (2,4‐dichlorophenoxyacetic acid) adsorption and degradation was determined for two soils in laboratory studies. The surfactants varied in water solubilities and hydrophilic‐lipophilic balance (HLB) values.

Adsorption of 2,4‐D was significantly decreased in both soils by the least water‐soluble surfactant, X‐35. Degradation of 2,4‐D was also significantly delayed by X‐35 to various extents in both soils. However, extent of degradation was independent of treatments after 70 days. Various hypotheses, based on surfactant properties, are offered to explain the adsorption and degradation results. When surfactant concentrations remain above the critical micrelle concentration, nonionic surfactants with low HLB values can significantly alter 2,4‐D behavior in soil. Surfactants with high HLB values appear to have little effect on 2,4‐D behavior.
Response of Semiarid Grassland Sites to Nitrogen Fertilization: I. Plant Growth and Water Use
Authors: Power J. F.
Published: July 2010

Although it has been repeatedly demonstrated that most perennial grassland ecosystems respond to N fertilization, knowledge of factors controlling N transformations involved in such responses is fragmentary. Eight rate‐of‐N‐fertilizer experiments were conducted for 5 or 6 years on established perennial grass sites near Mandan, North Dakota. Experiments were conducted within essentially the same precipitation and temperature regimes on sites differing in soil type, exposure, and grass species to determine their influence on N response. Above‐ground vegetation response to N fertilization depended primarily upon species — smooth bromegrass (Bromus inermis) was generally more responsive than crested wheatgrass (Agropyron desertorum) or native mixed prairie. No consistent patterns of root biomass response to N fertilization were obvious. At some sites or in certain years root biomass responses were fairly consistent, whereas at other sites or in other years, little response to N occurred. Water use efficiency (WUE) was greatest for bromegrass and least for native grasses, and was generally increased by N fertilization. WUE increased as aboveground growth increased, whether as a result of N fertilization or because of less evaporation at more protected sites. Cumulative dry matter response to N fertilization was highly correlated with cumulative fertilizer N added, with a different curvilinear relationships for each site.

These results indicated that the magnitude of fertilizer N responses by perennial grasslands is site specific. Although the same general mechanisms seem to operate at the different sites, magnitude of response was controlled by the plant species present and by some soil type × location factors that are presently ill‐defined. These latter factors appear to influence the capacity of the soil to immobilize fertilizer N, capability of above‐ground plant growth to take up fertilizer N, and many other N transformations, and may be related to relative availability of water. Consequently interpretations of fertilizer experiments conducted on only one soil type or with only one species must be interpreted with caution.
Response of Semiarid Grassland Sites to Nitrogen Fertilization: II. Fertilizer Recovery
Authors: Power J. F.
Published: July 2010

The fate of N fertilizer applied annually for 5 or 6 years at rates up to 200 kg N ha−1 year−1 was determined on eight perennial grassland sites in western North Dakota. The amount of fertilizer N found in plant tops, roots, and as residual soil inorganic N, and the sum of these three fractions were determined for each site. The amount of fertilizer N recovered in each of these fractions was linearly correlated with the amount of fertilizer N applied to each site in almost all instances. Fertilizer N recovered in top growth was highest for smooth bromegrass (Bromus inermis) (about 80% of that applied), and least for the native prairie grasses (about 15% of applied), with intermediate values for crested wheatgrass (Agropyron desertorum). Likewise fertilizer N recovered in roots was greatest for bromegrass (near 15%), whereas soil inorganic N content was usually greatest under native range. Total fertilizer N recovered in these three fractions was usually near 50% for bromegrass sites, but only about 30% for native range sites. There was no evidence of appreciable runoff or deep percolation of nitrates. Fertilizer N not recovered was either immobilized in other forms of soil organic matter or lost to the atmosphere in gaseous forms. Available evidence indicates that only small quantities of fertilizer N would be expected to be immobilized in organic forms other than in plant roots, thereby suggesting that gaseous loss of applied N may have been significant at these dryland perennial grass sites.
Forest Soil Variability on Northeastern Flood Plains
Authors: Mollitor A. V. , Leaf A. L. , Morris L. A.
Published: July 2010

Flood plain areas in eastern New York and western Vermont were sampled for 19 surface and 19 subsurface soil properties. On the basis of physiography, two site types were identified for stratification of data: (i) lateral accretion deposits and (ii) vertical accretion deposits. Nested analyses of variance of the 38 soil properties of these alluvial Entisols and Inceptisols shows that, of the variables measured, all with the exception of surface K concentration, K and P content and subsurface K content were significantly less variable within sample plots than among plots. It also shows that surface reaction, P concentration and P content, subsurface clay, silt plus clay, bulk density, reaction, P concentration, Ca concentration, and P content were less variable within types than between types. Sample size requirements to estimate plot means for each property were calculated. Surface soils tend to be less variable than subsurface soils and vertical accretion soils are less variable than lateral accretion soils.
The Effect of Hydroxy‐Al and Hydroxy‐Fe Polymers on Montmorillonite Particle Size
Authors: Frenkel H. , Shainberg I.
Published: July 2010

Potentiometric and photometric titration of Al‐ and Fe‐montmorillonite suspensions with NaOH and Na2B4O7 are presented. Hydroxy‐Al polymers formed during the neutralization reaction apparently acted as cementing agents and prevented the dispersion of the structure. When an excess of NaOH is added, the hydroxy‐Al polymers disintegrate and complete dispersion of the Na‐montmorillonite takes place. No aluminates are formed upon neutralization of Al‐montmorillonites with Na3B4O7, and hence no dispersion takes place.

