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Volume 51 Issue 5, September-October 1987
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Convenient and reliable techniques for estimating intact soil hydraulic properties are required for predictions of soil-water flow in the environment. The dependence of sorptivity, S, on water supply potential, Ψ0, is used here to find the dependence of the intact field soil hydraulic properties soil-water diffusivity, D(θ), hydraulic conductivity, K(θ), and soil-water characteristic Ψ(θ) on water content, θ. The approximations used in deconvoluting sorptivity are examined critically using a simple parametric D(θ) that gives analytic solutions applicable to most known soil behavior. We show that the Parlange approximation differs from the exact solution by <5% over a very wide range of D(θ) and over the entire water content range. A rapidly convergent iterative scheme in which this approximation forms the initial estimate is introduced for situations where greater accuracy is required. The technique is tested for a repacked soil, Ustochrept, and the D(θ) derived from S(Ψ0) agrees excellently with conventional measurements. We use the disc permeameter to find S(Ψ0) at 20 sites for an intact field soil, Haplustalf. The D(θ) derived from these measurements is not strongly θ-dependent. This is attributed to the shape of Ψ(θ), which, in contrast to repacked samples, shows that as θ approaches saturation, Ψ approaches zero gradually. The capillary length found from the K(Ψ) measurements is only 23 mm. Both findings are attributed to the presence of biopores in the field soil. Sorptivity may be used to determine reliably intact soil hydraulic properties whose magnitudes reflect the intricacies of field soil structure.
This study examines the effect of pore solution composition and temperature on the measured and calculated diffusion coefficients (Dm and Dc, respectively) for Sr2+ in a compacted mixture of bentonite (50 wt%) and sand. Dm for Sr2+ and Cl- in the soil was determined at a dry bulk density of ∼1.7 Mg m−3 using deionized water (DW) and two synthetic groundwater solutions (SGW) with ionic strengths of 0.27 and 1.4 mol L−1 to saturate the soil, and at 25, 60, and 90°C. The Dc for Sr2+ was calculated from Dc = Doτ/(1 + ρbKd/θv), where Do is the diffusion coefficient of Sr2+ in free solution; τ is a tortuosity factor, obtained for the compacted soil from Cl- diffusion experiments; ρb is the dry bulk density; θv is the volumetric moisture content; and Kd is a distribution coefficient that accounts for the interaction of Sr2+ with the soil. Both Dm and Dc for Sr2+ increased with an increase in the ionic strength of the saturating solutions and with an increase in temperature. The Dm values were, however, always greater than Dc values by a factor of 6.2 to 8.0 for DW and 1.3 to 1.8 for the SGW with an ionic strength of 1.4 mol L−1. This difference is believed to be the result of obtaining Kd values in solutions that differed significantly from the pore solution of the compacted soil. Nevertheless, the results indicate that Dc values, which are often more convenient and less time-consuming to obtain than Dm values, can at least be used to establish relationships and trends between the diffusion rates of some contaminants in clay-based materials and the properties of these materials.
Sand grain roundness and sphericity were evaluated for 50 soil samples from Atlantic Coastal Plain soils to determine relationships of sand grain roundness and sphericity to the soils' cone index (mechanical impedance), bulk density, and the dense soil angle of repose. A previous investigation collected undisturbed cores from 50 tillage-induced pans in the Atlantic Coastal Plain, and determined cone index, bulk density, and the dense soil angle of repose. One hundred sand grains were isolated from each of the 50 soil materials. Roundness was determined for each grain by comparing the grain's projected image to standard images in published roundness charts. Sphericity was also determined for the 100 grains per soil by measuring selected grain axes. Mean values for roundness and sphericity were determined for each soil sample. Mean roundness values ranged from 0.44 to 0.57 across sites, but 74% of the sites had mean roundness values between 0.45 and 0.49 inclusive. Mean sphericity values ranged from 0.74 to 0.81, but 72% of the sites had mean sphericities between 0.78 and 0.81 inclusive. Correlation coefficients for relations of cone index, bulk density, and dense soil angle of repose to roundness and sphericity were generally ≤0.26 and not significant (0.10 level). Sphericity and roundness were not significant variables in regression models describing variations in cone index and the dense soil angle of repose. Roundness was not a significant variable in regression models describing variations in bulk density among sites, but sphericity was a significant variable in models that were based on particle size characteristics alone.
Dryland crops grown in semiarid environments often do not completely cover the soil, leaving a portion of the soil surface exposed to a condition of rapid soil-water evaporation. Quantitative separation of soil evaporation and crop transpiration is important if cultural practices or cultivars are to be evaluated. This study was designed to evaluate a combined energy and water balance model, ENWATBAL, to describe the concurrent heat and water fluxes in a row crop. Inputs to the model include soil and plant variables and daily weather data. Measurements were made for a period of 74 d over a cotton (Gossypium hirsutum L.) canopy during 1985 on an Olton soil (fine, mixed, thermic Aridic Paleustolls) at Lubbock, TX. Data collected included soil-water content, soil temperature, root distribution, soil evaporation with microlysimeters, and leaf area index, for both an irrigated and a dryland plot. The values for daily evaporation and evapotranspiration calculated with the model were within 1 standard deviation of the measured values. Cumulative evaporation and evapotranspiration from the model agreed with measured values within 7% for the dryland and 8% for the irrigated plot. Estimated soil-water and temperature profiles also agreed closely to measured values. Soil evaporation was found to be 30% of evapotranspiration, for both the irrigated and the dryland plot. The ENWATBAL model provides a reliable method of evaluating the effects of management practices and crop selection on the water-use efficiency of crop production in a semiarid area.
Computer Assisted Tomography (CAT) is commonly used in diagnostic radiology to make nondestructive images and analyses of cross sections of the human body. CAT scanning may also be useful in imaging and measuring spatial distribution and changes in water distribution in porous media. The purpose of this paper is to review some of the details of CAT scanning that are of importance to the application of CAT scanning porous media and to evaluate the use of the CAT scanner to measure the spatial distribution of water in three different porous media. The scanner's response to changes in the spatial distribution of water in three different porous phenolic foam materials after draining for 16 h was investigated. Water content distributions were successfully detected with good resolution on the x-ray image. Comparisons of CAT vs. gravimetrically determined water content indicated a significant linear relationship between the methods. Results from these experiments indicate that the CAT scanner can nondestructively measure volume wetness in phenolic foam media. The clarity of the CAT images suggests that CAT scanning has great potential for studies where small and rapid changes in water content within small volumes of media are desired.
Electrical conductivities (EC) of saturated paste extracts of 225 soil samples collected from depths of 30 to 60 cm along five transects were determined. The field was irrigated using a two-line source sprinkler system that applied two different qualities of irrigation water. The sampling interval along each transect was 1 m. Forty-five soil samples were collected from each transect, with each transect separated by 10 m. The mean and four directional experimental variograms of the EC were computed. The east-west (0°) directional variogram showed a structure with a range of 19 m. The raw data showed a skewed distribution with two outliers. One hundred eleven of the total data points were used to check for the presence of a drift and to determine the best generalized covariance function. The best general drift, calculated with mean squares, was found to be of order one. Structural analysis confirmed that the best drift order was one, and the best generalized covariance fit had linear and cubic terms. The best fit covariance function had a mean square error (MSE) of 0.187 and a correlation coefficient of 0.98 from the jackknifing. The cross-validation of the best covariance fit was performed by removing each data point and estimating from the remaining data (MSE = 0.164). If the difference between the measured and estimated points was greater than twice the standard deviation, that point was considered to be an outlier. The results of cross-validation, when 111 data points were used, showed no outliers. The scatter diagram of the estimated values and reduced error showed no correlation (r = −0.0035). On the other hand, a high correlation (r = 0.93) was found between the estimated and the true values. The best covariance function with a drift of order one was used to estimate 225 measured values, as well as an additional 1260 values over the entire field with a grid size of 1 × 1.25 m. This technique allowed detailed information to be obtained from a limited number of data points with dependability.
The rate of dissolution of gibbsite was measured as a function of H+ concentration and anion concentration. The anions examined were nitrate, sulfate, and phosphate and the pH range used was 1.5 to 4.0. Rates of gibbsite dissolution were low and comparable to reported dissolution rates for feldspars. In the presence of nitrate and sulfate the dissolution reaction was first-order with respect to H+ below pH 2.5. In phosphate there was no dependence of the rate on H+. Above pH 3.5 in nitrate the reaction order with respect to H+ approached zero. The order of the reaction with respect to anion concentration was about 0.6, 0.4, and 0.9 for nitrate, sulfate, and phosphate, respectively. The rate dependence of gibbsite dissolution on H+ and anion concentration suggested that the mechanism of dissolution, as well as the rate, is a function of solution composition. In solutions containing ions not specifically adsorbed (e.g., NO-3 and SO2-4), proton attack of the surface is the rate-determining step. In solutions containing phosphate, anion attack predominated, and the rate of the reaction is not dependent on pH.
