bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Field Variability in Soil Hydraulic Properties on Solutions of Unsaturated Water and Salt Flows
Authors: Russo David , Bresler Eshel
Published: July 2010

Using actual field variability data and the stochastic approach, effects of spatial variability of soil hydraulic properties on the predictions of water and salt flow distributions, and of correlation structure, are evaluated. The governing water and salt flow equations are solved numerically using actual field data of soil hydraulic conductivity and differential water capacity. These data, which had been obtained previously from measurements made in 30 different locations in a field, were the same as those obtained from a Monte‐Carlo simulation that considered the correlations between the parameters of the hydraulic functions. Simulated values of pressure head (h), water fluxes (q), wetting front positions (Zf), and solute concentration (c) for each of the 30 locations in the field were used to estimate distribution types (normal or log‐normal) and its moments, for h, q, Zf, and c. The two‐point autocorrelation functions of pressure head, wetting front, and solute concentration have been calculated and used to estimate the integral scales of h, Zf, and c. Distances in the field in which the horizontal flow components were negligibly small compared with the vertical flow components were calculated and found to be in the order of 10 cm and larger. Field dispersion of solutes was calculated from the simulated salt distribution results. Values of field scale dispersivity were estimated to be larger than the pore scale dispersivity and to increase with soil depth. An “equivalent” uniform porous medium, which was defined at the soil surface, exists for large infiltration time when a unit hydraulic gradient may be assumed.
Areal Variation and Chemical Modification of Weathered Shale Infiltration Characteristics
Authors: Luxmoore R. J. , Spalding B. P. , Munro I. M.
Published: July 2010

Spatial variability of infiltration into a weathered shale subsoil were evaluated at a site proximal to one used for shallow land burial of low‐level radioactive waste at Oak Ridge National Laboratory. Double‐ring infiltrometers were installed at 48 locations on a 2‐ by 2‐m grid after the removal of 1 to 2 m of soil (Litz‐Sequoia association, Typic Hapludults). Infiltration rates were measured before and during the 0‐ to 20‐ and 239‐ to 259‐day periods following treatment with solutions of NaOH, KOH, NaF, NaAlO2, and Na2SiO3 at rates of 151 equivalents/m2. None of these chemical treatments significantly altered infiltration rate, indicating that chemical modification of soil exchange properties may be achieved without inducing hydrologic disturbance in these subsoils. A semivariogram analysis of infiltration data showed that areal variability was random; any spatial patterning must therefore occur at a smaller scale than 2 m. The frequency distribution of infiltration rate fitted a lognormal model with a geometric mean of 2 cm per day and a coefficient of variation of 130%.
Super Slurper Effects on Crust Strength, Water Retention, and Water Infiltration of Soils
Authors: Hemyari Parichehr , Nofziger D. L.
Published: July 2010

The effect of hydrolyzed starch polyacrylonitrile graft copolymer, commonly called “super slurper,” at rates of 0.0, 0.025, 0.05, 0.1, 0.2, and 0.4% by weight on the crust strength, water retention, and infiltration of selected soils was determined. The strengths of simulated crusts were measured for all the treatments. Infiltration rates were measured in the laboratory for untreated soils and soils treated with 0.4% super slurper. Water retentions were measured for all treatments by use of pressure plate and pressure membrane apparati.

Super slurper decreased crust strength and infiltration and increased water retention. The crust strengths of a sandy loam, a loamy sand, and a clay loam soil were reduced 84, 75, and 54%, respectively, by the addition of 0.4% super slurper. Infiltration rates were also reduced. Sorptivities for a sandy loam, clay loam, and loamy sand soil, treated with 0.4% super slurper, were reduced 38, 18, and 11%, respectively. Loamy sand and sandy loam soils treated with super slurper retained more water than the untreated soils. Super slurper had little effect on water retention in the clay loam soil.
Ammonia Losses from Surface‐Applied Urea and Ammonium Fertilizers as Influenced by Rate of Soluble Calcium
Authors: Fenn L. B. , Matocha J. E. , Wu E.
Published: July 2010

Previous research has shown that applying large amounts of soluble Ca with urea and NH4 fertilizers depressed ammonia (NH3) losses extensively. This paper reports effects of varying amounts of Ca on reduction of this loss. Ammonia loss was progressively less with increasing Ca/N ratios. In the greenhouse, a Ca/urea‐N equivalent ratio of 0.25 reduced NH3 losses to 11% of applied N. In the laboratory, this ratio reduced NH3‐N losses to 42% of applied N; without Ca, N losses were 75%.

Soluble Ca was effective in reducing NH3 losses from urea when surface applied to both acid and calcareous soils. Increased acidity from the application of soluble Ca salts on acid soils reduced the amount required to reduce NH3 losses. Soluble Ca applied with (NH4)2SO4 (AS) and NH4NO3 (AN) also reduces NH3 losses from calcareous soils. Reduction of NH3 losses from AN was due solely to lowered soil pH values. However, reduction of NH3 loss from urea and AS was possibly due both to CaCO3 precipitation and soil pH depression.
Corn and Cotton Root Growth in Response to Soil Impedance and Water Potential
Authors: Bar‐Yosef B. , Lambert J. R.
Published: July 2010

The equation dL/dt = C · L, which relates root elongation rate (dL/dt) to root length capable of growth (L), was tested on split root systems of corn and cotton under controlled laboratory conditions. Evidence is presented for the validity of the equation for the various parts of the root system when the growth period was up to 50 days. While the equation held, C, the specific root growth rate, was affected by soil impedance and water potential (ψ), varying between 0.02 and 0.15 per day for the cotton and between 0.03 and 0.28 per day for corn. When the various parts of the root system were under the same soil density (d) and different ψ, C varied with ψ according to a bell‐shaped relationship. When d was different, C decreased monotonically with increasing d values.

