bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate Dissimilation and Population Dynamics of Denitrifying Bacteria During Short Term Continuous Flow
Authors: Volz M. G. , Starr J. L.
Published: July 2010

A solution containing 100 µg ml−1 of NO3‐‐N, 200 µg ml−1 of glucose‐C, and 0.01N CaSO4 was supplied continuously to soil in acrylic plastic columns (6‐cm inside diam × 10‐cm length) for up to 96 hours while N2 gas was passed through the system. Concentrations of NO3‐‐N in the effluent decreased to 20 µg ml−1after 60 hours. Simultaneously, NO2‐‐N concentrations increased from traces to 65 µg ml−1 and more than 70% of applied C had been utilized after 60 hours. These results indicate that most C oxidation was coupled with NO3‐ reduction although nearly all applied NO3‐ was ultimately denitrified after 96 hours.

Denitrifiers estimated by a most probable number (MPN) technique increased from 1.1 × 103g−1 oven‐dry soil to maximum populations of 1.9 × 107 g−1 during 96 hours of infiltration. From measured biomass increases and soluble N concentrations as functions of soil depth at “quasi” steady states during the course of the experiment, specific denitrification rates per microbe, rd, were determined. These values ranged from 1.3 × 10−5 to 6.8 × 10−7 (µg N ml−1) hour−1 per denitrifier for 18 to 96 hours respectively; the decrease may have been due to the activities of different denitrifier species.

A heat shock treatment of soil which had been sampled before, during, and after the experiment and was then suspended in sterile distilled water indicated that most denitrifiers were present as vegetative cells, especially after 18 hours. In addition, after 96 hours a gram negative rod unclassified CDC VA‐1, very closely related to Pseudomonas cepacia, capable of growth on yeast extract agar and in vitro denitrification was the sole denitrifier species isolated at dilutions near extinction using a MPN technique. These data indicate that, irrespective of the physiological diversity of denitrifier species present prior to anaerobiosis, a single bacterial type may become dominant as a result of a given set of environmental conditions.
Quantitative Relationships Among Nutrients Leached From Soils
Authors: Terman G. L.
Published: July 2010

This study was undertaken in an attempt to quantify relationships among anions (An) and cations (Cat) leached from soils. Several sets of published data on leaching of ions from acid and nonacid soils were evaluated by linear regression calculations based on the chemical equivalency of Σ Cat and Σ An leached. Calcium, Mg, K, and Na comprised most of Σ Cat, and NO3, SO4, and Cl, most of Σ An. Bicarbonate (HCO3) is also leached from nonacid soils; H is assumed to account for most of the excess of Σ An over Σ Cat in leachates from acid soils. The regression coefficient for each cation on Σ An indicates its contribution to anion leaching and that for each anion on Σ Cat indicates its contribution to cation leaching. Amounts of each ion leached from a given soil depended largely on amount of soluble ion present and amounts of leachate. Calcium and NO3 tended to dominate Σ An and Σ Cat leached if these ions were applied or were abundantly present in a soil. Magnesium, Na, SO4, and Cl were increasingly important as the proportionate supply of each increased. Potassium was not leached in amounts appreciable enough to influence amounts of anions lost, and HCO3, although present in appreciable amounts in nonacid soils, apparently was not related to Σ Cat leached. Amounts of ions leached were much more closely correlated with leachate volumes among soils and time periods than with leachate volumes from various treatments for a given time period.
Test of a Soil Water Model Under Field Conditions
Authors: Beese F. , Van der Ploeg R. R. , Richter W.
Published: July 2010

A 218‐day experiment on a fallow loess soil was carried out to study infiltration and redistribution under natural field conditions. On an experimental plot of 6 by 6 m tensiometers had been installed in 11 depths: 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 cm. They were read at short irregular intervals. The precipitation was measured daily. The hydraulic functions of the layered, horizontal soil and a relation between potential evaporation, actual evaporation, and the soil suction at 5‐cm depth had been established previously. With use of these soil and atmospheric data the unsaturated soil moisture flow equation was solved numerically. Purpose of the numerical analysis was to determine if the unsaturated soil moisture flow equation does describe observed soil moisture behavior for such a long period. It was found that the calculated soil suction values for all depths deviated less than 15% from the measured ones. It is concluded that the unsaturated moisture flow equation can be useful means to supplement field measurements on infiltration, redistribution, evaporation, and internal drainage.
A Quick Method for Estimating Soil Water Diffusivity Functions
Authors: Miller R. D. , Bresler Eshel
Published: July 2010

Published data for horizontal infiltration into air dry (θd) nonsodic stable soil, imply a regression equation D(θ) = 0.001 m2 exp [8(θ‐θd)/(θw‐θd)] where the limit of wetting is θw and m is a constant relating visual position, xf of wetting front at time t, m = xf/(t)1/2. If m isn't constant, D(θ) may not exist.
Factors Influencing the Crust Test for in situ Measurement of Hydraulic Conductivity
Authors: Baker F. G.
Published: July 2010

Field trials using the crust test were used to determine the influence of five parameters on the saturated and unsaturated hydraulic conductivity values measured on two soils of different structure. These factors were (i) the diameter, (ii) the height of the soil pedestal used in the test, (iii) the degree of soil wetness at which k was measured, (iv) soil structure, and (v) operator effects. Diameter and height were found to strongly affect measurement when they had low values. These two design factors were dependent on the wetness and structure of the soil. Operator differences were small.
Sulfuric Acid as an Amendment for Reclaiming Soils High in Boron
Authors: Prather R. J.
Published: July 2010

