bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Aluminum Adsorption on Clay Minerals and Peat
Authors: Jardine P. M. , Zelazny L. W. , Parker J. C.
Published: July 2010

Mechanisms of Al adsorption on Ca‐saturated kaolinite, montmorillonite, and peat were studied by miscible displacement methods. Partially neutralized 1.0 × 10−4 M AlCl3 solutions with basicities of 1.0 were leached through monomineralic columns and effluent analyzed for monomeric and polymeric Al, titratable acidity, and desorbed Ca as functions of time. Polymeric Al was preferentially adsorbed by kaolinite throughout the displacement experiment whereas montmorillonite preferentially adsorbed monomers at short times and polymers at longer times. Selective adsorption of monomeric or polymeric Al on peat was not evident. Aluminum adsorption kinetics on kaolinite, montmorillonite, and peat was described by two simultaneous reactions—a relatively rapid reaction involving Al‐Ca exchange and a slower reaction involving Al polymerization on the adsorbents. This scenario is supported by potentiometric titrations of effluent Al and by analyses of effluent Ca, and adsorbed, exchangeable and nonexchangeable Al basicities. Negligible adsorption of Al on gibbsite and quartz indicated that surface bound Al on kaolinite and montmorillonite may serve as a template for adsorption of more Al.
Transient Microsite Models of Denitrification: III. Comparison of Experimental and Model Results
Authors: McConnaughey P. K. , Bouldin D. R. , Duxbury J. M.
Published: July 2010

Experiments were designed to investigate the validity of proposed reaction‐diffusion models of denitrification. Brass respirometers were used to measure fluxes of oxygen (O2), carbon dioxide (CO2), and nitrous oxide (N2O) from a 5 × 10−3‐m layer of saturated soil incubated at 25°C. Gaseous fluxes were measured as a function of time after wetting, with and without 0.42 mol m−3 of acetylene (C2H2) present in the headspace. The presence of C2H2 in the headspace doubled O2 fluxes 35 to 60 h after incubations commenced. When C2H2 was not present, N2O evolution was negligible after 25 h of incubation. Nitrous oxide fluxes predicted by the models were compared to those observed experimentally. When C2H2 was present, the models predicted N2O fluxes reasonably well (r2 = 0.90 and 0.78) for initial nitrate (NO−3) N levels of 7.1 and 15.9 mg N kg−1 soil, respectively. When C2H2 was not present, the models predicted the experimentally observed initial flux of N2O if an 8 to 10 h lag in N2O reductase activity was included in the models. The best model for describing N2O fluxes in these experiments used differential rates of Michaelis‐Menten reduction without NO−3 and nitrite (NO−2) inhibition of N2O reduction. Experimental techniques and parameter characterization, however, need considerable refinement. Independent measurements are needed to quantify relationships between reaction order and kinetic parameters. Still, given the general agreement between observed and predicted fluxes, there can be little doubt that the reaction‐diffusion models are essential to a better understanding of denitrification.
Tillage Effects on Soil Thermal Properties
Authors: Potter K. N. , Cruse R. M. , Horton R.
Published: July 2010

Theoretical considerations indicate soil thermal properties may be altered by tillage, but few field studies have been conducted to compare soil thermal properties as affected by conservation or notill management systems. Surface‐soil thermal properties were determined in the row zone for three soils in three tillage systems: conventional till, chisel plow, and no‐till. The apparent thermal diffusivity was determined by harmonic analysis of soil temperature data, volumetric heat capacity from the volume fraction of the soil components, and thermal conductivity by the line source heat‐probe method. Soil volumetric heat capacity was similar for all tillage treatments. Thermal diffusivity was significantly greater in the notill system than in conventional and chisel plow tillage systems, indicating that thermal conductivity also was greater in the no‐till system. Direct determination of thermal conductivity by the line source heat‐probe method at one site indicated that thermal conductivity was more than 20% greater in no‐till than in the conventional till system. Percentage surface residue cover had a greater influence on soil temperature and soil heat flux than soil thermal properties.
Nutrient Losses from Timber Harvest in the Idaho Batholith
Authors: Clayton James L. , Kennedy Debora A.
Published: July 2010