The flux of water uptake by cotton and corn had a peak at a matric potential between −0.13 and −0.20 bar and was about 0.02 and 0.03 ml cm−1 root day−1, respectively.
Predicting Nitrogen Mineralization in Chaparral Soils
Authors: Marion G. M. , Kummerow J. , Miller P. C.
Published: July 2010

Nitrogen mineralization is a key process in supplying N for plant growth in terrestrial ecosystems. The objectives of this study were to evaluate N mineralization in chaparral soils and to evaluate an N mineralization simulation model.

The chaparral soils contained 0.4 to 54 ppm potentially mineralizable N, which is considerably less than typical agricultural soils (generally > 100 ppm potentially mineralizable N). The quality of the organic matter with respect to N mineralization (N mineralization/total N) was low for chaparral soils relative to agricultural soils; this may be due to soil toxins (allelopathic compounds) or a highly resistant organic matter in chaparral soils. The potentially mineralizable N was highly correlated to total soil N (r2 = 0.82) but poorly correlated to C/N ratio (r2 = 0.07).

The simulation model is based on laboratory soil N mineralization curves developed from long‐term soil incubations with adjustments for field soil temperature and moisture. Because of temperature and moisture limitations, simulated field N mineralization rates were only 3 to 27% of optimal rates; environment is as important as substrate quantity and quality in estimating field N mineralization. The simulation model estimates of annual N mineralization in two chaparral stands agreed to within ± 10% with independent estimates of N mineralization developed by solving a system N balance equation. The proposed N mineralization model should be useful for estimating annual soil N availability, which is an important step in developing N fertilizer prescriptions for intensively managed lands.
Selection of Variables to be Used in Statistical Analysis of Field‐Measured Soil Water Content
Authors: Cassel D. K. , Nelson L. A.
Published: July 2010

Interpretations and inferences drawn from soil water content measurements collected in agronomic field studies are dependent upon the particular method of data analysis. The purpose of this study was to examine alternative approaches for analyzing soil water content data measured by neutron attenuation. Data from tillage studies conducted at two locations on the Atlantic Coastal Plain were used to demonstrate and compare the methods of data analysis. Analysis of variance was performed on the field‐measured data (total soil water content measured by neutron attenuation) and on either six or eight relevant soil water variables derived from them. Derived variables included (i) the net change in total water content between successive measurement dates; (ii) a transformed soil water content; and (iii) six variables derived using bulk density and 15 bar soil water contents to provide estimates of plant‐available water.

The total soil water content variable has a coefficient of variation (C.V.) of about 12%, and the cost of collecting data and analyzing it is relatively low. Differences in total water content between successive dates have C.V.s generally about 100%. Requiring the measurement of the 15 bar percentage and bulk density values, which allows plant‐available water to be calculated, increases the costs of data collection. Incorporation of this information into the water variables results in data which have a C.V. of about 30%. In field experiments, the investigator should select the appropriate soil water variable only after examining the relative costs, expected C.V.s, and the anticipated use of the data.
The Swelling of Clay: III. Dissociation of Exchangeable Cations
Authors: Low Philip F.
Published: July 2010

Values of ζ, the zeta potential, were determined for 34 different Namontmorillonites by electrophoresis. These values were used in the equations of diffuse double‐layer theory to obtain the corresponding values of σ', the surface charge density at the outer limit of the Stern layer. In addition, data on cation exchange capacities and specific surface areas were used to calculate the corresponding values of σ, the surface charge density at the particle surface. From the respective values of σ′/σ, it was found that < 2% of the exchangeable cations were dissociated. This low degree of dissociation was confirmed by using double‐layer theory and experimental data from another study. Then a representative value of σ′ was used in the appropriate equations to obtain data from which a theoretical curve of the swelling pressure, Π, vs. interlayer distance, λ, was constructed. Comparison of this curve with the experimental curve of Π vs. λ indicated that double‐layer repulsion makes a relatively small contribution to Π. The necessary conclusion is that Π develops primarily because of surface‐water interaction.
Transport of Sediment Nitrogen and Phosphorus in Runoff through Cornstalk Residue Strips
Authors: Alberts E. E. , Neibling W. H. , Moldenhauer W. C.
Published: July 2010

A rainfall simulator study was conducted on a Sidell silt loam (Typic Arguidolls, fine‐silty, mixed, mesic) in northwest‐central Indiana to evaluate the effectiveness of different lengths and percentage covers of cornstalk residue strips in reducing total nitrogen and available phosphorus discharges associated with the sediment. A 2.7‐m long residue strip with 50% surface cover reduced nutrient discharges by about 70% when the nutrient loads entering and leaving the residue strip were compared. Reductions in sediment and nutrient discharges with increasing length and percentage cover of the residue strips were almost proportional.

The sediment was separated by sieving and gravity sedimentation into 10 size fractions ranging from > 2 to <0.002 mm in diam. About 50% of the sediment entering the residue strips was composed of particles >0.05 mm. The 2.7‐m long residue strip with 50% surface cover filtered out most of the particles >0.05 mm. As a result, 85% of the sediment leaving this residue strip was in the <0.035‐mm size fractions.

