bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating Soil Temperature by Linear Filtering of Measured Air Temperature
Authors: Persaud N. , Chang A. C.
Published: July 2010

Linear dynamic filtering techniques were used to model the relationship between time series of average daily air temperature and soil temperature at the 10‐cm depth. The data utilized consisted of 730 consecutive daily observations of these two variables measured at Brawley, Calif., for the period 1 Jan. 1962 to 31 Dec. 1963. The soil temperature measurements were made in a bare and level Holtville silty clay soil completely exposed to the sum. Spectral analysis procedures were used to first identify and then to obtain the factors for filtering the frequency components contributing most to the variance of each temperature series. The annual cycle (frequency 2π rad d−1 ÷ 365) contributed 82.30 and 91.10%, respectively, and the semiannual cycle (frequency 2π rad d−1 ÷ 365) contributed, respectively, 2.36 and 1.56%, of the variance of the air and soil temperature series. The analysis also showed that the annual and semiannual cycles of the soil temperature series lagged the corresponding cycles of the air temperature series by 2.5 and 10.4 d, respectively. After removing the annual and semiannual cyclic components from each series, Box‐Jenkins transfer function modelling techniques were used to describe the filter relating the residual stochastic series. The transfer function was then used in conjunction with the results of the spectral analysis to yield a relation for estimating the soil temperature at the 10‐cm depth using the air temperature as input. The residual variance of this estimation was 58.5% less than the residual variance using a linear regression equation.
Numerical Analysis of the Snow‐Plow Effect
Authors: Barry D. A. , Starr J. L. , Parlange J.‐Y. , Braddock R. D.
Published: July 2010

A mathematical model describing the snow‐plow effect, i.e. the removal of adsorbed ions from soil particles by an incoming solution with relatively high solute concentration, is analyzed. It is shown that an accurate numerical solution to the model must be obtained to investigate the influence of the parameters entering the problem. The numerical solution helps generate simple rules that allow for straightforward but accurate construction of snow plows in practical situations. The numerical results are also used to evaluate an earlier analytical approximation and are compared to experimental observations.
Selecting Rhizobium meliloti for Inoculation of Alfalfa Planted in Acid Soils
Authors: Lowendorf Henry S. , Alexander Martin
Published: July 2010

A study was conducted to obtain Rhizobium meliloti strains suitable for use with alfalfa grown in acid soils. Thirteen strains of R. meliloti were examined for their ability to grow in acidified culture medium, and seven of these were characterized for the ability to survive in acid and limed nonsterile soils or grow in the presence of the host legume, Medicago sativa L. The pH values of the most acid, defined medium that permitted growth of the bacteria from a small inoculum ranged from pH 5.3 to 6.0. For R. meliloti 411SE1 and GH1‐1SE1, the minimum pH that allowed for growth, the critical pH, was not a dependable indicator of survival in a more acid medium. Strains of R. meliloti with relatively low critical pH values survived better in a limed soil but not in acid soils than strains with higher critical pH values. Three strains of R. meliloti previously identified as good inoculants for alfalfa in acid soils did not consistently survive better than other strains in a planted or unplanted acid soil of pH 5.3. However, the plants increased the population densities of these three strains more than other strains. These results suggest that R. meliloti strains suitable for inoculation of alfalfa in acid soils may be selected not by simple saprophytic properties but by their stimulation by the host legume in acid soils.
Relationships Between Enzyme Activities and Microbial Growth and Activity Indices in Soil
Authors: Frankenberger W. T. , Dick W. A.
Published: July 2010

Soil enzyme activities are often used as indices of microbial growth and activity in soils. Quantitative information concerning which soil enzymes most accurately reflect microbial growth and activity is lacking. Relationships between the activities of 11 soil enzymes and microbial respiration, biomass, viable plate counts, and soil properties were determined in surface samples of 10 diverse soils. Correlation analyses showed that alkaline phosphatase, amidase, α‐glucosidase, and dehydrogenase activities were significantly (P < 0.01) related to microbial respiration as measured by CO2 evolution in soils which had received glucose amendments. Phosphodiesterase, arylsulfatase, invertase, α‐galactosidase, and catalase activities were correlated at the 5% level while acid phosphatase and urease activities were not significantly correlated to microbial respiration. There was no significant correlation between the 11 soil enzymes assayed and CO2 evolution in the 10 unamended soils. Only phosphodiesterase and α‐galactosidase activities were significantly (P < 0.05) related to microbial numbers obtained on some selective culture media. Alkaline phosphatase, amidase, and catalase were highly correlated (P < 0.01) with microbial biomass as determined by CO2 evolution after chloroform fumigation pretreatment. The organic C content in the 10 surface soils was correlated (P < 0.05) with acid and alkaline phosphatase, phosphodiesterase, arylsulfatase, amidase, urease, and invertase activities. Urease activity was also positively correlated with total N and cation exchange capacity and negatively correlated with the percentage of sand. These relationships suggest that urease can exist in soil as an extracellular enzyme in a three‐dimensional network of organo‐mineral complexes. Of the 11 enzymes evaluated, alkaline phosphatase, amidase, and catalase were concluded to be the most satisfactory choices in determining the relative activity and mass of the microbial population in soils. The activities of these enzymes were highly correlated with both microbial respiration and total biomass in soils.
Corn Yield‐Fragipan Depth Relations on a Zanesville Soil
Authors: Frye W. W. , Murdock L. W. , Blevins R. L.
Published: July 2010