Nutrient budgets for a mature ponderosa pine/Douglas‐fir [Pinus ponderosa Dougl./Pseudotsuga menziesii (Mirbel) Franco var. glauca (Beissn.) Franco] forest in the southwestern Idaho batholith are used to evaluate the potential for accelerated nutrient losses associated with timber harvesting. Soils formed from granitic rock in the Idaho batholith are commonly shallow, coarse textured, and highly erodible following disturbance. Cycling and annual budgets for K, Ca, Mg, S, P, and N are described for an undisturbed control watershed, and accelerated losses assoicated with clearcutting, helicopter yarding, and broadcast burning of slash are evaluated in an adjacent treated watershed. There were small but statistically significant increases in dissolved N losses of approximately 10 times preharvest rates for a 4‐yr period following treatment. Dissolved transport of other elements was not increased. Small but significant increases in sediment nutrient transport of all elements occurred 3 yr following harvest. The largest losses in nutrients were due to bole removal and ranged from 4% of total ecosystem N to 21% of ecosystem K. Rates of replacement from precipitation, primary mineral weathering, and N2 fixation would restore the ecosystem to the nutrient status prior to harvest in 50 yr. Based on these findings, logging systems that minimize erosion should not cause unacceptable nutrient loss over a normal timber stand rotation.
Titration Method for Determination of Clay‐Sized Carbonates
Authors: Bloom P. R. , Meter K. , Crum J. R.
Published: July 2010

The carbonate content of soil clay suspension samples obtained by the pipet method was determined by the titration of the excess acid after reaction with an acetic acid buffer. The clay samples were reacted with a pH 4.0 buffer and titrated after 30‐min of bubbling with air. Two variations of the method were evaluated. One was for use with an automatic titration and the other for manual titration. The accuracy of the two methods was demonstrated using a suspension of clay‐sized reagent grade CaCO3. The coefficient of variation for the determination of CaCO3 in soil clays by the automatic titration method was <0.15 for samples containing <4 mg of CaCO3. The precision was greater for samples with CaCO3 contents up to 26 mg. With greater quantities of CaCO3 the 30‐min reaction time was insufficient for complete dissolution because the rate of CaCO3 dissolution decreases with increasing suspension pH. The coefficient of variation for the manual titration method was <0.05 for all samples analyzed. The maximum quantity of CaCO3 that could be determined by the manual titration method was 55 mg.
Spatial and Spectral Relationships Between Field‐measured Denitrification Gas Fluxes and Soil Properties
Authors: Folorunso O. A. , Rolston D. E.
Published: July 2010

The relationship of the spatial variability of field‐measured denitrification gas fluxes to the variability of physical and chemical soil properties affecting denitrification were investigated in order to better understand the denitrification process in the field. The values of N2O, N2, and CO2 fluxes, soil‐water content, soil temperature, water soluble organic C, and NO‐3 were determined from four transects, each with 36 observations, in a Yolo loam (Typic Xerorthents) field site. Spectral analysis indicated the presence of spatial cycling of some parameters. Cospectra and coherency spectra were used to establish relationships between variables in the frequency domain. Spectra of N2O + N2 flux gave evidence that denitrification was cycling with a period of 4 to 5 m for some of the strips. Spectra of soil‐water content (0–0.15 m depth) showed that soil‐water content was also cycling at a period of about 5 m. Spectra of other variables showed less consistent cycling. Cospectra of N2O flux vs. most variables provided evidence of both positive and negative correlations over different frequency ranges. The cyclic nature of the soil‐water content in the surface soil appears to be the primary cause of cycling of the denitrification gas flux at a period of 4 to 5 m. Cycling of water soluble organic C at periods different from that of water content also caused some periodic behavior in denitrification gas fluxes. Without using spectral and coherency techniques, standard correlation or regression methods would have provided little evidence of significant causal effects on denitrification.
Potassium Exchange in Five Southern California Soils with High Potassium Fixation Capacity
Authors: Shaviv A. , Mattigod S. V. , Pratt P. F. , Joseph H.
Published: July 2010