A backtitration technique was used to collect proton isotherm data for an Al oxide, and was found to be stoichiometrically related to the cation and anion isotherm behavior. The adsorption of various ions by the Al oxide surface was modeled based on: (i) two surface sites, (ii) pH + salt-dependent reactions (H+ and Cl-, 2OH-, or Na+ and OH-), (iii) competitive salt-dependent reactions (Na+ or Cl-), (iv) CO2(aq) pH-dependent reactions with the surface-OH groups, and (v) presence of an unknown M+Cl- salt (0.0005 M). The total number of Al sites was 1.7 µmol m−2 or 3.4 µmol m−2 of total available sites. The pH of point of zero salt effect (PZSE) represented the surface condition in which the negative charges (or cation surfaces) equaled the positive charges (or anion surfaces); the cation exchange capacity (CEC) equaled the anion exchange capacity (AEC) at this value. The CEC-AEC data and proton isotherm data were stoichiometrically correlated. The pH of PZSE values ranged from 7.50 to 7.76 depending on the electrolyte concentration present, with lower values as the concentration increased. The negative shifts in the PZSE values are due to anion impurities initially present on the surface and positive shifts are due to cation impurities.
The adsorption of Se by goethite was studied as a function of time (10 min–24 h), temperature (295.5 and 303.5 K), pH (4–11), particle concentration (3–300 mg/L), total Se concentration (0.02–5 × 10−5 M), oxidation state [Se(IV) and Se(VI)], and competing anion concentration [(anion)/(Se(IV) = 0.25 to 50 000] in order to assess the influence of these factors on Se mobility. The data indicate that (i) the surface sites of goethite are heterogeneous, (ii) the adsorption of selenite [Se(IV)] reaches equilibrium in 2 h and is completely reversible with respect to pH, (iii) the removal of selenite from solution increases with decreasing pH and increasing particle concentration, (iv) the adsorption edge for selenite shifts to lower pH values with increasing total selenite concentrations, (v) selenite adsorbs much more strongly than selenate [Se(VI)], and (vi) the influence of additional anions on selenite adsorption depends on the relative affinity of the anions for the surface and the relative concentrations of the anions. For a given anion concentration ratio, the competition sequence with selenite is phosphate > silicate ≥ citrate > molybdate > bicarbonate/carbonate > oxalate > fluoride > sulfate. Therefore, the conditions that favor the mobility of Se in the environment with respect to adsorption are alkaline pH, high Se concentrations, oxidizing conditions, and high concentrations of additional anions that strongly adsorb.
A simple titrimetric method is described for the estimation of Ca and Mg carbonates in soils. It involves the determination of acid-soluble Ca and Mg of the carbonate phase after the removal of soluble and exchangeable cations by ammonium acetate (NH4OAc). Twenty-six tropical soils, which contain free carbonate, were used in this study. The results obtained by the proposed method were compared with those obtained by acid neutralization, calcimeter, and titrimetric methods. Analysis of variance revealed no significant difference between the percent CaCO3 equivalent obtained by the four methods when the acid neutralization method was corrected against proton adsorption. However, the proposed method has the advantage of estimating Ca and Mg carbonates. The proposed method requires no special equipment and is less time-consuming if it follows the routine determination of exchangeable cations or the cation exchange capacity (CEC).
An experimental method was developed to measure simultaneously the net proton surface charge density (σH) and surface excesses of metal (nM) and ligand (nL) on an Oxisol suspended in a ML electrolyte solution. The soil sample was first saturated with a LiClO4 solution whose pH and ionic strength were equal to the maximum values to be used in the adsorption experiments. The ionic strength then was decreased, LiClO4 was exchanged for ML (ML = NaCl or KNO3), and a soil paste was prepared to allow reproducible sampling of small quantities of the whole soil. A discontinuous titration followed in which the soil paste was equilibrated with a series of ML electrolyte solutions of specific pH and ionic strength. Values of nM and nL were measured at 25°C, and it was shown that the point of zero net charge (PZNC) ≈ 4.2, independent of the electrolyte and its ionic strength in the range 4 to 500 mol m−3. Given a negligible permanent surface charge, typical of Oxisols, PZNC = PZNPC (point of zero net proton charge). The net proton surface charge density then could be calculated from titration data renormalized to the PZNC. The net proton surface charge of the Ha-plustox used in this study vanished at pH 4.2 and showed very little dependence on ionic strength, indicating the dominant role of kaolinitic and organic matter constituents in determining its surface properties. Surface complexation reactions between the soil and a 1:1 electrolyte solution were characterized quantitatively by intrinsic equilibrium constants calculated according to the triple layer model. The average values found were similar to those that have been obtained previously for specimen hydrous oxides suspended in 1:1 electrolyte solutions.
The adsorption of selenite by five alluvial soils from the San Joaquin Valley, California, was investigated with respect to the effects of soil composition and pH. Soil samples were prepared in the form of Na-saturated pastes. Adsorption experiments were carried out in a 50 mol NaCl m−3 background at initial selenite concentrations comparable with those found in natural soil systems. The samples were equilibrated under N2-stirring in a constant-temperature apparatus with pH and redox conditions monitored. Selenite adsorption by the soils decreased uniformly with increasing pH in the range 4 to 9 and was independent of soil series above pH 6.
The adsorption envelope for selenite on two alluvial soils from the San Joaquin Valley, California, was investigated with respect to variations in solution composition. Sodium-saturated soil pastes were mixed with solutions containing sulfate, phosphate, and Ca ions in a background electrolyte of 50 mol NaCl m−3. The effects of increasing chloride concentration were investigated at 100 mol NaCl m−3. No discernible change in the amount of selenite adsorbed was found as a result of increased chloride concentration or through the addition of 16 mmol Na2SO4 kg−1. In contrast, an initial concentration of phosphate comparable to that of selenite resulted in a decrease of selenite adsorbed by approximately one-half. The addition of 100 mol CaCl2 m−3 resulted in significant increases in selenite adsorption on both soils above pH 5, which could be attributed to precipitation or an increase of surface charge through Ca adsorption.
The extractability of P from two weakly acid soils that had been amended with three forms of P [KH2PO4, single superphosphate (SSP), and Chatham Rise phosphorite (CRP)] was investigated in an incubation study under field conditions. In a sequential extraction sequence with water, P release from soils incubated for 9 and 27 weeks with KH2PO4 and SSP declined with increasing extraction number. In contrast, P extracted from CRP-treated soils increased, indicating a slow dissolution of phosphate rock. Washing with 0.1 M NaCl to remove exchangeable Ca resulted in a large increase in P extracted subsequently with water, regardless of whether sorbed P (as in KH2PO4- and SSP-treated soils) or particulate Ca phosphate (as when CRP was added) was the source of the extracted P. A high proportion (up to 80%) of the added P could be recovered by water extraction when exchangeable Ca was replaced by Na. Significantly, P recovery did not decrease with time of contact between soil and P as it did before exchangeable Ca was replaced with Na. The removal of exchangeable Ca accelerates the dissolution of Ca phosphates by creating a sink for Ca. The results obtained suggest that sorbed P may enter into chemical association with Ca, possibly at metal oxide surfaces, and that this interaction with Ca constitutes an important P retention mechanism in acid soils that contain adequate exchangeable Ca.
We analyzed climatic and textural controls of soil organic C and N for soils of the U.S. Great Plains. We used a model of soil organic matter (SOM) quantity and composition to simulate steady-state organic matter levels for 24 grassland locations in the Great Plains. The model was able to simulate the effects of climatic gradients on SOM and productivity. Soil texture was also a major control over organic matter dynamics. The model adequately predicted aboveground plant production and soil C and N levels across soil textures (sandy, medium, and fine); however, the model tended to overestimate soil C and N levels for fine textured soil by 10 to 15%. The impact of grazing on the system was simulated and showed that steady-state soil C and N levels were sensitive to the grazing intensity, with soil C and N levels decreasing with increased grazing rates. Regional trends in SOM can be predicted using four site-specific variables, temperature, moisture, soil texture, and plant lignin content. Nitrogen inputs must also be known. Grazing intensity during soil development is also a significant control over steady-state levels of SOM, and since few data are available on presettlement grazing, some uncertainty is inherent in the model predictions.
When a 15N-enriched N source is added to the soil, denitrification results in a nonrandom distribution of N2 isotopes. As a result, it has been necessary to apply highly enriched 15N-fertilizers to allow mass spectrometry (MS) determinations of 28N2, 29N2, and 30N2 to quantify the N2 evolution. An alternative method, based on the determination of N2 evolution by measurement of the 28N2/29N2 ratio with emission spectrometry (ES), is proposed. An apparatus consisting of a cuvette and a sampling system was developed. The sampling system was evacuated to <10−1 Pa before gas from the cuvette system was fed into a reservoir (10 mL), through a liquid N2 trap and into five discharge tubes for ES. The final pressure in the tubes was 4 to 5 × 102 Pa before they were sealed off, and the 28N2/29N2 ratios in the gases were determined with ES. It was verified that random distribution of 28N2, 29N2, and 30N2 was obtained in different N2-gas mixtures made from natural atmosphere and 98 atom % 15N-N2 by the high frequency discharge of the ES. The system was used to measure fertilizer N2 loss when 15N-enriched KNO3 was applied at a depth of 2.5 cm in flooded soil. After 60 d, 18% of the applied KNO3 was lost as N2.
