bluuebunny/crossref_metadata_2025 huggingface dataset:
Crust Formation and Clay Migration Effects on Infiltration Rate
Authors: Helalia Awad M. , Letey J. , Graham R.C.
Published: July 2010

A rainfall simulator study was conducted in the laboratory to investigate the effects of a cationic polymer (CP‐14), soil column thickness, water quality, and initial soil‐water content on infiltration rate (IR) and clay migration through soil. The water quality variable was imposed by synthesizing waters typical of canal water (CW) and well (WW) water from the San Joaquin Valley in California. The main difference between the waters was the electrical conductivity, which was 0.05 and 0.70 dS m−1 for CW and WW, respectively. The IR increased with increasing polymer concentration, and the highest incremental effect was between 0 and 5 mg L−1 polymer. The effluent clay concentrations were very small with WW but high with CW. The effluent clay concentrations tended to decreased with increased polymer concentration. The IRs increased, whereas the effluent clay concentrations decreased, with increased woil column thickness. There was, however, appreciable migration of clay beyond the 30‐cm soil thickness. The IR was slightly higher and the effluent clay concentration slightly lower in initially prewet as compared to air dry soil. If clay retention in columns clogged pores, the IR would be expected to decrease as soil column thickness increases. The results were opposite, suggesting that other mechanisms were involved. The formation of a crust at the soil surface having low hydraulic conductivity would be consistent with the observed results. Increased polymer concentrations were associated with increasing hydraulic conductivity of the crust, but had no consistent effect on the hydraulic conductivity of the underlying layer. Thus, the main treatment effect was on crust formation. Scanning electron micrographs showed loose, bare particles on the soil surface underlain by a dense compacted layer with or without polymer treatments. Below the dense layer the structure was more open. Therefore, under our experimental conditions, crust formation appears to be a more significant factor affecting IR than clogging of pores by clay migration. The relatively small difference in IR between CW and WW could be larger in the field where long‐term soil clogging could be more effective.
Soluble Organics from Forest Litter and their Role in Metal Dissolution
Authors: Pohlman Andrew A. , McColl John G.
Published: July 2010

The effect of soluble organics from O1 and O2 litter of seven overstory and understory forest species on dissolution of Al, Fe, Mg, and Mn from two forest soils was investigated. Litter was leached in absence and presence of soil under controlled laboratory conditions, and the leachates were analyzed. In absence of soil, different litters varied widely in their ability to release dissolved organic carbon (DOC) and metals. No significant correlations (p > 0.1) between protons consumed and DOC, Al, Mg, and Mn released from litter were found. In the presence of soils there was a direct relationship between organics released from litters and Al and Fe dissolved from soils but not for the other two metals. The predominant class of organics found in all litter leachates were acids and neutrals, and their contents were directly proportional to total organics dissolved. Thus, hydrophobic plus hydrophilic acid, base, and neutral content of litter leachates corresponded to mean values of 49.6, 8.8, and 41.1%, respectively, for all litters. Total acid content was composed of 30.6% hydrophobics and 18.5% hydrophilics. A good correlation was obtained between soil dissolved Al and hydrophobic acids (r = 0.91, p < 0.001), Al and Fe, and hydrophilic acids (r = 0.93, r = 0.85, p < 0.001, respectively). Polyphenolics constituted from 10 to 23% of the DOC content of both O1 and O2 litter extracts. Polyphenolic content was highly correlated with dissolved Al (r = 0.94, p < 0.001) and with dissolved Fe (r = 0.80, p < 0.001). Five aliphatic acids and six aromatic acids were detected and quantified. Free‐organic acids with high chelating abilities such as oxalic, malic, gallic, and protocatechuic acids made up 60 to 80% of the identified free‐acid content of six litter leachates. Significant correlation was obtained between total free‐organic acid content and dissolved Al (r = 0.87, p < 0.001) and Fe (r = 0.82, p < 0.001) from soils.
Goethite and Hematite Formation in the Presence of Clay Minerals and Gibbsite at 25°C
Authors: Schwertmann U.
Published: July 2010

After 8.4 yr at 25 °C under water, ferrihydrite was almost completely converted into a mixture of goethite and hematite. In contrast, aging in the presence of various clay minerals and gibbsite retarded (kaolinite, illite, smectite, gibbsite) or even blocked (soil smectite, allophane) transformation. The conversion rate was inversely related to the final Si concentration in solution. In addition, the presence of clay minerals resulted in higher hematite to goethite ratios, lower mean crystallite dimensions for both oxides, and the incorporation of Al into the goethite and hematite structures. Similar effects have been observed for coexisting goethite and hematite in soils.
The Effect of pH on Sodium‐Calcium and Potassium‐Calcium Exchange Selectivity for Cecil Soil
Authors: Rhue R. D. , Mansell R. S.
Published: July 2010

