bluuebunny/crossref_metadata_2025 huggingface dataset:
Geostatistical Analysis of Soil Chemical Properties of Large Land Areas. II. Kriging
Authors: Yost R. S. , Uehara G. , Fox R. L.
Published: July 2010

The use of soil analyses to construct maps of soil properties and to identify areas of particular interest or requiring separate management, is important in soil science. Recent developments in geostatistics permit increased ability to summarize and interpret such soil analyses. Soil analyses from transects on the Island of Hawaii were used for estimating soil P sorption over the entire island by means of an optimal geostatistical technique called kriging. Displays of P sorption information obtained by kriging were compared with those obtained by a more common method of spline interpolation. The map of kriged points corresponded more closely with known soil behavior than did the spline map. Kriging further provided estimates of the reliability of the resulting map. Areas were identified where additional samples would be most useful in reducing the estimation variance which indicates map reliability. The necessity of considering nonstationarity and using universal kriging was evaluated. Universal kriging, either by prior polynomial trend removal or by local polynomial trend removal during estimation, was not beneficial in spite of widely varying P sorption and a significant polynomial trend in the data. Results suggest ordinary kriging is useful in summarizing and interpreting soil analyses and that ordinary kriging seems quite robust to certain degrees of nonstationarity.
Positive Permanent Charge in Oxisols
Authors: Tessens E. , Zauyah Siti
Published: July 2010

The existences of a positive permanent charge can be inferred from charge characteristics of highly weathered tropical soils; it was found to be related to isomorphous substitution of Ti(IV) for Fe(III) in iron oxides. Comparable near‐constant values were found from anion adsorption at pH 7.0 to 9.0. It was concluded that both positive and negative permanent charge can coexist in the same soil.
Potential for Nutrient Depletion by Short Rotation Harvest of Sweetgum
Authors: Francis John K. , Baker James B.
Published: July 2010

This study was conducted to determine if short rotation harvests of sweetgum (Liquidambar styraciflua L.) could deplete a clayey soil of nutrients. Sixteen trees in late summer and another 16 in early winter were harvested to determine the nutrient distribution in an 11‐year‐old plantation. Nutrient removal for several harvesting alternatives were projected. Nutrient removal would be in the order of August whole‐tree chip > November whole‐tree chip ≫ harvest of bole with bark > harvest of bolewood only. Nutrient losses through less intensive harvests are made up for by nutrient additions in rainfall. Even at the high rate of removal incurred with summer whole‐tree chipping, hundreds of 11‐year rotations would be necessary to deplete the soil of nutrients.
Design for a Field Sprinkler Infiltrometer
Authors: Zegelin S. J. , White I.
Published: July 2010

A sprinkler infiltrometer using air pressure to drive water through an interchangeable nozzle onto a field plot has been designed and tested for use in infiltration and redistribution studies. Application rates with uniform distribution are selected by electronically pulsing a solenoid valve between the pressurized water supply and the nozzle. A field test demonstrated the use of the infiltrometer in measuring the time to incipient ponding and the development of the water content profile.
On the Use of the Langmuir Equation in the Interpretation of “Adsorption” Phenomena: II. The “Two‐Surface” Langmuir Equation
Authors: Sposito Garrison
Published: July 2010

A rigorous, mathematical representation of a sorption isotherm as a Stieltjes transform is employed to prove a theorem about the “two‐surface” Langmuir equation. This theorem states that, if the distribution coefficient for an ion sorbed by a soil is a finite, decreasing function of the amount sorbed, q, and extrapolates to zero at some finite value of q, then the sorption isotherm can always be represented mathematically by a two‐surface Langmuir equation. Since the proof of this theorem does not depend on the chemical mechanism of ion sorption, it follows that the adjustable parameters in the two‐surface Langmuir equation cannot be interpreted in terms of surface reactions without additional, independent evidence that only adsorption on two kinds of surface site actually is involved in the ion sorption reaction.
Comparison of the Abilities of Hydroxamic, Synthetic, and Other Natural Organic Acids to Chelate Iron and Other Ions in Nutrient Solution
Authors: Cline Gary R. , Powell P. E. , Szaniszlo P. J. , Reid C. P. P.
Published: July 2010

Chelation modeling was used to predict the abilities of hydroxamate siderophores (HS) and other natural organic acids to chelate Fe and other ions in a modified Hoagland nutrient solution as a function of pH (4.0–10.0). Experimentally determined levels of chelated Fe (pH 5.0–10.0) agreed with our predicted results and with values previously predicted for EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), and EDDHA [ethylenediamine di(o‐hydroxyphenylacetic) acid].

The natural HS, Desferrioxamine B (DFOB), and an unknown mixture of HS isolated from the ectomycorrhizal fungus Boletus edulis, remained fully chelated with Fe at all values of pH. Modeling predicted DFOB to be 99.9% chelated with Fe even in nutrient solution of pH 10.0. No significant chelation of Fe was measured or predicted above pH 6.0 for malate, malonate, oxalate, succinate, α‐ketoglutarate, or pyruvate. Only 4% of citrate was chelated with Fe at pHs 6.0 and 6.4 as determined by direct measurement and computer modeling, respectively.