The effect of microorganisms on the fate of Cd in soil suspensions was investigated. Samples of four soil types were suspended in growth media amended with Cd(NO3)2 (20 mg/L) and incubated aerobically or anaerobically at 28 ± 1°C. At various time intervals, aliquots were withdrawn, and Cd concentrations (total and free Cd2+) and pH were determined in the supernatant. The results of the short- and long-term studies indicated that in all soils tested the extent of Cd disappearance (total and free Cd2+) in nonsterile soil supernatants was significantly greater than in the corresponding sterile controls. However, during the subsequent long-term 8-week aerobic incubation, a significant amount of Cd (including free Cd2+) was released into solution of nonsterile suspensions, while no increase in Cd concentration was observed in the sterile suspensions. Under anaerobic conditions, a continued disappearance of Cd from the non-sterile soil supernatants was observed during an incubation period of up to 24 weeks. Under aerobic conditions, the pH of the nonsterile soil suspensions decreased to approximately pH 5.5, whereas the pH remained approximately 8.0 during anaerobic incubation. The rate and degree of Cd immobilization or mobilization was also dependent on the soil types used. Of the four soils tested, Morrison (Ultic Hapludalfs) sandy loam from a coniferous forest site exhibited the highest degree of Cd mobilization, accounting for up to 100% of total Cd immobilized. Our results suggested that soil microbial activity is responsible for both binding of Cd to and its subsequent release from soil.
The extent and subsequent availability of soluble organic N in soil mineralization extracts were determined using initially air-dry soil samples. Involved were eight Southern Plains agricultural soils comprising five soil orders. The major losses of soluble organic N occurred during the initial leaching prior to incubation, and are attributed to factors not directly associated with the mineralization procedure (e.g., freshly decomposed plant residues, pretreatments, etc.). Often, these losses were as high or higher than initial values for inorganic N. Thereafter, the organic N losses represented, on average, only about 5% or less of the inorganic N produced in surface soil samples during 84 d of aerobic mineralization. This was the case for both indigenous and fertilizer-incorporated N. Subjecting the soluble organic N in the mineralization extracts to subsequent aerobic, anaerobic, or autoclave procedures indicated no excessive N availability. Distribution of the soluble organic N components in the extracts did not differ greatly from that of soil. In general, soluble organic N losses were not a major factor associated with recovery of mineralized N.
The spatial variability exhibited by soil denitrification rates is high. As is typical for natural denitrification rate measurements, the individual rates of most samples of a given data set are low; however, a few samples often exhibit extremely high rates. Such data are characterized by highly skewed sample frequency distributions. This study was initiated to investigate the underlying mechanisms responsible for these observations. It was found that "hot-spots" of high specific denitrification activity were associated with particulate organic C material in the soil. The high specific activities of these hot-spots (incubated under aerobic conditions with no amendments) were similar to the denitrification activity of the bulk soil measured under conditions of anaerobiosis with added glucose and NO3. This observation served as the basis of a computer model that evaluates the influence of the density and dispersion pattern of these high activity sites on the measured rates of denitrification. Histograms generated from computer simulations are very similar to histograms obtained for real data, supporting the concept that the patchy dispersion of particulate organic material in soil is a major factor influencing the variability of natural denitrification rates.
Samples from the surface horizon of a cultivated Aquoll were ultrasonically dispersed and separated into particle size fractions. Humic acids (HAs) were extracted from the whole soil and each particle size fraction. Residual humic acids (RHAs) were obtained from the residue of each HA extraction by treating with HCl-HF and reextracting. Chemical analyses showed that the fine silt fraction had the highest C and N contents. Although δ15N values and proportions of mineralizable N increased with decreasing particle size, C/N ratios decreased. Mineralizable N appeared to be related to both the total N content and the characteristics of the minerals with which the organic matter was associated. Nitrogen in sand and silt fractions was more resistant to mineralization than in clay fractions. Extractions with 0.5 M NaOH removed more of the C and N from the fine-clay fraction than from the whole soil or any of the other fractions. Carbon-13 nuclear magnetic resonance (NMR) spectra showed that HAs extracted from clays were more aliphatic than HAs extracted from larger particle sizes. The major aliphatic components in the clay size fractions appeared to be alkanoic and hydroxyalkanoic acids. Compared with HAs, RHAs, were more homogeneous, contained fewer proteinaceous materials and carbohydrates, were more aromatic, richer in phenolic OH and CO2H groups, had higher molecular weights, and contained more free radicals.
The effect of complexing agents on Fe mobility was investigated using a simulated root-soil system that consisted of 0.24-mm o.d. cellulose fibers embedded in a clay-agar matrix. Complexing agents diffused into the clay-agar matrix from a solution flowing through the fibers and their effect on Fe flux to the fiber surface was determined by following Fe concentration in the effluent solution from the fibers. Experiments with the chelating agents ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine di-(o-hydroxyphenylacetic acid) (EDDHA), and ethylene glycol-bis-(2-amino-ethylether) tetraacetic acid (EGTA) demonstrated that solubilization of Fe qualitatively followed patterns predicted from known thermodynamic stability constant-pH relationships. The concentration of Fe in the fibers 24 h after introduction of either EDTA, DTPA, or EDDHA was increased from close to 0 to 30 to 100 g Fe L−1, whereas EGTA had no measurable effect on Fe solubility. The measured fluxes of Fe were compared with calculations based on diffusion and reaction. An equilibrium model, where the complexing agent was assumed to equilibrate instantaneously with the soil (reaction rate constant Kr = 1), predicted concentrations of Fe 103 times greater than those observed. A first-order kinetic model, which was solved by numerical methods, gave results similar to those found experimentally when Kr was on the order of 10−7. The partial success of the thermodynamic stability constant approach was reconciled with the kinetic model by considering Kr to combine both kinetic and equilibrium factors.
Three soils from Colorado that varied in texture and organic matter (OM) content were treated with sodium borate (Na2B4O7·10H2O) at rates of 0, 10, 20, and 40 mg B kg−1 soil. Alfalfa (Medicago sativa, 'Ladak', 'Rambler', 'Riley', and 'Agate') was planted in the soils in the greenhouse and cut twice at the 30% bloom stage. Plant tissue digests and soil extracts (ammonium bicarbonate-diethylenetriaminepentaacetic acid [AB-DTPA], saturation, hot water, and mannitol-CaCl2) were analyzed for B using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Alfalfa yield was significantly (α = 0.01) reduced with increased B application rate in the Ascalon sandy loam and Ulysses loam soils, whereas no yield reduction was observed in the Keith silt loam soil (Aridic Argiustoll, Haplustoll, and Argiustoll, respectively). Yield response for the pooled soils were poorly correlated (r2 from 0.23–0.58) to the four soil extractants; however, yield reduction due to B toxicity corresponded to critical plant B levels of 850 mg B kg−1 and 975 mg B kg−1 for the first and second harvests, respectively. The inclusion of NH4OAc-extractable Ca into the regression equation of soil B vs. yield significantly increased the correlation (r2 = 0.77). Multiple linear regression analysis utilizing Mallow's Cp statistic increased the adjusted coefficient of determination (R2) to 0.87 for all of the soil B extractants upon inclusion of soil variables (pH, % clay, OM content) into the equation. Although NH4OAc-extractable Ca did not appear in any of the best subsets, this was probably the result of it's high correlation with percent clay (r2 = 0.98) and OM content (r2 = 0.98).
The fertility of acid subsoils may be improved by the injection of fertilizer materials into narrow slits that can be cut in subsoils during tillage operations. Little information is available to describe the effects that soil properties and added fertilizers have on the diffusion of Ca2+ and Mg2+ in acid subsoils. Laboratory studies were conducted with an acid subsoil of a Marvyn sandy loam soil (fine loamy, siliceous, thermic, Typic Hapludult) to determine the effects of fertilizers, bulk density, and volumetric moisture (Θ) on the diffusion of Ca2+ and Mg2+. The soil was treated with either dolomitic limestone, NH4NO3, NH4H2PO4, Ca(H2PO4)2, or Ca(NO3)2. Limestone was applied at a ratio of 79 g kg−1, whereas the remaining treatments were applied to provide 2.64 g kg−1 of either NO-3 or H2PO-4. The rates were used to simulate the concentrations that would occur in the zone of injection if the amendments were injected into the subsoil under field conditions. Calcium diffusion coefficients (De) measured with a cation exchange resin paper method ranged from 2.4 × 10−9 cm2 s−1 in the check to 3.9 × 10−6 cm2 s−1 in the Ca(NO3)2 treatment, and counter De for Mg2+ ranged from 3.6 × 10−9 cm2 s−1 in the check to 5.1 × 10−6 cm2 s−1 in the Ca(NO3)2 treatment. All treatments increased De for Ca2+ and Mg2+ relative to the check. In general, De increased as the concentration of Ca2+ and Mg2+ in the soil solution increased, and as the proportion of the extractable cation associated with the solid phase decreased. Diffusion coefficients for Ca2+ and Mg2+ increased as Θ increased from 0.12 to 0.30. Calcium and Mg2+ De reached a maximum at a bulk density of 1.6 to 1.7 Mg m−3 and then decreased slightly as bulk density increased to 1.9 Mg m−3. Bulk density effects were more pronounced at soil-water pressure head values <0.033 MPa.
The Fertility Capability Classification (FCC) system is a technical soil classification system developed to evaluate soil properties affecting crop response to fertilization and to aid in making fertilizer recommendations. It was developed primarily for use in lesser developed countries. Results from a series of experiments involving application of K to flue-cured tobacco (Nicotiana tabacum L.) in North Carolina were used to determine the usefulness of the FCC system for predicting crop response to fertilization in the southeastern USA. Six rates of K, ranging from 0 to 224 kg ha−1, were applied to flue-cured tobacco at 13 locations for 3 yr. Tobacco leaf yield response to K differed significantly among FCC soil groups. Optimum rates by soil group varied from 0 to 112 kg ha−1, compared with 84 kg ha−1 across all soils. The highest optimum rates occurred on soils with sand or loamy sand surfaces >0.5 m thick, whereas the lowest rates were on soils with loamy surfaces. Extractable soil K level in the Ap horizon (soil test K) was not related to response to K, either overall or within FCC groups. The FCC system was useful in evaluating tobacco leaf yield response to fertilization. It appears that the FCC system could be used to improve fertilizer recommendations.