Cation exchange capacity (CEC) and cation‐exchange equilibria involving Na, K, and Ca were measured on the <50µm fraction of Cecil sandy loam soil (Typic Hapludult) at pH values between 4 and 8. This was achieved by equilibrating the soil separate in acetate buffers followed by equilibration in 0.1 M chloride solutions. Exchangeable cations were removed by five sequential extractions with 0.5 M Mg(NO3)2. The CEC increased two‐ to threefold between pH 4 and 8, indicating the presence of a large amount of pH‐dependent charge. CEC measured with Ca exceeded that measured with Na and was presumed to result from a greater amount of exchange between Ca ions in solution and hydrogen on the soil organic fraction. In Na‐Ca and K‐Ca exchange systems, Ca accounted for most of the increase in adsorbed metal cation charge as pH increased from 4.5 to 6.5. Estimates of exchangeable hydrogen were obtained from the relationship between CEC and pH and included in calculations of adsorbed mole fractions. Vanselow selectivity coefficients indicated that the Cecil soil preferred Ca over Na but that selectivity for Na increased sharply at low pH and low Na mole fractions. The selectivity for K relative to Ca also increased with decreasing K mole fraction with K preferred over Ca at low K mole fractions. Potassium added to Na‐Ca systems displaced more Na than Ca from the exchanger, resulting in an apparent increase in selectivity for Ca relative to Na.
The Point Representation of Soil
Authors: Holmgren George G. S.
Published: July 2010

The ambiguities of the current pedon concept are shown to derive from a dual reference to the incompatable logics of J.S. Mill and P.W. Bridgeman. It is argued that location is the proper referent for soil observations and that operational definitions should apply only to the process of sampling and not to the creation of spatial bodies. An alternate pedon definition is proposed that spatially and temporally relates individual observations to a common point of geographic reference. This allows for the systematic assignment of one‐, two‐, and three‐dimensional soil features to point locations as realizations of a sampling procedure.
Factors Influencing the Dispersibility of Clay in Worm Casts
Authors: Shipitalo M. J. , Protz R.
Published: July 2010

Earthworm activity is believed to be beneficial for the maintenance of good soil structure; however, some research suggests that it promotes soil degradation. Factors affecting the contribution of casting activity to aggregate stability were assessed by measuring clay dispersibility in casts produced by Lumbricus terrestris L. and Lumbricus rubellus Hoff. in laboratory cultures when provided alfalfa (Medicago sativa L.), bromegrass (Bromus inermis Leyss.), red colver (Trifolium pratense L.), or corn (Zea mays L.) leaves or no food. Fresh, moist casts were 26 to 41% more dispersible than uningested, moist soil. Aging reduced dispersibility of moist casts produced under alfalfa, red clover, and corn leaf diets and after 32 d casts were 26% more to 16% less dispersible than uningested, moist soil. Casts aged moist and analyzed after air drying were unaffected by aging but were 9% more to 49% less dispersible than uningested, dried soil. The effects of aging and drying increased as cast organic carbon content increased, therefore L. rubellus casts, which contained more incorporated organic matter than those of L. terrestris, were less dispersible than L. terrestris casts for most treatments. The initial dispersibility increase was due to interparticle bond disruption caused by ingestion and peristalsis. Restoration and improvement in stability was probably due to thixotropic hardening and bonding of clay with incorporated organic debris. Because fresh worm casts are highly dispersible, surface casting activity in areas exposed to raindrop impact may contribute to soil erosion and crusting. Casting activity should enhance soil aggregate stability if casts are aged or dried before being subject to dispersion.
Soil and Plant Response to Three Subsoiling Implements
Authors: Busscher W. J. , Karlen D. L. , Sojka R. E. , Burnham K. P.
Published: July 2010

Many Southeastern Coastal Plain soils require deep (>0.45 m) inrow tillage or subsoiling to disrupt dense tillage/traffic pans and/or eluvial (E) horizons. Three subsoiling implements [Super Seeder (SS), ParaTill (PT), and Kelly (KE)] were compared on Norfolk (Typic Paleudult) loamy sand to assess their effectiveness in developing and maintaining a proper rooting environment for corn (Zea mays L.). Soil strength (cone index) for the implements was evaluated with and without conventional surface tillage (disking). All three subsoiling implements effectively disrupted the E horizon regardless of surface tillage, but the 67% stand establishment in nondisked treatments was significantly lower than for disked treatments (92%). However, yields were not significantly different. Significant differences in soil strength were measured among subsoiling implements at the beginning of each growing season. In 1985 mean profile soil strength was lower (P ≤ 0.10) for SS and PT than for KE. In 1986, soil strength was lower (P ≤ 0.10) for SS than either PT or KE. The consistent difference between SS and KE occurred because SS disrupted a larger area than the thinner‐shanked KE. Nondisked treatments had mean soil strength that was 0.32 MPa lower within the row than disked treatments, but disked treatments had mean soil strength that was 0.37 MPa lower between the rows. Soil strength results suggest that Coastal Plain soils, which have been subsoiled, are less likely to restrict root development regardless of implement with, or without, prior surface tillage.
Neutron Moisture Meter Calibration in Large Diameter Boreholes
Authors: Tyler Scott W.
Published: July 2010

In studies of soil moisture flux in the arid, alluvial basins of Nevada, drilling technologies have been developed to easily and economically install 15‐cm diam. Steel casing to depths of up to 100 m. Laboratory and field calibration of a low source strength (3.7 × 108 Bq or 10 mCi) neutron moisture meter was carried out to determine the impact of such large casing on tool performance. Both laboratory and field tests showed that a quadratic calibration equation relating returned thermal neutron counts (N) to the volumetric water content (θ) of the form
urn:x-wiley:03615995:saj2sssaj198803615995005200030053x:equation:saj2sssaj198803615995005200030053x-math-0001 was acceptable to determine soil profile water content. The density of thermal neutrons returned to the detector was considerably reduced when compared to reported fluxes in traditional small diameter aluminum access pipe. This reduction is attributed to the increased air gap between the tool and the soil, and neutron capture by the steel casing.
Integral Estimates of the Sorptivity
Authors: Lockington D. , Parslow J. , Parlange J.‐Y.
Published: July 2010