Nutrient concentrations of the fractions >0.21 mm entering the residue strips were higher than those concentrations of the 0.05‐ to 0.01‐mm fractions entering the strips. Nutrient concentrations of the fractions <0.21 mm and >0.01 mm increased as the sediment moved through the residue strips, with the effect being related to residue length and percentage cover. Residue reduced the transport capacity of runoff below its sediment load, which caused the denser particies within these size fractions to be deposited. The less dense particles that were not deposited were composed of a greater proportion of small silt and clay primary particles, which increased the nutrient concentrations.
Problems in Direct Steam Distillation of Soil for Mineral Nitrogen Determination Due to Carbonates
Authors: Clausen C. R. , Russelle M. P. , Flowerday A. D. , Olson R. A.
Published: July 2010

A follow‐up study to one on Mg2+ interference in NO3‐ measurement by direct steam distillation of soil revealed an added problem of low recovery with the method when used on calcareous soils. The CO32‐ ion was presumed responsible, prompting the current investigation on the effect of soil CO32‐ and Mg2+ levels on NH4+ and NO3‐ determination by the method.

Four series of CO32‐ amendments to distillation flasks were made to simulate soil levels of (i) low solubility CO32‐ [CaCO3 and 3 MgCO3·Mg(OH)2], (ii) soluble CO32‐ (K2CO3), (iii) Mg2+ and soluble CO32‐ combinations, and (iv) soluble CO32‐ in a Mg2+‐free system. All received 40 ppm N as NH4NO3 with NH4+ and NO3‐ measured by prescribed distillation procedures. The results show that Mg2+ and CO32‐ Independently suppress recovery of NO3‐ and Interact to interfere with both NH4+ and NO3‐ determination in direct distillation of calcareous soils.
Determination of Sorptivity based on In‐situ Soil Water Redistribution Measurements
Authors: Chong S. K. , Green R. E. , Ahuja L. R.
Published: July 2010

A simple, physically based algebraic equation is derived for calculating sorptivity as a function of antecedent soil water content. The wetting front matric pressure head, Hf, determined from the field profile redistribution data in a previous study, is utilized in an equation which gives sorptivity, S, as a function of fillable porosity, i.e., the difference between the satiated and antecedent soil water content, (θs − θi), satiated hydraulic conductivity, Ks, and wetting front matric pressure head, Hf, namely, S2 = −2(θs − θi)KsHf. The final equation gives S explicitly as a function of antecedent water content, θi, with θs and Ks being constants for a given soil. The calculated sorptivity is assessed by its use in the Talsma‐Parlange infiltration equation and subsequent comparison of predicted and measured infiltration. The method was tested on seven different sites with 14 infiltration measurements on Oxisol soils of Hawaii. The percentage error between predicted and measured cumulative infiltration ranged from 2.1% to 51.9%, with an average error of 21.8% for the 14 comparisons.
Infiltration Prediction based on Estimation of Green‐Ampt Wetting Front Pressure Head from Measurements of Soil Water Redistribution
Authors: Chong S. K. , Green R. E. , Ahuja L. R.
Published: July 2010

A simple, physically based algebraic equation was derived to calculate the wetting front matric pressure head, Hf, in the Green‐Ampt equation of infiltration. The derivation of the equation involved combining the simple hydraulic conductivity function with the wetting front matric pressure head function proposed by R. G. Mein and C. L. Larson (1971). The parameters in the derived equation were determined from fitting a power function to the experimental data of soil water content and soil water pressure head vs. elapsed time obtained during the post‐infiltration redistribution period. In the derived equation, Hf is expressed as a function of antecedent soil water content. At low initial water contents, the equation shows that Hf is essentially a constant. Evaluation of the calculated Hf values was accomplished by utilizing Hf in the Green‐Ampt equation to predict infiltration at seven field sites for soils at initial water contents below field capacity. Predicted cumulative infiltration was compared with infiltration measured with a double‐ring infiltrometer. The resulting Green‐Ampt predictions were accurate for initially dry soils, with a correlation value of r = 0.94 and a relative error of 12.1%.
Dissolution Rate of EDTA‐extractable Phosphate from Soils
Authors: Onken A. B. , Matheson R. L.
Published: July 2010

The kinetics of phosphorus (P) dissolution in EDTA (ethylenedi‐aminetetraacetic acid) solution were investigated for several soils for the purpose of determining if the dissolution rate constants could be related to crop response to applied P. Eight kinetic models were evaluated using coefficients of determination (R2) and standard errors of estimate (SE). Additionally, the effects of temperature and soil‐solution ratio on P dissolution in the EDTA solution were determined.