Solubility constants, derived for Fe(OH)3 (amorphous) (amorph.) and FePO4 (amorph.), indicated that FePO4 (amorph.) can control Fe solubility in nutrient solutions of low pH and reduce the ability of ligands to chelate Fe, relative to conditions in which Fe solubility is governed by Fe(OH)3 (amorph.).

Since our results indicate that microbially produced hydroxamate siderophores have a significant influence on Fe solubility, we discuss how such ligands could be of importance in the Fe nutrition of plants under natural soil conditions.
Denitrification in No‐Till and Plowed Soils
Authors: Rice Charles W. , Smith M. Scott
Published: July 2010

No‐till and plowed soils were compared with regard to denitrifying activity. To assay denitrification with minimal physical disruption of the soil, an important consideration in the study of tillage effects, a procedure was developed employing acetylene (C2H2) inhibition of nitrous oxide (N2O) reduction in intact soil cores. This approach and a short‐term, anaerobic soil slurry assay were consistent in indicating greater denitrifying activity in no‐till than in plowed Maury silt loam soil. In the intact core assay, ratios of no‐till to plowed soil activity were >1 on all sampling dates, and were as high as 77. Intact cores from a Crider (Typic Paleudalfs) soil showed a similar tillage effect, but tillage had inconsistent effects on both soil water content and denitrifying activity in a Tilsit (Typic Fragiudults) soil. It is suggested that the generally higher soil moisture contents observed in no‐till soils, rather than tillage per se, are primarily responsible for higher denitrifying activity. Enhanced denitrification may account, in part, for the lower soil NO‐3 concentrations and higher N fertilizer requirements sometimes reported for no‐till soils.
Estimating Saturated Hydraulic Conductivity from Soil Morphology
Authors: McKeague J. A. , Wang C. , Topp G. C.
Published: July 2010

Guidelines were developed for estimating the saturated hydraulic conductivity (Ksat) class of soil horizons from observations of soil morphology by checking estimates against Ksat values measured in the field by an air entry permeameter. For 78 soil horizons ranging in texture from sand to clay, the estimated Ksat class (of eight classes) was the same as the measured class for 45% and within one class of the measured class for 87% of the horizons. Some horizons fell into each of the classes defined, from H1 (>50 cm/h) to L3 (<0.017 cm/h). The major factors contributing to high Ksat values were abundant biopores, textures coarser than loamy fine sand, and strong, fine to medium blocky structure. The lowest values were associated with clayey horizons that had been compressed or puddled by cultivation. Useful estimates of Ksat can be made during soil survey by careful observations of morphology and frequent checks of estimates against measured values.
Comparison of Fall and Spring Application of 15N‐Labeled Urea to Douglas‐Fir: I. Growth Response and Nitrogen Levels in Foliage and Soil
Authors: Heilman P. E. , Dao Thanh , Cheng H. H. , Webster S. R. , Harper S. S.
Published: July 2010

Movement, transformation, and recovery of fertilizer N by analysis of soil and foliage of seven‐ and nine‐year‐old Douglas‐fir were followed over a two‐year period at two relatively high quality sites in western Washington. Urea fertilizer labeled at approximately 8 atom percent 15N was applied at 224 kg N/ha at the end of November 1977 and in late April 1978. High rainfall followed the fall fertilizer treatment and low rainfall occurred after the spring treatment. Differences in variability in fertilizer recovery, fertilizer movement, and tree response to fertilization appeared to be related to differences in rainfall patterns shortly after fertilization. On the average, fall fertilization gave better volume growth response than spring fertilization, but substantial variation in response was observed between sites and season of application.

Fertilizer N did not appear in substantial concentrations in foliage until after 6 weeks, with high levels of 15N still evident in foliage after 2 years. With the spring treatment, fertilizer N could have appeared earlier in the newly formed foliage, but this foliage was not sampled until August. The increase in total percent N in foliage lasted only about 1 year following spring treatment and 15 months following fall treatment. Peak concentrations of ammonium N in soil occurred in samples collected 9 d to 3 weeks after fertilization. Ammonium content in the soil declined rapidly and approached control levels at 24 weeks. However, at one site, nitrification was active and relatively high nitrate content was present in the soil at 24 weeks.

Recovery of fertilizer N from analysis of soil was variable, averaging 59 ± 10% of the application at 3 d and about 100% between 9 d to 3 weeks. After two growing seasons, recovery from analysis of soil averaged only 38 ± 6%. Substantial increases in mineral N levels were observed in the soil beyond the quantity applied as fertilizer (the priming effect). Data from early samples of foliage showed increased concentration of N possibly resulting from this phenomenon. However, after the middle of the first growing season following treatment, no increased concentration of N in foliage from soil organic matter was evident.
Quantitative Evaluation of Water Adsorption on Soil Clays
Authors: Karathanasis A. D. , Hajek B. F.
Published: July 2010