Laboratory results indicated that sulfuric acid can effectively aid in reclaiming soils high in boron. Results of a study, using 80‐cm columns of a soil high in B, indicated that a surface application of 3.22 metric tons/ha of concentrated (96%) H2SO4 followed by leaching with 3 pore volumes, p.v. of water was nearly as effective in reducing the level of water‐soluble soil B as was leaching with 16 p.v. of water. A direct pH effect on B adsorption affinity can explain the enhanced reclamation effect at the soil surface but cannot account for the beneficial effect found at lower soil column depths. Data suggested that competition by silicate ion for adsorption sites may be contributing to the enhanced desorption of B at lower soil depths.
Enzymatic Activities and Extractable Organic Matter in Soils Invaded by Lycopodium tristachyum Fairy Rings
Authors: Spalding Brian P. , Duxbury J. M.
Published: July 2010

The interaction of fairy rings of Lycopodium tristachyum Pursh. with the soil which they invade was examined by measurement of various soil enzymatic activities and extractable soil organic matter. The activities of cellulase, xylanase, inulinase, α‐galactosidase, invertase, peroxidase, chitinase, and polygalacturonase were enhanced in soil under the rings compared with soil just outside the rings. The activity of urease was lower under the ring while the activity of β‐glucosidase was unaffected. The amount of nitrogen, hexose, and phenolics extracted by 0.01M CaCl2 during autoclaving was enhanced in soil under the ring. The level of reducing substances extracted by dilute buffer and the optical density of buffered extracts were similarly elevated. Extractable lipid, humic acid, and β‐humus were independent of soil location. Significant correlations between some readily extractable organic components and the activities of chitinase, invertase, xylanase, and α‐galactosidase in the soil were observed.
Uptake by Barley of Water Table‐ or Surface‐applied Cadmium
Authors: Kirkham M. B.
Published: July 2010

Solutions of Cd were placed for 66 days at the bottom or top of columns (42‐cm long by 15‐cm diam) containing fine sandy loam soil, half of which were planted with barley (Hordeum vulgare L. ‘Liberty’) and half of which were bare, to determine rate of movement upward or downward of Cd. Three solutions with Cd, as CdSO4, were used: distilled water with 0.1 µg/ml Cd; distilled water with 10 µg/ml Cd; secondary effluent with 10 µg/ml Cd. An average of 200 ml/day was added to the top or bottom of columns with plants; there was no drainage water with top additions. An average of 100 or 50 ml/day was added to the top or bottom, respectively, of columns without plants. Drainage water, which collected at the bottom of columns without plants and watered from the top, was analyzed daily for Cd. Plants and soil were analyzed weekly for Cd concentration.

In less than 7 days, Cd applied at the surface moved to the bottom and Cd applied at the bottom moved to the surface. At harvest, plants treated with Cd at the bottom contained up to three times more Cd than plants treated with Cd at the top because roots of plants with Cd at the bottom contained higher concentrations of Cd than roots of plants in columns with Cd at the top. Columns without roots had higher concentrations of extractable Cd than columns with roots. Concentrations of Cd in leachate from columns receiving 10 µg Cd/ml effluent were about two times higher than concentrations of Cd in leachate from columns receiving 10 µg Cd/ml water. About the same amounts of Cd were leached out of columns receiving 0.1 µg Cd/ml water or 10 µg Cd/ml water. The results showed that barley roots more readily absorbed Cd placed in a shallow water table than Cd placed in the soil surface.
Distribution Pattern of Inorganic Nitrogen Following Anhydrous Ammonia Injection into a Vertisol
Authors: Khengre S. T. , Savant N. K.
Published: July 2010

Distribution patterns of inorganic forms of N and diffusion coefficients of NH4+ were studied after injection of 800 mg of anhydrous NH3‐N per dish, each dish containing 1 kg of soil (Vertisol, bulk density 1.20 g/cm3) maintained at 1/3‐bar moisture percentage and incubated for 120 days. Bell‐shaped distribution patterns of NH4+ and undissociated NH3(aq) were observed. Diffusion coefficients of NH4+ decreased with incubation time. During a 15‐day incubation period, diffusion coefficients of NH4+ increased with increase in moisture content up to 36% (cm3/cm3), but decreased with further increase in moisture content. A temporary accumulation of NO2‐‐N was noticed up to 30 days of incubation at the periphery, but eventually NO2‐‐N was observed near the injection point through 90 days. Production of NO3‐‐N was first observed at the periphery followed by virtually even distribution throughout the retention zone.
The Soils of the Intertidal Zone of Rookery Bay, Florida
Authors: Coultas C. L.
Published: July 2010

The intertidal zone of Rookery Bay, Florida is vegetated primarily with mangrove trees. Mangroves are important to the south Florida fisheries. This work was undertaken to characterize and classify the intertidal soils of Rookery Bay in order to better understand and manage these areas.