Relatively high values of R2 and low values of SE indicated that P dissolution in EDTA solution for the soils used was most often best described by the two‐constant rate equation, the Elovich‐type equation, and the differential rate equation. None of the models best described the dissolution for all soils. Using R2 and SE for evaluation, the best relationships found between dissolution rate constants and yield response to applied P were for the two‐constant rate equation (R2 = 0.97; SE = 2.58) and the differential rate equation (R2 = 0.95; SE = 2.69). Soil‐solution ratio affected the values of dissolution rate constants, with those obtained from the differential rate equation most sensitive. The Arrhenius equation described reasonably well the effect of temperature on values of the dissolution rate constants.
Transformations of Amide Nitrogen in Soils
Authors: Frankenberger W. T. , Tabatabai M. A.
Published: July 2010

Amides added to soils are hydrolyzed to ammonium (NH+4) and their corresponding carboxylic acids. Studies of transformations of amide‐N in soils deserve attention because amides have potential as nitrogen (N) fertilizers. In this work, the transformations of amide‐N (200 µg/g of soil) were studied in field‐moist soils incubated under aerobic conditions at 30°C for 14 days. The recovery of inorganic N (as NH3, NH4+, NO2‐, and NO3‐) produced from 25 amides or their derivatives was determined and compared with those obtained with (NH4)2SO4 and urea added to five soils. Results showed that with the exception of cyanamide, dicyandiamide, benzenesulfonamide, and sulfanilamide, which resisted decomposition, all other amides were readily hydrolyzed in the five soils used. With most of the amides studied, the inorganic N produced was accumulated as NO3‐. The recovery of nitrogen as NO3‐ from each of five soils treated with urea, acetamide, propionamide, 2‐cyanoacetamide, n‐butyramide, oxamide, or DL‐lactamide was <50% of the N added. The average percentage of NH4+‐N recovered from the soils used exceeded 40% of the total inorganic N produced when thioacetamide, fluoroacetamide, and 2‐chloroacetamide were added to soils. With one sandy soil, the addition of urea, formamide, N‐benzylformamide, and p‐nitrobenzamide resulted in accumulation of NO2‐, ranging from 5 to 21% of the inorganic N recovered. Appreciable amounts of NH3 were volatilized when formamide, acrylamide, 2‐cyanoacetamide, p‐nitrobenzamide, and urea were applied to soils, especially from the sandy soil. The average recovery of amide‐N as inorganic N from the five soils used ranged from 4% with dicyandiamide to 100% with formamide.
Adsorption and Reduction in Bioactivity of Polychlorinated Biphenyl (Aroclor 1254) to Redroot Pigweed by Soil Organic Matter and Montmorillonite Clay
Authors: Strek H. J. , Weber J. B.
Published: July 2010

Aroclor 1254 polychlorinated biphenyl (PCB) applied to untreated (1.4% organic matter) and H2O2‐treated (0.2% organic matter) Lakeland sand at rates of 0, 50, 100, 150, and 200 ppm caused significant reductions in redroot pigweed (Amaranthus retroflexus L.) growth at the high rates of application. Polychlorinated biphenyl decreased plant height in the H2O2‐treated soil much more than in the untreated soil. A greater decrease in dry weight also resulted in the H2O2‐treated soil, but only at the 200 ppm rate. In one study, soil was amended with montmorillonite clay and organic matter (peaty muck) at rates of 0, 2.5, 5.0, and 10.0% by weight and treated with 200 ppm PCB. The organic matter proved to be much more effective than montmorillonite in reducing PCB toxicity to pigweed at the lower rates of addition (2.5 and 5.0%), but no differences were noted between the two adsorbents at the 10% rate. Adsorption of 14C‐labeled PCB closely resembling Aroclor 1254 by the untreated and H2O2‐treated soils, montmorillonite clay, organic matter, and activated carbon was measured. The order of highest to lowest adsorption was as follows: activated carbon ≫ organic matter > montmorillonite clay > Lakeland sand > H2O2‐treated Lakeland sand. These experiments suggest that organic matter content of a soil, and clay content to a lesser extent, are involved in reducing the availability of soil‐applied PCB to pigweed. Differences in reduction of PCB toxicity to pigweed are explained by differences in adsorption by the adsorbents.
Phosphate Rock Dissolution and Availability in Cerrado Soils as Affected by Phosphorus Sorption Capacity
Authors: Smyth T. J. , Sanchez P. A.
Published: July 2010

The reactivities of two phosphate rocks (PR), North Carolina and Patos de Minas, were compared in seven acid soils from the Cerrado of Brazil during 158 days of laboratory incubation. Four soils are classified as Typic Acrustox and the remaining three Typic Haplustox, Aeric Tropaquept, and Ustoxic Quartzipsamment. Dissolution was accompanied by measurements of resin‐ and Olsen‐extractable P and exchangeable Ca. North Carolina PR was more reactive than Patos de Minas PR. Changes in Olsen‐P were more indicative of the PR dissolution process than resin‐P. Maximum PR reactivity, as measured by increases in calcium, occurred in those soils maintaining the lowest amounts of Olsen‐extractable P. Such soils have the highest clay and free Fe2O3 contents and, consequently, the highest P sorption capacities. Maintenance of low levels of solution P is considered an important driving force for PR dissolution in these acid soils. Consequently, high P sorption capacity favored the dissolution of PR in such soils. The “i” modifier in the Fertility Capability Classification system separated those soils in which phosphate rocks reacted rapidly from those that reacted at a slow rate.
Clay Minerals in Northern Plains Coal Overburden as Measured by X‐ray Diffraction
Authors: Klages M. G. , Hopper R. W.
Published: July 2010