A fragipan is a dense, somewhat indurated, very strongly acid, and slowly or very slowly permeable soil horizon that can be a physical or a chemical barrier to plant root growth. Erosion of a fragipan soil decreases the volume of soil for root growth and water storage. The effect of depth to a fragipan horizon on yield of corn (Zea mays L.) was measured during a four‐year study on a Zanesville silt loam (Typic Fragiudalf, fine‐silty, mixed, mesic). In 3 of the 4 years, susceptibility to water stress increased with decreasing depth to the fragipan horizon. Greater depth to the fragipan was associated with an increased volume for rooting and water storage, resulting in higher grain yields.
Atterberg Limits as Indices of External Surface Areas of Soils
Authors: Hammel J. E. , Sumner M. E. , Burema J.
Published: July 2010

Surface area measurements on soils are usually laborious and require expensive equipment. The relationship between Atterberg limits (plastic and liquid) and surface area is investigated with a view to being able to estimate the latter from the former. The results show that there is a very strong relationship (r2 > 0.9) which permits surface area to be estimated rapidly and cheaply.
Statistical and Stochastic Analyses of Hydraulic Conductivity and Particle‐Size in a Fluvial Sand
Authors: Byers Elizabeth , Stephens Daniel B.
Published: July 2010

An untilled medium‐grained fluvial sand near Socorro, N. Mex., was sampled in horizontal and vertical transects to study the statistical and stochastic properties of particle‐size parameters and saturated hydraulic conductivity. Hydraulic conductivity is log‐normally distributed, whereas the 10% finer, median, and geometric mean particle sizes are normally distributed. The strongest correlation between hydraulic conductivity and particle‐size distribution parameters is that of the log of hydraulic conductivity with the 10% finer particle size. Stochastic analyses using the autocorrelation function and spectrum indicate that the log of hydraulic conductivity and particle size are characterized by dissimilar spatial correlation structures in the vertical directions. In general, particle size is more structured, regular, and predictable and shows a close similarity with the stratigraphy as observed in the field. On the other hand, hydraulic conductivity in the vertical direction may best be modeled as a simple random variable. Variogram and kriging analyses indicate that both hydraulic conductivity and particle size are relatively isotropic in the horizontal plane and that marked similarities in spatial structure exist in this plane. The spatial distribution of saturated hydraulic conductivity in the horizontal plane is estimated reasonably well using the empirical relationship between particle size and conductivity along with the kriged estimates of the 10% finer particle size.
Nitrification of Fertilizer and Mineralized Ammonium in No‐Till and Plowed Soil
Authors: Rice C. W. , Smith M. S.
Published: July 2010

The influence of tillage on nitrification was examined using a variety of assays of no‐till and conventional tillage (plowed) soils. Ratios of NO‐3 to NH+4 were higher in plowed soils except immediately after fertilization. However, concentrations of total inorganic soil N were about equal in the two tillage systems. Nitrification rates, following NH+4 additions to mixed sieved soils and to intact soil cores in the laboratory, were measured under various moisture regimes. Tillage did not consistently affect nitrification when soils of both tillage treatments were maintained at the same water content. Yet, nitrification was sensitive to soil moisture and since water evaporated more rapidly from plowed soils, nitrification was sometimes more rapid in no‐till soils. One week after addition of 15NH+4 to field plots, more NH+4 had been converted to NO‐3 in the no‐till soil. It is suggested that nitrification of NH+4 fertilizer often will be more rapid in no‐till soils because of more favorable moisture conditions. Without NH+4 additions, however, nitrifier substrate (NH+4) limitations may be more severe in no‐till soils, causing slower or less complete NH+4 oxidation.
Annual Cycles of Carbon Dioxide Level in Soil Air
Authors: Buyanovsky G. A. , Wagner G. H.
Published: July 2010

The CO2 concentration of the gaseous phase of a silt loam soil (Udollic Ochraqualf) was studied under cultivation of wheat (Triticum aestivum), corn (Zea mays L.), and soybeans (Glycine max L. Merr.) over a 2‐year period. Disposable chromatographic tubes for direct field measurements of CO2 in soil air were used. Dynamics of CO2 in the soil air were observed to be conditioned by both biological and abiotic factors. Under wheat, periods of highest CO2 concentration (6–8%) corresponded to times of intensive decomposition of plant residue within the soil profile. Under corn and soybeans, highest CO2 concentrations were related to the periods of intensive plant growth. Soil moisture and soil temperature combined, were found to be responsible for just > 50% of CO2 fluctuations. The influence of water tension on CO2 in the soil atmosphere was more significant (r2 = 0.83) if data were restricted to that where temperature was 20 ± 2°C, and in transformations of the two parameters were used. The ln‐to‐ln dependence was linear within the limits from field capacity to wilting point. Under conditions of optimum soil water content, ln of CO2 concentration increased linearly with ln of soil temperature within the limits of 10 to 20°C.
Measurement of Gas Diffusion Coefficient under Relatively Low Air‐filled Porosity
Authors: Sallam A. , Jury W. A. , Letey J.
Published: July 2010