The second‐order accuracy of several well‐known integral estimates of the sorptivity is shown to be limited to a particular class of rapidly varying diffusivities. This class includes the exponential and power‐law diffusivities commonly used in the description of soil‐water flow. The derivation of the sorptivity estimates and the argument for second‐order accuracy are clarified and a new formula for the sorptivity is derived that applies to a wider class of diffusivities.
Quasi‐Analytical Solutions of the Soil Water Flow Equation for Problems of Evaporation
Authors: Novak Michael D.
Published: July 2010

Quasi‐analytical solutions of the one‐dimensional soil water flow equation applied to problems of evaporation are derived and compared with exact numerical solutions available in the literature. Constant‐concentration and constant‐flux surface boundary conditions and semi‐infinite and finite soil columns are considered. For the semi‐infinite soils the quasi‐analytical technique of Philip and Knight (1974) is very successful in predicting the water content profiles for the constant‐concentration condition, and only moderately so for the constant‐flux condition. Their iterative procedure for the flux‐concentration function converges rapidly in the constant‐concentration case but an analogous procedure diverges in the constant‐flux case.

For finite soils the simple assumption that the rate of drying of the column is independent of depth in the flow equation leads to accurate predictions of the water content profiles for the constant‐concentration case, and for the constant‐flux case if the potential evaporation is low, the soil is shallow, and/or the initial hydraulic diffusivity is high. For conditions other than these roughly accounting for the higher rate of drying that occurs near the surface in this case greatly improves the agreement.
Inhibition of Hydroxyapatite Precipitation in the Presence of Fulvic, Humic, and Tannic Acids
Authors: Inskeep William P. , Silvertooth Jeffrey C.
Published: July 2010

The kinetics of precipitation of hydroxyapatite (Ca5(PO4)3OH, HAP) may be important in explaining the oversaturation of many natural waters with respect to pure HAP. Consequently, the objectives of this study were to determine the rate of HAP precipitation in the absence and presence of organic acids commonly found in soil solutions, which might act as potential inhibitors of solid phase precipitation. In well‐stirred solutions, the forward rate of HAP precipitation (R) between pH 7.4 to 8.4 was described with the experimentally derived rate equation: R = skfγ2γ3[Ca2+][PO3‐4], where s = HAP surface area (m2L−1), kf = forward rate constant (L2mol−1m−2s−1), γ2 and γ3 = di‐ and trivalent ion activity coefficients calculated from the Davies equation, and brackets represent concentrations of free hydrated species (mol L−1). The average kf in the absence of organic acids was 173 ± 11 L2mol−1m−2s−1. In the presence of 0.6 mM, 0.68 mM and 0.98 mM CTS (total soluble organic C) added as fulvic, humic, or tannic acid, the kf decreased to 2, 19, and 16 L2mol−1m−2s−1, respectively. The mechanism of precipitation inhibition in the presence of these acids appears to be adsorption of the organic ligand on the HAP seed crystals, thereby blocking sites for crystal growth. Smaller molecular weight organic acids such as citric, gallic, syringic, adipic, and azealic acid were not as effective at inhibiting HAP precipitation per unit CTS present, which may indicate the importance of larger molecular weight acids on actual physical coverage at the HAP surface. The inhibition of HAP precipitation in the presence of humic, fulvic, and tannic acids may explain why many soil solutions are supersaturated with respect to pure HAP, and why increases in P concentrations are observed in many agricultural studies in the presence of sludge or manure.
Potentially Mineralizable Nitrogen in Disturbed and Undisturbed Soil Samples
Authors: Cabrera M. L. , Kissel D. E.
Published: July 2010

Calculation of the correct nitrogen (N) fertilizer rate for a crop requires an estimate of the amount of N that mineralizes from soil organic matter during the growing season. A method proposed by Stanford and Smith for estimating N mineralization sometimes results in overpredictions which may be due to the use of disturbed soil samples. To study the effect of soil disturbance, we measured N mineralized in disturbed and undisturbed soil samples, and determined models that properly described the data for each type of sample. A double exponential model was required for disturbed samples, whereas a single exponential model was adequate for undisturbed samples. Although in general, models fitted to disturbed samples could not be used to predict N mineralized in undisturbed samples, they could be used to estimate the parameters of the single exponential model for undisturbed samples. Parameters estimated using this approach, together with daily values of soil temperature and water content, allowed reasonable predictions of the amounts of N mineralized in fallow plots on Haynie (coarse‐silty, mixed, calcareous, mesic Mollic Udifluvent) and Wymore (fine, montmorillonitic, mesic Aquic Argiudoll) soils. Parameters of the single exponential model for undisturbed samples could also be estimated from total N and clay contents of the soil. The results suggest that it may be possible to obtain accurate estimates of N mineralized in the field by estimating, instead of determining, the parameters of the single exponential model for undisturbed samples.
Horizontal and Vertical Kriging of Soil Properties Along a Transect in Southern New Mexico
Authors: Nash M. H. , Daugherty L. A. , Wierenga P. J. , Nance S. A. , Gutjahr A.
Published: July 2010