Mathematical models were tested for changing x‐ray diffraction data to percentages of clay minerals in coal overburden. Various factors for adjusting peak areas were tested on 50 eastern Montana samples that contained smectite, illite, and kaolinite, with lesser amounts of other minerals. Cation exchange capacities (CEC) of the clays were estimated from the calculated mineral percentages and correlated against measured CEC. The best model gave an r2 of 0.89. It was used for estimating clay mineralogy at six mine sites in the Northern Great Plains. Average mineral contents in the surface 8 to 38 m of five of seven drill holes in the Montana‐Wyoming border area were 40% smectite, with 20% each of illite and kaolinite. Clays from greater depths in the same area had no smectite and an average of 50% each of illite and kaolinite. All samples from a mine in central North Dakota were high in swelling clay, with an average of 60% smectite and 10% vermiculite. Samples from four holes at a mine in eastern Wyoming were all high in kaolinite, having an average of 50% with 30% illite and 10% interstratified smectite‐vermiculite.
Diffusion of Potassium, Calcium, and Magnesium in Bozeman Silt Loam as Influenced by Temperature and Moisture
Authors: Schaff B. E. , Skogley E. O.
Published: July 2010

A laboratory experiment was conducted to study the influence of temperature and moisture on the diffusion of potassium (K), calcium (Ca), and magnesium (Mg) to an H‐saturated resin sink in Bozeman silt loam with bulk density of 1.45 g/cm3. Diffusion of K and Ca to the resin sink was significantly (P < 0.005) influenced by temperature (5, 15, and 30°C), but that of Mg was not. Soil moisture (10, 17, and 28%) significantly (P < 0.005) influenced the diffusion of all three cations. The temperature by soil moisture interaction was significant for all three cations. The concentrations of extractable K, Ca, and Mg in four concentric soil layers, each about 1 mm in thickness, around the resin sink also were measured during the 96‐hour diffusion period. The concentration of each cation in each layer was significantly influenced by temperature and moisture.
Availability and Extractability of Phosphorus from Soils Having High Residual Phosphorus
Authors: Adepoju A. Y. , Pratt P. F. , Mattigod S. V.
Published: July 2010

Surface soil materials from the 0‐ to 15‐cm depth of 12 sites were cropped in the greenhouse to determine quantities of phosphorus (P) removed in harvested forage and to correlate chemical soil tests with P removal by crops. Soil samples taken before and after cropping were analyzed for P extracted by NaHCO3 and by an anion‐exchange resin (AER). Quantities of P extracted by NaHCO3 and by AER before cropping were significantly correlated with total P removed by cropping, with the NaHCO3‐extracted P producing the higher correlation coefficients. However, in terms of relationships of P removed by cropping with extractable P, the soils separated into two groups. The first group, characterized by relatively high ratios of P removal in crops to extractable P, particularly for soil samples taken after cropping, tended to have relatively high pH, high soluble Ca, and clayey textures. The second group, having lower ratios of P removal to extractable P, tended to have neutral pH values and relatively low soluble Ca and sandy textures. The data suggest that the estimation of quantities of available P from soil analysis might be highly dependent on soil characteristics and the nature of the P compounds that have accumulated.
A Theoretical Study of the Inclusion of Dispersion in Boundary Conditions and Transport Equations for Zero‐order Kinetics
Authors: Parlange J.‐Y. , Starr J. L. , Barry D. A. , Braddock R. D.
Published: July 2010

The transport of a solute in a soil column is considered for zero‐order kinetics. The visible displacement of the solute is affected by dispersion. The dispersion coefficient enters both the transport equation and the boundary condition. It is shown that the latter is the most important effect and a simple equation is proposed to describe solute transport, which takes into account the influence of dispersion in the boundary condition, but not in the transport equation. Validity and limitations of this equation are discussed in some detail by comparison with the complex but exact solution for zero‐order kinetics.
Substitution of Ammonium and Potassium for Added Calcium in Reduction of Ammonia Loss from Surface‐applied Urea
Authors: Fenn L. B. , Matocha J. E. , Wu E.
Published: July 2010

Ammonia (NH3) volatilization loss from surface application of urea must be reduced if urea is to gain further acceptance for use in pastures and on other non‐ or low‐tillage systems which do not permit soil incorporation. The method used to reduce NH3 loss should not increase costs of the N fertilizer significantly. Preferably, the material used should itself be a fertilizer nutrient.

The nitrate salts of the monovalent cations NH+4, K+, and Na+ were tested as substitutes for chloride or nitrate salts of Ca2+ to depress NH3 losses when mixed with surface‐applied urea. Ammonia losses were measured from soils with different cation exchange capacities (CEC) in the laboratory, with residual N quantified by growing sudangrass on the variously treated soils under greenhouse conditions.

Laboratory and/or greenhouse data indicate that NH3 loss from surface‐applied urea was most effectively reduced by Ca salts. Substitution of K, Na, and NH4 salts for Ca salts was increasingly effective as soil CEC increased. Monovalent salts were effective in reducing NH3 losses if the soil had exchangeable Ca2+ + Mg2+. In sand, however, monovalent salts did not reduce NH3 losses. The order of effectiveness on nonsandy soils was Na+ = K+ > NH+4 in reducing NH3 loss.