Quantitative water adsorption determinations were obtained from clay fractions of soil and sedimentary samples by both adsorption isotherms and low temperature thermogravimetry and differential scanning calorimetry techniques. Isotherms at 35°C were obtained with a sealed evacuated quartz spring system and a cathetometer. The weight of water required for monolayer coverage was calculated by application of BET and Langmuir equations. Surface areas based on adsorption by the BET equation were more suitable than from Langmuir, especially when hydroxy‐interlayered or zeolite impurities were present. Quantifications of expanding 2:1 minerals by surface area, weight loss, and enthalpy methods compared favorably. Correlation coefficients comparing methods were high (r = 0.97) and average deviations were small (±3.9%). Water adsorbed by clays at 52% relative humidity was exactly double the monolayer BET value. Water vapor adsorption level for montmorillonitic clay fractions was always >9.0%. Monolayer adsorption limits between mixed and kaolinitic mineral classes ranged from 2.2 to 2.4%. These relationships indicate that water adsorption can be used to aid routine clay mineral analysis for classification purposes.
Evaluation of Methods for Determining the Apparent Thermal Diffusivity of Soil Near the Surface
Authors: Horton R. , Wierenga P. J. , Nielsen D. R.
Published: July 2010

Field‐measured values of soil temperature were used to calculate the apparent thermal diffusivity of the upper 10 cm of soil with six different methods. The limitations of the six methods were analyzed both in terms of the calculated results, and for the quantity and quality of data required to make the calculations. Four of the six methods, Amplitude, Phase, Arctangent, and Logarithm, provided explicit equations for the thermal diffusivity. These explicit methods required only a few measurements of temperature, and calculations were simple to perform; however, the results were found to be erratic and in general inconsistent with known or more reliable estimates of the apparent thermal diffusivity. Two methods, Numerical and Harmonic, which made use of larger numbers of temperature measurements to implicitly solve for the apparent thermal diffusivity, generally provided more reliable estimates. Calculated values of the apparent thermal diffusivity by both methods were used in predicting soil temperature for comparison with measured temperature. Even under partly cloudy conditions both methods predicted temperatures very well. In general the data requirement of the Numerical method was 12 to 24 measures of temperature per day at three depths, while the Harmonic method only required 8 to 12 measures of temperature per day at two depths.
Copper(II) Binding by Humic Acid Extracted from Sewage Sludge: An Electron Spin Resonance Study
Authors: Boyd Stephen A. , Sommers Lee E. , Nelson Darrell W. , West Douglas X.
Published: July 2010

Electron spin resonance (ESR) spectroscopy was used to study the binding of Cu2+ by humic acid (HA) extracted from sewage sludge. Electron spin resonance spectral data of the Cu‐HA complex and some adducts with nitrogen donors (pyridine, 1,10‐phenanthroline, ethylenediamine) showed that Cu2+ formed two equatorial bonds with HA oxygen donor ligands. The ESR data presented were consistent with the formation of a Cu‐chelate in the original Cu‐HA complex. The ligand field strength of the HA oxygen donor ligands coordinated to Cu2+ was stronger than that of H2O. The above results were consistent with an earlier ESR characterization of a soil Cu‐HA complex. The Cu2+ ion also appeared to form axial bonds with HA donor ligands originating from proteinaceous materials associated with the sludge HA fraction. Characterization of an adduct with glycylglycine showed that the dipeptide formed coordinate honds with Cu2+ bound to HA.
Sodium‐Calcium and Sodium‐Magnesium Exchange on Wyoming Bentonite in Perchlorate and Chloride Background Ionic Media
Authors: Sposito Garrison , Holtzclaw Kenneth M. , Charlet Laurent , Jouany Claire , Page A. L.
Published: July 2010

The exchange of calcium and magnesium for sodium at 298 K on Wyoming bentonite was investigated in perchlorate and chloride background media maintained at pH 7.0 and at a total cation normality of 0.05N. In the perchlorate medium, the apparent total adsorbed metal charge was independent of the exchanger composition and equal to 0.97 ± 0.06 molc kg−1 (average for Na‐Ca and Na‐Mg exchanges). In the chloride medium, the apparent total adsorbed metal charge increased with the amount of calcium or magnesium adsorbed, tending to a value near 1.3 molc kg−1 as the clay became saturated with the bivalent metal cation. These results were interpreted as evidence for the adsorption of CaCl+ or MgCl+ complexes in the exchange experiments conducted in the chloride medium. A detailed analysis of the exchange data led to the conclusion that a Ca‐montmorillonite or Mg‐montmorillonite suspension in a chloride background consists of quasicrystals with bivalent cations adsorbed on the internal surfaces and monovalent metal‐chloride complexes adsorbed on the external surfaces.
Melanoidins and Soil Organic Matter: Evidence of Strong Similarities Revealed by 13C CP‐MAS NMR
Authors: Benzing‐Purdie Laure , Ripmeester John A.
Published: July 2010

Melanoidins of molecular weight higher than 12000 were synthesized by reaction of xylose with glycine (I), xylose with ammonium sulfate (III), and glucose with glycine (II) and compared with a well‐humified fraction of an organic soil. Microanalytical data for all four substances were very similar. The CP‐MAS spectra of the three melanoidins strongly resemble that of the organic soil fraction. Melanoidins (I) and (II), like the organic soil fraction, are highly aliphatic and have the same distribution of carbon types: aliphatic, carbons bonded to the electronegative atoms O and N, aromatic, carboxyl, and carbonyl. Acid hydrolysis of melanoidin (I) yielded no xylose and < 1% glycine, indicating that these starting components are not main constituents of the polymer. These findings not only add weight to Maillard's hypothesis, that melanoidin formation “may be at the origin of humic substances in nature,” but allow us to suggest that some of the nitrogen in soil which is still unidentified may exist in melanoidin‐type polymers.
Growth of Rhizobium in Unamended Soil
Authors: Pena‐Cabriales J. J. , Alexander Martin
Published: July 2010