The K exchange with Ca and Mg in five southern California profiles with high K fixation capacity was studied. The objective was to obtain a correlative relationship between K selectivity with varying proportions of K, Ca, and Mg on the exchanger phase of the soils. A linear relationship between EP (the ratio of adsorbed K to adsorbed Ca and Mg) and potassium adsorption ratio (PAR = [K+]/([Ca2+]+[Mg2+])1/2) was found for all the soils investigated. A representative relationship EP = 0.134 + 0.026 (PAR), with high degree of correlation (r = 0.955), was found for the surface layers (0–30 cm) of all five soils studied. A sharp decrease in KG, the Gapon selectivity coefficient with EP increasing from 0 to 0.2 and ending with a levelling of KG values between 0.7 to 3.2 (mol−1 L)1/2 was observed for all the soil profiles. The KG relationship with potassium fixation showed a similar trend for all the soil profiles.
A Simple Microbial Bioassay for Plant Available Manganese
Authors: Germida J. J. , Karamanos R. E. , Stewart J. W. B.
Published: July 2010

A bioassay using the soil bacteria Bacillus brevis or Ensifer adhaerens for determining plant‐available Mn in organic soils was developed. For this assay, a 1:10 soil‐agar plug was prepared in a nutrient agar plate and then overlaid with semisolid nutrient agar inoculated with either test organism. Manganese‐induced zones of growth stimulation were measured after 24‐h incubation at 27°C. There was a linear relationship between the logarithm of standard concentrations of Mn and the zone of growth stimulation. The enhanced growth was a specific response to Mn; Ca, Co, Cu, Fe, Mg, Mo, Ni, Sr, Zn, NO‐3, PO3‐4, and SO2‐4 did not stimulate growth of either organism. Addition of glucose as a C and energy source or yeast extract as a source of vitamins and growth factors had no effect on growth. Six organic, six Mn‐amended organic, and 17 mineral soils were tested with this assay. This new assay clearly identified five nonamended organic soils that were Mn‐deficient as determined by the growth of spring wheat (Triticum aestivum) in a growth chamber study. There was a statistically significant correlation between the zone of growth stimulation on bioassay plates and plant relative yields, Mn concentration, and Mn uptake. The DTPA extracts of these soils did not predict this Mn deficiency. Separation of responding from nonresponding soils was achieved using the E. adhaerens bioassay. This assay allows rapid and inexpensive identification of Mn‐deficient soils.
Effect of Temperature on Organic Carbon‐texture Relationships in Mollisols and Aridisols
Authors: McDaniel P. A. , Munn L. C.
Published: July 2010

Data from 143 grassland soils of Montana and Wyoming classified as Mollisols or Aridisols were analyzed to determine the effect of soil temperature regime on the relationship between organic carbon (C) and texture. Using existing data, average weighted organic C content to a 40‐cm depth was calculated for each soil and correlated with several variables, including elevation, weighted clay and sand contents to a 40‐cm depth, and sand/clay ratio. For all soils, organic C was significantly correlated with sand (r = − 0.27) but not with clay (r = 0.01). When soils were grouped by combinations of temperature regime and classification at the order level, organic C levels were highest in cryic soils (Cryoborolls) and lowest in mesic Aridisols. Correlations of organic C with sand and clay contents were highest for mesic Mollisols and mesic Aridisols and decreased as temperature regimes became colder. Sand/clay ratio was significantly correlated with organic C in mesic soils only, and therefore may not be useful in distinguishing between Typic and Borollic subgroups of frigid Aridisols in Soil Taxonomy. Results suggest that sand and clay contents have limited value in predicting organic matter levels in cold arid and semiarid grassland soils.
Effect of Physical and Chemical Profile Modification on Soybean and Corn Production
Authors: Hammel J. E. , Sumner M. E. , Shahandeh H.
Published: July 2010