Potassium as KNO3 or KCl can be used effectively to partially replace (Ca + Mg) nitrate or chloride salts with urea to reduce NH3 losses. Ammonium nitrate was ineffective in reducing NH3 losses except where high N application rates were used or where little or no soil CEC existed. The efficacy of NH4NO3 seemed to be due to its acidic nature more than displacement of exchangeable Ca2+ + Mg2+.
Field Vs. Laboratory Determined Hydraulic Conductivities of Some Slowly Permeable Horizons
Authors: Watts F. C. , Huckle H. F. , Paetzold R. F.
Published: July 2010

Saturated hydraulic conductivities K(µm/s) of soils of spodic and argillic horizons were measured in several Florida soils. The soils were Haplaquods, Haplohumods, Glossaqualfs, and Argiaquolls. Two methods of measurement were compared. The core method consistently gave larger hydraulic conductivity values than the piezometer method. The lowest K(µm/s) rates were in argillic horizons. The permeability classification of most soils studied depended upon the measurement method used.
Salt Status of Glacial Till Soils of North‐Central Montana as Affected by the Crop‐Fallow System of Dryland Farming
Authors: Ferguson Hayden , Bateridge Tom
Published: July 2010

Paired samples from adjacent dry‐farmed and native grassland areas of glacial till soils of north‐central Montana were analyzed for soluble salts to determine if crop‐fallow farming has caused increased salt leaching. The results indicate that approximately 50 years of crop‐fallow farming has significantly reduced the soluble salt content of some soils. From an edaphological standpoint the salt reduction in the root zone is beneficial. However, up to 90 t/ha of salt have been moved in the soil toward (to) the groundwater table; this is the source of the salts causing groundwater salinization and saline seeps.
Perched Water Tables on Hillsides in Western Oregon: II. Preferential Downslope Movement of Water and Anions
Authors: Hammermeister D. P. , Kling G. F. , Vomocil J. A.
Published: July 2010

Perched water tables on hillsides in western Oregon potentially provide a means by which pollutants from agricultural and domestic sources may enter surface waters and consequently degrade the quality of these waters. This paper reports the results of experiments which were carried out to investigate the flow of solutes and water from buried line sources in and above perched water tables on three different hillsides in western Oregon. In the saturated soil and rock mantles of two hillsides, evidence suggests that water and solutes flow preferentially through large continuous voids. The evidence includes the very high maximun rate of anion movement downslope, the failure of pore velocities calculated from Darcy's Law to predict the rate and direction of anion movement, the short time before high levels of anions are detected downslope, and the spatial variability in the maximum rates of anion movement over the depth and width of sites. On the third hillside, tracer anion movement and soil water pressure measurements indicate that preferential flow occurs through large continuous pores during heavy rainfall while the surrounding soil and rock mantle remains unsaturated. Finally, experiments with Rodamine WT dye show that a variety of continuous voids of different origins and sizes conduct water and solutes preferentially in the soil and upper regions of rock on these hillsides.
Identification of Ferrihydrite in Soils by Dissolution Kinetics, Differential X‐ray Diffraction, and Mössbauer Spectroscopy
Authors: Schwertmann U. , Schulze D. G. , Murad E.
Published: July 2010

Ferrihydrite is a poorly crystalline, natural Fe3+ oxide which occurs in ochreous spring precipitates and hydromorphic soils of humid temperate climates. The identification of ferrihydrite in soils is complicated by its association with goethite, quartz, and layer silicates.

The following criteria were used to identify ferrihydrite in Fe‐oxide accumulations from soils: high solubility in acid oxalate, five to six broad x‐ray diffraction lines, and the existence of a typical magnetic hyperfine field distribution at 4K in Mössbauer spectra rather than a discrete field value. Identification of low concentrations of ferrihydrite (≲ 20% oxalate‐soluble Fe) by x‐ray diffraction was made possible by subtracting diffraction data obtained after oxalate treatment from data obtained before such a treatment (differential XRD). Oxalate treatment preferentially dissolves ferrihydrite over goethite. This led to an increase in the quadrupole splitting observed in Mössbauer spectra from ∼0.10 to ∼0.23 mm s−1, resulted in a significantly narrower field distribution, and intensified the goethite DTA peak.
Construction of Soil Thermocouples for the Novice
Authors: Culik M. N. , Doran J. W. , Richards K. A.
Published: July 2010

Soil temperatures affect the physical, chemical, and biological properties of most soils. Consequently, measurement of soil temperatures is important to understanding the effects of management practices that alter soil temperatures on the soil ecosystem. Thermocouples are often used for measurement of soil temperature where large amounts of data are collected and the use of other temperature‐sensing devices is either too expensive or impractical. However, information on the construction and design of soil thermocouples is often difficult to assemble. Procedures and recommendations are given in this note which will aid the novice in assembling materials, constructing, and connecting thermocouples for measurement of soil temperatures.
Characterization of Copper Availability and Corn Seedling Growth by a DTPA Soil Test
Authors: Dragun James , Baker Dale E.
Published: July 2010

A greenhouse experiment was conducted to determine (i) the physical and/or chemical properties of soils which control Cu availability; (ii) if 0.0004M DTPA (diethylenetriaminepentaacetic acid) effects a small exchange of Cu in soils; and (iii) if pCu, estimated by iterative computer calculations based on DTPA stability constants, reflects the availability of Cu in soils. The growth and Cu accumulation of corn seedlings were studied using 16 northeastern United States soils, each treated to contain 125, 250, and 500 ppm total Cu. Soil pH, percent organic matter, cation exchange capacity (CEC), percent clay, percent silt, percent sand, percent Na2O, and DTPA‐extractable Cu were measured in order to relate soil properties to Cu availability and seedling growth.