The fractionation of soil B and the plant availability of each fraction have not been examined extensively. This laboratory and greenhouse research was conducted to study the distribution and plant availability of B in different soil fractions. Total B in the 14 soils under study ranged from 21.5 to 96.3 mg kg−1. A trace to 0.34% of the total B was in a water-soluble form; ≤0.23% was 0.02 M CaCl2 extractable (nonspecifically adsorbed B); from 0.05 to 0.30% was mannitol exchangeable (specifically adsorbed B); and from 0.23 to 1.52% was acidified NH2OH·HCl extractable (B occluded in Mn oxyhydroxides). Ammonium oxalate solution (pH 3.25) extracted from 2.8 to 34.4% of the total soil B in the dark (B occluded in noncrystalline Al and Fe oxyhydroxides) and from 17.5 to 73.9% under ultraviolet (UV) light (B occluded in crystalline Al and Fe oxyhydroxides). Residue B, which was considered to be in association with soil silicates, accounted for 2.4 to 79.2% of the total B. Boron concentration in corn (Zea mays L.) tissue correlated positively (α = ≤0.05) with water-soluble B, CaCl2 extractable B, mannitol exchangeable B, and acidified NH2OH·HCl extractable B. The sum of these four fractions, which were related to B availability, accounted for only 0.4 to 2.0% of the total B in the 14 soils. Boron concentration in corn tissue was unrelated (α = 0.05) to NH4-oxalate extractable B (either in the dark or under UV light) and to the residue B fraction. These relationships indicate that B in noncrystalline and crystalline Al and Fe oxyhydroxides and in silicates was relatively unavailable for plant uptake.
The range in soil environments has likely contributed to variation in the determination of that level of K availability at which no further yield increase to K is expected. Potassium response of soybean [Glycine max (L.) Merr.] from three different soil environments was studied in the field to determine if a single index of K availability could be found. Relationships between grain yield, R1-R2 leaf K concentration, ammonium acetate exchangeable K, Ca, Mg, and water soluble K, Ca, and Mg were determined. Significant (P ⩽ 0.05) yield responses to added K were found at all three sites, as were increases in R1-R2 leaf K. Water soluble K, K/Mg, and K/(Ca + Mg)1/2 were more stongly related to plant response than extractable K, K/Mg, or K/(K + Ca + Mg). All soils provided optimal K nutrition to soybeans at soil test levels ≤100 mg K kg−1 soil, as determined by neutral, molar ammonium acetate solution. Determinations of soil solution phase composition may improve our understanding of the role(s) of soil properties on divergent patterns of response to K nutrition.
Dystochrepts formed in mica schist residuum occur on steeply sloping sideslopes, whereas associated Hapludults are found on gently sloping ridgetops in the Piedmont province of Georgia. In this study, morphological, physical, chemical, and mineralogical properties of Dystrochrepts and associated Hapludults were examined to determine the influence of weathering intensity differences within the pedon and across the Dystrochrept → Hapludult developmental sequence. More intense weathering at the soil surface has resulted in higher exchangeable Al contents, lower pH values, and a relative accumulation of total Si, quartz, sillimanite, opaque minerals, and clay-sized mica and vermiculite. In contrast, biotite was more abundant at depth. Total Al was closely related to clay distribution within the pedon. Less intense weathering in the Dystrochrepts, apparently related to shorter development time, has led to coarser textured sola with higher base saturations, higher total Mg, K, and Na contents, and a greater abundance of fine sand-sized biotite and K-feldspar. Quartz in the fine sand fraction was concentrated in the Hapludult. Kaolinite was the dominant clay mineral in the Hapludult. Regularly interstratified mica-vermiculite was identified in subsurface horizons of the Dystrochrept and is believed to be a transitory intermediate in the transformation of mica to vermiculite.
Clayey soils formed in glaciolacustrine sediments in semiarid and subhumid regions of Saskatchewan were studied to understand their genesis and to examine their classification according to the amended definition of Vertisols. Although slickensides were common to all soils, semiarid soils displayed weak horizons, whereas subhumid soils had argillic horizons and prominent mollic epipedons. All the soils had high potential to swell and shrink, and were characterized by seasonal moisture deficits sufficient to induce cracking. Soil displacement, as evidenced by slickensides, was attributed to differential wetting in the subsoil. Pedoturbation, as a result of such displacement, has been sufficient to prevent strong horizon formation in semiarid soils but insufficient to counter leaching and illuviation in subhumid soils. Blocky and prismatic structure, when dry, and microfabric considerations support a B horizon designation in these soils, which otherwise exhibit indistinct horizons when moist. It is suggested that Vertisols with frigid and cryic soil temperature regimes should be grouped into a new suborder, Borerts. It is also suggested that soils that have diagnostic horizons other than mollic be excluded from Vertisols even when accompanied by intersecting slickensides.
Corrosion of steel specimens was monitored in 15 Texas soils in order to test the current system for assessing soil corrosivity. Corrosion, measured in situ at two depths using electrical resistance probes, was a function of many soil properties and could not be adequately described using any single property. The current system, developed by the USDA-SCS, which places soils into corrosion potential classes based on soil characterization data and descriptions, was found to overestimate corrosivity of many soils. A revised system was developed that more accurately predicted corrosion rates of buried steel under field conditions. Soil properties used in the revised system include electrical conductivity, texture, exchangeable acidity, and wetness class. When the two systems were tested using an independent set of data collected by the National Bureau of Standards, soil corrosion potential classes of the revised system correlated with actual corrosion better than the current SCS system.
Statistical relationships were determined between soil pH, effective cation exchange capacity (ECEC), surface area, and some other soil properties for selected soils of southern Nigeria. The soils were mostly hydromorphic with a pH range of 3.6 to 8.1. Exchange acidity was virtually due to exchangeable Al (r = 0.99). Negative ΔpH values indicate a dominant silicate clay mineralogy. The ΔpH (pHKCl-pHH2O) was correlated with exchangeable Na (r = −0.56), sand content (r = 0.51) and organic C (r = 0.34). Effective cation exchange capacity was low, average of 7.1 cmolc kg−1. No exchangeable Al was found above a soil pH (KCl) of about 4. A derived variable, ΔCEC (difference between CEC measured at pH 8.2 and ECEC), was used as a dependent variable to test pH dependence. The variability observed in ΔCEC values was found to be related to clay content (r = 0.65), exchangeable K (r = −0.11), and organic C (r = 0.34). A regression analysis with BET-N2 (Brunauer, Emmett, and Teller) specific surface area as the dependent variable showed a strong relationship with clay content (r = 0.96) and ΔpH (r = −0.44) in the best regression equation.
A preliminary second-order soil survey (1:15840) of Squaw Butte Range Exp. Stn., Oregon, identified a single shallow upland soil that supported six contrasting sagebrush communities. Six delineations of this soil, each associated with different vegetation, were sampled intensively to objectively determine if soil properties and classification differed between delineations. Plant communities represented six different sagebrush (Artemisia) habitat types: A. longiloba/Agropyron spicatum, A. longiloba/(fescue) Festuca idahoensis, A. arbuscula/F. idahoensis, A. tridentata ssp. wyomingensis/A. spicatum, (F. idahoensis), and A. t. ssp. vaseyana/F. idahoensis-A. spicatum. Morphological properties of profile samples were statistically compared by defining aggregate horizons (tiers) that were common to all profiles. Stepwise discriminant analysis selected elevation, aspect, presence of E and BA horizons, clay content of the Bt horizon, and sand content of surface strata as those which best distinguished between plant communities. Evidence suggests that series separations are justified based on family and class distinctions of higher categories or differences in range of soil properties, including variations in horizonation, volumetric rock fragment content of A and Bt horizons, and structure of BAt horizons. Phase separation criteria suggested include aspect, parent material, slope, and surface texture. Structure type of subhorizons, subhorizon position, and nutrient content are soil properties that may also provide important discrimination between soils possessing different range potentials.
A complex soil landscape composed of two dominant soil components supporting a range of heterogeneous sagebrush communities was examined in order to determine if soil properties and classification differed among plant community types. Cluster analysis of 64 vegetation samples identified six recurring plant groupings (RPGs). Properties of RPG soil profiles were statistically compared by defining aggregate horizons (tiers) that were common to all profiles. Recurring plant groupings were characterized by relative canopy cover of Artemisia arbuscula, Artemisia tridentiata ssp. wyomingensis, Festuca idahoensis, Agropyron spicatum; total grasses, and total herbs. Stepwise discriminant analysis selected thickness of mollic epipedon, surface rock fragment cover, and thickness and weighted average dry consistence of the argillic horizon as those that best distinguished between RPG associated soils. Evidence suggests that series separations are justified based on family and class distinctions of higher categories or differences in range of one or more soil properties, including (i) horizon sequence, (ii) mollic epipedon thickness, (iii) structure of BAt subhorizon, (iv) thickness, and (v) weighted average dry consistence of the argillic horizon. Phase level separations of RPG associated soils from identical families are feasible if both physiographic and soil surface criteria are utilized together.