Knowledge of the diffusion coefficient is necessary for modeling gas movement through soil. Various equations have been proposed relating apparent gas diffusion to soil parameters. A laboratory study was conducted to measure gas diffusion through soil at low air‐filled porosity (0.05, 0.10, and 0.15) using an inert gas (Freon: CCl2F2). The Penman model DS/DA = 0.66a, where DA and DS are gas diffusion coefficients in air and soil, respectively, and a is the volumetric soil air content, greatly overestimated the measured DS at all porosities. The Millington‐Quirk model DS/DA = a3.33/φ2, where φ is the soil porosity, had the same curve shape but slightly underestimated the measured DS. Much better agreement between calculated and measured DS was obtained by reducing the exponent 3.33 in the Millington‐Quirk model to 3.10.
Moisture Regimes and Morphological Characteristics in a Hydrosequence in Central Massachusetts
Authors: Pickering E. W. , Veneman P. L. M.
Published: July 2010

Moisture regimes and associated soil mottling patterns were investigated over a 2‐y period in a Paxton‐Rainbow‐Ridgebury‐Scarboro hydrosequence in central Massachusetts. Changes in physical conditions in these coarse‐loamy fragipan soils were monitored with well points, tensiometers, soil temperature probes, and redox potential electrodes. Well‐drained soils appeared uniformly brown, reflective of a generally strongly oxidized environment. They also showed the greatest seasonal fluctuations in soil temperature ranging from 0 to 23°C. Matrix colors of highest chromas (6 or higher) occurred in the moderately well‐drained (MWD) soils where reducing and oxidizing environments coexist within the profile at some time during the growing season. Prominent ferrans and albans in the 2Cx horizons of MWD soils were related to sustained groundwater levels, although higher water tables often occurred for periods too short or too cold for development of strongly reducing conditions. The characteristics grey streaking patterns of fragipans were best expressed in the 2Cx horizons of MWD soils and can be attributed to reducing environments during periods with soil temperature above biologic zero when conditions are wet but unsaturated. Significant translocation and leaching of iron occurred in the somewhat poorly drained soils, as evidenced by olive‐grey matrix colors. Channel neoferrans and some neoalbans indicated that a reducing environment may persist within the B2 horizon long after it has become unsaturated. Lowest chroma colors in this hydrosequence was found in the very poorly drained soils where perennial conditions of saturation or near saturation exists up to the soil surface resulting in the strongest reducing environment and least fluctuations in seasonal temperatures.
Soil Mixing by Scarab Beetles and Pocket Gophers in North‐Central Florida
Authors: Kalisz P. J. , Stone E. L.
Published: July 2010

Soil mixing by scarab beetles (Peltotrupes youngi) and pocket gophers (Geomys pinetus) was studied on deep sands in north‐central Florida. Mound construction was monitored for 2 y on longleaf pine (Pinus palustris) (LLP) sites with dense and sparse wiregrass (Aristida stricta), and on sand pine (P. clausa) (SP) sites with dense and sparse scrub (Quercus spp.) understories. Adult beetles were active from November to April and constructed vertical tunnels at least as deep as 360 cm. Soil deposited in beetle mounds averaged 20 and 580 kg ha−1 yr−1 in SP stands with dense and sparse understories, respectively, and 1510 and 3700 kg ha−1 yr−1 in LLP stands with dense and sparse grass. Pocket gophers were absent from SP, but mounding averaged 8160 and 290 kg ha−1 yr−1 on LLP sites with dense and sparse grass. Mounding by beetles was as high as 7800 kg ha−1 yr−1, and pocket gopher mounds covered 4% of the surface area and weighed 37 500 kg ha−1 on some LLP sites. On areas with chemically contrasting soil layers, beetle mounds contained significantly greater amounts of extractable P, Ca, and Mg than the surrounding 0‐ to 10‐cm soil. Burrowing and upward soil transport also alter surface textures and produce tunnels that may function as root pathways through the generally dense subsoil. The occurrence and thickness of A horizons under LLP and E horizons under SP are also related to differences in extent of faunal mixing between the two vegetations.
Impact of Harvesting and Site Preparation on Physical Properties of Piedmont Forest Soils
Authors: Gent J. A. , Ballard R. , Hassan A. E. , Cassel D. K.
Published: July 2010

The impact of intensive forest management practices on soil bulk density, aeration porosity, and saturated hydraulic conductivity was examined to a depth of 0.3 m before harvest, after harvest, and after site preparation. Harvesting caused significant changes in soil physical properties to an average depth of 0.17 m in whole tree harvest plots and 0.22 m in skid trail plots. Disking was effective in restoring soil physical properties to preharvest levels in the upper 0.07 to 0.12 m of soil. Soil compaction in chop/burn plots may result in reduced root growth because of mechanical impedance, reduced aeration, or both.
Mineral Transformations in Soils Formed in Glacialmarine Drift, Northwestern Washington
Authors: Pevear D. R. , Goldin A. , Sprague J. W.
Published: July 2010

The Whatcom (Aquic Xerochrept) and Labounty (Typic Humaquept) series are soils formed in volcanic ash‐influenced, 10000‐year‐old glacialmarine drift. Surface horizons contain 5 to 10% volcanic ash; pyroxenes show pronounced cockscomb morphology, but associated hornblende is less weathered. Clay‐size minerals in unweathered drift are chlorite, smectite, mica, and in minor amounts, kaolinite and amphibole. The constant abundance of kaolinite throughout the profile and in the fresh parent drift suggests that it is not pedogenic. In the C horizon, chlorite has weathered to mixed‐layer chlorite/vermiculite (or chlorite/smectite) with 40 to 50% chlorite layers. The B horizon is dominated by chlorite, vermiculite, and chlorite/vermiculite. Smectite decreases upward and is absent from the uppermost part of the profile, where it has dissolved or possibly been converted to mixed‐layer kaolinite/smectite and chlorite/smectite.
Root Water Uptake and Soil Water Distribution: Test of an Availability Concept
Authors: Lascano R.J. , van Bavel C.H.M.
Published: July 2010