The application of geostatistical analysis to evaluate a soil transect was explored by measuring soil properties in four equal depths (0–0.3, 0.3–0.6, 0.6–0.9, and 0.9–1.2 m), at 30‐m intervals along a transect of 1800‐m length in southern New Mexico. Semivariograms were computed for clay, sand, coarse fragments, and CaCO3 percent for each depth along the transect. The horizontal semivariograms were combined to form one semivariogram to account for the anisotropy in the measurement procedure. A similar procedure was used for vertical semivariograms to account for the anisotropy in the measurement units. The combination of the equations describing the horizontal and vertical semivariograms was used in a kriging program. The kriging program was used to estimate values of soil properties at 2245 grid points from the 240 original measurements. Two‐dimensional, kriged contour maps of clay, sand, coarse fragments, and CaCO3 percent were constructed. It appears the kriging technique has excellent potential in preparation of two‐dimensional vertical contour maps of soil properties.
Potentially Available Nitrogen and Phosphorus Along a Chaparral Fire Cycle Chronosequence
Authors: Marion G. M. , Black C. H.
Published: July 2010

The objectives were to examine the effect of time, aspect, and soil horizon on N and P availabilities across a 4‐ to 85‐yr‐old post‐fire chaparral chronosequence. Nitrogen and P availabilites were measured with plant bioassays, soil incubations, soil chemical extractions, and field leaf analyses. The A horizons contained significantly higher levels of available N and P than B horizons. In general, N availability was higher in north aspect stands than in south aspects stands, while P availability was higher in south aspect stands than in north aspect stands. Nitrogen availability increased with increasing stand age up to 50 to 60 yr (aggradation phase); beyond 60 yr, N availability declined (degradation phase). Phosphorus availability decreased logarithmically with increasing age. Declining N availability in the older stands was due to declining total soil N and a decline in the fraction available; the declining P availability in the older stands was due to a decline in the fraction available. The lowering of both soil and plant N and P concentrations in older stands may contribute to stand senescence.
Estimating Soil Nitrogen and Carbon Pools in a Northern Hardwood Forest Ecosystem
Authors: Huntington T.G. , Ryan D.F. , Hamburg S.P.
Published: July 2010

An intensive soil sampling design was evaluated to determine what resolution could be obtained in N and C pool size estimates in a northern hardwood forest soil. Pits of measured volume were excavated by horizon in the forest floor and in three depth strata in the mineral soil. Future comparisons should be able to detect differences in N and C pool sizes ranging from 8 to 25% of the observed mean values depending upon the element and depth strata. Future sampling should detect changes of 230 and 130 kg N ha−1 in the forest floor (combined O horizons) and 0‐ to 10‐cm stratum in the mineral soil respectively. Similarly, changes of 5.9 and 2.4 Mg C ha−1 should be detectable for forest floor and 0 to 10 cm pools respectively. Soil N content for the forest floor was 1300 kg N ha−1. For the mineral soil depth strata (0–10 cm, 10–20 cm, 20 cm to the bottom of the B horizon), N contents were 1600, 1200 and 3100 kg N ha−1 respectively. Total solum N content was estimated to be 7200 kg N ha−1. Soil C contents for the combined O horizons, 0‐ to 10‐, 10‐ to 20‐ and ≥ 20‐cm strata were 30, 32, 27 and 73 Mg C ha−1 respectively. The total solum C content was estimated to be 160 Mg C ha−1. Concentrations of soil N and C were positively correlated with elevation over the 240 m range studied, but soil pools of N and C were not correlated with elevation or soil mapping unit.
A Small‐Plot Point Injector for Liquid Fertilizer Application
Authors: Benjamin J.G. , Cruse R. M. , Blaylock A. D. , Vogl L. V.
Published: July 2010

Point injection of liquid fertilizer has shown promise as an alternative to standard surface or subsurface fertilizer application, particularly with no‐till and ridge‐till planting systems. Field‐scale point injector applicators are difficult to use in small plots, especially with labeled fertilizer materials such as 15N. This paper describes the construction and use of a small, inexpensive fertilizer application system, which simulates fertilizer injection by a large point injection applicator. Use of the applicator for 3 yr has shown the unit to be relatively accurate, durable and compatible with a variety of fertilizer materials.
A Generalized Solution to Infiltration from a Surface Point Source
Authors: Healy R. W. , Warrick A. W.
Published: July 2010

A method is presented for the estimation of the time‐variant extent of the wetting front and wetted volume that develop in soil in response to infiltration from a surface point source. The method is based on a numerical finite‐differences solution of a dimensionless form of Richard's equation for axially symmetric flow. The generalized solutions are obtained from empirical equations, the coefficients for which are contained in a single table for a variety of soils and source strengths. Results for specific locations are obtained by application of scaling factors to the generalized results and possibly some interpolation. The method should be of particular value in the design of trickle irrigation systems by allowing simple estimation of rates and lengths of water application, as well as spacing between water emitters.
Sorption of Cadmium, Nickel, and Zinc by Kaolinite and Montmorillonite Suspensions
Authors: Puls Robert W. , Bohn Hinrich L.
Published: July 2010