Crop production on highly weathered soils is frequently limited by poor root penetration into the subsoil as a result of highly acid conditions. This results in reduced water uptake from the subsoil and may subject the crop to drought stress. As a result, the possibility of ameliorating the subsoil of a Typic Hapludult, both chemically and physically, was investigated in a field experiment in which four subsoil treatments were compared, namely, control, subsoil mixed to 1 m, subsoil mixed to 1 m with sufficient lime incorporated to neutralize exchangeable Al3+, and gypsum incorporated into the surface soil. The crops grown were soybeans [Glycine max (L.) Merr.] and corn (Zea mays L.). Deep incorporation of lime increased yields. Surface‐applied gypsum increased yields only in the 2nd and 3rd yr. Yield improvement resulted from deeper root penetration into subsoils, which was confirmed by water‐depletion measurements. This improved root proliferation was accompanied by a reduction in exchangeable Al3+ and an increase in exchangeable Ca2+.
Soil Heat Flux, Thermal Conductivity, and the Null‐alignment Method
Authors: de Vries D. A. , Philip J. R.
Published: July 2010

The null‐alignment method of estimating soil heat flux density(q) and thermal conductivity (λ) depends on calorimetry, and ignores convection of sensible heat by mass flow and processes involving latent heat. Study of the energy balance of drying bare soils indicates that the major errors of null‐point calorimetry are likely to arise from net evaporation in upper soil layers. A net evaporation rate of at least 1 mm/d probably occurred in the example used to introduce null‐alignment. This small evaporation rate changes the q profile so radically that null‐alignment may give λ‐values averaging about 52% of the correct ones. Diurnal variations of latent heat sink strengths, null‐points, and temperature gradients, combine to produce diurnal variation of the error in null‐aligned λ's, thereby explaining the reported diurnal variation of null‐aligned λ. Since errors tend to be large and negative in daytime, and small and positive at night, 24h avg are likely to be too small. Null‐alignment does not provide the precise measures of q and λ its exponents supposed, so that various null‐alignment‐based critiques of the Philip‐De Vries theory of heat and moisture transfer in soils, and of the De Vries model of λ, cannot be sustained. Of course there is much scope for improving both through incisive theory and precise experiment. All calorimetric methods of estimating q that ignore latent heat, not only null‐alignment, must involve serious errors in the presence of significant net evaporation in the soil.
Transformations of Inorganic Phosphorus During the Flooding and Draining Cycles of Soil
Authors: Sah R. N. , Mikkelsen D. S.
Published: July 2010

Phosphorus transformations that occur after anoxic soils are drained have been associated with acute P deficiencies in rotation crops following rice. Flooded rice may not respond to P fertilization while rotation crops respond markedly to P fertilization on similar soils. The changes that occur among the inorganic P forms during flooding and after drainage in four soils were investigated. Significant changes in the inorganic P fractions—aluminum‐P (Al‐P), iron‐P (Fe‐P), calcium‐P (Ca‐P), and reductant soluble‐P (RS‐P) occurred in soils during their flooding and draining cycles. Typically, the Fe‐P fractions increased and Al‐P fractions decreased when soils were flooded. The Ca‐P fraction increased during flooding in two soils that had initially high levels of Ca‐P but was almost unchanged in two other soils of lower Ca‐P content. The RS‐P fraction decreased during flooding in the soils subjected to annual flooding. During the drainage period, Fe‐P and Al‐P fractions decreased and the RS‐P fraction increased in flooded rice‐cropped (Oryza sativa L.) soils, probably due to occlusion of Fe‐P and Al‐P by hydrated Fe and Al oxides. The RS‐P fraction in Willows clay, a soil that had not been flooded recently, decreased during the drainage period. Phosphorus added as Ca(H2PO4)2. H2O was recovered mainly in the Fe‐P and Al‐P fractions. The recovery of Fe‐P was greater in flooded‐drained soils and Al‐P was greater in unflooded soils.
Decomposition of Methyl Nitrite in Solutions and Soils
Authors: Magalhães A. M. T. , Chalk P. M.
Published: July 2010