An experimental test was made of the hypothesis that the fractional water uptake by the root system from a soil layer is proportional to the root density and to the difference between the water potential in that layer and the mean leaf water potential. This theory adequately explained the water uptake by a cotton root system that was divided over a wet and a dry soil compartment. It was also established that the absolute rate of water uptake from each compartment could be accurately calculated from the measured potential difference between soil and plant leaf, and from a separately measured plant hydraulic resistance, which was shown to have a value of 0.67 × 109 s, independent of transpiration rate.
Enrichment of Transported Sediments with Organic Carbon, Nutrients, and Clay
Authors: Avnimelech Yoram , McHenry J. R.
Published: July 2010

Much of the nutrient inflow into impoundments is the result of erosion of soil particles on the watershed, together with adsorbed nutrients and their movement from the upland watershed soils. As the detached particles move downstream, they undergo selective size segregation and the nutrients are subject to selective desorption and adsorption between the particles and the water. During transport an enrichment of clay sized particles within the system occurs as well as that of P, N, and organic C. The ratio of the concentration of any given component in the eroded material system to that in the contributing soils is defined as the enrichment ratio. The selectivity of the erosional and sediment delivery processes involved in the transfer of eroded materials from watersheds to lakes or reservoirs is assumed to be proportional to the time, or distance, of travel. This study compares the composition of the eroded material at the onset and at the termination of the erosion, or sedimentation, cycle. From this information insight into the mechanisms affecting the compositional changes along the erosional route may be obtained. Organic carbon, total nitrogen, and total phosphorus concentrations and clay contents in sediments from 41 impoundments or lakes were compared with the equivalent parameters in the soils of the contributing watersheds. The enrichment ratio of a given component (S/So, the concentration of the component in the eroded material divided by its concentration in the soil) was theoretically predicted to be: S/So = 1/So × L, where L is a limiting value representing a stable level of this component in the erosion sequence. The measured enrichment ratios for organic C and total N were in good agreement with the theoretical model, the stable levels being 24 and 1.7 g kg−1 for organic C and total N. No such agreement was found for P and clay enrichment ratios, possibly due to the effect of the variable flow conditions on the selective erosion of these components.
Boron Toxicity to Sycamore of Minesoil Mixed with Sewage Sludge Containing Glass Fibers
Authors: Vimmerstedt John P. , Glover Thomas N.
Published: July 2010

Acid, infertile, erosive, barren “orphan” coal minesoils are a regional problem in the eastern coal fields. Learning how to establish permanent forest ecosystems on these minesoils is a goal of reclamation research in Ohio. This greenhouse research tested Newark, Ohio sewage sludge at 70, 160, 250, and 340 Mg ha−1 as treatments to promote growth of American sycamore (Platanus occidentalis L.) seedlings in toxic minesoils. Sycamore seed did germinate and grow in sludge‐amended minesoil, whereas growth was nil in the absence of sewage sludge. Soil pH, available P, exchangeable K and Ca, available Zn and extractable B all increased with sludge addition, but exchangeable Mg, available Mn and CEC declined. Regressions of N, P, K, Ca, Fe, and Cu content of seedlings on rate of sludge addition were significant and positive; a similar regression for manganese was significant and negative. Stress symptoms appearing on lower leaves of sycamore seedlings grown in sludge‐minesoil mixtures matched boron toxicity symptoms of sycamore produced in solution cultures containing 2 or 4 mg kg−1 of B and in mixtures of glass fiber insulation, a component of the sludge, with peat and vermiculite.
Characterization of Iron Oxide Minerals by Second‐Derivative Visible Spectroscopy
Authors: Kosmas C. S. , Curi N. , Bryant R. B. , Franzmeier D. P.
Published: July 2010

Derivative spectroscopy is a technique of calculating and plotting the first, second, or higher order derivative of the spectral curve relating absorption and wavelength. The second derivative greatly enhances minor convexities and concavities of the original (zero order) spectrum and gives a much narrower band width which provides improved resolution of subtle or overlapping bands. The visible spectrum and its second derivative were determined for natural and synthetic goethite and synthetic hematite. The two minerals have distinctive second‐derivative patterns. The minimum at 423 nm and the maximum at 447 nm in the second‐derivative patterns were used to estimate the amount of goethite in a mixture with kaolinite. Whole soil samples can be analyzed without pretreatment by this method, assuring that the result of the analysis is a property of the soil itself and not an artifact of a pretreatment.
Salinity and Uniformity of Water Infiltration as Factors in Yield and Economically Optimal Water Application
Authors: Feinerman E. , Knapp K. C. , Letey J.
Published: July 2010