Sorption is the predominant process governing metal ion movement in soils and includes the following physical and chemical mechanisms: adsorption, precipitation and absorption. This research attempts to use the hard‐soft‐acid‐base principle to explain sorption selectivity of the metal cations Cd, Ni and Zn by kaolinite and montmorillonite clays. The hard‐soft character of the clay surfaces, which is due to their surface functional groups, may be inferred by cation sorption selectivity experiments where pH and complex ion formation are controlled and monitored. Calcium saturated clays were suspended in Ca(ClO4)2, CaCl2 or CaSO4 and spikes of the above metals as divalent cations were added and their reactivity assessed within the framework of the HSAB Principle. For kaolinite in Ca(ClO4)2, metal sorption followed the sequence Cd > Zn > Ni. For montmorillonite in Ca(ClO4)2, metal sorption followed the sequence Cd ≈ Zn > Ni. In CaCl2 and CaSO4, the selectivity was different due to the presence of Cl− and SO2−4 which competed with the mineral surfaces for the divalent metal cations.
Reactivity of Phenolic Acids in Soil and Formation of Oxidation Products
Authors: Lehmann R. G. , Cheng H. H.
Published: July 2010

Phenolic acids were shown to be oxidized rapidly in the presence of MnO2 to form a number of soluble products which were detectable by high pressure liquid chromatography. Some of the oxidation products have higher molecular weights than the parent compounds as shown by mass spectrometry; however, no significant products of polymerization were detected. Tests with ferulic acid showed that these oxidized products were rapidly sorbed to MnO2 surfaces and became less extractable by acidified organic solvents except after acid or alkaline hydrolysis treatment. Reactions of the phenolic acids with a variety of soils demonstrated that similar oxidation reactions could also occur in natural soils, the extent of which appears, however, to be affected by the nature of soil organic matter on the soil mineral surfaces.
Field Soil Properties Influencing the Variability of Denitrification Gas Fluxes
Authors: Grundmann G. L. , Rolston D. E. , Kachanoski R. G.
Published: July 2010

The spatial variability of field denitrification gas fluxes was investigated in relation to water content, soil‐gas diffusivity, nitrate concentration, and water soluble organic C. Water was applied in a periodic fashion along a strip of Yolo soil (Typic Xerorthents) amended with chopped alfalfa hay and nitrate. Data were analyzed statistically using simple correlations and spectral and coherency analysis. Log spectrums showed that nitrate cycled at the frequency at which water content cycled and was negatively related to water content due to apparent leaching of nitrate from the high water application areas. Denitrification gas flux cycled at twice the frequency of water content with maximum fluxes occurring at the sides of the water peaks. Spectrums for water soluble organic C and gas diffusivity indicated no significant spatial cycling. Although denitrification gas flux was more highly correlated to soil‐water content than to any other variable, coherency analyses revealed no significant relationships between denitrification gas flux and water or nitrate at specific frequencies due to opposing effects related to nitrate leaching and small gas diffusivities at the soil surface. The spatial pattern of denitrification calculated from a simple equation was examined using spectral analysis and was found to be not representing measured denitrification gas flux adequately at the frequency at which water content cycled. The discrepancy between measured denitrification gas flux and calculated denitrification rates was attributed to very small gas diffusivities preventing gas transport to the surface and inadequate characterization of actual C and nitrate concentrations at microsites.
Oxidative Coupling and Polymerization of Guaiacol, a Lignin Derivative
Authors: Simmons Kathleen E. , Minard Robert D. , Bollag Jean‐Marc
Published: July 2010

In order to better understand the chemical reactions involved in humus formation, guaiacol, a lignin derivative, was enzymatically oxidized. Under the conditions used, seven oligomers—five dimers and two trimers—were formed and comprehensive structural analyses were performed on these products. The oligomers were predominantly polyphenolic in nature, resulting from C‐C coupling of the guaiacol monomer. Two oligomers were formed by C‐O coupling and one dimer had a quinonoid structure. Based on the product structures, reaction pathways for the oxidative oligomerization of guaiacol are proposed. In this reaction pathway scheme, free‐radical coupling of the oxidized guaiacol leads to the formation of four dimeric intermediates. Nonenzymatic reactions of the four intermediates result in the formation of the seven stable guaiacol‐derived oligomers. Such reaction schemes may elucidate the mechanism of humus formation.
Cultivation and Slope Position Effects on Soil Organic Matter
Authors: Woods L. E. , Schuman G. E.
Published: July 2010

Our objective was to determine the effect of land use and slope position on the organic matter (total and active) of two related soils with different A‐horizon thicknesses. To accomplish this, we sampled the surface 7.5 cm of soil from top, mid and bottom slope positions of paired native grassland and wheat‐fallow cropland toposequences of the Ascalon (Aridic Argiustoll) and Renohill (Ustollic Haplargid) soil series. We measured total organic matter (organic C and Kjeldahl N), and active organic matter (microbial biomass, and mineralized N and respired C in 20‐d laboratory incubations) concentrations. Concentrations of all measured properties were much lower in cultivated than in native sites, and smaller fractions of the total organic matter were in microbial biomass or in forms mineralized during incubation. Total organic matter concentrations increased downslope in the Renohill soil, but decreased downslope in the Ascalon soil. Active organic matter concentrations differed less between between slope positions than between land uses or soil series. Concentrations of active organic matter were equal in the two soils, even though the Renohill soil had been tilled longer (>25 yr vs. 1 yr) and had a thinner native A horizon (13 vs. 32 cm). One year of cultivation of the Ascalon soil reduced both its active organic matter concentrations and the fractions of the total organic matter in active forms by approximately the same amount as did 25 yr of cultivation of the Renohill soil.
Response of Soybean to Lime and Molybdenum on Ultisols in Northern Alabama
Authors: Burmester C. H. , Adams J. F. , Odom J. W.
Published: July 2010