Neutralization of Fe‐montmorillonite suspension with NaOH and Na2B4O7 resulted in gradual breakdown of the Fe‐montmorillonite particles. Hydroxy‐Fe polymers were not as effective in preventing the dispersion of the particles by adsorbed Na as hydroxy‐Al polymers.
Improved Growth of Onion and Bell Pepper in Saline Soils by Two Vesicular‐Arbuscular Mycorrhizal Fungi
Authors: Hirrel Marc C. , Gerdemann J. W.
Published: July 2010

The effect of 5 levels of salinity on the growth of onions (Allium cepa L. cv. ‘Early Yellow Globe’) and bell peppers (Capsicum annuum L. cv. ‘California Wonder’) inoculated with the mycorrhizal fungi, Glomus fasciculatus or Gigaspora margarita, was compared to uninoculated nonmycorrhizal controls. In soils with saturation extracts (ECe) of 1, 3, 4, 6, and 12 mmho/cm, mycorrhizal plants consistently outweighed the controls. Plants inoculated with Gl. fasciculatus, also, grew larger than those inoculated with Gi. margarita. In both onion and bell pepper, the effect of salinity on decreasing percent fresh weight was greatest in the nonmycorrhizal controls. Also, in bell pepper, decreases in percent fresh weights were less with plants infected by Gl. fasciculatus than with those infected by Gi. margarita. Thus, plants infected with mycorrhizal fungi may be more salt tolerant than uninfected nonmycorrhizal plants.
Use of Streptomycin for Suppressing Blue‐Green Algal Nitrogenase Activity During the Assessment of Nitrogenase Activity in the Rice Rhizosphere
Authors: Habte M. , Alexander M.
Published: July 2010

The addition of streptomycin at concentrations as low as 5 µg/ml to cell suspensions of blue‐green algae (cyanobacteria) or to blooms developing in a flooded soil caused greater than a 99% reduction in the nitrogenase activity of the cells in 24 to 72 hours. The antibiotic was not toxic to rice (Oryza sativa L.) at 250 µg/ml, and the nitrogenase activity of heterotrophs developing in puddled soils previously planted to rice was not significantly affected by concentrations as high as 50 µg/ml. The nitrogenase activity of heterotrophs developing in flooded or puddled soils not previously planted to rice was sensitive to concentrations of the antibiotic exceeding 10 µg/ml. In experiments involving the assessment of nitrogenase activity in the rice rhizosphere, streptomycin at concentrations as low as 2.5 to 5.0 µg/ml effectively curtailed the interference from blue‐green algal activity.
Effect of Gambel Oak on Forest Floor and Soil of a Ponderosa Pine Forest
Authors: Lefevre R. E. , Klemmedson J. O.
Published: July 2010

A study was conducted on the Beaver Creek Experimental Watersheds south of Flagstaff, Arizona to determine the effect of Gambel oak (Quercus gambelii Nutt.) in ponderosa pine (Pinus ponderosa Laws.) forests on some physical, N, and C properties of the forest floor and upper soil layers. Samples of L, F, and H layers of the forest floor and of the 0‐ to 5‐, 5‐ to 15‐, and 15‐ to 30‐cm soil layers were collected from randomly chosen replicated plots in five stand types representing a range in oak basal area from 0 to 75% of total basal area.

Weight, density, and thickness of L, F, and H layers responded differentially to change in oak basal area. These responses are attributed to structural features and decay characteristics of pine and oak leaf litter. With increasing oak in the stand, percentage N increased in all layers of the forest floor and in the upper 15 cm of soil. Amount of N increased in the H layer, the forest floor as a whole, and in the 0‐ to 5‐cm layer of soil. With increasing oak, percentage C remained the same in the forest floor, but increased significantly in the upper 15 cm of soil. Carbon/nitrogen ratio declined in L and F layers with increasing oak. Increased percentage C in 0‐ to 5‐ and 5‐ to 15‐cm soil layers with increased oak basal area coincided with decreased weight of these layers.
A Rapid in Situ Method of Extracting Water from Tidal Marsh Soils
Authors: Eleuterius Lionel N.
Published: July 2010

An inexpensive, easily constructed apparatus was developed to extract interstitial soil water from the soils of tidal marshes. Major components of the apparatus are a polypropylene bottle, polyethylene tubing, neoprene stopper, and plankton netting. The sampler can be easily placed at varying depths in the soil and left permanently in the field. The system can also be used for fertilizer and dye injection studies. Because of its simplicity, durability, and versatility this vacuum‐pressure lysimeter is well suited for use in the marsh.
Thermodynamic Study of Calcium‐Sodium and Calcium‐Magnesium Exchange in Calcareous Soils
Authors: Van Bladel R. , Gheyi H. R.
Published: July 2010

Montmorillonite calcareous soils and a Moroccan montmorillonite clay in the Ca form were used to determine the effect of temperature and varying ionic strength on Ca‐Na and Ca‐Mg exchange. Ca was selectively adsorbed over Na and, to a lesser extent, over Mg. Affinity for Ca over Na or Mg ions was greatest in the calcareous soils and varied approximately in the same order as the soil organic matter content. In the Ca‐Na system, the selectivity coefficient was rather independent of ionic strength. Enthalpy and entropy changes were negative for the substitution of Ca by Na. These results indicate that the preference of Ca was probably due to the overall entropy change.