A study was conducted to determine the conditions in unamended soil that favored growth of Rhizobium. Moistening a dry soil resulted in growth of R. japonicum and a strain of Rhizobium nodulating cowpeas but not of R. meliloti. The extent of decline resulting from desiccation was usually greater than the increase following wetting. The extent of growth varied among soils. A freezing‐thawing cycle did not promote growth of R. phaseoli and the cowpea Rhizobium. The latter bacterium was more tolerant to a freezing‐thawing cycle than the former. Rhizobium japonicum and R. phaseoli grew readily in the presence of germinating seeds and developing root systems of soybeans, kidney beans, red clover, cowpeas, oats, wheat, and corn; the population size varied among the plant species, and legumes were no more stimulatory than nonlegumes. The numbers of R. phaseoli in the rhizosphere of several plants declined in 1 week, the abundance of R. japonicum fell after 6 weeks in the soybean rhizosphere, but the population size of the cowpea Rhizobium was high for at least 20 weeks. Counts of R. japonicum in soil increased after the soil was amended with soybean nodules. It is suggested that appreciable rhizobium growth in unamended soil occurs only in the presence of germinating seeds, growing roots, and decomposing nodules.
Chemical Factors Affecting Root Growth in Subsoil Horizons of Coastal Plain Soils
Authors: Adams Fred , Moore B. L.
Published: July 2010

Lack of root growth into the acid subsoils of the Coastal Plain of the southeastern U.S. is a recognized yield‐limiting problem for many crops, but little has been done to identify root‐limiting factors by soil horizon. In an effort to delineate Al toxicity and Ca deficiency by horizon, representative profiles of six major soil series of Alabama's Coastal Plain were sampled by horizon to a depth of 1 m. Horizon samples were subdivided and treated with one of the following: (i) check, (ii) CaSO4, (iii) MgO, and (iv) Ca(OH)2. Growth rate of primary roots of cotton (Gossypium hirsutum L.) into each soil material was measured, and visual symptoms of Ca deficiency and Al toxicity on roots were noted. Five untreated soil horizons grew roots showing only symptoms of Al toxicity (all were Bt horizons, previously designated as B2t); five grew roots showing only Ca‐deficiency symptoms (all were E, EB, BE horizons, previously designated as A2, A3, and B1, respectively); three grew roots showing both Al toxicity and Ca deficiency (all were Bt horizons); five horizons grew normal‐appearing roots (E, BE, and Bt horizons). Calcium deficiency occurred when soil‐solution Ca activity was 0.27 mM or less and Ca saturation was 17% or less. Aluminum toxicity occurred in some Bt horizons with soil‐solution Al at <0.4 µM but not in E, EB, and BE horizons with Al ranging between 9 and 134 µM. This apparent contradiction in toxic levels of Al was probably the result of solution Al being chelated in eluviated horizons but not in illuviated horizons.
Organic Carbon, Nitrogen, and Phosphorus Concentrations and pH in Soil Profiles as Affected by Tillage Intensity
Authors: Dick W. A.
Published: July 2010

No‐tillage (NT), minimum tillage (MT), and conventional tillage (CT) practices were continuously applied to a Hoytville silty clay loam (Mollic Ochraqualf) soil (18 years) and a Wooster silt loam (Typic Fragiudalf) soil (19 years) in Ohio. The effect of the various tillage intensities on the profile (0–30 cm) distribution of organic C, N, and P concentrations and pH was investigated. Results showed that NT resulted in significantly (P < 0.05) higher organic C and N concentrations in the 0‐ to 15‐cm soil increment of the Hoytville soil but significantly lower concentrations in the 15‐ to 30‐cm soil increment. For the Wooster soil, NT resulted in higher concentrations in the 0‐ to 7.5‐cm soil increment. No significant differences were observed among tillage intensities in the 7.5‐ to 30‐cm soil increment. Comparison of organic C concentrations in the plow layer (0–22.5 cm) of the soils at the beginning of the long‐term tillage experiment and at present showed that concentrations remained constant or decreased 11% under NT in the Hoytville and Wooster soils, respectively. Present organic C concentrations in the Hoytville soil were decreased 12 to 14% by long term MT or CT while a 23 to 25% decrease was observed for the Wooster soil. Organic P concentrations under NT were significantly (P < 0.05) higher in the 0‐ to 7.5‐cm increment of the Wooster soil and significantly lower in the 22.5‐ to 30‐cm soil increment. Organic C/N, C/P, and N/P ratios were calculated and higher ratios were observed under NT than under MT or CT in the surface soil increments. Tillage intensity, however, had little effect on the ratios averaged over the entire profile (0–30 cm). Soil pH was 0.1 to 0.3 units lower (P < 0.05) under NT in all soil increments except in the 22.5‐ to 30‐cm increment of the Wooster soil where no significant differences in pH were observed among the tillage intensities.
Estimating Thermal Diffusivity Near the Soil Surface Using Laplace Transform: Uniform Initial Conditions
Authors: Asrar G. , Kanemasu E. T.
Published: July 2010