The soil factors affecting the mean soil Cu activity coefficient and therefore controlling Cu availability were pH and the silt fractions of Na‐bearing minerals. The DTPA at 0.0004M with a 1:10 soil‐to‐solution ratio did not effect a small exchange for Cu. For most soils, the DTPA extracted the labile Cu. Finally, when medium and fine‐textured soils are tested by the Baker DTPA soil test, resulting pCu values of approximately 11.9 and less should in general indicate high soil Cu availability (i.e., soil Cu availability ≧ 0.16 ppm) and reduced corn growth.
Influence of Solution Composition on Sorption of Zinc by Soils
Authors: Elrashidi M. A. , O'Connor G. A.
Published: July 2010

The effect of soil solution composition on Zn sorption was investigated in nine soils of varying physical and chemical properties. Most of Zn applied in 0.01 N CaCl2 solution was strongly sorbed by the soils and desorption by 0.01 N CaCl2 solution was negligible even after five desorption cycles. At initial Zn solution concentrations of ⩽ 10 ppm, sorption could be described by the Freundlich sorption isotherm equation. Deviations from this equation were observed at higher concentrations, suggesting the presence of more than one type of site or mechanism for Zn sorption in the soils.

The effects of anion species (Cl‐, NO‐3, and SO2‐4) and ionic strength on Zn sorption were examined at anion concentrations of 0.005, 0.02, and 0.1M. Complexation of Zn (as ZnSO04) in the SO2‐4 system was higher than in either the NO‐3 [Zn(NO3)+] or Cl‐ [Zn(Cl)+] system. However, under the experimental conditions examined, neither ionic strength nor anion complex formation significantly affected Zn sorption.

The presence of EDTA (Ethylenediaminetetraacetic acid) in the soil suspension significantly decreased Zn sorption by the three soils investigated. Only a slight difference in Zn sorption was observed whether EDTA was added to the (Zn containing) soil solution before or after contact with soil.

The influence of Ni and Cu on Zn sorption was significant only when metal concentration in the soil solution was in excess of the sorbing capacity of the soil. In this case, Cu was more effective than Ni in decreasing Zn sorption.
Influence of Salinity on Soil Enzyme Activities
Authors: Frankenberger W. T. , Bingham F. T.
Published: July 2010

Efforts were made to assess the levels of soil enzyme activities that have a specific role in the N, C, P, and S cycles of saline soils. Fieldmoist soil samples were treated with four rates of CaCl2, NaCl, and Na2SO4 solutions applied to produce electrical conductivity readings of saturation extracts (ECe) ranging up to 22 mmho/cm. The range of ECe values included threshold salinity levels associated with reduced yields of agronomic crops. After 7 d of equilibration, the following soil enzymes were assayed: amidase, urease, acid phosphatase, alkaline phosphatase, phosphodiesterase, inorganic pyrophosphatase, arylsulfatase, rhodanese, α‐glucosidase, α‐galactosidase, dehydrogenase, and catalase.

Soil enzyme activities decreased with increasing ECe; however, the degree of inhibition varied among the enzymes assayed and the nature and amounts of salts added. Dehydrogenase activity was severely inhibited by salinity, whereas, the hydrolases showed a much lesser degree of inhibition. Generally, the inhibition of soil enzyme activities by the salt solutions decreased in the following order when compared at the same ECe level: NaCl > CaCl2 > Na2SO4. Reduced enzyme activities in saline soils may be due to the osmotic desiccation of microbial cells releasing intracellular enzymes which become vulnerable to attack by soil proteases, a “salting‐out” effect modifying the ionic conformation of the active site of the enzyme‐protein, and specific ion toxicities causing nutritional imbalances for microbial growth and subsequent enzyme synthesis.
Graphical Diagnoses of Lodgepole Pine Response to Fertilization
Authors: Weetman G. F. , Fournier R.
Published: July 2010

A combined use was made of “mini” plots and graphical analysis of shifts in nutrient concentration, unit fascicle weight, and nutrient content for needles grown in the first year following spring fertilizer application. Nitrogen, phosphorus, and potassium were applied, in factorial design with five replications, to 17 precommercially thinned lodgepole pine stands in the interior of British Columbia.

The use of one bulked foliage sample from two sample trees per plot was sensitive to treatment differences. Phosphorous, potassium, calcium, and magnesium deficiencies were generally not diagnosed either with or without N additions. Mean fascicle weight increase for all trials was 20% for three N levels, suggesting a strong probability of appreciable 5‐year volume increases. Response to N additions was variable and could not be readily explained by site conditions. Non‐responsive stands showed luxury N uptake and suggested the presence of non‐nutritional growth constraints. Additional screening trials are recommended to sample the wide range of sites and climates. The technique was found to be time and cost efficient with the advantage of producing both response data and nutrient status diagnosis within 1 year of fertilizer application.
Modified Soxhlet Extractor for Pedologic Studies
Authors: Sobek A. A. , Bambenek M. A. , Meyer D.
Published: July 2010

The soxhlet apparatus has been used in the laboratory to stimulate geochemical weathering; however, the high extraction temperatures required in the soxhlet do not represent a realistic simulation of the weathering environment. A modified design of the original soxhlet did not eliminate the problems of extraction temperature or inaccurate volumes of solvent passing through the sample. These problems were solved by moving the extraction chamber away from the upward path of the refluxing solvent. Extraction temperature differences (approximately 52°C) were responsible for higher concentrations of leachate metal in the original soxhlet leachate when a minesoil sample was weathered. This modification permits exact volumes of solvent to be passed through the sample, as well as a reduction in extraction temperature that would allow study of the role of bacteria in the weathering process.
A Water Bath System to Observe Temperature Effects on Taproot and Lateral Root Development of Plants
Authors: Stone J. A. , Taylor H. M.
Published: July 2010

This paper describes a water bath system designed to provide accurate root‐zone temperature control and serial observation of taproot and lateral root development to a depth of 120 cm. The system consists of a 137.2‐ by 100.3‐ by 121.9‐cm deep constant‐temperature water bath, 12 2.5‐ by 30.5‐ by 121.9‐cm immersed acrylic plastic plant‐growth containers, movable lighting, and a derrick for removing the growth containers. The acrylic containers are lifted from the bath in tiers of three, and data recorded with photographs.