The experimental results were compared to theory based on a constant selectivity coefficient. The agreement of experimental and theoretical Na or Mg loading, calculated from the composition of the soil solution, was satisfactory.
Influence of Water Potential on the Survival of Rhizobia in a Goldsboro Loamy Sand
Authors: Mahler R. L. , Wollum A. G.
Published: July 2010

Inoculation of soybeans [Glycine max (L.) Merr.] at planting in North Carolina is apparently ineffective due to unfavorable environmental conditions. Water potential has been suspected to be a primary factor in inoculation failure; however, the lack of a suitable method to artifically control or create desired water potentials in laboratory environments has prevented investigation.

The objectives of this study were to (i) evaluate a technique designed to maintain soil water potentials for incubation studies, and (ii) to investigate the influence of water potential on the survival of 10 Rhizobium japonicum strains in a Goldsboro loamy sand (Aquic Paleudult). Dow Ziploc Storage Bags were employed to maintain desired water potentials while the most probable number (MPN) technique and plant infectivity tests were used to enumerate rhizobia.

Water potential was found to have a profound effect on numbers of rhizobia in a Goldsboro loamy sand. Rhizobial numbers were from one to three log numbers lower under water potentials of −15 bars than at potentials near field capacity. There was usually a depression of one log number at −5 bars. In most cases the 9‐week rhizobial numbers were less at water potentials of −0.10 bar than at potentials of −0.50 and −0.33 bars. Total aerobic bacteria and aerobic sporeformer numbers also declined at both high and low water potentials. Differences in ability to tolerate low water potentials were noted between the 10 serogroups tested. In general, isolates from serogroups 110, 122, and 138 survived in much greater numbers at water potentials of −15 bars than the other seven serogroup isolates. Isolates of serogroups 24, 31, 94, and 123 were particularly vulnerable to water stress as populations at 9 weeks were more than four log numbers less than the initial populations. Field soil water potential data confirmed that −15 and −5 bar values which reduce rhizobial numbers are found to be quite common in North Carolina.
Fertilizer Zinc Efficiency in Flooded Calcareous Soils
Authors: Amer Fathi , Rezk A. I. , Khalid H. M.
Published: July 2010

Effect of Zn sources and methods of application on rice (Oriza sativa var. Giza 159) was studied in relation to organic matter application and to N source. In addition to laboratory investigations, a pot experiment was conducted with 65Zn‐labelled soil (Vertic Torrifluvents) and two field experiments with labelled and nonlabelled Zn fertilizers.

Zinc oxide (ZnO) was superior to ZnSO4 in increasing grain yield and Zn content of flooded rice and in maintaining higher Zn concentration in the soil solution. With different methods of ZnSO4 application, rice yield and Zn uptake were in the order: applied to surface water 2 weeks after transplanting ≫ mixed with soil = surface applied to soil. The corresponding percentages of plant Zn derived from fertilizer and of Zn utilization from the applied fertilizer were 11.2, 8.46, and 6.26%; and 2.9, 1.4, and 1.0%, respectively. Effectiveness of organic matter in increasing yield and Zn content was greater when applied 2 weeks before transplanting than when applied at transplanting, as it decreased soil solution Zn during the first 2 weeks of anaerobic decomposition. The organic matter induced a temporary reduction in Zn content early in the season, but a good correlation was obtained between grain yield and Y leaf Zn at the midtillering and panicle initiation stages.

With combined Zn and organic matter application, urea as a N source resulted in higher yielding and Zn content than (NH4)2SO4. Specific activity measurements showed that under nonflooded conditions rice was largely dependent on the Zn labile pool, while flooded rice was able to derive Zn from an additional source. Results generally indicate that formation of sphalerite (ZnS) may play a major role in controlling Zn solubility in flooded calcareous soils.
Soil Temperature Regimes of the Central Appalachians
Authors: Carter Brian J. , Ciolkosz Edward J.
Published: July 2010