Because previous liming experiments in northern Alabama showed that critical soil pH for soybean [Glycine max (L.) Merr.] varied widely among sites, an on‐farm research program was initiated to delineate the separate effects of likely acid‐soil infertility factors in the area. Factorial treatments at 15 test sites included lime and Mo at rates of 0 and 4500 kg ha−1 and 0 and 100 g ha−1, respectively. Thirteen experiments showed yield increases from liming, 12 of which also showed yield increases to Mo. Yield responses due to correction of only Mo deficiency occurred in five experiments while liming appeared to alleviate Al toxicity, as well as Mo deficiency, in six. Increased Mo availability was accompanied by increases in soybean leaf‐N and by increased seed weights. The soil parameter that correlated best with Mo deficiency was the Fe/Mo ratio from an acid ammonium oxalate extract. The critical ratio was about 1540. Molybdenum deficiency in soybean was found to be widespread.
Cokriging Point Data on Moisture Deficit
Authors: Stein A. , van Dooremolen W. , Bouma J. , Bregt A. K.
Published: July 2010

Existing computer calculations by simulation of the moisture deficit (MD) were used for 500 point observations in an area of 404 ha with sandy soils in the Netherlands. The statistical prediction techniques kriging and cokriging were used to predict MD‐values in 100 points selected at random from the 500 available points. The MD‐data at the remaining 400 points were used for the predictions. The mean variance of prediction error (MVPE) and the mean squared error of prediction (MSEP) decreased only slightly when kriging is compared with cokriging using the mean highest water‐table level as a covariable. The number of MD‐values used in cokriging could, however, be reduced from 400 to 160 with only a small loss of accuracy in using 400 observations on the mean highest water‐table (MHW) as a covariable. As the MD‐variables being considered are four times as expensive to determine as the covariable, which is routinely estimated during soil survey, this also represents a considerable reduction of costs. Cokriging can thus be a useful technique to more effectively utilize available soil survey information.
Selection of a Parameter Describing Soil Surface Roughness
Authors: Lehrsch G. A. , Whisler F. D. , Römkens M. J. M.
Published: July 2010

The microrelief of the soil surface, termed soil surface roughness, affects water movement into a soil profile as well as seedling germination in the seedbed. When analyzing surface roughness, the selection of a measurable, physically significant parameter describing roughness is critical. An evaluation was conducted on eight roughness parameters, including maximum peak height, a microrelief index (the area per unit transect length between the measured surface profile and the least‐squares regression line through all measured positions of the transect), peak frequency, and MIF (the product of the microrelief index and peak frequency). The objective of the study was to select the parameter being the best descriptor of soil surface roughness. An automated, noncontact profiler was used to obtain surface profiles along transects, 5‐cm apart, of 1‐m by 1‐m plots after a cultivation and a simulated rainfall application at each of three different stages of soybean [Glycine max (L.)] development. For each cultivation, surface profiles were obtained on bare plots before rainfall and on adjacent vegetated plots after rainfall. The common logarithm of the MIF parameter was selected as the best descriptor of surface roughness because of its sensitivity to simulated rainfall as a source of variation, and its consistent response to such rainfall. MIF can also account for spatial dependency and can be measured relatively precisely.
Carbon Movement in Runoff and Erosion Under Simulated Rainfall Conditions
Authors: Lowrance Richard , Williams Randall G.
Published: July 2010

Organic C loss in erosion contributes to depletion of soil organic matter in continuously cultivated soils. Runoff, erosion, and C movement were measured from eight 39.6 m2 plots under simulated rainfall in order to assess C movement from a coastal plain soil. Plots were located at the Univ. of Georgia Coastal Plain Exp. Stn. near Tifton, GA, on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudults). Four soil cover conditions were duplicated on the eight plots: two‐row peanuts (Arachis hypogea L.), four‐row peanuts, continuous fallow, and bare‐bedded. Samples were taken during rainfall simulator events in March, July, and September 1985 and April 1986. Continuous fallow plots had significantly higher C concentrations in runoff and higher sediment concentrations. Sediment from the four‐row peanut plots had the highest C content, 5.83%. Total loads of C and sediment and total runoff were about twice as high from the bare‐bedded plots. Approximately 1.0% of the total soil C could be moved annually from the continuous fallow plots with a lower percentage from the other treatments. Runoff as well as sediment and C loads were lowest for simulated rainfall during September when peanuts had been inverted and were on the soil surface. Events in March and April produced lower runoff and lower sediment and C loads than events in July. Apparently the residue cover in the spring was more effective at preventing runoff and erosion than the partial crop canopy in July.
Detachment of Soil as Affected by Fertility Management and Crop Rotations
Authors: Hussain S. K. , Mielke L. N. , Skopp J.
Published: July 2010