Most intertidal soils are classified as Typic Sulfihemists‐Typic Sulfaquents. They consist of thin organic deposits over fine sands to sandy clay loam. Spodic Psammaquents also occur at higher elevations. These soils are very poorly drained, saline, and saturated with extractable bases. Most soil samples became more acidic upon drying, probably due to the oxidation of S containing materials. Total S ranged from 0.75% to 1.77% in the sulfidic horizon.
Multiple Tensiometer Flushing System
Authors: Huber M. J. , Dirksen C.
Published: July 2010

A system for simultaneous flushing of a large number of tensiometers is described. It includes a multiple shutoff valve and a manometer with movable bottom. Flushing procedures are described; they are fast and simple. It can be used with any direction of installation of tensiometers or tubing, for instance, when all tubing is kept below the soil surface to reduce temperature fluctuations. A concentric tubing arrangement reduces air diffusion into the measuring tubing. The system offers potential for improved data quality and reduced need for flushing.
Field Measured and Simulated Corn Leaf Water Potential
Authors: Reicosky D. C. , Lambert J. R.
Published: July 2010

The dynamic nature and magnitude of field‐measured leaf water potential for sweet corn (Zea mays L.) was compared with that predicted by the model TROIKA. Some plant parameters for corn were estimated from the literature and field observation, whereas the moisture desorption curve and the hydraulic conductivity‐water content relationship were determined for the Varina sandy loam. Leaf water potential‐relative water content relationships were determined in the greenhouse. Hourly microclimate data were used as input to the model, and the predicted and observed values of leaf water potential were compared for 3 days during the growing season. Generally, the model predicted leaf water potential with reasonable accuracy throughout the day. Water potential gradients in the soil were small as compared with those across the root and across the stomatal opening.
Multicomponent Cation Adsorption During Convective‐Dispersive Flow Through Soils: Experimental Study
Authors: Lai Sun‐Ho , Jurinak J. J. , Wagenet R. J.
Published: July 2010

The adsorption of Na+, Mg2+, and Ca2+ from aqueous solutions flowing through soil was examined under different total cation concentrations and input pulse volumes. The pulses of Na+ and Mg2+, which were introduced into a Ca2+‐saturated Yolo loam soil column, appeared separately in the effluent. The degree of separation decreased with total concentration, but was not affected significantly by the pulse volume. At constant total concentration, the initial appearance of the Na+ pulse in the effluent was not affected by input volume; the appearance of the Mg2+ pulse was delayed with increasing pulse volume. The experimental results were compared to theoretical calculations based on a single component linear equilibrium model. At a low loading (a small amount of adsorbate with respect to a large amount of adsorbent), the agreement of the theoretical model and the experimental results was satisfactory. However, when the loading was increased, the discrepancy between the calculated values and the experimental results increased.
Potassium and Rubidium Adsorption and Diffusion in Soil
Authors: Baligar V. C. , Barber S. A.
Published: July 2010

Uptake of cations by plant roots growing in soil is believed to be influenced by the relative adsorption strengths of cations by soil exchange sites. The adsorption of K and Rb by four soils was investigated to determine the differences in adsorption of K and Rb which may occur and how they are affected by soil properties with the view of using this information to evaluate the uptake mechanisms for K and Rb by plant roots growing in soil.

Rubidium was adsorbed preferentially to K by all four soils. Selectivity coefficient kRb/K, indicating the size of the effect ranged from 1.9 to 4.4. Adding K decreased kRb/K, increased the amount of nonexchangeable Rb, and decreased exchangeable Rb. There was a negative correlation (r2 = 0.78) between exchangeable K in the soil and kRb/K. The level of K in the soil had a greater effect on kRb/K than varying types of exchange sites present due to differences in clay and amounts of organic matter in the four soils investigated. The size of the selectivity coefficient indicated that the difference between K/Rb ratios in the solution and exchange phases of these soils used and differences between soils made them suitable for use in plant uptake studies of the mechanisms of K and Rb uptake.
A New Approach to Soil Testing: III. Differential Adsorption of Potassium
Authors: Stout W. L. , Baker D. E.
Published: July 2010

Donnán type ratios were used to develop an index to account for the differential adsorption of K in two widely different soils of the Rayne and Hublersburg series. This index was used to calculate an adjusted K requirement for the soils using the approach of Baker. Three corn hybrids (Zea mays L.) were grown in the two soils treated with different levels of K and multiple regression analysis was used to relate soil test variables to plant K content.

Most of the variation in the index, KE/S, was associated with soil effects, making the index useful in characterizing the two soils with respect to differential K adsorption and in calculating soil K requirements. Over 60% of the variation in plant K content was explained by the soil K requirement calculated from the index. Compared with a critical K level of 98 ppm exchangeable K for soils with a CEC of 10 meq/100 g and a KE/S of 1.0, the comparable critical values for K were 71 ppm for the Rayne and 114 ppm for the Hublersburg.
Compaction and Soil Structure Modification by Wheel Traffic in the Northern Corn Belt
Authors: Voorhees W. B. , Senst C. G. , Nelson W. W.
Published: July 2010

Increasing size and weight of farm tractors is causing increasing concern about soil compaction. Controlled wheel‐traffic studies in Minnesota on a silty clay loam showed that wheel traffic of normal farming operations could compact the soil to a 45‐cm depth. Penetrometer resistance was a more sensitive indicator of soil compaction than was bulk density. Wheel traffic increased soil bulk density by 20% or less, whereas penetrometer resistance was increased by as much as 400%. Fall tillage essentially alleviated bulk compaction in the 0‐ to 15‐cm layer. Plowing was more effective than disking or chiseling in decreasing compaction in the 15‐ to 30‐cm layer. Compared with plowing, bulk density and penetrometer resistance values for chiseling or disking were about 5 and 40% higher, respectively. Compaction below the tillage depth was not completely ameliorated by annual freezing and thawing.