Procedures were developed for obtaining visible spectra of dry and moist soil powders on a Cary 17D spectrometer. Accuracy and precision were checked by measuring the colors of: (i) 28 chips of the Inter-Society Color Council-National Bureau of Standards (ISCC-NBS) Centroid Color Chart, (ii) 279 chips of the Munsell Soil Color Chart, and (iii) 12 selected soil samples. Measured Munsell values were not significantly different from nominal values. Measured hue and chroma were significantly different from nominal hue and chroma, but the difference was approximately 0.25 units of chroma and, thus, is relatively small. Average deviations for duplicate measurements of Munsell hue, value, and chroma of 12 silt loam and silty clay loam soil samples were <0.1 unit of hue, value, or chroma and maximum deviations were <0.2 units. Precision was similar for both dry and moist samples. Increased accuracy and precision make it possible to quantify small differences in soil color that are difficult to quantify using only visual color matching.
Iron and Al oxides and hydroxides have been shown to stabilize pure clay systems from the effect of high exchangeable sodium percentage (ESP). This study examined the effect of Fe and Al additions on the stability of a California Alfisol with serious crusting problems. Changes in saturated hydraulic conductivity were used as a measure of treatment effectiveness. Saturated hydraulic conductivity (HC) of a sandy loam equilibrated with sodium adsorption ratio (SAR) 20 CaCl2-NaCl solution and leached with distilled water was faster for samples treated with 20 and 40 mmol kg−1 of FeCl3 or AlCl3 compared with untreated and 10 mmol kg−1 treatments. The FeCl3 treatments were more effective than AlCl3 treatments in maintaining HC. Analysis of the column effluent showed that more Al than Fe was removed during leaching. Much of the Fe added to the soils is recovered in oxalate and citrate-bicarbonate-dithionite (CBD) extracts, but little Al is recovered because the added Al is removed with the effluent. The stabilizing effect of hydroxy-Fe polymers against the deleterious effect of exchangeable Na was related to the charge on the polymers and not with the total amount extracted.
Material handling methods used in the construction of soils after surface mining often result in a soil with physical and structural characteristics that restrict root development. A method to quickly and easily predict root system performance and compare mine soils on the basis of their suitability for root growth is needed. This study was conducted to determine the effectiveness of penetrometer resistance (as measured by a constant rate cone penetrometer) and bulk density as parameters for predicting root system performance. Both penetrometer resistance and bulk density data fit well into a multiple linear regression model that could be used to predict root length density in the lower portion of the root zone (67–110 cm depth). Results suggest that in the mine soils studied, both bulk density (R2 = 0.81) and penetrometer resistance (R2 = 0.73) are useful predictors of root system performance.
In the humid southeastern USA, little attention is given to the effect of electrolyte concentration or low levels of Na on clay dispersion, although dispersion-related phenomenon such as surface crusting and erosion are common. Our objective was to determine the effect of electrolyte concentration, sodium absorption ratio (SAR), and soil pH on saturated hydraulic conductivity of three soils that differed in parent material. Cores packed with sieved soil at different pHs were leached with 10 pore volumes of solution at varying SAR and electrolyte concentrations. The relative decrease in conductivity during leaching was recorded as a measure of clay dispersion and subsequent clogging of pores. The Cecil soil (Typic Hapludult), which is derived from granitic parent material, was easily dispersed and hydraulic conductivity was sensitive to small changes in electrolyte concentration, SAR, or pH. The Davidson (Rhodic Paleudult) and Iredell (Typic Hapludalf) soils, derived from mafic parent material, were flocculated and insensitive to changes in electrolyte concentration and pH except at very high SAR. The implications are that southeastern soils may differ greatly in structural stability and this may be related to parent material. Dispersive soils need to be identified and managed in an appropriate manner.
The infiltration rates (IR) for water were measured at 30 random sites within a 1-ha field by sprinkler and flood infiltrometers. A portable rainfall infiltrometer was used to measure the infiltration rate under water-drop impact conditions, and double-ring infiltrometers were used to measure IR in flooded conditions. No spatial dependence of the steady-state IR values measured with the two methods was found. The mean steady-state IR measured with the flood infiltrometer was 57.8 mm h−1 with a coefficient of variation (CV) of 41.8%. The mean steady-state IR measured with the sprinkler infiltrometer was 8.6 mm h−1 with a CV of 14.7%. This difference was due to the formation of a soil surface seal from the impact of falling drops. The seal's hydraulic conductivity was much lower and less variable than that of bulk soil. Frequency distributions of the steady-state IRs measured with the two methods were different; that from the double-ring infiltrometer had a small deviation to the left, while that of the sprinkler infiltrometer had a large deviation to the right. The distribution of steady-state sprinkler IR values corresponds with the distribution in the cation exchange capacity (CEC) and exchangeable sodium percentage (ESP) in the field, verifying the known dependence between surface seal formation and the soil CEC and ESP relationship. This dependence was not found for the IR values measured by flooding. No correlation was found between the IR values measured by the two methods. Thus, for soils that seal, it is impossible to predict IR under water drops from measurements under flooding conditions.
Limited data on pressures induced by waterdrop impact on soil surfaces restricts our understanding the mechanism of soil detachment due to raindrop impact. Impact pressures on rigid surfaces are known but their application to soil surfaces is questionable. This study was undertaken to measure vertical pressures of waterdrop impact on soil surfaces. A 1-mm diam piezoelectric transducer was developed and measurements of impact pressures as a function of radial distance from drop center were made. Dickinson loam (coarse-loamy, mixed, mesic Typic Hapludoll) and Ida silt loam (fine-silty, mixed [calcareous] mesic Typic Udorthent) with bulk densities of 1.0 and 1.2 Mg/m3 and with matric potentials of −0.5 and −2.5 kPa were used. The waterdrop had a diameter of 5.6 mm and a fall height of 14 m. Average peak impact pressures were greatest at a distance of 1.8 to 2.3 mm from center of impact and of the order of 190 to 290 kPa. These stress levels are almost two orders of magnitude less than those for impact on a rigid surface. Much of the difference between soil and rigid cases was due to nonrigid, nonhomogeneous nature of the soil material. The remainder of the difference in stress levels was thought to be due to the effect of soil granularity or to the presence of surface and shear waves generated by impact.
Eliminating or reducing storm runoff in the Southern Great Plains can increase soil-water storage, decrease erosion, and increase crop yields. The primary objectives of this study were (i) to examine the potential of furrow dikes as a conservation practice to retain runoff and increase crop yields, and (ii) to examine the effects of furrow diking on sorghum [Sorghum bicolor (L.) Moench] and sunflower (Helianthus annuus L.) production. Analyses of 28 yr of runoff records show furrow diking has the potential to retain 25 to 30 mm of runoff annually. The maximum annual runoff retention by diking observed during the 14 crop years of research (three separate experiments conducted between 1980 and 1985) was 111 mm. The maximum increase in sorghum yield measured as a result of diking was 2.46 Mg/ha. Conditions responsible for maximum yield responses of sorghum to diking were: (i) annual cropping, (ii) large rainfall/runoff events occurring prior to or early in the growing season, and (iii) limited growing season precipitation. Diking increased annual cropped sorghum yields on graded and contour furrow treatments by 49 and 14%, respectively, whereas water use efficiencies were increased by 25 and 16%. Yields and water use efficiencies from diked treatments on graded and contour furrows were as great as yields and water use efficiencies from a leveled minibench treatment, indicating that from a crop production standpoint, furrow diking was as effective as land leveling in retaining runoff and increasing crop yields. Sunflower yields were increased significantly by diking during 1 yr out of 3 when sunflower was grown after 76 weeks of fallow, whereas sorghum yields were not affected by diking after fallow. Decreasing row spacing from 1.0 to 0.75 m resulted in a significant increase in the 3-yr avg yield of sorghum and sunflower of 1.0 and 0.14 Mg/ha, respectively, when grown after fallow, indicating that considerable opportunity for improving summer crop production may exist simply by changing to a narrow row spacing. A regression equation relating runoff from graded furrows to runoff from contour flat-tilled graded terraces showed increased runoff from graded furrows, particularly from small storms.
By-product phosphogypsum (PG) was applied to the surface of topsoil samples from three sandy Georgia Ultisols at a rate of 5 Mg ha−1 in 0.3-m2 runoff trays to test the efficacy of this amendment in enhancing infiltration of these soils. Simulated rainfall was applied at 50 mm h−1 for 2.5 h in an initial 1-h (dry) event and three subsequent 0.5-h (wet) events applied 24 h later. In the absence of gypsum, infiltration rate stabilized at 10 mm h−1 for the Cecil soil (Typic Hapludults), 5 mm h−1 for the Wedowee (Typic Hapludults), and 1 mm h−1 for the Worsham (Typic Ochraquults), with surface crusting and sand sorting apparent on all the soils. Surface-applied PG roughly doubled the final infiltration rate of the Cecil and Wedowee soils, and increased infiltration of the Worsham to a lesser degree. Cumulative and average infiltration was significantly higher on all of the PG-amended soils. Soil loss on the Worsham and Wedowee soils was decreased by 50% with the use of PG, and was reduced by 30% on the Cecil. Sediment concentrations were somewhat lower during the wet events with PG treatment for the Worsham and Wedowee soils, showing that less detached soil was available for transport. Although sediment particle sizes for control soils were 15 to 30% clay and 60 to 75% silt, PG-amended soils showed no clay-sized sediment in the runoff, but higher silt contents. Electrical conductivity measurements of the runoff suggest the very low electrolyte concentrations in the untreated soils promote dispersion, resulting in pore blockage and high sediment transportability, whereas PG maintained a high enough electrolyte level (0.5–1.3 dS m−1) to keep soil clays flocculated, thereby reducing crusting and sediment availability.