Soil temperatures were measured for 3 years at depths of 25 and 50 cm at four sites in four areas on a north‐south transect from northern Pennsylvania to northern West Virginia. Each site was at a different elevation. The mean annual soil temperature (MAST) was estimated using: (i) an average of four readings (taken in mid‐January, April, July, and October; at all sites), (ii) an average of 12 readings (one taken each month; at each site in one area), and (iii) a mean annual air temperature (MAAT) at one site in each area. A prediction equation was derived from the seasonal readings at a 50‐cm depth (Y = 11.7 — 0.0061X1 — 0.0034X2, where relative latitude = X2 in kilometers, elevation =X2 in meters and Y = MAST in degrees centigrade). Using the prediction equation the mesic‐frigid soil temperature boundary was found to be 572 ± 125 m (1,875 ± 410 feet at Coudersport, Penn., 755 ± 78 m (2,475 ± 255 feet) at Philipsburg, Penn., 921 ± 35 m (3,020 ± 115 feet) at Kegg, Penn., and 1,088 ± 26 m (3,570 ± 85 feet) at Davis, W.V. The prediction equation indicates that the mesic‐frigid soil temperature boundary rises rapidly in elevation from north to south and there are areas of Pennsylvania, Maryland, West Virginia, and Virginia that have frigid soil temperature regimes. The data also indicates that: (i) MAST can be estimated from seasonal readings at 25 cm as well as 50 cm, (ii) MAST at 50 cm can be estimated from monthly or seasonal readings, and (iii) MAAT averaged 1.2°C below MAST.
Determining the Volume of Sampled Soil When Using the Four‐Electrode Technique
Authors: Nadler A.
Published: July 2010

A theoretical discussion of the ratio between apparent resistivity and real resistivity of a soil layer as a function of (i) layer thickness/electrode spacing ratio; (ii) the soil layer thickness and resistivity of an underlying layer; and (iii) horizontal distance of a different medium from the current electrode is presented. Laboratory experimental work was carried out in order to study the effects the electrode spacing and current density have on the determination of the electrical conductivity of soil solution. It was found out that the depth sensed by a Wenner Configuration would be deeper than the inner electrode spacing for most field situations and especially where there are large variations in conductivity (due to salinity or water content) with depth. The laboratory calibration of the salinity probe should be done in a volume of about 2.5 liters or greater. The volume sensed by this method is greater the lower is the water content. The implications in laboratory calibration‐field measurements relationships are discussed.
Carbaryl Adsorption on Calcium‐Bentonite and Soils
Authors: Aly M. I. , Bakry N. , Kishk F. , El‐Sebae A. H.
Published: July 2010

Adsorption of carbaryl on Ca‐bentonite, and two Egyptian soils, a Nile alluvial and a highly calcareous soil, was carried out at different temperatures. Carbaryl adsorption increased as the temperature decreases. Ca‐bentonite exhibited the highest degree of adsorption followed by the Nile alluvial soil and the calcareous soil.

The calculated partial molar heat of adsorption ΔH* for bentonite, alluvial and calcareous soils were −3.8, −0.924 and −10.282 kcal/mol, respectively, indicating that adsorption may be physical in nature. The ΔG* values of the three systems were −0.570, −0.118, and −0.346 kcal/mol, respectively, indicating that the adsorption reaction was spontaneous in all cases. The adsorption data followed the Freundlich adsorption equation. The entropy values for the adsorption of carbaryl by the three adsorbents were −15.0, −36.7, and −8.0 entropy units indicating that carbaryl adsorption is favored by the alluvial soil that contains the highest organic matter content.
A Model of Zinc Movement to Single Roots in Soils
Authors: Bar‐Yosef B. , Fishman Svetlana , Talpaz H.
Published: July 2010

The movement of zinc in soils can be influenced by the pH of the soil and the presence of synthetic chelates or soluble organic matter capable of forming metal‐organic complexes. To understand how these complexes and pH may contribute to zinc uptake by plants, the basic processes involved in zinc transport and absorption by a single root were formulated and the resulting differential equation solved simultaneously.

The model considers diffusive and convective flow of several zinc species, H+ and a chelating agent, flow of water to the root, and chemical equilibria between adsorbed and solution phase ions and between complexed and uncomplexed cations. The model assumes transient conditions with respect to water and ions and makes allowance for the adsorption isotherm and the biologically determined parameter relating flux of uptake to concentration to be concentration‐dependent.

Within the range of studied cases, root permeability to ions and water is the most effective mechanism in controlling Zn uptake. Excretion of H+, and probably other means of reducing the pH near the root, are more effective in enhancing Zn uptake than excretion of complexing agents. A generalization of this conclusion is subject to improved experimental results of reactions between zinc‐organic complexes and soils. Among the soil characteristics, which include maximum adsorption capacity and bonding energy related coefficients for the various ions, the maximum adsorption capacity is the most important one in determining Zn uptake.
The Effects of Sodium and Organic Matter in Sewage Effluent on Water Retention Properties of Soils
Authors: Burns S. , Rawitz E.
Published: July 2010

The effect of 90 days of sewage effluent irrigation by drippers on water redistribution after irrigation was investigated on two soil layers of different texture and organic matter content. Changes in soil salinity, organic matter content, surface area, and water‐retention properties were monitored for 90‐ and 60‐day periods of effluent irrigation. The experiments were carried out in columns under constant temperature conditions. Soil depth was 3 cm and its mass was 100 g.