Wheel‐induced compaction was more persistent in individual soil structure units than in bulk soil. Strength and density of wheel tracked clods were greater and average aggregate diamter was larger than that of nontracked clods, a difference which persisted overwinter.
Ammonia Volatilization Reaction Mechanism Between Ammonium Sulfate and Carbonate Systems
Authors: Feagley S. E. , Hossner L. R.
Published: July 2010

The mechanism by which NH3 is lost in the reaction between (NH4)2 SO4 and CaCO3, BaCO3, MgCO3, and a calcareous Norwood silt loam soil was investigated. Results obtained in the laboratory indicated that the reaction proceeded through an NH4HCO3 intermediate.

The ratio of NH3 to CO2 volatilized approached a 2:1 ratio of NH3/CO2 gases for the first 2 to 6 hours of the reaction. It then decreased to an apparent equilibrium ratio of 1:1 for the remainder of the 96‐hour reaction period. The pH of the reaction interface between (NH4)2SO4 surface applied to CaCO3 was never > 8.4. These data indicate that at no point was there a high enough pH to form (NH4)2CO3. Thus, if any solid formed it would be NH4HCO3 and not (NH4)2CO3.
Urea Fertilizer Effects on Dissolved Nutrient Concentrations in Some Forest Soils
Authors: Otchere‐Boateng J. , Ballard T. M.
Published: July 2010

Nutrient concentrations in soil solutions near the surface and below the root zone were measured for 8 months after fall application of urea (448 kg N/ha) to four soils under second‐growth forest in southwestern British Columbia. Surface soil solution pH increased due to ureolysis within a few days, while concentrations of some cations were reduced, with Ca and Mg decreasing more than K and Na. Nitrate concentrations peaked at least 3 months after fertilization. With pH decline accompanying nitrification in fertilized plots, concentrations of Ca and Mg increased substantially over concentrations in unfertilized control plots whereas K and Na showed smaller increases. Effects on Ca, Mg, K, and Na are consistent with interpretations based on pH‐dependent cation exchange capacity and Donnan equilibria. Maximum total N, NO3‐N, and Ca concentrations below the root zone were 11.2, 11.0, and 10.0 mg/liter, respectively, and occurred with a recently afforested, coarse‐textured soil which was low in incorporated organic matter and lacked a forest floor.
Gravimetric vs. Volumetric Determination of Water Storage in Vertically Unstable Tillage Layers
Authors: Steinhardt Reuven
Published: July 2010

Methods of determining water storage (W) in a tillage layer of changing height are analyzed to compare the effects of agrotechnical management on W. Changes in W may be evaluated from a single estimate of the solid mass per unit area at a state of reference and periodic observations of the gravimetric water content of the tillage layer, which is equivalent to the usual procedure in stable soils.
Laterally Confined Flow From a Point Source at the Surface of an Inhomogeneous Soil Column
Authors: Merrill S. D. , Raats P. A. C. , Dirksen C.
Published: July 2010

Solution of a linearized flow equation for steady, axisymmetric, laterally confined infiltration from a point source located at the soil surface is compared with pressure head patterns measured in an undisturbed column of sandy loam. The geometry approximates an array of trickle irrigation emitters. The hydraulic conductivity could be represented as an exponential function of both the pressure head and the depth in the column. This implies that steady, multidimensional flow in the column is described by a linear flow equation.

Measured and predicted distributions of pressure head agreed most closely at an application rate of 0.5 cm/day. Increase in the size of a saturated zone about the point source at application rates higher than 0.5 cm/day caused isolines of pressure head to be distorted from the predicted shape. Flow patterns for homogeneous and heterogeneous soil are compared.

Trickle irrigation systems are usually operated intermittently. Measured distributions of pressure heads under intermittent application were compared with steady infiltration patterns. A steady‐flow solution will give an approximate prediction of intermittent pressure head patterns for continuously repeated application cycles over part of the flow region and during part of the time.
Serious Interferences in the Determination of Trace Metals in Soils by Flame and Flameless Atomic Absorption Spectrometry
Authors: Mubarak A. , Hageman L. , Howald R. A. , Woodriff R.
Published: July 2010

Negative interfering effects on the carbon rod atomizer (CRA) absorbances of Mn, Fe, and Ni were found to occur in the presence of the chlorides of the major cations (Ca, Mg, Na) in the soil solution. These interferences were corrected either by precipitation of the chlorides with silver nitrate or by incorporating a relatively high level of sulfuric or nitric acid into the sample volume. Magnesium ion, irrespective of the associated anion, was found to lower the Cd signal on the CRA. High concentrations of MgSO4 caused lowering of the Mn signal when using air‐acetylene flame. This lowering effect of MgSO4 was avoided upon using N2O‐acetylene flame. No interferences were noticed for Mn and Zn when using the constant temperature furnace developed at Montana State Univ.
Formation of Humic Acid Like Compounds by the Ectomycorrhizal Fungus, Pisolithus tinctorius
Authors: Tan K. H. , Sihanonth P. , Todd R. L.
Published: July 2010