An experiment was initiated on Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in 1981 to compare the effects of fertility management and crop practices on splash detachment of soil. Experimental treatments included comparisons of crop rotations of soybean [Glycine max (L.) Merr.] after corn (Zea mays L.) (SB), corn after soybean (C), and oat/red and yellow sweetclover (Avena sativa L./Trifolium pratense L. and Mellilotus officinalis Lam.) after corn (O/CL). For each crop rotation, there were two management options, either added manure (OR) or herbicide plus chemical fertilizer (HF). The seventh treatment was continuous corn (CC) with herbicide, chemical fertilizer, and insecticide. Soil surface samples from each treatment were subjected to rainfall intensities of low (35 mm h−1), medium (62 mm h−1), and high (120 mm h−1). Total splash detachment of soil from simulated rainfall was linearly related to rainfall intensity. For all crop rotation treatments, total splash detachment generally was greater for manured soils than from soil with herbicides and fertilizer. Continuous corn had the lowest soil splash detachment at low intensity, second highest splash detachment at medium intensity, and the highest splash detachment at high intensity. This trend clearly indicated that rate of splash detachment of CC was higher than from soil under crop rotations. The splash detachment rates were 48, 40, 39, and 31 mg cm−3 for CC, C, SB, and O/CL, respectively. Treatment by rainfall intensity interaction was significant, which suggested that intensity and crop rotation were not independent in their effect on soil splash detachment. Soil aggregation as inferred from geometric mean diameter (GMD) indicated that CC had the lowest degree of aggregation (150) as compared to 211 for C, 225 for SB, and 313 for O/CL.
Improved Apparatus for Preparing Nitrogen‐15 Labeled Anhydrous Ammonia
Authors: Vanden Heuvel R. M.
Published: July 2010

An all‐stainless steel apparatus is described that allows for dilution of highly 15N‐enriched liquid anhydrous ammonia (LAA) with natural abundance LAA to accurately and precisely produce up to 142 mL of LAA for 15N‐enrichments up to that being used for dilution. Such flexibility of 15N‐labeling is useful for studies where 15N‐enrichment requirements are diverse. The apparatus, calibrated for various volume‐pressure combinations of anhydrous ammonia gas at room temperature, allows for sequential recovery of selected amounts of 15N‐enriched and natural abundance LAA in a liquid N2 cold trap. The apparatus is constructed from commercially available components and the cylinders used for collecting the 15N‐labeled LAA are easily adaptable for use in laboratory and field N investigations.
Direct Observation of Phosphate Precipitation in the Goethite/Phosphate System
Authors: Martin Ronald R. , Smart Roger St. C. , Tazaki Kazue
Published: July 2010

A combined scanning Auger, XPS, scanning SIMS, and TEM (electron diffraction) investigation of naturally‐occurring goethite surfaces in contact with 10−3 M KH2PO4 solution for 90 d at 60 °C has shown that isolated crystallites of the mineral griphite, Fe3Mn2(PO4)2.5(OH)2, are formed by reprecipitation from solution. No adsorbed phosphate can be detected on the goethite surface above 0.1 atomic % and there is no phosphate penetration of the goethite crystals. Evidence concerning initial adsorption of phosphate, before recrystallization, is reconsidered. The results suggest that phosphate retention in Fe oxide systems may be due primarily to precipitation rather than adsorption.
A Laboratory Technique for Releasing and Measuring Denitrification Products Trapped in Soil
Authors: Holt L. S. , Christianson C. B. , Austin E. R. , Katyal J. C.
Published: July 2010

Several laboratory denitrification studies have shown an incomplete 15N balance at their conclusion. This incomplete 15N balance could be attributed to trapped gaseous products of denitrification within the soil. Incubation trials were designed to determine whether a complete 15N balance could be achieved if these trapped gases were released and included in the 15N balance. At the end of a preliminary incubation trial using flooded soils, 80% of the fertilizer was found in the soil and water fraction while the measured loss through denitrification into the headspace was only 2.6% with 70% in the soil and water fraction. When the incubation vessel was thoroughly shaken prior to sampling, fertilizer N recovery in the gaseous phase increased to 26.7%. This indicated that most of the gaseous products of denitrification had been trapped within the soil, and a nearly complete 15N balance was obtained.
Nitrogen‐15 Uptake by Eggplant Under Sodium Chloride Stress
Authors: Pessarakli M. , Tucker T. C.
Published: July 2010

Plant growth and nutrient uptake are adversely affected under salt stress conditions. This study was conducted to examine the effects of NaCl stress on growth of eggplant (Solanum melongena L., cv. Syria), and 15N uptake and distribution in plant shoots and roots. Absorption pattern of 15N by eggplant from normal (−0.03 MPa osmotic potential) and NaCl salinized (−0.3 and −0.6 MPa osmotic potentials) nutrient solutions was investigated in a growth chamber. The 21‐d‐old seedlings were grown for 7 d in complete Hoagland solution before and 7 d after the completion of salt treatments. This was followed by 3‐d growth in minus N solution with respective salinity levels, and a 90‐d 15N uptake period after 15NH415NO3 addition to nutrient solutions. Nutrient solutions were sampled at 5‐d intervals for 15N disappearance from the pots (plant absorbed). Plant tissues were analyzed for distribution of 15N in shoots and roots. Lowering the osmotic potential of culture solution decreased total N and 15N uptake by plants at all salinity levels. Increasing salinity decreased dry matter production and water uptake to a greater extent than 15N absorption. Nitrogen‐15 concentration was substantially higher in shoots and roots of salinized plants as compared with the controls at the 90‐d harvest. Only at the 30‐d harvest was 15N concentration in shoots significantly higher than in roots at each salinity level. Any level of NaCl in the root medium appears to be detrimental to eggplant growth in terms of dry matter production as well as nitrogen (N and 15N) and water uptake.
Solution Parameters Influencing Dissolved Organic Carbon Levels in Three Forest Soils
Authors: Evans A. , Zelazny L. W. , Zipper C.E.
Published: July 2010