Temporal and spatial variability of selected soil chemical properties were determined within and among three forested mid-Cumberland Plateau landtypes at two locations. Major soils included Typic Fraguidults on uplands, Humic Hapludults on slopes, and Aquic Dystrochrepts in first-order bottoms. Temporal soil variability was measured at monthly intervals for 25 consecutive months from samples taken from 0.5- by 0.5-m subplots within two 2.5- by 2.5-m plots on each landtype. Spatial variability samples were collected from similar, adjacent plots during a 1-week period. A total of 300 spatial and 300 temporal observations were taken for each soil property in each of three soil horizons. Extractable Ca, Mg, and K, and pH in H2O and KCl were measured for A, AB, and Bt horizons, and total C was determined for A horizons. Magnitudes of variability were statistically compared using a procedure robust for nonnormally distributed data. Magnitudes of soil variability were significantly related to landtypes at the Bonferroni significance level. Only three of 16 soil variables differed in magnitudes of spatial vs. temporal variability. Variability on sites was of the order slopes > bottoms > uplands. Soil morphological features and parent materials appeared to strongly influence magnitudes of temporal and spatial variability.
Intensive measurements are required to precisely define soil temperature, heat flux, and thermal properties of heterogeneous forest soils. Fifty detailed profiles of temperature, density, and water content were used with the conduction heat flow equation to estimate soil thermal properties for a clearcut harvest area in a mixed conifer forest in southwest Oregon. These profiles were used to determine the accuracy with which soil temperatures could be modeled and the number of soil layers required to characterize a given field site. The soil was modeled as a profile of between 1 and 21 layers of known (measured) volumetric heat capacity and measured initial and boundary conditions. Soil thermal conductivity for each layer was determined for each of 50 datasets using an iterative numerical procedure. The accuracy of the various models was assessed by comparing the error between measured and modeled profiles. For the skeletal soil studied, a numerical model and field measurements of four soil layers proved to be the best combination of accuracy and simplicity. The assumption of a homogeneous (1-layer) profile was satisfactory in several cases. The need for detailed field measurements was assessed by comparing modeled and measured soil temperature: minimum and maximum temperature, duration of high temperature and low temperature events, and positive and negative heat flux. Models based on measurements from four or more soil layers predicted soil temperature within ±0.3°C of measured values. Models based on two or more measured soil layers were within ± 0.006 MJ m−2 of measured daily positive heat flux.
Data from the Regional Forest Nutrition Research Project (RFNRP) in Washington and Oregon were analyzed to improve stand-specific prediction of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] response to urea fertilization. The response variable (relative difference in volume growth between fertilized and control plots 4 yr after fertilization with 448 kg N/ha) was regressed against 28 stand and site variables (e.g., age, elevation, forest floor C/N ratio, soil cation exchange capacity, etc.) using stepwise multiple regression analysis. Data from 120 installations were stratified by thinning level (thinned or unthinned), geographic location (provinces), and site quality (site index and class). Forest floor C/N ratio was the dominant variable related to response. In thinned installations of high site quality (site classes 1 and 2), 60% of variation in response was explained by the forest floor C/N, and 75% of the variation in response was explained with inclusion of surface soil exchangeable K. In thinned, low site quality stands, response was not as well related to forest floor C/N. Analysis of the data by province indicated that S may be limiting in southwest Oregon and P in coastal Washington.
Soil properties under stands of vegetation dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and grass were examined 14 yr after spraying with 2,4-dichlorophenoxy acetic acid (2,4-D) to control sagebrush. Changes in only a few soil chemical properties were found after conversion to grassland. Phosphorus and K were apparently redistributed from depth to the surface 5 cm of soil by grass-dominated vegetation. Conversely, surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. No changes attributable to vegetation conversion were found for total C, Na, Mg, cation exchange capacity, base saturation, pH, bulk density, or potential net N mineralization rates at any depth. In situ net N mineralization rates at a 5- to 15-cm depth were measured under and between shrubs for both vegetation conditions 15 yr after spraying. Nitrogen mineralization was similar from positions between and under former shrubs in converted (grass) vegetation, whereas in the sagebrush vegetation, mineralization rates were higher under live sagebrush plants than in interspaces between plants. Undershrub net N mineralization rates were higher under shrubs in the sagebrush vegetation than under former shrubs in the grass vegetation. Essentially, control of big sagebrush, in the absence of grazing, had no effect on site fertility. The spatial distributions of the elements and of their cycling, however, have been altered.
A method for measuring the total 15N content of an air sample containing 15N-N2O and 15N-N2 has been developed. A high voltage arcing process is used to rapidly decompose N2O into N2 and NOx, to randomly distribute the N isotopes between the N2 and NOx pools, and to fix a sample of N2 as NOx. A routine mass spectrometric 15N analysis based on the 29:28 ion signal ratio of either the N2 pool or the NOx sample after conversion to N2 will be equivalent to the 15N content of the original sample. Two methods of 15N analysis were shown to be equally accurate and precise. The air sample may be arced and the N2 analyzed by direct inlet into the mass spectrometer while cryogenically trapping the NOx, or the NOx may be reduced to an NH+4-N salt that can be stored and analyzed later. If only a small air sample is available, 10 mL of air (at ambient pressure and temperature) can be mixed with ultrapure O2 to a N2/O2 ratio of 9:91 in a 90-mL arc vessel and arced at atmospheric pressure for at least 150 s to produce sufficient NOx to yield 1 mg of fixed N for mass spectrometric analysis. The arc method measures the combined 15N content of the major gas species produced by denitrification by a single analysis and may be applicable for field studies.
Phosphorus fertilizer applied with the seed or knifed into the soil as a band application has been shown to be more effective than broadcast P. Several experiments have shown that P fertilizer applied as a band becomes increasingly superior compared with broadcasting P as the P rate increases to the optimum rate. Phosphorus distribution in the band was judged to be a potential contributing factor. Therefore, an experiment was conducted to determine the distribution of P fertilizer solution in the band as affected by P rate and band spacing. A solution applicator was utilized to deliver fertilizer solution as ammonium polyphosphate (10-15-0, N-P-K) to application knives set about 3 cm above the surface of a catch paper. The fertilizer solution was placed on the paper and the distribution of the fertilizer droplets was measured. Knife spacings of 30, 45, 60, and 75 cm along with four P rates (7.5, 15, 22.5, and 30 kg ha−1), five traveling speeds (1.6, 2.6, 4.5, 7.1, and 9.8 km h−1), and three delivery tube sizes (0.9, 1.1, and 1.5 i.d.) were used. The results indicate that at lower rates the P solution is not distributed as a continuous band but rather as droplets of different sizes. At 7.5 and 15 kg P ha−1, the band consists of droplets at all banding spacings. Continuous bands of solution were formed at 22.5 and 30 kg P ha−1 at spacings >40 and 50 cm. Traveling speed affected the distance between droplets. The greater the speed the smaller the distance between the droplets. The increasing superiority of banding compared with broadcasting as the P rate increases may possibly be explained by the distribution of droplets in the band, where a continuous band may provide greater opportunity for the roots to utilize the fertilizer. When droplets are widely scattered, many droplet-root contacts are necessary to supply adequate P to the plant, but in a continuous band, only one contact may be sufficient for root uptake of adequate P if the roots continue to proliferate along the continuous P fertilizer band.
Large areas of lowland rice (Oryza sativa L.) soils in South and Southeast Asia are calcareous. Field studies in the 1983 dry and wet seasons evaluated the effects of N source and application method on N loss and N utilization in a calcareous clay loam soil using the 15N-balance technique. In the 1983 wet season and the 1984 dry season, crop recovery of the residual 15N remaining after the first crop was determined. When urea supergranules (USG) were deep point-placed, the partial pressure of ammonia (pNH3) in the floodwater was negligible. High floodwater pNH3 was calculated with split application of fertilizer. Farmers' split of prilled urea (PU) gave the highest pNH3 (0.44 Pa in the wet season). pNH3 in the floodwater peaked on the third day and dropped to negligible thereafter. Deep placement (10 cm) of USG had the highest grain yield in the dry season. Ammonium sulfate produced a yield similar to that of urea. The highest 15N recovery by the crop (straw + grain) was 78% in the dry season and 64% in the wet season with deep point placement of USG. Nitrogen-15-balance data showed that with point placement of USG, 3% N was not accounted for after harvest in the dry season and 10% in the wet season. In contrast, when urea or ammonium sulfate was split-applied using improved timing and water management (researchers' split), 26 to 28% of applied N was not recovered at harvest in the dry season and 36 to 41% in the wet season. Soil N fractionation showed that 14 to 26% of 15N-labeled fertilizer was immobilized into the acid-hydrolyzable organic N fraction in the dry season and 9 to 18% in the wet season. With point placement of USG and band placement of urea, the decrease in the value of hydrolyzable organic N fraction at harvest indicated N release for plant use during the cropping season. Applied N immobilized into the nonhydrolyzable organic N and fixed in the nonexchangeable N was not significant.