Formation of organic compounds by the ectomycorrhizal fungus, Pisolithus tinctorius, was studied to establish the relationship of these microbial products to humic and fulvic acids. The fungus was grown in a Melins‐Norkrans liquid culture with either sucrose or a mixture of L‐malic and L‐succinic acid as the C and energy source. The biologically synthesized substances were characterized by chemical and infrared analyses. The fungus grown on the malic‐succinic acid medium produced a black substance, whereas the organism grown on sucrose yielded only small amounts of a greenish‐brown colored compound. The greenish‐brown substance behaved similarly to fulvic and humic acids, when subjected to fractionation procedures using NaOH and HCl. The fraction soluble in base and acid had an infrared spectrum resembling that of fulvic acids. The fraction soluble in NaOH but insoluble in HCl had infrared features of humic acid. The black substance was insoluble in NaOH and HCl, and identification of infrared spectra revealed the black colored product to be uronic acids.
Influence of Polyethylene Mulch and Magnesium Salts on Tomatoes Growing on Loamy Sand
Authors: Jones U. S. , Jones T. L.
Published: July 2010

Plant‐soil responses to mulching with 0.0375 mm thick white‐overblack polyethylene plastic and to two sources of Mg were studied by analyzing soil samples, plant tissues, and yields associated with three crops of irrigated tomatoes (Lycopersicon esculentum Mill.). These crops were grown on 5.51 m2 plots of Blanton loamy sand in 1976‐77. Ten and 20 kg/ha of Mg as MgSO4 · 7H2O and 20 kg/ha of Mg as CaMg(CO3)2 were added each season to mulched and unmulched soil. Yield of marketable tomatoes, S and Mg content of the fourth leaf from tip, and exchangeable Ca, Mg, and buffer pH of soil to a depth of 60‐cm were measured. Yield was significantly increased in the first crop where Mg was added, either as MgSO4 · 7H2O or dolomite on mulched soil. Tomato‐leaf Mg (0.78%) of the second crop was greatest where 20 kg/ha of Mg as MgSO4 · 7H2O was added to the mulched plots although the yield increase was not significant. Leaf Mg content was significantly increased by 20 kg/ha of Mg as MgSO4 · 7H2O in second and third crops whether or not plastic mulch was used. Dolomite increased Mg in the leaf of the third crop. Mulched soil (0 to 15 cm deep) had a higher buffer pH and exchangeable Mg and Ca than did the uncovered soil. No significant difference in cations was noted at greater soil depths.
Partial Substitution of Mycorrhizal Fungi for Phosphorus Fertilization in the Greenhouse Culture of Citrus
Authors: Menge J. A. , Labanauskas C. K. , Johnson E. L. V. , Platt R. G.
Published: July 2010

The interaction between P fertilization of citrus and the mycorrhizal fungus Glomus fasciculatus was examined in a greenhouse study. A low fertility loamy sand (4.6 ppm P) was provided with all necessary soil nutrients except P. This soil received superphosphate [Ca(H2PO4)2 · H2O] at rates of 0, 6, 28, 56, 278, and 556 ppm of P. Seven replicate mycorrhizal and nonmycorrhizal Brazilian sour orange and Troyer citrange seedlings were grown at each P fertility level. After 5 months, mycorrhizal sour orange which received 0 fertilizer P were similar in size to non‐mycorrhizal sour orange which were fertilized with 278 ppm P. Mycorrhizal citrange which received 0 fertilizer P were similar in size to nonmycorrhizal citrange which were fertilized with 56 ppm P. Dry weights of mycorrhizal sour orange seedlings were significantly greater than nonmycorrhizal sour orange seedlings when fertilized with 0, 6, 28, and 56 ppm P (947, 1089, 347, and 253% greater, respectively). Dry weights of mycorrhizal citrange seedlings were significantly greater than nonmycorrhizal citrange seedlings only when fertilized with 0 and 6 ppm P (746 and 300% greater, respectively). The %P in leaves of both citrus cultivars was enhanced by the mycorrhizal association at all P fertility levels. Variation in absorption of K, Mg, and Na by the citrus cultivars appeared to be primarily influenced by P concentrations of the seedlings. Variation in absorption of Zn, Cu, and Mn appeared to be influenced by both P concentrations of the seedlings and the presence of the mycorrhizal fungus. The number of G. fasciculatus spores/cm3 of soil which were associated with inoculated plants decreased with increasing P fertility levels. With mycorrhizal sour orange, numbers of spores decreased from 10.1 spores/cm3 soil at 56 ppm P soil to 0 spores/cm3 soil with plants at 556 ppm P. With mycorrhizal citrange, numbers of spores decreased from 5.7 spores/cm3 soil at 28 ppm P to 0 spores/cm3 soil at 56 ppm P. No correlation was found between soil P or % P in leaves, roots or stems of seedlings and the elimination of spore production.
Mössbauer and X‐Ray Evidence for the Pedogenic Transformation of Hematite to Goethite
Authors: Bigham J. M. , Golden D. C. , Bowen L. H. , Buol S. W. , Weed S. B.
Published: July 2010

Soils of the Appling series (Typic Hapludults; clayey, kaolinitic, thermic) are extensive in the Piedmont Province of the southeastern United States. Typically, these soils exhibit colors grading from brown (7.5YR) in the upper B horizons to red (2.5YR) in the saprolite. Fine clay separates (<0.2µm) from the brown (B21t horizon) and red (C2 borizon) zones of a representative pedon of the Appling soil were analyzed to determine if the color transition reflected a change in iron mineralogy. Concentration of secondary iron forms by alkali dissolution of gibbsite and silicate clay minerals enabled the x‐ray identification of aluminous geothite and hematite in the C2 clay but only aluminous goethite in the B21t material. These results were substantiated by Mössbauer spectroscopic analyses of the natural clays, which gave spectra characteristic of finely divided hematite and/or goethite. Subnormal effective internal magnetic fields (relative to standard goethite and hematite) were also measured and were in keeping with the effect of Al substitution. Presence of both goethite and hematite in the saprolite but only goethite in the B21t material suggests a pedogenic transformation of hematite to goethite.
In Situ Transformations of Nitrogen‐15 Labeled Materials in Sonoran Desert Soils
Authors: Westerman R. L. , Tucker T. C.
Published: July 2010

Influences of ammonium, nitrate, organic N sources and organic C amendments on microbial respiration, N transformations and gaseous losses were measured under natural environmental conditions in two field experiments. Microbial respiration was increased by addition of wheat straw and barley grain. Addition of N as (15NH4)2SO4 and K15NO3 alone did not increase CO2 evolution significantly.