The results led to the formulation of a hypothesis to explain the observed increased water retentivity of soils under effluent irrigation. The sodium and organic matter additions to soil via the waste water were found to interact in their effects on the active surface of soil particles. As a result of this interaction, drainage of the heavier soil, impaired during effluent irrigation, improved by subsequent drying. It then showed little damage upon simulated rainfall application. In contrast, drying of the sandier soil did not significantly improve its drainage properties, and subsequent “rainfall” resulted in severe clogging.
Phosphorus Nutrition of Rhizobium japonicum: Strain Differences in Phosphate Storage and Utilization
Authors: Cassman K. G. , Munns D. N. , Beck D. P.
Published: July 2010

Phosphate accumulation from defined liquid medium was assessed in six strains of Rhizobium japonicum grown at high P (2 × 10−3M orthophosphate in solution). The total cell P concentration ranged from 1.6 to 2.4% dry mass depending on strain, and correlated with subsequent growth after transfer to medium without added P. Stored cell P could support up to four or five generations. Steps to ensure high‐P storage in inoculant cultures might have practical utility.

Growth ceased when total cell P dropped to 0.3%. Electron microscopy indicated a tendency of deficient cells to become elongated, distorted, and packed with lightly staining granules (perhaps poly β hydroxybutyrate).

High‐P cells of all the strains contained from 5 to 7 electrondense granules. Their total volume varied between 0.1 and 0.5% of the cell, depending on strain; and related linearly to percent of P in the cell. The granules occurred only when cell P was already high (> 1.5%) and disappeared within 1 day after transfer to medium without P. They may be polyphosphate storage granules. They provided P sufficient at most for 1 to 2 generations.

Cells grown at an intermediate external solution‐P concentration buffered at 6 × 10−6M, resembling that in fertile soil, had few granules and moderate stored P (1.3 to 1.7%). Invasion of P‐depleted rhizospheres by rhizobia from soil probably cannot depend on previously stored P: it must also require efficient uptake from very dilute‐P concentrations.

External gum was abundantly produced at low‐ and moderate‐P supply, but not at the high P concentrations routinely supplied in laboratory media.
Growth of Rhizobium Strains at Low Concentrations of Phosphate
Authors: Cassman K. G. , Munns D. N. , Beck D. P.
Published: July 2010

A technique was developed for assessing effects of P on growth, in defined liquid media at orthophosphate concentrations comparable to those in soil solutions. Phosphate was supplied in sorbed form on iron oxide (goethite) separated from the liquid medium by a dialysis membrane. Depending on the level of sorbed P, concentrations in solution were established in the range 0.05 to 30 µM. Analytical monitoring indicated that concentrations above 0.1 µM were buffered against depletion by cell growth until populations exceeded 106 cells per ml.

The system was used to compare P responses of seven strains of soybean and cowpea rhizobia grown from P‐depleted inocula at initial densities of 104 cells per ml. Two P‐efficient strains grew as rapidly at the lowest concentration (0.05 µM) as in a control medium at 2,000 µM. They would seem unlikely to be P‐limited in the field. Other strains were less efficient. One strain could barely grow at P concentration below 1 µM; this strain could have difficulty colonizing P‐deficient soils or normal rhizospheres.

Large differences in tolerance to low P among strains may be agronomically important. The technique could be simplified for routine screening of strains; and its operation at submicromolar concentrations could be improved for research on nutrition and requirements of P‐efficient rhizobia and other organisms.
Effects of Water and Nitrogen Management on Yield and 15N‐Depleted Fertilizer Use Efficiency of Irrigated Corn
Authors: Russelle M. P. , Deibert E. J. , Hauck R. D. , Stevanovic M. , Olson R. A.
Published: July 2010

The objective of this experiment was to evaluate the effects of irrigation sequence and of time and rate of nitrogen application on the dry matter production and fertilizer use efficiency of irrigated corn (Zea mays L.), grown on a representative fine‐textured soil of eastern Nebraska, and to monitor the movement of fertilizer N in this soil. During 1974–1976, 15N‐depleted ammonium sulfate was banded at rates of 112, 168, or 224 kg N/ha at planting or sidedressed at the eight‐leaf growth stage. No N was applied in 1977–1979. In 1974–1977, irrigation applications of 5, 7.5, or 10 cm of water were made at 2‐, 3‐, or 4‐week intervals, respectively, until a total of 30 cm had been applied. The plots were uniformly irrigated in 1978–1979.

Grain yield and N uptake in 1974–1976 were not influenced by time of N application, and were highest with light, frequent irrigation. From 1977–1978, yield increased with previous N rate in response to residual mineral N in the soil. During both treatment and residual years, fertilizer N recovery in the grain was greater with sidedressing and increased with N rate. Heavier, infrequent irrigation decreased tracer N recovery in 1974–1976. Maximum fertilizer use efficiency was obtained with the low N rate, applied as a sidedressing, and with light, frequent irrigation.
Ion Micromilling Applied to the Ultramicroscopic Study of Soils
Authors: Bresson L.‐M.
Published: July 2010

The electron transmission microscopic (TEM) study of undisturbed soil materials requires the preparation of thin sections of about 1,000Ä thick. This seems to be possible only by ion micromilling.