Total layer charge and charge of octahedral sheets of 2:1 soil clays were estimated by combining alkylammonium ion exchange technique and the Hofmann and Klemen effect. The estimation of charge before and after Hofmann and Klemen effect (Li-saturation and heat treatment) gave the total layer and tetrahedral charge, respectively. The difference of total and tetrahedral charge provided the charge contribution of octahedral sheets, assuming that a complete neutralization of octahedral charge was achieved by Li+ migration during the heat treatment. As much as 50% of the charge was found to be located in the octahedral sheets in soil smectites and soil vermiculites. Clays with total layer charge in the vermiculitic range that accommodated both double (1.8 nm) and single (1.4 nm) interlayers of glycerol in the interlayer spaces formed only double-layer complexes after Li+ treatment, indicating a reduction in total layer charge, plus a random distribution of charge in both octahedral and tetrahedral sheets of each 2:1 layer. Trioctahedral vermiculites with a total layer charge comparable to the total layer charge of dioctahedral soil vermiculites gave only single layer complexes with glycerol after Mg-saturation. These sorption characteristics can be explained in terms of Coulomb's law and the higher concentration of negative charge of trioctahedral vermiculites in the tetrahedral sheet compared with dioctahedral soil vermiculites.
The distribution of hydroxy-interlayered minerals (HIM) was studied in Ultic Haplaquods with respect to horizon and location within the soil matrix. Mineralogy of the clay fraction and of tenacious grain coatings was determined for selected horizons by means of x-ray diffraction and differential scanning calorimetry. Smectite and kaolinite were the dominant layer silicates in A and E horizons, where sand grains were stripped of coatings and clay occurred as floccules. Hydroxy-interlayered minerals were the dominant layer silicates in Bh and E′ horizons where grains were coated. Tenacious coatings removed by ultrasound from sands occurring in the Bh and E′ horizons contained more HIM and less quartz than any other portion of the soil matrix. Podzolic stripping of coatings in A and E horizons and transformation of HIM to smectite via interlayer depolymerization could explain the observed HIM depth distribution. Higher HIM concentrations in tenacious coatings in Bh and E′ horizons suggest that the coatings predated podzolization. Hydroxy-interlayered minerals in Btg1 horizons dispersed in deionized water more readily than did kaolinite, suggesting that differential dispersion in conjunction with a fluctuating water table may be a factor in pedogenic redistribution of clay minerals.
Soil salinization has resulted from seepage of water from drainage ditches in eastern North Dakota. The present study was undertaken to determine the effect of these processes on the geochemistry of shallow groundwater and on the evaporite mineralogy of the affected soils. In the chloridic system studied, SO2-4 concentrations of groundwater and saturation extracts were controlled by the solubility of gypsum. Calcium concentrations were controlled by gypsum solubility in the sulfatic system. Shallow groundwater samples collected near the recharge sources were undersaturated with respect to gypsum and oversaturated with respect to calcite. Considerable redistribution of gypsum was observed in soil profiles of strongly salinized transects of the chloridic system. Sulfate enrichment relative to Ca2+ was observed in groundwater and soil extracts collected near drainage ditches of chloridic sites. Mineralogy of efflorescent crusts included gypsum, epsomite, hexahydrite, thenardite, and konyaite in the sulfatic system, and halite, eugsterite, thenardite, konyaite, bloedite, and gypsum in the chloridic system.
Fine clays (<0.2 µm) from the matrices and clay films of soils from two Michigan hydrosequences were analyzed by x-ray diffraction to determine depth distributions and relationships to weathering and translocation processes associated with position in the hydrosequence. Illite contents of matrices generally increased, whereas vermiculite decreased with depth. This depth function was most prominent in the well and moderately well drained soils and diminished with decreasing natural drainage. Vermiculite content was negligible in both, and smectite was found in only one of the two poorly drained soils. Clay films from the well and moderately well drained soils had a mixed mineralogy of illite, kaolinite, and vermiculite, whereas those from the somewhat-poorly drained soils were primarily illitic. Where present, clay films from the poorly drained soils contained smectite in addition to illite and kaolinite. Depth distributions of matrix clay minerals in the better drained soils suggested that illite had weathered to vermiculite and hydroxy-interlayered vermiculite. Prolonged saturation and associated higher pH values may have favored illite-smectite transformations in the poorly drained positions. We suggest that hydrosequence differences in moisture content of the eluvial zones resulted in a differential dispersion of clay minerals upon wetting. This may have led to selective translocation and the observed differences in clay film mineralogy.
Forest floor beneath three even-aged pin cherry (Prunus pensylvanica L.)-birch (Betula alleghaniensis Britton and B. papyrifera Marsh.) stands were analyzed for concentrations of Ca, Mg, K, N, P, C, and total forest floor mass. A 93-yr-old even-aged northern hardwood stand served as the preharvest comparison. A trend of net forest floor material loss continued beyond canopy closure, with the Oa horizon being responsible for the change. Nutrient concentrations did not change in the Oi horizon over time. The Oe showed a peak Ca concentration at 30 yr of more than two and one-half times that of the younger and preharvest stands. Nitrogen concentration decreased in the Oe horizon and the C/N ratio widened at 10 yr. The Oa horizon had no change in Ca or Mg, but K and N increased significantly in the 10- and 30-yr stands.
Horizons (O, A, E, B, and C) of forest soils from Vermont, New York, New Hampshire, and Virginia were equilibrated with various rates of either acid (H2SO4) or base (CaCO3). Most titration curves had a logistic shape with a lower asymptote (between pH 0.3 and 3.1) and an upper asymptote (around pH 7). The lower pH asymptote was highly correlated with equilibration solution Al and with soil pH measured in 1 M NaF. The specific buffer capacity (SBC) of the 26 horizons was related to organic matter (OM). Higher OM levels caused greater SBC. The buffer capacity of the OM was 0.4 mol kg−1 OM−1 pH−1. Using pH, pHNuF, OM, and horizon depth, it is possible to estimate the amount of acid currently in the soil (compared to a reference pH), the quantity of acid needed to lower the pH by a given amount, the amount of pH decrease associated with a given amount of acid input, the lower pH asymptote, and the pH at which solution Al is above a given concentration.
Published collection efficiencies (volume of water collected divided by percolating volume calculated from a water balance) of zero-tension lysimeters are <10%, suggesting that samples collected by such lysimeters may not be representative of the water percolating downward. By increasing catchment area to 2500 cm2, and by pushing the lysimeter rim upward into the soil, collection efficiency was increased to 36% under grass and 17% under forest; failure rate (proportion of lysimeters yielding <50 mL) was decreased from 60 to 6% under grass and to 23% under forest.
The monolith and lacquer peel methods of soil profile collection proved to be unworkable for an 8-m high wall that contained both fine loams and loose gravel. A new procedure was developed that has advantages over either of the commonly used procedures. Polyurethane foam is injected as a binder and filler between the soil and the field backing board. The foam dries hard overnight making it possible for two people to remove 2-m sections of profile on the following day. The field backing board is also the final mounting board, so less time is spent in the laboratory preparing samples than with the traditional monolith procedure. Polyurethane foam makes it possible to collect larger profiles that can be more easily managed than the traditional monolith. It can be used on a wider range of textures than the lacquer peel method, and requires less time in the field because foam requires less drying time than lacquer. The foam method is an efficient way to collect large soil profiles.
An improved method is presented for separating whole soil into a mineral-free organic fraction (light fraction) and an organomineral fraction (heavy fraction) by flotation in a dense inorganic salt solution. In the existing method, the heavy fraction is settled by centrifugation and the light fraction decanted. In the improved method, the light fraction is aspirated from the solution surface by suction after the soil suspension is allowed to settle. The improved method costs less, is more reproducible, and is practical in coarse-textured soils where heavy fractions do not form stable pellets during centrifugation.
The Uhland type soil core sampling equipment was used to obtain cores 74 mm in diameter and 76 mm high from the surface 0.25 m of an alluvial soil in Louisiana. Samples were taken in pairs; one sample was taken by hammering the cutting head into the soil, and the other sample was taken by pressing the cutting head into the soil using a hydraulic cylinder. Data for 26 pairs of samples showed that the saturated hydraulic conductivity for the hammered samples averaged 2.36 µm/s, and that for the pressed samples averaged 4.28 µm/s. The difference was statistically different at the 99.5% level. Average oven-dry weight of soil in the cores was 6 g greater for the hammered than for the pressed cores.
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CodeCanyon Roman Numerals for WordPress 5487968
Plugin \ Utilities
Numerals \ WordPress \ Plugin \ Convert \ Display \ Website \ MMXIII \ Please
Plugin - Roman Numerals for WordPress 5487968 by outerbridge @ CodeCanyon
Plugin \ Utilities
About Roman Numerals for WordPress
Do you want to.
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Rather than seeing ? 2013 on your website, perhaps you'd rather give your site the Hollywood touch with: ? MMXIII ? Just add the [romandate] shortcode to your website and the Roman Numerals plugin will do the rest!
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subset: commoncrawl


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Jesse Eisenberg Compares Comic-Con to Genocide
When I watched the Comic-Con panel for Batman v Superman: Dawn of Justice, I thought to myself, "Man, Jesse Eisenberg does not look happy to be here."
When I watched the Comic-Con panel for Batman v Superman: Dawn of Justice, I thought to myself, "Man, Jesse Eisenberg does not look happy to be here."
As revealed yesterday, Batman vs. Superman will have a major presence at Comic-Con. The entire cast will be there to show off new footage from the film, and if rumors are to believed, we'll also have the new Justice League assembled on stage. But, if you aren't going to Comic-Con this year (or you simply can't wait another week), we have some good news for you: Warner Bros. has released five new Batman vs. Superman photos for your viewing pleasure.