A simplified method based on the numerical integration of the Laplace transform of the one dimensional heat conduction equation in porous media was used to estimate the thermal diffusivity near the surface. The method is based on the analytical solution of the equation of heat conduction and accepts any functional relationship that realistically describes the surface soil temperature as a boundary condition. An optimization scheme was suggested for selecting proper values of Laplace transform parameter s based on maximum duration of the experiment. The method was used to compute thermal diffusivities of two different soil types for a wide range of soil moisture and temperature conditions. Thermal conductivities for each soil were calculated using the computed diffusivities and heat capacities. A comparison of the conductivities estimated with the Laplace transform and the measured values by a transient method showed good agreements between the two methods. A similar comparison between the Laplace transform and the DeVries' model showed significant differences between the two methods.
A General Soil Volume Change Equation: I. The Two‐Parameter Model
Authors: Giráldez Juan V. , Sposito Garrison , Delgado Carlos
Published: July 2010

A physically based equation containing two adjustable parameters (the slope of the load line and the air‐entry water content) is proposed to describe the volume of a swelling soil as a function of its water content. This equation was shown to give an excellent representation of 18 sets of soil volume change data for both laboratory and field measurements. In many cases, a satisfactory description of volume changes could be obtained by setting the slope of the load line equal to the specific volume of liquid water and adjusting only the value of the air‐entry water content. The proposed equation should be useful in computer models of water movement in swelling soils.
Applicability of Fick's Law to Gas Diffusion
Authors: Jaynes D. B. , Rogowski A. S.
Published: July 2010

The comparison of Fick's Law for the diffusion of gas i in a vapor to the equations based on the kinetic theory of gases shows that only for certain special conditions is the Fickian diffusion coefficient, DFi, independent of the mole fraction of i and the diffusional fluxes of the other gases. These conditions include the diffusion of a trace concentration of gas through a gas mixture of any composition, equimolar, counter‐current diffusion in a binary gas mixture, and diffusion in a ternary mixture where one gas is stagnant. In an O2, CO2, N2 atmosphere, variations in diffusion coefficient of at least 10% from the tracer values are possible with variations in the mole fractions of the gas or the relative magnitude of their fluxes. The temperature and pressure dependency of the diffusion coefficient must also be recognized.
A Chelating‐Resin Method for Characterizing Soluble Metal Complexes
Authors: Hendrickson L. L. , Corey R. B.
Published: July 2010

A method is presented to differentiate between free and complexed trace metals in solution at concentrations at or below the sensitivity of flameless atomic absorption spectrophotometry using a pH and solution composition consistent with natural systems. The method utilizes a pH‐adjusted chelating resin saturated with Ca and selected trace metals that maintains pH and solution metal activities essentially constant when equilibrated with a Ca(NO3)2 solution. Equilibration of this solid‐phase buffer with a Ca(NO3)2 solution containing a soluble complexing agent results in a soluble metal concentration in excess of that obtained when equilibrated with Ca(NO3)2 alone. The increase in the soluble metal concentration is attributed to the formation of soluble metal complexes. The resin method was verified by evaluating Cd, Zn, and Ca complexation by EDTA (ethylenediaminetetraacetic acid). Relative selectivity coefficients were consistent with published values, and the concentration of EDTA added to the system was accurately determined. Solution Cd concentrations were also increased by Cl‐ addition to an extent consistent with published formation constants. The ability of the method to evaluate complexation of several metals simultaneously may make it more attractive than existing methods for characterizing simple monofunctional complexing agents. The method was also used to characterize soluble complexing agents extracted from a sludge‐amended soil. The results indicated that a portion of the ligands had approximately 105.5 times greater affinity for Cd and Zn than for Ca. This marked selectivity for Cd and Zn is much greater than existing selectivity data for similar systems obtained under conditions of low pH and/or unrealistically high metal levels and is likely attributable to the much greater Ca to metal ratios maintained by the resin system.
Behavior of Bromacil and Napropamide in Soils: II. Distribution After Application from a Point Source
Authors: Gerstl Z. , Yaron B.
Published: July 2010

The distribution of napropamide [2‐(α‐naphthoxy)‐N,N‐diethylpropionamide] and bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil) when applied from a point source was determined in several soils. The parameters studied were application rate (4 and 1.5 L/h) and the effect of wetting and drying cycles. In general, napropamide, which was moderately adsorbed by the soils, was concentrated around the emitter; at a high application rate the compound moved laterally more than vertically and at a lower application rate it penetrated to a greater depth. After several cycles of wetting and drying, napropamide was partially leached out of the emitter zone into the soil volume, the amount of leaching being related to the soil texture. Bromacil, which was weakly adsorbed by the soils, was more uniformly distributed in the soil but did exhibit slight retardation in the heavier soils. The effect of application rate was similar to that observed for napropamide; however, after several cycles of wetting and drying, bromacil was completely leached from around the emitter in all soils and was concentrated at the outer edges of the wetted zone.
Evaluation of an Automated Assay System to Measure Soil Radionuclides by L X‐Ray and Gamma‐Ray Spectrometry
Authors: Nyhan J. W. , Drennon B. J. , Crowell J. M.
Published: July 2010