This thinning technique necessitates particular precautions due to the fragility of permeated soil materials. The resins generally used for the making of thin sections are suitable as long as their polymerization is very good. Handling of the sample must be done under a stereomicrosocope with great care. It may prove useful before bombardment to glue the sample (3 mm in diam, 30 µm in thickness) between two electron microscope grids with a single central hole. The required thickness is reached when small holes appear in the sample. The thickness of the ultrathin sections can be irregular because the thinning rate of the sample varies considerably with its chemical composition, the type of its crystal lattice, and the state of its surface. Therefore, the only areas visible with a TEM appear as halos around holes. Artifacts induced by ion bombardment seem to be negligible compared with those that appear during observation by TEM. The ultrathin sections thus obtained allow the morphology of soil constituents and their ultramicroorganization to be studied at very high magnifications; hence, they are extremely useful for studies of mineral weathering, microstructures, and microfabrics.
Properties of Natraqualfs in the Upper Coastal Plain of Mississippi
Authors: Pettry D. E. , Brent F. V. , Nash V. E. , Koos W. M.
Published: July 2010

Natraqualfs were studied on poorly drained, silty, fluvial terraces in the humid Coastal Plain region of Mississippi. They are underlain by contrasting geologic formations of different ages. The soils have fine‐loamy and fine‐silty textural families. Soil reaction of pedons ranges from extremely acid to strongly alkaline. Acid Natraqualfs are dominant on older geomorphic surfaces, and they are deeper to natric horizons than alkaline pedons. Argillic subhorizons have a SAR > 13 and an exchangeable sodium percentage (ESP) > 15 to qualify as natric horizons. Exchangeable Ca + H is greater than Mg + Na in the acid Natraqualfs. Soil extracts have relatively low electrical conductivities and electrolyte concentrations. Sulphate and chloride are the dominant water‐soluble anions. Barite is a common mineral constituent of the natric horizons.
The Influence of Soil Water Potential and Soil Texture on the Survival of Rhizobium Japonicum and Rhizobium Leguminosarum Isolates in the Soil
Authors: Mahler R. L. , Wollum A. G.
Published: July 2010

Water stress and differences in soil texture are thought to be primary factors in inoculation failure in the southeastern United States. There is, however, a lack of quantitative data relating the effect of soil water potential on rhizobia survival in soils of differing textures.

The objectives of this study were to investigate the effect of soil water potential on the survival of slow‐ and fast‐growing rhizobia in soils varying in texture. Rhizobium japonicum serogroup isolates 122 and 123 and Rhizobium leguminosarum serogroup isolates WA‐01 and WA‐02 were incubated in seven different soils maintained at water potentials of −0.3, −1.0, −5.0, and −15.0 bars for periods to 7 weeks. The most probable number (MPN) technique and plant infectivity tests were used to enumerate rhizobia.

Soil water potential and soil texture were both found to play important roles in the survival of the four rhizobia isolates. Rhizobia populations were always greatest at −0.3 bars. Populations were proportional to decreasing water potentials to −15.0 bars. Populations were lowest in the sands and clay loam soils. Conversely, populations were usually highest in the sandy loams, silt loams, and sandy clay loam soils.

Differences between the four isolates were also observed. Rhizobium japonicum serogroup isolates 122 and 123 survived in greater numbers than the R. leguminosarium isolates during the initial incubation period. R. leguminosarum isolate WA‐02, however, performed as well as or better than the R. japonicum isolates after 1 week for most soil textures and water potentials. Rhizobia populations declined during the first week of incubation and increased, in most cases, by the seventh week.
Effect of Electrolyte Concentration and Soil Sodicity on Infiltration Rate and Crust Formation
Authors: Agassi M. , Shainberg I. , Morin J.
Published: July 2010

The effects of electrolyte concentration and soil sodicity on the infiltration rate and extent of crust formation of a calcareous and a noncalcareous soil were studied using a rain simulator. The infiltration rate was more sensitive to the sodicity of the soil and to the electrolyte concentration of the applied water than was the permeability of the underlying soil. The mechanical impact of the raindrops and the relative freedom for particle movement at the soil surface may account for the greater sensitivity of the infiltration rate. These observations suggest that crust formation is due to two mechanisms: (i) a physical dispersion of soil aggregates caused by the impact action of the raindrops, and (ii) a chemical dispersion which depends on the soil exchangeable sodium percentage (ESP) and the electrolyte concentration of the applied water.
Devarda's Alloy Method for Total Nitrogen Determination
Authors: Liao Christina F. H.
Published: July 2010

A modified semimicro‐Kjeldahl procedure for total nitrogen (N) determination to include No3‐‐N, NO2‐‐N, or both is described. The method involves use of Devarda's alloy as a reducing agent in the pretreatment procedure to convert NO3‐‐N, or NO2‐‐N, into NH4+‐N in 6N H2SO4 with subsequent Kjeldahl digestion of the sample using a mixture of K2SO4 − Se and concentrated H2SO4. The proposed method was effective in recovering NO3‐‐N or low‐level NO2‐‐N from water, soil, plant, and organic N compounds in total N determinations. The method gives essentially the same or slightly higher values for total N in a variety of soils when compared with other commonly used methods. The advantage of the proposed method is that it includes both NO3‐‐N and low‐level NO2‐‐N in one single pretreatment procedure and gives a smooth digestion during the subsequent Kjeldahl analysis.
The Soil Sequence of Late Pleistocene Glacial Outwash Terraces from Spokane Floods in the Idaho Panhandle
Authors: Parsons R. B. , Weisel C. J. , Logan G. H. , Nettleton W. D.
Published: July 2010

Glacial Lake Missoula was the source of the catastrophic Spokane Floods through northern Idaho, eastern Washington, and the main stem of the Columbia River. About 2,000 km3 of water was impounded behind ice dams that were repeatedly breached. Giant current ripples, huge gravel bars, coulees, and dry cataracts attest to the enormity of the floods.