A column study was conducted using selected horizons from three soils that were leached with pH 4.8 solutions containing either SO2−4 (0–0.208 mmol L−1) or NO−3 (0–0.16 mmol L−1) at various ionic strengths (0.2–2.53 mmol L−1). The quantity of dissolved organic C (DOC) release into the soil solution decreased with increasing ionic strength, with DOC levels remaining constant for ionic strengths > 1.10 mmol L−1. The addition of SO2−4 (0–0.208 mmol L−1) to the leaching solution resulted in elevated DOC levels over a wider range of ionic strengths, while DOC levels increased substantially for NO−3 additions only at conditions of low ionic strength <0.5 mmol L−1 and higher NO−3 concentrations > 0.048 mmol L−1. The portion of total measurable DOC attributed to anion source, compared to that of ionic strength, was observed to increase under conditions of low ionic strength and high anion concentration. Results suggest that anion composition and ionic strength may regulate DOC levels in solution.
Estimating Molecular Diffusion Coefficients of Urea in Unsaturated Soil
Authors: Sadeghi A. M. , Kissel D. E. , Cabrera M. L.
Published: July 2010

A correct value for the molecular diffusion coefficient of urea in soil (Ds) is required to accurately predict urea movement in soil by molecular diffusion. In previous work, to estimate Ds in a simulation model of urea diffusion, we used an empirical equation of Papendick and Campbell that describes Ds for a dissolved species in soil to be a product of a tortuosity factor squared, the species diffusion coefficient in water (Dw), and the volumetric water content. Comparisons of measured and computed urea concentration with depth indicated that this equation was not adequately general over a wide range of soils. The objective of this study was to modify the parameters in the equation and, if necessary, develop a new relationship to estimate the value of Ds in soils. Laboratory studies were conducted on seven soils in which the clay content ranged from 10 to 51%. Urea concentrations with depth at 48 h following surface‐application were measured and also computed using numerical techniques with an initial estimate for Ds instead of computing it using Papendick and Campbell's equation. The Ds was modified incrementally, until the difference between computed and measured concentrations was minimized. In all seven soils, good agreement was obtained between measured and computed urea concentrations with depth. The maximum depth of urea movement occurred in Kahola soil (approx. 3.5‐cm deep), whereas least movement occurred in Crete soil (approx. 2.6‐cm deep). Nonlinear regression analysis gave a better relationship (Ds = 0.18 × Dw (Θv/porosity)2.98, R2 = 0.88) when relative water content (Θv/porosity) of the seven soils was substituted for the volumetric water content (Ds = 0.73 × Dw (Θv)2.58, R2 = 0.66) in Papendick and Campbell's equation.
Water Flow Through Layered Anisotropic Bedded Soil with Subsurface Drains
Authors: Rogers J. S. , Selim H. M.
Published: July 2010

Results for steady‐state water flow in layered bedded soils with subsurface drains are presented. The soil was assumed to consist of one or more layers bounded below by an impervious barrier and above by a soil surface of uniform slope. Each soil layer was considered water‐saturated and uniformly isotropic or anisotropic within the layer. Anisotropy was defined such that ζ ≠ κ where ζ and κ are the horizontal and vertical hydraulic conductivities, respectively. The finite element method was used in the numerical solution for steady and saturated flow. Although the numerical techniques presented can handle any number of layers, results are only presented for one‐ and two‐layered profiles. The effect of the degree of anisotropy (R) and equivalent hydraulic conductivity (K) for individual layers (where R = [ζ/κ]1/2 and K = [ζ κ]1/2) on drain outflow, water seepage along the soil surface, and the relative flow within each layer was investigated. The presence of subsurface drains increased the total flow into the bedded soil surface and decreased (often eliminated) water seepage outflow along the sloping soil surface. The influence of the depth of subsurface drains below the ground surface was dependent upon both K and R of the soil layers. In general, higher K and higher R in the layer containing the subsurface drain resulted in higher drain flows.
Glass Microelectrode Techniques for In Situ pH Measurements
Authors: Conkling B. L. , Blanchar R. W.
Published: July 2010

Glass pH‐sensitive microelectrodes with lengths < 0.1 mm and diameters < 0.05 mm have many potential uses for in situ soil pH measurements. Physically stable glass microelectrodes which responded rapidly to pH were constructed and their response to soil chemical and physical influences measured. The pH of nine inorganic salts and organic acid solutions measured with the glass microelectrode were compared to those measured with a glass macroelectrode. A slope of 0.92, an intercept of 0.35, and regression coefficient of 0.99 indicated good agreement. Soil suspension pH measured with glass micro‐ and macroelectrodes was compared for eight soils. A slope of 1.26, an intercept of −1.19, and regression coefficient of 0.96 indicated a slight variation. These differences were partly attributed to unavoidable electrode placement problems. In general pH measured with macro‐ and microelectrodes compared very well. The influence of soil water pressure gradients in the range of −10 to −1500 kPa near the pH and reference electrodes on microelectrode pH measurements was studied. No significant differences in pH values due to moisture gradients were observed when the reference electrode was placed in soil at water pressures greater than −33 kPa. Standard deviations in pH where the glass microelectrode was placed in soil with water pressures from −10 to −1500 kPa varied from 0.07 to 0.17 indicating that moisture gradients have little influence on measured pH. Results indicate that glass pH microelectrodes are suitable for use in soil systems.