An automated radionuclide assay system was evaluated for performing soil radioassays using L x‐ray and gamma‐ray spectrometry. Wet chemistry assay procedures were shown to be considerably more time consuming than similar analyses of soils on this radionuclide assay system. The detection limits of 241Am and Pu were determined, as well as the reproducibility of radionuclide assay results. The L x‐ray spectrometric measurements were compared with radiochemical analysis on several tuff samples. The assay system's intrinsic germanium detector was found to respond linearly to varying low concentrations of 241Am and Pu, both of which were easily detected in the presence of elevated concentrations of 137Cs.
Competitiveness and Symbiotic Effectiveness of Five Strains of Rhizobium Trifolii on Red Clover
Authors: Materon L. A. , Hagedorn C.
Published: July 2010

Little information is available on seasonal Rhizobium‐red clover (Trifolium pratense L.) interactions, competitiveness, and persistence, and dinitrogen fixation rates in livestock production areas of the southeastern United States. Five introduced strains of Rhizobium trifolii were examined on red clover at two locations (on a ultisol and a vertisol) over two consecutive growing seasons. Double antibiotic resistance acquisition and intrinsic antibiotic tolerance were used to measure the proportions of nodules produced by the inoculum strains. Strains 162BB1, RP113‐7, and LM1 were highly competitive and persistent, and accounted for > 94% of the assayed nodules at both soils over both seasons. Strain 162P17 occupied 90 to 93% of the nodules in the establishment year at both sites. However, in the following season nodule occupancy of 162P17 declined to 83 and 59% at the ultisol and vertisol sites, respectively. A major decline in nodule occupancy by strain TA1 was observed to the extent of its being virtually eliminated by the indigenous Rhizobium populations of both soils during the second season. Higher forage and crude protein production were associated with strains 162BB1, RP113‐7, and LM1 at both locations and seasons. Results showed that red clover, when effectively nodulated by competitive and persistent strains of R. trifolii, can become established and productive under conditions found in the Lower South.
Nodulation of Cowpeas and Survival of Cowpea Rhizobia in Acid, Aluminum‐Rich Soils
Authors: Hartel Peter G. , Whelan Anne Marie , Alexander Martin
Published: July 2010

A study was undertaken to determine whether the reduced nodulation of cowpeas [Vigna unguiculata (L.) Walp.] grown in certain acid, Al‐rich soils resulted from the poor survival of the potentially infective rhizobia. Two strains of Rhizobium capable of nodulating cowpeas were used. The lowest pH for growth in defined liquid medium was 4.2 for one strain and 3.9 for the other. Only the latter was Al tolerant and could grow in a defined liquid medium containing 50 µM KAl(SO4)2. The survival of the bacteria and their ability to nodulate cowpeas in three soils were measured after the soils were amended with Ca or Al salts to give pH values ranging from 5.7 to 4.1 and extractable‐Al concentrations from <0.1 to 3.7 cmol(p+)/kg of soil. Only small differences in survival in 7 or 8 weeks were noted between the two strains. Plants inoculated with the Al‐sensitive strain bore significantly fewer nodules in the more acid, Al‐rich soils than in the same soils with higher pH values and less extractable Al. No significant reduction in nodule number was evident for plants inoculated with the Al‐tolerant strain and grown in the more acid, Al‐rich soils compared to cowpeas grown in the same soils with higher pH values and less extractable Al. It is suggested that the Al content of soil is not a major factor in the survival of cowpea rhizobia but that it does have a significant effect on nodulation.
Soil Water Matric Potential Effects on Aggregate Stability
Authors: Francis P. B. , Cruse R. M.
Published: July 2010

The effect of soil water matric potential (ψm) is not considered with most techniques utilized to evaluate aggregate stability. Rather, aggregate stability usually is measured at ψm of 0 Pa or at an unknown ψm. The objective of this study was to determine ψm effects, in the range of 0 to −3,000 Pa, on stability of natural soil aggregates obtained from a fencerow and from plots having a range of management histories. Aggregate stability, considered inversely related to the mass of soil detached by impact of falling water drops, increase markedly as ψm decreased from 0 to −500 Pa. Similar ψm changes at ψm < −500 Pa had smaller effects on aggregate stability. Significant differences in stability of aggregates obtained from plots with different cropping and/or manuring histories, were sometimes undetectable at ψm ≤ −500 Pa but were more consistently detected at ψm = 0 Pa. Data from this study indicate that aggregate stability is very sensitive to ψm, particularly at ψm near zero. Techniques for comparing aggregate stability between soils or soil treatments should ensure equal values of ψm exist for all aggregates. Measurements made over a range of ψm should yield better comparisons of aggregate stability between soils than measurements made at one ψm.
Replications and Subsamples Needed to Show Treatment Responses on Forest Soils of the Coastal Plain
Authors: Lloyd F. Thomas , McKee William H.
Published: July 2010

This research illustrates how randomized, complete‐block designed field studies can be insensitive to detecting treatment‐caused differences in the concentration of soil nutrients. An example shows that variation without compositing can be so large that 727 blocks are needed to be 90% confident of detecting a difference in total nitrogen of 100 µg g−1. Graphs are presented for determining the optimum numbers of blocks and chemical determinations per plot. The results show that compositing does not affect the number of chemical determinations per plot, but does reduce the number of blocks in direct proportion to the reduction in variance resulting from compositing. A hypothetical example shows that the number of blocks can be reduced from 727 to 15 by constructing blocks with less natural variation between treatment plots and by compositing 20 sample cores for each chemical determination.
The Impact of Harvesting and Site Preparation on the Physical Properties of Lower Coastal Plain Forest Soils
Authors: Gent J. A. , Ballard R. , Hassan A. E.
Published: July 2010