The sequence of five late Pleistocene outwash terraces and a Holocene terrace were studied in the Hoodoo Valley of Bonner County, Idaho. The geomorphic surfaces document that there were at least five Spokane Floods. Kootenai taxadjunct, Bonner, and Rathdrum soils occur on each of the outwash terraces, have different topographic positions within the giant current ripple microrelief, and have contrasting thicknesses of reworked volcanic ash over the flood deposits. Similar soils on the five terraces indicate that the time factor of soil genesis is negligible and that the flood events occurred in rapid succession.
Laboratory Evaluation of Soil Mixtures for Sports Turf
Authors: Taylor D. H. , Blake G. R.
Published: July 2010

The suitability of soil mixtures for sports turfgrass areas is often determined by measuring physical properties of laboratory‐packed samples. The objectives of this study were (i) to establish a basis for choice of laboratory packing conditions for preparing test samples; and (ii) to determine whether physical properties of soil mixtures after in‐situ settling on sports turfgrass areas were correlated to physical properties of the same mixtures packed and tested in the laboratory.

Seven soil mixtures varying from 76 to 97% sand by weight were packed in the laboratory by applying impact energies of 3.0, 4.5, and 6.0 J/cm2 to samples at water potentials of −30, −100, −330 mbar. Comparisons of Ksat and bulk density of laboratory‐packed samples with sustained infiltration rate and bulk density of mixtures after turf growth and compaction under greenhouse conditions indicated a packing combination of 3.0 J/cm2 packing energy to a sample at −100 mbar water potential was equal or preferable to any other combination.

Using this laboratory packing combination, Ksat, bulk density, and air porosity at −30, −40, −60, and −100 mbar water potentials of undisturbed cores from golf greens were compared to corresponding properties on disturbed samples taken from the greens and packed in the laboratory. Laboratory‐packed samples were not indicative of the properties of soil mixtures after settling in situ on greens. Sand content was a better measure of the physical qualities of soil mixtures in the field than were physical properties of laboratory‐packed samples.
A Physicoempirical Model to Predict the Soil Moisture Characteristic from Particle‐Size Distribution and Bulk Density Data
Authors: Arya Lalit M. , Paris Jack F.
Published: July 2010

A model to predict the moisture characteristic of a soil from its particle‐size distribution, bulk density, and particle density parameters is presented. The model first translates a particle‐size distribution into a pore‐size distribution. Then, the cumulative pore volumes corresponding to progressively increasing pore radii are divided by the sample bulk volume to give the volumetric water contents, and the pore radii are converted to equivalent soil water pressures using the equation of capillarity.

To compute the pore volumes and the pore radii, the particle‐size distribution curve is divided into a number of segments. The solid mass in each segment is assumed to form a matrix with a bulk density equal to that of a natural‐structure sample. For a unit of sample mass, an equivalent pore volume for each segment is computed from Vvi = (Wi/ϱp)e and the corresponding pore radius from: ri = Ri[4eni(1‐α)/6]1/2, where Vvi is the pore volume, Wi is the solid mass, ϱp is the particle density, e is the void ratio, ri is the mean pore radius, Ri is the mean particle radius, ni is the number of particles, and α is an empirical constant ranging in value from 1.35 to 1.40. The formulation for the pore radius is based on spherical particles and cylindrical pores.

Model predictions for several soil materials show close agreement with the experimental data.
Soil and Geologic Mapping Over Mafic and Ultramafic Parent Materials in Maryland
Authors: Rabenhorst M. C. , Foss J. E.
Published: July 2010

Comparisons were made of soil and geologic mapping in regions of mafic and ultramafic lithology. Samples from 39 locations were collected and analyzed for weak acid‐extractable Ca and Mg. Identification of parent materials was facilitated by mineralogical examination of the < 20‐µm fraction of the subsoil by x‐ray diffraction techniques. Comparisons and analyses indicate that some serpentine soil units have been mapped over nonserpentine mafic rock. The Ca/Mg ratios of serpentine soils differ significantly at the 0.01 level from those soils formed from nonserpentine mafic rocks. In areas where mafic and serpentinitic parent materials occur in association, weak acid‐extractable Ca/Mg ratios can be used as an aid in distinguishing soils formed from these parent materials. In such areas, soils with Ca/Mg ratios < 0.10 have a 98% probability of having formed from serpentinitic rather than from nonserpentine mafic parent materials.
Effects of Pyrophosphate, EDTA, and DTPA on Zinc Sorption by Montmorillonite
Authors: Asher L. E. , Bar‐Yosef B.
Published: July 2010

The effects of pyrophosphate (PP), pH, ionic strength, EDTA, and DTPA on zinc (Zn) sorption by montmorillonite were studied in order to evaluate the role of pyrophosphate in Zn solubilization. In such a system PP dissolution of organic matter and its subsequent complexation of Zn was limited and would not affect the interpretation of the results. The effectiveness of PP in complexing Zn was dependent on the levels of Ca, initial PP concentration, and pH of the montmorillonite suspension. Decreased sorption of PP with increasing pH, as well as markedly greater sorption of PP by Ca‐montmorillonite than by K‐montmorillonite, suggests the existence of a sorption process which could include surface adsorption and precipitation.