Significant immobilization of added inorganic‐15N occurred with few exceptions in all treatments except nitrate alone. Organic‐15N in soils amended with wheat straw increased with increasing N rates with both inorganic N sources. Inorganic‐15N was practically void in both soils at the end of 12 months. Mineralization of 15N‐labeled barley grain occurred but at a very low rate and no significant accumulations of inorganic‐15N were observed.

Gaseous losses of N at the end of 12 months varied from 73 to 94% of the inorganic‐N added alone, with the greatest loss occurring from K15NO3. The incorporation of wheat straw stimulated immobilization of added N and reduced gaseous losses to 30 to 86% of the total N applied and the smallest loss occurred with (15NH4)2SO4. The average loss of mineralized organic‐15N derived from barley grain for the two soils was 19% of the total N added. Most of the gaseous losses occurred within the first 3 months, the period of the measurable rainfall.

Analyses of subdivided soil sections (0–5 and 5–10 cm) showed that 95 to 100% of 15N remaining in the soil was in the upper 5‐cm layer indicating that leaching was not appreciable in any treatment.
Interaction of Added Gypsum in Alkaline Soils with Uptake of Iron, Molybdenum, Manganese, and Zinc by Sorghum
Authors: Olsen S. R. , Watanabe F. S.
Published: July 2010

Experiments with tomato plants (Lycopersicon esculentum Mill.) in nutrient cultures indicated previously that Mo accentuated Fe deficiency at low levels of available Fe. This interaction may be important in alkaline soils where pH favors a low Fe availability and high Mo availability from native soil levels. When such interactions exist, this information will help interpret the relationship between response predicted by a soil test for available Fe and actual response. This interaction was confirmed in six soils where sorghum plants (Sorghum bicolor L. Moench. var. RS‐610) increased in Fe uptake and/or Fe concentration as Mo was decreased by adding CaSO4 at 30 ppm of S. The CaSO4 decreased Mo from 2.33 to 1.26 ppm and increased Fe from 56 to 65 ppm in sorghum. An increase in Mo above native levels decreased the Fe concentration from 57 to 51 ppm and Fe uptake frmo 369 to 306 µg/pot in sorghum. Also, CaSO4 consistently increased Mn concentrations from 70 to 90 ppm, and Zn from 56 to 80 ppm in sorghum. Knowledge of these interactions will help to interpret plant responses to natural levels of these micronutrient in soils and disturbed lands or to induced levels from sewage, other wastes, and fertilizers.
Nitrogen Release Patterns from Deep Placement Sites of Urea in a Wetland Rice Soil
Authors: Savant N. K. , De Datta S. K.
Published: July 2010

Release patterns of N from deep placement sites of prilled urea (PU), supergranule urea (SGU), sulfur‐coated urea (SCU), and urea in mudball (MBU) were studied in in situ wetland Maahas clay at the International Rice Research Institute. Nitrogen release from PU and SGU was rapid during first day after placement and decreased thereafter. Nitrogen release from urea in a mudball was slower than that from PU or SGU. Deep placed SCU released N at a markedly slower rate than MBU throughout 45 days after placement. Nitrogen release from deep placement sites of the different forms of urea appeared to be a diffusion‐controlled process.
Soil Properties Influencing Strength of Canfield and Geeburg Soils
Authors: McCormack D. E. , Wilding L. P.
Published: July 2010

This study was conducted to determine the relationships between in situ shear strength and soil properties in two contrasting soil series. Shear strength was measured using a vane forced into the soil by a truck‐mounted hydraulic sampler. Selected horizons at five sites of each soil series were tested. Vane shear tests were performed both in the fall and in the spring; 144 tests were performed.

Soil moisture content, bulk density, and clay content were found to be of most influence on vane shear strength. Multiple regression analysis showed that coarse clay content is positively correlated with shear strength and fine clay content is negatively correlated. These four variables explain 83% of the variation in vane shear strength. Remolded shear strength in the Bt horizons of both soils is < 0.15 kg/cm2. The soil properties that explain most of the variation in shear strength are used in the classification of soil series, or are directly associated with these properties. Determination of soil strength using the vane shear test is quick and inexpensive. The high correlation between the test results and soil properties suggests that further study of the potential use of the vane shear test in the soil survey is warranted.
Inhibition of Nitrification by Acetylene
Authors: Walter H. M. , Keeney D. R. , Fillery I. R.
Published: July 2010