Nobody — and we mean nobody — does Comic-Con quite like Marvel. In 2006 Marvel Studios held their first ever Comic-Con panel (announcing the Captain America and Thor movies) and has returned every year since. They've ruled the roost with dynamic, exciting presentations that mix showmanship with big announcements. But, that's all about to change. Guardians of the Galaxy director James Gunn confirmed last night that, for the first time in nine years, Marvel Studios is skipping Comic-Con.
The nerds are Clark Gregg's people. The star of (what is it now? approximately 78?) Marvel's many films and television's 'Agents of S.H.I.E.L.D.' has found his home amongst his many fans, especially those who attend the year's various Comic-Cons. Fresh off yet another Comic-Con, Gregg hit 'Jimmy Kimmel Live' to chat about the experience with host Jimmy Kimmel. In short, he loves it. But, then again, it seems like Gregg relishes his now-trademark role as Phil Coulson, well, just kind of a lot.
Do you feel a lump in your throat, or a tingle down your spine? Beware, as Comic-Con 2014 has officially caught 'The Strain,' providing a full panel for Guillermo del Toro's new FX vampire vision! We're on hand in Hall H for the blood-soaked panel, so find out what 'The Strain' has in store for its first season with our full recap from Comic-Con 2014!
The 'Sons of Anarchy' will make their final ride on FX this fall, and Comic-Con 2014 is SAMCRO's first stop on the tour. With the seventh and final season of FX's road-rashing biker drama ahead, find out what series creator Kurt Sutter and the cast had to say and show from 'Sons of Anarchy' season 7 with our full recap of today's hard-hitting panel!
The Avengers were out in force last night during Marvel's eye-popping Comic-Con panel, and despite plenty of mirth and goodwill on the packed panel itself, the footage shown to the crowd hinted at a much darker story to come in Joss Whedon's 'Avengers 2.'
We know there are some who are still on the fence about the upcoming 'Teenage Mutant Ninja Turtles' film, but going by the awesome new footage we saw at Comic-Con 2014, this movie might surprise you. If you want to know more about the work that went into bringing your beloved childhood heroes back to the big screen, check out our interviews with star Megan Fox, director Jonathan Liebesman, and the producers, straight from San Diego.
If you were dying to see the 'Mad Max: Fury Road' trailer shown on Saturday at Comic-Con 2014, the wait is over: Warner Bros. has released the first official trailer for the film online in all of its insane, violent and explosive glory.
Perhaps this time we will let "our hero" Godzilla get some actual rest before dispatching him to battle the world's other major MUTOs? Is that too much to ask? We've known for months that Legendary is eager to stay in the 'Godzilla' business after the success of this summer's awesome Gareth Edwards' feature film -- after all, they did announce a sequel to the film within days of it hitting the big screen -- but there have been plenty of lingering questions as to when that would happen and who (or what) we could expect to see in the next feature.


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Oh my gawd, an Airedale! We "went through" two of these beautiful dogs when I was a kid. They are SUPER smart! The king of the terriers! Love them! Agreed - nothing like an Airedale
Welsh terrier, I have one and its the smartest and most terrifying animal I have ever seen. And I love her to death


text:
Feb - March 2014: The Irish Times published my series of investigative pieces concerning sex and relationship education in Irish schools, which were supported by the Mary Raftery Journalism Fund.
The articles, published in Weekend Review and Education Today over four weeks, addressed how schools frequently use unaccountable external agencies - including Youth Defence, Pure in Heart, and the Irish Family Planning Association - to provide information on abortion, contraception, and sexuality. I also looked at how teachers and parents are addressing teenage sexuality.
The articles were shared almost 4,000 times on social media. I was a guest for a half-hour slot on Today FM's Ray D'Arcy Show to discuss sex education. The topic of sex education was widely taken up by national media and explored by other media outlets including RTE's Prime Time, to whom I provided informal advice, and TheJournal.ie.


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Casablanca Belle & Boutique Hotel Cartagena
Calle del Tejadillo N.38-71, Cartagena de Indias, Colombia
The stylish 4-star Casablanca Hotel offers a tasteful accommodation in a tourist area of Cartagena. Remodeled in 2012, the property features original architecture.
Set in Centro district of Cartagena, just 10 minutes' drive from Convento La Popa de la Galera, Iglesia de la Trinidad and Museo del Oro Zenu. The hotel is 100 meters away from Walled City, Museo de Arte Moderno and Santo Toribio Church.
Boutiques and a mall are also set close by.
A stunning view over the city welcomes guests to Luxury Junior Suite and Junior Suite with standard décor offering a minibar, iPod docking station, free Wi-Fi, satellite TV and plasma TV.
The restaurant serves international dishes.
Cano Gallery train station is 10 minutes' walking distance from the hotel. The hotel is around 5 minutes' drive from Rafael Nunez airport.
Guests can rent bicycles and cars on site.
Casablanca Hotel offers a wellness center, a Jacuzzi and a solarium.
Important information
- Children and extra beds
- One child under the age of 12 may stay at the price of COP 220000 per person per night in an extra bed.
- Parking
- Free Wi-Fi
- 24-Hour Check-In
- 24-Hour Front Desk
- Non-Smoking Rooms
- Soundproofed Rooms
- Rooms/Facilities for Disabled
- Gay Friendly
- Safety Deposit Box
- Business Center
- Projector
- News Stand
- Rooftop terrace
- Garden
- Elevator
- Bicycle storage
- Credit Card Accepted
- Wheelchair Access
- No Pets Allowed
- Continental Breakfast
- Buffet
- Restaurant with air conditioning
- Breakfast room
- Poolside Snackbar
- Cafe
Leisure & Sports
- Outdoor Swimming Pool
- Children's Swimming Pool
- Spa & Wellness Centre
- Exercise Gym
- Solarium
- Jacuzzi
- Barbeque Grills
- Beach umbrellas
- Sun terrace
- Chaise lounges
- Massage
- Free shuttle
- 24-Hour Security
- 24-Hour Room Service
- Tours/ticket assistance
- Wedding Services
- Business services
- Fax/Photocopying
- Newspaper service
- Currency Exchange
- Medical Service
- Bellboy
- Bicycle Rental
- Self-service laundry
- Ironing Service
Room Amenities
- In room air conditioning
- Free Wi-Fi in Rooms
- Fan/extractor
- In-room desk
- Rollaway Beds
- Wardrobe
- Mini-Bar
- Mini-refrigerator
- Direct dial telephone
- Private Bathroom
- Bathtub
- Hair dryer
- Room toiletries
- Down/feather pillows
- Plug adaptor
- AM/FM Alarm Clock
Calle del Tejadillo N.38-71, Cartagena de Indias, Colombia
A stunning view over the city welcomes guests to Luxury Junior Suite and Junior Suite with standard décor offering a minibar, iPod docking station, free Wi-Fi, satellite TV and plasma TV.
Please, select dates to see available rooms.
Availability and rates
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If you have any questions regarding your reservation made through our website, please go to our Contact Us page.
Contact Us
Casablanca Belle & Boutique
Calle del Tejadillo N.38-71, Cartagena de Indias, Colombia
What's nearby
- Local attractions
- San Diego F.M. Cafe-Sports-Bar200 m
- Walled City500 m
- Plaza Santo Domingo450 m
- Templo de Santo Domingo450 m
- Palacio de la Inquisicion500 m
- Naval Museum of the Caribbean700 m
- Museo de Arte Moderno850 m
- Cartagena's Walls500 m
- The Coches Square400 m
- Cartagena's Cathedral400 m
- Airports
- Rafael Nunez4.4 km


text:
Posted 14 May 2015
Link to this post
I'm trying to implement an imagebrowser and I want to have one controller for several editors with imageBrowser. but I want to use different root in each one.
how can I make the "path" send a prefix with the file name?
or how can I send more data with the read request (or any other request the imageBrowser allow)?
Posted 18 May 2015
Link to this post
Hello Dekel,
This functionality is not supported by our server-side implementation out of the box. However, you can pass parameters to the read method, so that it distinguishes between the images:
.Read(r => r.Action("Read", "ImageBrowser", new { foo = "bar" }))
Alas, you would need to modify the image browser implementation on the server, so that it takes this parameter into account.
Posted 18 May 2015
in reply to
Alex Gyoshev
Link to this post
I've already tried that with no luck.
I also looked at the request the the imagebrowser is generating but didn't see my custom parameter :(
Posted 18 May 2015
in reply to
Link to this post
Sorry. My mistake. it does work.
I tried without the r.Action...


text:
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We're here to help with layout, colors, photo editing, and etiquette advice. We even send you a free digital proof.
You can request edits by clicking "Request free designer assistance" at the end of personalization. If you have questions, please contact us at any time online at help.paperculture.com or via phone toll-free at 877-77-CULTURE (877-772-8588).
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Lala Watkins may be a wild designer but she's a child at heart, usually caught eating ice cream and watching cartoons. In her designs, she summons her powers of cuteness, laughter, and vivid colors to create smiles for everyone, adding an extra dash of sugar to every piece she makes.


text:
Darya London's 'Ashley Pendant' is hand crafted with Swarovski crystals and brass chain. The pendant is very light and perfect for wearing all day. It goes seamlessly with your day to day denims or your swankiest evening dresses.
Swarovski Crystals and Brass Chain.
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