The impact of intensive forest management practices on soil physical properties was examined by collecting intact, 7.6‐cm diameter soil core samples to a depth of 30 cm before harvest, after harvest, and after site preparation in plots established in primary skid trails and areas receiving whole‐tree and conventional tree‐length harvesting treatments. Site preparation for all plots was shear, burn, chop, and bed. Harvesting increased bulk density and decreased aeration porosity in all sampled areas. Significant changes in these properties were detected to the 30‐cm depth in the skid trail plots. However, significant changes in the whole‐tree and tree‐length plots were limited to the upper 15 cm of soil. Harvesting also significantly decreased saturated hydraulic conductivity to a depth of 8 cm in the skid trail plots and 15 cm in the tree‐length plots but had no significant effect in the whole‐tree plots. Bedding proved to be effective in offsetting soil compaction in the whole‐tree and tree‐length plots by forming a new soil surface, 19 cm in height, over the surface which was trafficked during harvest. Bedding may not be as effective in the skid trail plots because the soil found at the original surface under the bed was compacted to the extent that root growth may be inhibited.
A Technique for Parallel Placement of Access Tubes
Authors: Römkens M. J. M. , Whisler F. D.
Published: July 2010

A technique has been developed for parallel insertion of access tubes into a soil. The technique requires hydraulic equipment of the Giddings type supplemented with machined attachments. The results show a minimum of nonparallelism in both the parallel and perpendicular directions to the plant row.
A Pressure Transducer for Field Tensiometers
Authors: Marthaler H. P. , Vogelsanger W. , Richard F. , Wierenga P. J.
Published: July 2010

Field‐installed tensiometers are generally equipped with pressure gauges or mercury manometers. These read‐out devices require much maintenance, while the cost of gauges is high when used in large quantities. This paper describes a pressure transducer system for field‐installed tensiometers. The system consists of a pressure transducer with attached syringe needle and digital read‐out. The needle is inserted through the septum stopper which closes the upper end of the tensiometer. The pressure in the air below the septum stopper, in equilibrium with the water pressure, is read on the digital read‐out, which is calibrated in millibars. Upon withdrawal of the needle from the tensiometer, the septum stopper seals the tensiometer. The pressure transducer system is easy to use and requires little maintenance. Possible errors with the measurement system are discussed.
Calculation of Sorptivity from Constant‐Rate Rainfall Infiltration Measurement
Authors: Chong S.‐K.
Published: July 2010

The incipient ponding time equation developed by Kutilek and Parlange and Smith were rearranged and used for calculating sorptivity under constant‐rate rainfall conditions. The equations were tested using the field‐measured data obtained in Hawaii by Dangler et al. In the calculation, the incipient ponding time is assumed equal to the time of first appearance of runoff from the experimental plot. Additionally, the A value in the Philip two‐term infiltration equation is assumed to the Ksat/3. The results showed that the sorptivity values calculated from both equations have only a 1.22% difference. The accuracy of the calculated sorptivity was assessed by its use for predicting infiltration. In the comparison of cumulative infiltration, the correlation coefficient between measured and estimated values is > 0.9 with a mean error percentage of 20.09 and a median of 10.57%.
Use of Kinetics for the Study of Exchange Reactions in Soils
Authors: Harter Robert D. , Lehmann Robert G.
Published: July 2010

Since exchange reactions are exceedingly rapid and soil phases must be separated for analysis, kinetic methods are difficult to use for their characterization. However, these methods can be used to identify the extent and contribution of exchange reactions to the retention of adsorbate ions. The difference between theoretical start concentration and the intercept of a log‐normal plot of a kinetic reaction indicates the magnitude of the initial reaction(s), and a charge balance between ions lost from solution and exchange ions gained by solution will confirm whether the reaction is partly or entirely exchange. Using different initial concentrations, it is possible to construct isotherms for the exchange reaction.
Soil Acidity and Liming: I. Effect of the Extracting Solution Cation and pH on the Removal of Aluminum from Acid Soils
Authors: Oates Kenneth M. , Kamprath E. J.
Published: July 2010

Extractable Al is one criterion used for predicting the lime requirement of acid soils; therefore, a reliable measurement of extractable Al across a broad range of soil properties is desirable. The amount of Al removed from exchange sites may be affected by the exchanging cation and the extracting solution pH. This study was conducted to determine (i) the efficiency of Cu, La, and K, and (ii) the effect of solution pH in removing Al from soils with different organic matter content. Nine soils with an organic matter range of 0 to 58% were successively extracted seven times with Cu2+, La3+, and K+ nonbuffered chloride salt solutions and buffered acetate solutions at three pH values. With the buffered acetate solutions there was no cation effect in the removal of Al from mineral soils, but for organic soils (> 30% organic matter) there was an efficiency order with Cu > La > K. The nonbuffered chloride salts of La and K removed similar amounts of Al from mineral soils, but La removed more Al than did K from organic soils. The Al removed was linearly related to extractant solution pH for organic soils, but did not change appreciably for mineral soils when the solution pH was below pH 4.2.
Application of Phosphorus, Potassium, and Zinc to Corn Grown for Grain or Silage: Nutrient Concentration and Uptake
Authors: Rehm G. W. , Sorensen R. C. , Wiese R. A.
Published: July 2010