The effects of irrigation water salinity and uniformity of infiltered water on average crop yields, economically optimal water applications, and profits are analyzed for steady‐state and transient salinity conditions. Input data specific for corn (Zea mays L.) are used in the analysis to illustrate results. Except at very low water application levels, decreasing uniformity of infiltered water results in decreasing yield at a given water application rate and at all levels of water salinity under both steady‐state and transient conditions. Profitmaximizing water applications increase under conditions of increased irrigation water salinity, decreased uniformity of infiltered water, and decreased water price; whereas profits decrease with increased salt concentrations and decreased infiltered water uniformity. Economically optimal water applications and profit can vary by factors of three or more depending on water prices, salt concentrations, and uniformity of infiltered water. Therefore accurate determination of these variables is important for decision making at the farm level.
Trace Metal Chemistry in Arid‐Zone Field Soils Amended with Sewage Sludge: IV. Correlations Between Zinc Uptake and Extracted Soil Zinc Fractions
Authors: LeClaire Joseph P. , Chang A. C. , Levesque C. S. , Sposito Garrison
Published: July 2010

The surface horizons of two field soils that had been amended with composted or liquid sewage sludge for 3 to 6 y were extracted with a series of reagents [KNO3, H2O, NaOH, EDTA (ethylenedinitrilotetraacetic acid), HNO3, in sequence] and with DTPA (1,4,7‐triazaheptane‐1,1,7,7‐pentaacetic acid) to characterize the zinc (Zn) pool in the soils with respect to lability and bioavailability. Statistical correlation analysis, comparing the extracted Zn fractions with the concentration of Zn in the leaves of barley (Hordeum vulgare L.) grown on the two soils, led to the following conclusions: (i) Zinc extracted by KNO3 and H2O in sequence is associated with the highly labile, soluble pool, dominated by Zn2+, which determines immediate bioavailability. (ii) Zinc extracted by KNO3, H2O, and NaOH in sequence has a strong, positive, 1:1 correlation with DTPA‐extractable Zn and, therefore, is associated with the labile, plant‐available Zn pool. (iii) EDTA‐extractable Zn represents a reservoir of potentially bioavailable Zn, and (iv) HNO3‐extractable Zn is associated with a nonlabile pool that is not bioavailable. These general relationships between extracted Zn fractions and bioavailability were applicable to both soils investigated and did not depend on the type of sludge applied or the length of time of sludge application.
Phosphate Sorption by Soils: III. The P Diffusion‐Precipitation Model Tested for Three Acid Sandy Soils
Authors: van Riemsdijk W. H. , van der Linden A. M. A. , Boumans L. J. M.
Published: July 2010

A recently developed diffusion‐precipitation model was tested for three acid sandy soils: two topsoils and one subsoil. It is shown that experimental data fit the model when constant P concentrations are used. As the model predicts no particular curve, third degree polynomials were used to describe the data. For further testing, increasing and decreasing P concentrations were used. Comparison of experimental and computer simulation data show that the model is also valid for varying concentrations. The concentration at the metal‐oxide/metal‐phosphate interface (indicated as C4) is relatively high: 0.1 to 0.25 mmol/L. The diffusion‐precipitation model is useful in modeling P behavior in soils.
An Improved Woodruff Buffer for Estimation of Lime Requirements
Authors: Brown J. R. , Cisco J. R.
Published: July 2010

The dominant quick‐test method of estimating soil lime requirements in the USA Corn Belt and adjacent area is the Shoemaker, McLean, Pratt (SMP) buffer method. This work was done to compare an improved Woodruff buffer with the SMP buffer to determine which most accurately estimated soil lime requirement. This study used a Ca(OH)2‐CaCl2 soil titration procedure and incubation of soils with finely ground, chemically pure CaCO3 to compare the accuracy of the original Woodruff procedure, the SMP single buffer procedure, and the new Woodruff procedure in estimating the lime requirements of 89 soil samples. The results supported 1961 findings by Ohio workers that the original Woodruff procedure drastically underestimated lime requirements. The results also supported the literature that the SMP procedure underestimates low lime requirements. The SMP tended to overestimate high lime requirements. Based upon the results of this study, the new Woodruff procedure was a better predictor of lime requirements than the SMP procedure.
Using Radar to Investigate Organic Soil Thickness in the Florida Everglades
Authors: Shih S. F. , Doolittle J. A.
Published: July 2010

A ground‐penetrating radar (GPR) system consisting of a control unit, power distribution unit, graphic recorder, tape recorder, and an antenna with a center carrier frequency of 120 MHz was used to investigate the Florida Everglades' Agricultural Area (EAA) organic thickness. Seven important factors that affected the results of GPR were the speed of antenna advance, antenna frequency selection, soil depth determination, soil moisture content, resonance problems, triple bands appearance, and data extension. Two sites located in the EAA were chosen to demonstrate the application of GPR techniques. The results showed that the GPR using a 120 MHz antenna was applicable to investigate the thickness of organic soil in the EAA. The deviations between auger boring data and radar image were within 8 cm in 91% of all samples, and within 12 cm in all samples. The correlation coefficient between the boring and the radar depth was 0.84.
Soil Water Variation in Spoil and Undisturbed Sites in North Dakota
Authors: Schroeder S. A. , Bauer A.
Published: July 2010

Analyses of total soil water monitored over a 7‐yr period on reshaped, vegetated spoil and nearby undisturbed grassland sites indicate that little, if any, water percolated beyond the rooting zone (0–122 cm) at either the spoil or undisturbed grassland sites. Total soil water below the rooting zone decreased over time, presumably due to upward movement by unsaturated flow in response to gradients created in the rooting zone by evapotranspiration. The spoil sites contained more total soil water in 1974 than the undisturbed sites but greater evapotranspiration losses at the spoil sites had presumably decreased soil water to a level nearly equal to that of the undisturbed sites by 1981.
Effects of Acid Irrigation on Carbon Dioxide Evolution, Extractable Nitrogen, Phosphorus, and Aluminum in a Deciduous Forest Soil
Authors: Johnson Dale W. , Todd D. E.
Published: July 2010