The role of hydrolysis as a process affecting the concentration of CH3ONO in the soil atmosphere was investigated by measuring the sorption of CH3ONO and the formation of NO‐2 and NO‐3 in two soils (−33‐kPa soil water potential) and three solutions in the dark at 20°C for 10 h. Soil pH and the pH of distilled H2O decreased on absorption of CH3ONO. In acidic solutions (distilled H2O and 0.1 M H2SO4), > 90% of CH3ONO was recovered as NO‐3, whereas to an alkaline soil and 0.2 M NaOH, > 80% was recovered as NO‐2. Only 0 to 7% of CH3ONO remained in the atmosphere. In an acid soil only 50% of CH3ONO was recovered as [CH3ONO + NO‐2 + NO‐3]‐N. Recoveries of N in γ‐irradiated and nonirradiated soils did not differ significantly. The data indicate that CH3ONO was rapidly hydrolysed in solutions and in soils [CH3ONO + H2O ⇌ CH3OH + HNO2], and that NO‐3 formed via the self‐decomposition of HNO2. The low recovery of N in the acid soil may have been due to the participation of HNO2 in chemodenitrification reactions. The rapid hydrolysis of CH3ONO is likely to inhibit the emission of CH3ONO formed in soils, and to cause the sorption of CH3ONO evolved from soils in closed systems.
Organic Matter Inputs to Soil After Growth of Carbon‐14‐Nitrogen‐15 Labeled Maize
Authors: Hétier J. M. , Andreux F. , Schouller E. , Marol C.
Published: July 2010

After growth of doubly labeled (14C and 15N) maize (Zea mays L.), two loamy soils were labeled by root exudation and rhizodeposition, and by direct microbial immobilization of N. Fresh roots were then carefully separated and washed, eliminating organic and organomineral cementing agents by acid and alkaline solubilizing reagents, and the remaining insoluble humin was water dispersed in order to separate coarse, medium, and fine fractions. At harvest time, fresh roots represented 85% of the total C input, and rhizodeposition 15%. Sixty to 70% of the N input was still in living roots at this time, and other organic forms of N were more a result of microbial activity than of rhizodeposition. The largest and most homogeneous organic fraction was the finest insoluble fraction, in which about half of the label for both C and N was found.
Effect of Irrigation Method and Acetylene Exposure on Field Denitrification Measurements
Authors: Terry R. E. , Jellen E. N. , Breakwell D. P.
Published: July 2010

An increased understanding of denitrification in situ may contribute to the development of agricultural practices that minimize denitrification losses from cropland. The objectives of this study were to: (i) observe the effects of sprinkle and flood irrigation on denitrification losses; and (ii) to evaluate the effects of acetylene (C2H2) exposure on inhibition of nitrification and C2H2 decomposition. Acetylene was introduced into the soil atmosphere of field plots either by flood irrigation with C2H2‐treated water or by continuous diffusion of C2H2 from dispersion tubes placed in the soil to a depth of 25 cm. Some plots received C2H2 through dispersion tubes continuously for 42 d, while rotated plots received the gas for 7 d and were then abandoned in favor of fresh plots. Denitrification losses from the fallow, clay loam soil were approximately 16‐kg N when the soil was flood‐irrigated and approximately 3‐kg N when the soil was sprinkle‐irrigated. Soil environmental conditions within the disintegrated structure of the flood‐irrigated soil promoted denitrification losses. Nitrification rates in C2H2‐treated soils were only 30 and 87% of control rates, but nitrification rates recovered within 4 d after removal of the gas. The complications of nitrification inhibition by acetylene in field denitrification studies may be minimized by intermittent exposure of soil to acetylene or by rotation of experimental sites. Soil microorganisms began to metabolize C2H2 after 7 d of continuous exposure. The problems of C2H2 decomposition and decreased C2H2 partial pressures were overcome by rotating field plots every 7 d.
Identification of Some Trace Metal Minerals in a Mine‐waste Contaminated Soil
Authors: Mattigod S. V. , Page A. L. , Thornton I.
Published: July 2010