The effect of C2H2 on nitrification in soils was determined to evaluate the use of C2H2 in field and laboratory denitrification studies. The presence of as little as 0.1% (vol/vol) C2H2 completely inhibited nitrification. The effect of C2H2 was reversible, but an 8‐ to 10‐day period was required before nitrification returned to the rate in the control. The results suggest that the C2H2 approach must be limited to those experiments in which either only nitrate fertilizers are used or where nitrification is assumed complete before denitrification commences.
Dissolution and Transport of Gypsum in Soils: II. Experimental
Authors: Glas T. K. , Klute A. , McWhorter D. B.
Published: July 2010

Experimental information on the dissolution of gypsum and the subsequent transport of the dissolved species in a soil‐water system was obtained by adding distilled water to the top of 30‐cm long columns containing a soil‐gypsum mixture and by measuring the calcium concentration in the solution phase as a function of time at different positions in the columns. The measured concentration‐time curves are compared with results from two models — the first based on equilibrium chemical principles and the mixing‐cell concept, and the second based on a combination of the one‐dimensional convection‐dispersion equation and a first‐order kinetic expression describing the dissolution process. Under the specific experimental conditions studied, the dissolution process appeared to be kinetically controlled and could not be described by the solubility‐product relationship.
Pyrolysis‐Gas Chromatography‐Mass Spectrometry of Soil Humic Fractions: II. The High Boiling Point Compounds
Authors: Martin F. , Saiz‐Jimenez C. , Cert A.
Published: July 2010

Pyrolysis‐gas chromatography‐mass spectrometry studies of soil fulvic and humic acids were made. The high boiling point compounds produced by pyrolysis were separated in a column packed with Chromosorb AW DMCS 80–100 mesh coated with 10% FFAP. Humic acids with a high nitrogen content yielded a complex variety of protein derivatives, such as alkylpyridines, alkylpyrroles, alkylbenzonitriles, indoles, piperidines, pyrazines, and pyrrolidones. Humic acids with low N content yielded a smaller number of heterocyclic nitrogen compounds. Lignin derivatives were also identified, but the amount varied in different samples. Furanes were not as prominent as protein and lignin fragments. Acid hydrolysis released proteins, polysaccharides, and lignins, which could be considered as companion materials of a humic “core”. The majority of the pyrolysis compounds from the residue after hydrolysis were identified as alkylbenzenes, alkylnaphthalenes, phenols, benzofuranes, indenes, and fluorenes. Alkanes and alkenes were noted in trace amounts. Pyrolysis behavior of fulvic acids differed from that of humic acids. They produced poorly resolved pyrograms with smaller number and a lower intensity of peaks, from which only furfurals, phenols, benzofuranes, and naphthalenes could be identified.
Water‐Dispersible Soil Organic‐Mineral Particles: II. Inorganic Amorphous and Crystalline Phases in Density Fractions of Clay‐Size Particles
Authors: Spycher G. , Young J. L.
Published: July 2010

Water‐dispersible clay‐organic particles from six epipedons and one Bh horizon were fractionated by density. After oxidation of organic matter in hydrogen peroxide, the amorphous particle phase was removed using a kinetic method and analyzed for Si, Al, and Fe. Light particles contained high levels of amorphous oxides and a poorly ordered phyllosilicate matrix. Heavy particles had low levels of amorphous oxides and a more crystalline matrix. A continuum in particle compositions and properties between the density extremes was observed and explained in terms of an aggregate model proposed in part I of the study.

Molar silica to alumina ratios of the amorphous phase in particles ranged from 0.2 to 6.7. Low ratios (<1) occurred in particles from an Aquod Bh horizon and were attributed to organically complexed Al. The amorphous particle phase, mineral matter dissolving at a fast rate, was allophanic (low ratio) in two Andepts, and highly siliceous in an Argid. Intermediate ratios in other soils may have resulted in part from disordered phyllosilicates.
Prediction of Field Soil Water Content
Authors: Cameron D. R.
Published: July 2010

A 3‐year experiment was conducted to monitor and subsequently predict field water contents using the water transport model. Saturated hydraulic conductivities and soil water characteristic curve results were measured and averaged for each soil layer. The Millington‐Quirk (MQ) method was used to calculate average model parameters. Direct use of the MQ‐derived conductivity and diffusivity functions did not give an exact fit to the observed field results. However, when reasonable adjustments were made to the K(θ) and D(θ) functions the prediction was improved considerably. The methodology for “averaging” and utilizing field data to derive model parameters, and subsequent adjustment or optimization of the model parameters all require more research if we hope to use the unsaturated flow equation for field water content prediction.
Intensive Site Preparation and Sediment Losses on Steep Watersheds in the Gulf Coastal Plain
Authors: Beasley R. S.
Published: July 2010

The hydrologic effects of three methods of intensive site preparation—brush chopping, shearing and windrowing, and bedding on contour—were measured during the 1976 and 1977 water‐years on three small watersheds on steep terrain in northern Mississippi. After site preparation, the treated watersheds were fertilized, limed, sown with clover (Trifolium subterranean L.), and planted with loblolly pine seedlings (Pinus taeda L.). An undisturbed watershed served as a control. Site preparation exposed soil on 37% of the chopped watershed, on 53% of the sheared and windrowed watershed, and on 69% of the bedded watershed. First‐year sediment losses for the chopped, sheared, bedded, and control watersheds were 12.5, 12.8, 14.2, and 0.6 metric tons/ha, respectively. Sediment concentrations for the four watersheds were 2,471, 2,837, 2,808, and 2,127 mg/liter of stormflow. Most of the first‐year sediment losses occurred during months of highest stormflows, November, January, February, and March. Stream channel scouring was a major source of sediment on the site prepared watersheds.