A study was initiated to determine the effects of sulfuric and nitric acid irrigation on CO2 evolution, and N, P, and Al availability in a deciduous forest soil. Irrigation with H2O, H2SO4, or HNO3 at 0.05 mol (p+) m−2 and 0.5 mol (p+) m−2 for 1 yr had no consistent effect on CO2 evolution, soil NH+4, extractable P, or extractable Al in a deciduous forest soil under field conditions. Irrigation with HNO3 caused temporary increases in soil NO‐3, but irrigation with H2SO4 had no effect on soil NO‐3. Nitrogen mineralization and nitrification by aerobic incubation were also unaffected by treatments. Seasonal variations in CO2 evolution, NH+4, and extractable P were pronounced, with peaks in CO2 and NH+4 in June and a peak extractable P in August.
Design of an Optimal Sampling Network for Estimating the Variogram
Authors: Russo David
Published: July 2010

Kriging techniques for interpolating spatial phenomena have recently been applied by soil scientists to map soil properties in heterogeneous field. A fundamental component of these techniques is the variogram which has to be estimated experimentally. A method to design an optimal sampling network for estimation of the variogram is proposed. Using a constant number of pairs of points (Np) per lag class, the criterion for selecting the location of the sampling points is the uniformity of the values of the lag vector, h, within a given lag class, for each of the lag classes which cover the field domain. For a given sample size, N, the method provides a set of scaling factors which in turn is used to calculate the new locations of the sampling points by an iterative procedure. Using the aforementioned criterion, the best set of the sampling points is selected. Analysis of the results showed that by using the proposed method, the variability of h within a given lag class, as well as the variability of h among the lag classes, was considerably reduced relative to the situation where the original locations were used. The method was found to be sensitive to both N and Np as well as to the initial locations of the points. The effect of the method on the estimation of the variogram was tested using simulated realizations of a two‐dimensional stationary and isotropic field. The results for fifty different realizations showed that the variograms which had been estimated from data generated on the coordinates of the sampling points provided by the method were smoother and fitted the theoretical variograms better than those which were estimated from data generated on the original coordinates of the sampling points. When only the smaller lag classes were considered, the differences between the two sets of the variograms become smaller.
Use of Chelating Resins in Metal Adsorption Studies
Authors: Turner M. A. , Hendrickson L. L. , Corey R. B.
Published: July 2010

Metal adsorption characteristics obtained using conventional batch equilibration methods are often of limited use for predicting the behavior of trace metals under natural conditions due to inadequate control of the composition and pH of the equilibrium solution. Much of the existing adsorption data has also been obtained using unrealistically high metal concentrations and in response to total soluble metals rather than unassociated metal ions. These limitations were overcome via the use of chelating resin to establish and maintain constant pH and metal activity in a solution of constant ionic strength and composition. The Cd/Ca ratio of the resin was varied to provide a range of Cd activities (0–1.5 µM) consistent with normal soil solution concentrations when equilibrated with 0.01M Ca(NO3)2. A series of these prepared resin systems were equilibrated with an Fe gel, a muck, and an intact soil to obtain Cd adsorption data in response to Cd activities as low as 10−8M. These resin systems can also be used to describe metal adsorption as a function of ionic metal concentrations in systems containing soluble complexing agents. The resins can provide ionic metal concentrations below the sensitivity of flameless atomic absorption spectrophotometry, and the activity of several trace metals can be maintained by the same resin, thus enabling evaluation of metal competition for adsorption sites. In some cases, the resin system may eliminate the requirement for a complete adsorption isotherm, since metal adsorption can be determined in response to one or more predetermined metal activities.
Assessment of Copper‐Soil Bond Strength by Desorption Kinetics
Authors: Lehmann R. G. , Harter R. D.
Published: July 2010

Kinetics of copper desorption from the A horizon of Paxton soil was investigated following addition of Cu at the rates of 1.6, 3.9, 6.3, and 7.9 µmol Cu/g soil (100, 250, 400, and 500 µg Cu/g soil). The Cu was allowed to react with the soil for 30 min to 4 d, at which time Na‐citrate was added in a 1:1 Cu/citrate charge ratio. Copper adsorption pH was maintained at 5.6, and desorption occurred at pH 6.0. From the desorption kinetics, it appeared that Cu was initially retained on two types of sites. Up to about 1.6 µmol Cu/g was preferentially retained on high energy sites. If Cu addition exceeded this amount, the excess was retained on low energy sites. Within about 24 h, a portion of the Cu initially bound to low energy sites shifted to sites intermediate in energy between the initially observed low energy and high energy sites.
A Simplified Soil and Plant Phosphorus Model: I. Documentation
Authors: Jones C. A. , Cole C. V. , Sharpley A. N. , Williams J. R.
Published: July 2010