At initial PP concentrations of 1.92 mM, Zn solubilization decreases monotonically with increasing pH, while at 9.6 mM initial PP, a minimum in Zn solubilization is observed at about pH 6.0. This trend of solubilization could be attributed to decreased Zn sorption and increased Zn complexing with PP. At pH greater than about 7.5, PP is comparable to EDTA and DTPA in Zn solubilization, but only at PP molar concentrations some 40 times greater than the organic ligands. Equilibration time (2 to 192 hours) had little effect on PP concentration or on Zn concentration. Regardless of which of the ligands was used, the sorption of Zn reached completion in most cases within 2 hours. For EDTA and DTPA, provided that their concentration was greater than Zn concentration, sorption of Zn was found to be a relatively slow process. Approximately 40% (EDTA) and 20% (DTPA) of the initial Zn was sorbed after 192 hours.
Field Testing of a Two‐dimensional Soil Moisture Model Simulating Water Table Fluctuations
Authors: Fayer Michael J. , Hillel Daniel
Published: July 2010

An attempt has been made to test the validity of a two‐dimensional model of soil‐water dynamics in a sloping field, with respect to groundwater level fluctuations during several infiltration‐drainage cycles. The data from rain recorders, runoff plots, water table wells, tensiometers, and an evaporation pan were used to describe the various initial and boundary conditions. Soil hydraulic properties were determined from undisturbed cores and in situ methods. Comparisons of the predicted and measured water table positions were used to judge the model's capabilities. After two one‐week periods of no rainfall, during which the actual water table fell 11 and 79 cm, the predicted water table levels were within 1.5 and 8 cm, respectively, of the measured levels. Before and immediately after periods of rainfall, the predicted water table levels were usually within 2 cm of the measured levels. As the water table rose in response to the rainstorm, however, the predicted rise was only one‐half that measured in the field. Altering the shape of the moisture characteristic programmed in the model nearly doubled the predicted rise. Hence the discrepancy between prediction and observation may be due to insufficient accuracy in determination of the soil moisture characteristic in the very wet range, or to failure to account for air occlusion or hysteresis.
Revised Methods for Rapid Quantitative Determination of Minerals in Soil Clays
Authors: Karathanasis A. D. , Hajek B. F.
Published: July 2010

A set of quantitative mineralogical methods was revised and evaluated for routine and rapid mineralogical characterization of clays from southern soils and sediments. The procedures adopted consist of soil dispersion in a pH 9.5 suspension by ultrasonics, centrifuge fractionation to give 300 mg of clay, K‐ and Mg‐saturation by millipore filtration for x‐ray diffraction (XRD), x‐ray emission spectroscopy (XRES), differential scanning calorimetry, and thermogravimetric analyses. Smectite, vermiculite, kaolinite, halloysite, gibbsite, and calcite were quantified from thermal data, hydroxyinterlayered vermiculite and quartz from XRD, using indigenous kaolinite determined by thermal methods as an internal standard, and free iron oxides and mica from XRES analysis. The mean total recovery on 79 samples was 99.9 ± 0.6%. Very good agreement and small average deviations were obtained between mineral quantities determined by these procedures and values reported by other laboratories for several of the same samples. Because the accuracy of the data exceeded most quantitative mineralogical interpretative needs, these methods can be used for routine quantitative mineralogical characterization of most southern soils.
A Differential Model for One‐dimensional Cation Transport in Discrete Homoionic Ion Exchange Media
Authors: Persaud N. , Wierenga P. J.
Published: July 2010

The heterogeneous system at equilibrium consisting of an aqueous solution of a counterion, I, in contact with a cation exchanger saturated with another counterion, J, was treated as a Donnan system. An equation was thus developed to describe the equilibrium adsorption isotherm of the cation I, as a function of the concentration of I and J in the equilibrium solution. This equation adequately described experimental “batch” equilibrium isotherms for selected cations on a synthetic cation exchange resin and on a natural soil material. The equation was incorporated into a differential convective‐dispersive solute transport model, and the resulting differential equations were integrated numerically using an implicit finite difference scheme. Simulations were done to test the ability of the transport model to describe the elution curves for Na+, Li+, and Cs+ from miscible displacement experiments in water‐saturated and water‐unsaturated laboratory columns packed with the materials used for the adsorption studies. The model was successful in predicting the results of these experiments in the water‐saturated columns. It was successful in predicting only the general shapes of the experimental elution curves in the water‐unsaturated columns. These latter experimental curves were shifted to the right or left of the simulated curves and showed extensive tailing. It was concluded that other physical and chemical effects not accounted for in the transport model, such as diffusion kinetics between “mobile” and “immobile” water in the water‐unsaturated columns were responsible for these discrepancies.