A scheme involving the use of particle and density separations was used to isolate and identify by x‐ray diffraction (XRD) and scanning electron microscopy/energy dispersive x‐ray analysis (SEM/EDX), several trace metal minerals in a mine‐waste contaminated soil from Shipham, England. The heavy density (> 3.3 Mg m−3) fraction of this soil contained smithsonite, leadhillite, barite, rutile, goethite, and hematite. The scheme of particle separations appears effective in that the mineral fractions which constitute a minor fraction of a soil matrix can be isolated and identified directly.
Distribution of Nitrogen Forms and Availability Indices in Profiles of Differently Managed Soil Types
Authors: Hadas Aviva , Feigenbaum Sala , Feigin A. , Portnoy Rita
Published: July 2010

Various chemical methods have been used to predict the N mineralization potential of soils, but studies have been restricted mainly to surface soil layers, to which most N mineralization is attributed. In this study, the distribution of N forms, extracted from soil by different chemical methods, and the relationship between them were determined within the profiles of several soil types. All N parameters tested were significantly correlated with total N. The fractions of several N parameters of total N changed with soil depth: oxidative release of NH4+ by acid KMnO4, N extracted by NaHCO3, and NH4+ and hexosamine in soil acid hydrolyzate all increased, whereas amino acids and amidase activity decreased with soil depth. Soil type also influenced some N parameters: acid KMnO4 extracted relatively more NH4+ from calcareous than noncalcareous soils; a smaller fraction of total N was acid hydrolyzable in soils with a greater surface area; and amidase activity was considerably higher in cultivated clay soils.
Soil Respiration in a Winter Wheat Ecosystem
Authors: Buyanovsky G. A. , Wagner G. H. , Gantzer C. J.
Published: July 2010

Respiration of a silt loam soil (Udollic Ochraqualfs) was studied under cultivation of winter wheat (Triticum aestivum L.) over a 3‐yr period. Evolved CO2 was measured by the alkali absorption method during 24‐h periods at intervals of usually two weeks. Extended estimates of CO2 evolution were made after extrapolating the measured results, in accord with abiotic influences, to include the longer time intervals. Among the abiotic factors examined in relation to evolution of CO2 during the annual agricultural cycle, the most significant was temperature and second, soil water content (R2 = 0.67 for two factors combined). Better models were obtained when the annual cycle was split into two periods, that with predominating plant activity from October through June, and that when CO2 arose solely from the activity of heterotrophs from harvest to planting. Although factors affecting CO2 evolution were the same, predictability increased, and up to 88% of changes in soil respiration during the first period were related to soil temperature and moisture content of the 0‐to 10‐cm layer. For the second period, air or soil temperature plus moisture of the soil at 20 to 30 cm accounted for 76% of the variability. Using models developed for both periods, average annual respiratory loss of C under wheat in Missouri was approximated at 640 g m−2. Maximum soil respiration, presumably from decomposition activity on freshly incorporated residues, occurred during a 56‐d period after harvest, and accounted for 40% of the total annual amount of CO2 evolved from soil. Differences in seasonal patterns of soil respiration and photosynthetic uptake of CO2, indicate that no more than one‐fifth of the photosynthesis requirement for CO2 by winter wheat is produced by soil respiration during the growing season.
Effect of Sequence in Extraction of Trace Metals from Soils
Authors: Miller W. P. , Martens D. C. , Zelazny L. W.
Published: July 2010