The structure of a simple soil and plant P model designed for use in the Erosion‐Productivity Impact Calculator (EPIC) agriculture management model is described. The model maintains pools of stable, active, and labile inorganic P; fresh organic and stable organic P; and grain, stover and root P. The model has a daily time step, simulates P uptake and transformations in up to ten soil layers of variable thickness, and is sensitive to soil chemical and physical properties, crop P requirements, tillage practice, fertilizer rate, soil temperature, and soil water content. Fertilizer P is added to the labile inorganic P pool which is in rapid equilibrium with the active inorganic P pool. The relative sizes of the labile and active inorganic pools are soil specific and are based on soil classification, texture, and chemical properties. Movement of active inorganic P to the stable inorganic P pool simulates slow adsorption of inorganic P. Crop P uptake from a soil layer is sensitive to crop P demand and the amounts of labile P, soil water, and roots in the layer. Stover and root P are added to the fresh organic P pool upon their death and/or incorporation into the soil. Decomposition of fresh and stable organic matter may result in net immobilization of labile P or net mineralization of organic P.
A Simplified Soil and Plant Phosphorus Model: III. Testing
Authors: Jones C. A. , Sharpley A. N. , Williams J. R.
Published: July 2010

Testing of a simplified soil phosphorus model is described. Changes in organic P content of the surface soil due to cultivation are simulated relatively accurately for periods of up to 40 years at several locations in the Great Plains. Simulated changes in organic P contents of the subsoil are smaller than those of the topsoil. Concentrations of soil test P are accurately simulated over periods of up to 20 years with and without fertilizer P applications in several soils. Simulated responses of maize (Zea mays L.) and wheat (Triticum aestivum L.) to soil test P concentrations are similar to those found in three published studies. Fertilizer P required to maintain adequate P fertility is accurately simulated for maize and wheat at several locations in the U.S.
Soil Test Values for Phosphorus, Potassium, and Zinc as Affected by Rate Applied to Corn
Authors: Rehm G. W. , Sorensen R. C. , Wiese R. A.
Published: July 2010

The change in land use of the Nebraska Sandhills from native grassland to intensive production of irrigated corn (Zea mays L.) has provided a unique opportunity for the study of changes in nutrient levels of soils as affected by repeated fertilization. This study was initiated in northeast Nebraska in 1974 and continued through 1978 for the purpose of examining the effects of repeated application of P, K, and Zn on corn yield and changes in soil test values for these nutrients. Soil samples were collected prior to fertilization in 1974 for the purpose of site characterization. Soil samples (0–15 cm) were collected after each growing season where corn was harvested for grain and for silage. At the end of the 1978 growing season, samples were collected from each plot at depths of 0 to 15, 15 to 30, 30 to 60, 60 to 90, and 90 to 120 cm. Routine soil test procedures were used to analyze all samples for P, K, and Zn. Repeated application of fertilizer P and Zn produced rapid yearly increases in the soil test values for each nutrient. Repeated fertilization with K produced increases in soil test values for K but at a slower rate than changes in levels of P and Zn. Method of harvest appeared to have no influence on the soil test values for P and Zn. Average soil test values for K were lower when corn was repeatedly harvested for silage. Although relatively high rates were applied, there was no apparent movement of either P or Zn below the tillage zone. Repeated application of K produced increases in soil test values for K at depths as low as 120 cm.
Effects of Artificial Desurfacing on Alfisols and Ultisols in Southern Nigeria: II. Changes in Soil Physical Properties
Authors: Mbagwu J. S. C. , Lal R. , Scott T. W.
Published: July 2010

Changes in soil physical properties of two Alfisols and an Ultisol in southern Nigeria as affected by desurfacing to simulate varying levels of soil erosion were monitored for two consecutive seasons (3 and 7 months after exposure). These investigations were conducted at Ilora (Alfisol), Ikenne (Alfisol), and Onne (Ultisol) in southern Nigeria. All measurements were made on the top 5 cm of the undisturbed control and the desurfaced soils. Following topsoil removal some deleterious changes in soil physical properties occurred on the exposed subsoils. Seven months after removal of 10 cm of topsoil, bulk densities had increased from 1.37 to 1.45 Mg m−3 at Onne, 1.23 to 1.50 Mg m−3 at Ikenne, and 1.27 to 1.42 Mg m−3 at Ilora. These increased bulk densities were reflected in decreased total and macroporosities. Seven months after 10 cm of topsoil removal, total porosity was reduced from 48 to 45% at Onne, 52 to 43% at Ikenne, and 52 to 46% at Ilora. Available water‐holding capacities of the surface 5 cm of exposed subsoils following 5 cm of topsoil removal were reduced during 7 months by 61% at Onne, 23% at Ikenne, and 12% at Ilora. Corresponding reductions in saturated hydraulic conductivities of these soils were 75%, 65%, and 35% three months after exposure. Also reduced were the moisture retention at 0.01 MPa suction, and the clay contents of the exposed subsoils. Generally, the magnitude of these changes in physical properties was less for the undisturbed control than for the desurfaced soils. These results strengthen the argument that these structurally unstable soils of the tropics should be managed extremely carefully.
Influence of Field Environment and Fertilizer Management on Ammonia Loss from Flooded Rice
Authors: Fillery I. R. P. , Simpson J. R. , De Datta S. K.
Published: July 2010