Second‐year sediment yields from the chopped, sheared, and bedded watersheds decreased to 2.3, 2.2, and 5.5 metric tons/ha, while sediment from the control watershed decreased to 0.1 tons/ha. Sediment concentrations were 670, 794, 2,346, and 393 mg/liter for the four watersheds. In relation to annual precipitation, total stormflow decreased on all treated watersheds the second year.
Cole Determination by Thermomechanical Analysis
Authors: Hajek B. F.
Published: July 2010

The coefficient of linear extensibility (COLE) is used as a criterion to differentiate vertic from typic subgroups. The ratio, (Lm − Ld) ÷ Ld, in which Lm is the length at 1/3 — bar moisture tension and Ld is the air‐dry length of a soil clod, is used to calculate this coefficient. Length changes can be obtained from measurements of moist and dry soil cores. COLE can also be calculated from moist and dry bulk density values. The objective of the study was to evaluate the use of the thermomechanical analyzer (TMA) for the measurement of soil ped length change as the ped is dried. The TMA unit is available as a plug‐in module for thermal analysis systems. Field moist (approximately at field capacity) and 1/3 — bar soil peds were selected from six soils and analyzed by this method. TMA‐COLE values from 0.126 to 0.010 were calculated from length change values. About 30 min was required for each measurement of field moist peds. This is a rapid procedure for shrinkage estimation since it requires essentially no preliminary preparation.
Dispersion in Soil Columns: The Snow Plow Effect
Authors: Starr J. L. , Parlange J.‐Y.
Published: July 2010

Miscible displacement and tracer techniques were utilized to study the exchange and transport of cations in a column of soil with a low cation exchange capacity. The specific case studied was one in which an unlabeled CaCl2 solution was at least 10 times greater than that of the initially labeled Ca present in the soil solution and on the exchange. Most of the exchange was observed to take place at the front of the in coming solution, resulting in a labeled solute concentration at one pore volume of the breakthrough curve that is much greater than the initial concentration of the labeled soil solution and complete removal of initially adsorbed ions in two pore volumes. A theoretical approximation is developed which predicts the phenomenon adequately.
Variability of Mechanical Impedance in a Tilled One‐hectare Field of Norfolk Sandy Loam
Authors: Cassel D. K. , Nelson L. A.
Published: July 2010

The spatial variability of field‐measured values of mechanical impedance makes it difficult to detect significant differences in impedance effected by different management and/or tillage practices. This study was conducted to examine sources of cone index (CI) variation and to develop models to predict CI in a 1‐ha field of Norfolk sandy loam for three different tillage practices.

Cone index measurements, obtained using a hydraulic cone penetrometer, were collected in four randomized blocks (B) for each of three tillage treatments imposed prior to planting. Tillage treatments were mold‐board plowed plus disked (N); chiselplowed (C); and subsoiled plus bedded (S). Penetrometer probes in each plot were taken at seven positions (P) on four transects normal to the soybean [Glycine max (L.) Merr.] rows and to a depth (D) of 41 cm. The maximum CI value within the 0‐ to 14‐, 14‐ to 28‐, and 28‐ to 41‐cm depth increments for each probe was used in the statistical analyses.

The best predictive model for each tillage treatment was selected based upon the correlation coefficient, coefficient of variation, standard deviation, and the normality of the residuals as tested by the Kolmogorov‐Smirov statistic. Using these statistics, it was determined that the CI data must undergo a log transformation prior to model development. As much as 40% of the observed spatial variability for treatment N was explained by the full model. The depth variable (D) was the only significant term. The D, P, and P × D terms in the CI model were significant at the 0.01 probability level for treatment S and the full model containing these terms accounted for 71% of the variation. Finally, the D and B terms were significant at the 0.01 probability level and the model accounted for 63% of the spatial variability encountered in treatment C.
An in‐situ Dewpoint Hygrometer for Soil Water Potential Measurement
Authors: McAneney K. J. , Tanner C. B. , Gardner W. R.
Published: July 2010

An in situ device for determining the soil water potential by measuring the dewpoint temperature depression is described. A saturated ceramic plug is used to provide hydraulic contact between the soil and an air‐tight measuring chamber housing a four‐terminal thermojunction. The ceramic and the thermojunction references are thermally clamped to the copper body of the instrument in order that temperature differences between the vapor source (the internal evaporating surface of the ceramic) and the reference junctions are minimal. Thus, the device reduces the major source of error that plague conventional soil psychrometers in the presence of temperature gradients. A hygrometer placed perpendicular to an imposed thermal gradient in a soil column recorded a maximum zero offset voltage of 0.22 µV as compared with 130 µV from a Wescor psychrometer under the same conditions.

Provided the ceramic remains saturated, the response of the hygrometer to changes in soil water matric potential is extremely rapid. Two bean plants (Phaseolus vulgaris L., c.v. “Tender‐green”) growing in a 2‐liter container of silt loam soil were subjected to wetting and drying cycles in the laboratory. Simultaneous measurements of leaf and soil water potential illustrate the capacity of the soil hygrometers to track changes in soil water matric potential.

In the presence of solutes, the instrument is diffusion limited. The time constant for salt equilibration, with our geometry and using KCl as the solute was 23 hours. This is consistent with a diffusion coefficient of 2 to 3 × 10−6 cm3 sec−1. For this reason the application of this design should be restricted to circumstances where the osmotic contribution to the total water potential is either small or not changing rapidly. These criteria are generally satisfied in the humid regions.