Temperature distribution within the bath has been measured at water temperatures ranging from 5 to 35°C and in the acrylic containers at water temperatures ranging from 17 to 29°C. Temperatures remained within ±0.3°C of the setting throughout the water bath for 25 d with no detectable spatial variability. Temperature gradients within the acrylic growth containers are presented.
Shear Resistance Enhancement of 1.22‐Meter Diameter Soil Cross Sections by Pine and Alfalfa Roots
Authors: Waldron L. J. , Dakessian S. , Nemson J. A.
Published: July 2010

Plant roots have been shown to increase soil shear resistance through direct mechanical reinforcement and thereby enhance soil stability on slopes. Because of their potential large diameter and length, the roots of trees may be especially significant in such soil reinforcement. To provide large rooting volumes simulating natural conditions and shear cross sections many times larger than potential tree root diameters, we constructed 12 1.22‐ by 1.22‐m cylindrical soil containers in which two artificial soil profiles were prepared. Replicates of each profile type were planted to alfalfa, yellow pine, or were kept clear of plants. A large pneumatic direct shear device sheared both root‐free and root‐permeated materials along a horizontal plane at the 0.6‐m depth at either constantly maintained shear stress levels (creep shear) or at constant shear displacement rates.

Creep shear at the 0.6‐m depth showed that roots of 14‐month‐old alfalfa increased the shear resistance of homogeneous clay loam and a clay loam/gravel interface simulating a soil‐weathered rock boundary by 32 and 50%, respectively. Constant shear displacement rate experiments at the same depth on similar samples permeated by roots of yellow pine planted 54 months earlier showed shear resistance increasing steadily with displacement over the entire test displacement range. At 75 mm displacement, the shear resistance of the pine‐rooted soil was about two times that of the nonrooted in both profile types. The superiority of pine roots to alfalfa roots in increasing soil shear strength in these experiments is in accord with field observations that woody plants are more effective than herbaceous plants in stabilizing soil against slips and slides. Pine root‐size distributions determined 11 months after the last shear test were combined with root tensile strengths and Young's moduli previously measured and used in model simulations of root reinforcement with good results.
Kinetic Properties of L‐Histidine Ammonia‐Lyase Activity in Soils
Authors: Frankenberger W. T.
Published: July 2010

Enzyme kinetic analyses were performed to characterize the L‐histidine ammonia‐lyase‐catalyzed reaction in soils. The velocity curves of soil L‐histidine NH3‐lyase as a function of substrate concentration displayed sigmoidicity. The apparent [S]0.5 values of this enzyme in eight soils ranged from 26 to 41 mM (avg = 32 mM) and the apparent Vmax values ranged from 51 to 97 µg NH4‐N released·g of soil−1·48 h−1. The velocity of this enzyme was described by the Hill equation which measures the deviation in hyperbolicity of saturation curves. The experimental data yields strong cooperativity in terms of the Hill coefficient (napp = 4.0 to 5.5) and shape of sigmoidicity ([S]0.9/[S]0.1 = 2.2 to 3.0). The Ea (activation energies) and Q10 values for the L‐histidine NH3‐lyase catalyzed reaction in seven soils at temperatures below inactivation (< 60 °C) ranged from 37.0 to 65.4 kJ/mol and 1.51 to 2.58, respectively.
Growth and Survival of Cowpea Rhizobia in Acid, Aluminum‐Rich Soils
Authors: Hartel Peter G. , Alexander Martin
Published: July 2010

A study was undertaken to determine whether Al‐sensitive cowpea Rhizobium survives in acid, Al‐rich soils. The lower pH limit for growth of 20 strains in a defined liquid medium varied from pH 4.2 to less than pH 3.6. The mean lower limit for growth was pH 3.9. Several of the strains clumped in this medium at pH 4.5. Of 11 strains that were tested for tolerance to high levels of Al in a defined liquid medium at pH 4.5, nine tolerated 75 µM Al, and the other two were sensitive to levels above 15 µM. Three strains, one Al‐tolerant, one Al‐sensitive, and one Al‐tolerant or Al‐sensitive depending on the presence of vitamins in the medium, were selected for studies in Al‐rich sterile and nonsterile soils. These rhizobia did not survive in soils of less than pH 4.7 sterilized by 60Co irradiation. When inoculated into sterile soil at pH 4.7, the consistently sensitive strain initially failed to proliferate and then grew slowly, but populations of the other two rhizobia increased rapidly. No consistent relationship was found between the Al tolerance of these three rhizobia and their growth and survival in four acid, Al‐rich soils. The data suggest that Al is of minor importance to growth and survival of cowpea Rhizobium strains in acid soils.