The importance of ammonia volatilization after urea application to flooded rice (Oryza sativa L.) was assessed in six experiments at two field locations in the Philippines, using a nondisturbing micrometeorological technique. Earlier studies had produced conflicting results probably because the techniques used did not conserve the balance of physical, chemical, and biological processes that affect ammonia loss in this ecosystem. Urea was either broadcast and incorporated immediately before transplanting of rice seedlings (BI treatments) or broadcast into the floodwater 14 or 21 d after transplanting (AT treatments) and 5 to 7 d before panicle initiation (PI treatments). Ammonia volatilization proceeded rapidly and continued for 6 to 10 d after urea was applied. In the AT treatments, NH3 loss accounted for 47% and 27% of the urea‐N applied. Ammonia loss showed pronounced diurnal fluctuations that were synchronized with fluctuations in floodwater pH, between maxima of 8.6 to 9.0 at 1200 to 1400 h and minima of 7.8 to 8.0 at 0500 to 0600 h in the AT experiments. Floodwater pH in nonfertilized areas showed similar trends, indicating that fertilizer addition was not the prime cause of the pH fluctuations. Ammoniacal N in the floodwater accumulated to ≃ 14 g m−3 in the AT studies, but the concentrations decreased during daytime and increased again at night, with a net loss of ammonia during the day. Differences in wind speed appeared to account for most of the difference in NH3 loss observed between the AT treatments. Rates of ammonia loss (10–15%) were lower when urea was applied at a later growth stage (PI), even though floodwater ammoniacal N again rose to 13 g m−3. In contrast to the AT studies, floodwater pH at PI did not exceed 8.0 to 8.3. Apparently, shading of the floodwater by the rice canopy lowered the photosynthetic activity of the aquatic biomass and thus reduced the degree of CO2 depletion and the potential for NH3 loss. Ammonia volatilization loss after urea incorporation (BI treatment) accounted for only 13% of the N applied at Los Baños. This sharp reduction in loss, compared with those after AT applications, was largely due to lower floodwater urea and ammoniacal N concentrations from 2 days after application in a system where urea was largely incorporated into the soil.
Ammonia Volatilization from Urea and Urea Phosphates in Calcareous Soils
Authors: Stumpe J. M. , Vlek P.L.G. , Lindsay W. L.
Published: July 2010

Ammonia volatilization from urea is a considerable problem if fertilizer is surface applied, whether by choice (minimum tillage) or by lack of implements, which is common in the tropics. Urea phosphate [CO(NH2)2·H3PO4] was tested in several experiments as a means of reducing ammonia volatilization losses. Incubation experiments using 15N‐labeled urea were conducted to evaluate ammonia loss from urea, urea phosphate, and urea‐urea phosphate mixtures (N content = 460, 190, 370, and 350 g kg−1, respectively), applied at rates up to 100 kg N ha−1 to a variety of soils using a range of initial moisture contents. Evolved ammonia was measured by collection in an external acid trap. Ammonia volatilization losses from surface‐applied urea ranged from 10% to 30% of that applied, dependent on soil type. Initial soil moisture affected the timing of N loss, but not the total amount. Addition of urea with phosphate (190 g N kg−1) slightly decreased ammonia loss from 17.0% to 12.2% of the applied N on a highly calcareous (225 g CaCO3 kg−1) Mollisols. On the other hand, NH3 losses from a slightly calcareous (20 g CaCO3 kg−1) Vertisols were 10.5% and 3.1%, and from a slightly calcareous Entisols (2.6 g CaCO3 kg−1) were 14.4% and 4.4% of the applied N for urea and urea phospate, respectively. The relative savings of urea‐N were much higher in low CaCO3 soils (approximately 70%) than in the highly calcareous soil (approximately 30%). Mixtures of urea and urea phosphate were substantially less effective in reducing ammonia volatilization with relative reductions ranging from 0% to 20%. Detailed studies of the mobility and reactions of urea phosphate in soils revealed that rapid precipitation of calcium phosphates near the placement site and the diffusion of urea away from the placement site were responsible for the poor performance of granular urea phosphate in highly calcareous soil. It is concluded that urea‐urea phosphate mixtures should probably not be recommended as a means of reducing ammonia volatilization on highly calcareous soils, though its use on noncalcareous soils and soils low in CaCO3 merits further testing.
Development and Validation of a Numerical Model Simulating Evaporation from Short Cores
Authors: Reynolds W. D. , Walker G. K.
Published: July 2010

A theoretically‐based assessment of the short core evaporimeter technique for measuring evaporation from the soil surface can be conducted using numerical simulation. As an initial step, a numerical model is developed that simulates evaporation from isothermal, homogeneous, finite soil columns with a specified initial water content profile. Features of this model include nonlinearized solution of the highly nonlinear surface boundary condition, automatic adjustment of time‐step size according to a mass balance criterion, remaximization of program efficiency at each time‐step, and the use of soil surface temperature as the primary forcing function. The validity of the model was established through its ability to realistically simulate the constant and falling rate stages of soil drying, including root‐time behavior, and by its good mass conservation and stability characteristics. Drying of a clay soil with an initial uniform water content of 0.40 cm3w cm‐3pm for 12 000 min under a constant evaporative demand of 4.4 × 10−4 cm3w cm‐2pm min−1 could be simulated with a time‐step size ranging from 10 to 13.7 min, a specific mass (i.e. flux) balance of < 3%, a cumulative mass balance of < 0.3%, and with generally < five iterations per time‐step. A discretization analysis revealed that for the first centimeter below the soil surface a 0.2‐cm nodal spacing was required to obtain accurate estimates of the evaporative flux and the near‐surface water content profile. Below that depth, however, nodal spacing can be greatly increased without serious reduction of accuracy. Successful validation of the model supports extension to field conditions.