Although the nutrient composition of the ear leaf of corn (Zea mays L.) at tasseling or silking has been used widely in estimating the nutrient status of this crop, addition of a fertilizer to correct a discovered nutrient deficiency is very difficult, if not impossible, at this late stage of growth. Development of “critical” levels of plant nutrients in corn tissue at earlier stages of plant development should he more practical and useful. Twenty‐three treatment combinations of rates of P, K, and Zn from a 53 factorial arrangement were selected and applied annually to a sandy soil for irrigated corn that was grown for either silage or grain production from 1974 through 1978. Whole plant samples were collected when the corn was 40 to 60 cm tall. Ear leaf samples at silking and grain and whole plant samples at physiological maturity were collected. All samples were analyzed for P, K, and Zn.

The P concentration in whole plants at the early growth stage increased linearly as the rates of applied P and K were increased. In general, the P concentration of the ear leaf at silking increased linearly as the rate of applied P was increased for both systems of harvest. For the whole plant samples at the early growth stage, the critical P level was 0.220% P in the silage harvest system and 0.256% P in the grain harvest system. The critical levels for the ear leaf at silking were 0.220 and 0.225% P for the respective harvest systems. Phosphorus uptake by young plants, compared to the P concentration, was more closely associated with relative yield. When corn was harvested for silage, P uptake by young plants, rather than the P concentration of the ear leaf, was more closely associated with relative yield in 3 of the 5 years. Under the grain harvest system, P uptake by young plants was more closely associated with relative yield compared to the P concentration of the ear leaf tissue in all years.
Formation of Calcic and Argillic Horizons in Selected Soils of the Texas Coast Prairie
Authors: Sobecki T. M. , Wilding L. P.
Published: July 2010

In a previous paper the soil‐geomorphic relationship and microtopographic expression were described for Mollisols with calcic horizons and associated noncalcareous Alfisols of the Texas Coast Prairie. This paper describes the development of calcic and argillic horizons in the above soils. Microfabric of soil carbonates, carbonate clay depth functions, and acid residues from carbonate nodules confirm the pedogenic nature of carbonates in the Mollisols. Carbonate contents in the calcic horizons range up to 40%, with up to 50% of the total carbonates in the clay‐size fraction. Clay‐size carbonates have impregnated the soil matrix in the upper part of the main zone of carbonate accumulation, forming a dense K‐fabric. Such abundance and expression decrease with depth. Complex pedological features—fine‐grained calcans, crystallaria, and coarse‐grained carbonate glaebules—in lower horizons of the Mollisols suggest a fluctuating water table within 1 m. Carbonate‐free clay distribution data supported the microfabric analyses, which indicate the lack of argillic horizons in the Mollisols. Associated leached Alfisols have well‐expressed argillic horizons. Lateral redistribution of allogenic and authigenic carbonates from microdepressions to adjacent micro‐highs via saturated and unsaturated moisture flow is proposed to explain carbonate distribution in some landscapes of the Texas Coast Prairie. A weathering origin for the carbonates was discounted because weatherable minerals in parent sediments were insufficient to account for the 550 to 750 kg/m2 of carbonate in the calcic horizons. Carbonates inherited with fluviatile‐deltaic sediments are considered the single most plausible carbonate source for these soils.
Bromide and Phosphate in Runoff Water from Shaped and Cloddy Soil Surfaces
Authors: Ahuja L. R. , Lehman O. R. , Sharpley A. N.
Published: July 2010

Effects of soil surface shaping and clods on the release of applied bromide and phosphate to runoff were investigated experimentally with small pervious boxes and simulated rainfall. The soil material used for the surface shaping experiment was a sample of Ruston loam subsoil, < 4 mm in size. Phosphate as Ca (H2PO4)2 · H2O was mixed with the dry soil (0.008% P by weight) before packing in boxes. Triangular ridges, 3.5 cm in width and 1.7 cm in height, were made either along the slope or across the slope of the soil surfaces. Both types of ridges exposed about 12% more surface area than the control soil boxes without ridges. The soil boxes were wetted with a KBr solution (4000 ppm Br) before application of rainfall. Average Br concentration of runoff from a 1‐h, 6.8 cm/h, rainfall in both lengthwise‐ and cross‐ridged boxes was nearly four times that of the control boxes. The ridging also increased dissolved and reactive P concentration of runoff, but only by about 15%. When the upper 2.5 cm of the packed soil consisted of 4‐ to 20‐mm clods, the average Br concentration of runoff was nearly 48 times that of the control, even though the infiltration was 2.5 times more. Increasing the thickness of the surface cloddy layer to 5.0 cm delayed the start of runoff considerably, and yet the Br concentrations of runoff were higher then those with a 2.5‐cm layer of clods. In another soil (Parsons clay subsoil material), having more stable clods than Ruston loam, the Br concentrations of runoff were two orders of magnitude greater than control.