While many workers have utilized various reagents for sequential extraction of soil trace metals, few studies have examined the order of extraction for key steps in the sequential procedure. In this study, several sequences involving both adsorbed and structural (occluded) metal extractants were evaluated to determine the most appropriate sequential methodology for extracting different forms of Cu, Fe, and Mn. For “specifically adsorbed” metals, Pb(NO3)2 and CH3COOH were used. The results showed that the former reagent extracted less Cu, Mn, and Fe and was probably more specific in replacing metals covalently bound to adsorption sites. Lead nitrate was therefore placed before CH3COOH extraction in the sequence. Chao's NH2OH·HCl reagent and K4P2O7, used for Mn oxide and organic metal removal, respectively, were found to solubilize significantly different amounts of Cu and Mn depending on sequence, with K4P2O7 extracting more metal when used first. As NH2OH·HCl has little effect on organic metals, it should be used before K4P2O7. Noncrystalline and crystalline Fe compounds are solubilized next, using a variety of reagents, and residual (silicate lattice) metals are dissolved in the final step. A nine‐step sequential method is proposed to characterize trace metals in agricultural, polluted, and waste‐amended soils.
Influence of Tannic Acid on Retention of Copper and Zinc by Aluminum Precipitation Products
Authors: Goh Tee Boon , Violante A. , Huang P. M.
Published: July 2010

The influence of pH on the adsorption of Cu and Zn from solution by precipitation products of Al formed both in the absence and presence of tannic acid was studied. The results show that well crystallized Al hydroxides formed in the absence of tannic acid have low specific surface and thus adsorbed the least amounts of these trace metals per unit weight basis. The presence of tannic acid during the precipitation reaction of Al significantly modifies the adsorption behavior of the hydrolytic products by increasing the specific surface and adsorption capacity. This result is attributable to the structural distortion of the Al precipitation products by tannate ligands and the exposed edges, carboxylate and phenolic groups on the surfaces. The adsorption processes of the Al oxides for Cu and Zn were influenced by the presence of ionized organic functional groups of tannic acid coprecipitated with the poorly ordered Al oxides. The infrared spectra establish the presence of carboxylate COO‐ ions in the oxides prepared.
Water Extraction by Single Plant Roots
Authors: Hainsworth J. M. , Aylmore L. A. G.
Published: July 2010

Application of computer assisted tomography to x‐ray attenuation measurements has been used to study the drawdowns in soil‐water content associated with single plant roots. Drawdowns have been measured at different depths along radish (Raphanus sativus cv long scarlet) roots growing in soil at two different initial water contents while the plants were subjected to either a high or low transpirational demand. This novel approach has provided the most detailed observations of this type yet obtained, particularly by a nondestructive technique. Soil resistance to water flow is clearly of significance even at the high soil‐water potentials used since it has been observed to markedly influence water uptake. Comparisons between these experimentally determined drawdowns and those predicted by an analytical approach indicate that this model does not adequately describe the extraction process. In particular, the assumption that a plant root acts as a uniform absorbing cylinder along its length is clearly erroneous. While a numerical model gives a closer fit to the experimental data, it is clear that improvements in the physical concepts on which this is based are necessary to accurately describe the position and shape of the drawdowns.
Solution Aluminum Anomalies Resulting from Various Filtering Materials
Authors: Jardine P. M. , Zelazny L. W. , Evans A.
Published: July 2010

Commercially available filter papers and membranes of varying composition were examined for their effect on solution Al. This investigation was conducted in order to assess the impact of filter materials on environmental water samples and solubility studies. Many of the filter materials in equilibrium with unneutralized and partially neutralized AlCl3 removed a significant portion of Al from solution (0‐87% of added Al). The loss of solution Al resulted from the negative charge and/or residual anion content of the filter material. Filter discs that resulted in large losses of solution Al generally had high levels of F‐, PO3‐4, and/or SO2‐4 and had an appreciable cation exchange capacity. Removal of residual salts from uncharged membrane filters essentially eliminated any loss of Al from solution. Potentiometric titration analyses of the equilibrium Al solutions indicated marked titration curve distortions for several filter materials, which was related to their residual contaminants.
Effect of Corn, Sugarbeets, and Fallow on Zinc Availability to Subsequent Crops
Authors: Leggett G. E. , Westermann D. T.
Published: July 2010

Field observations indicated that Zn deficiency of beans (Phaseolus vulgaris L.) was sometimes more severe than expected when grown on fallowed soil that was low to marginal in available Zn. The objectives of this study were to determine the effects of fallow, sugarbeets (Beta vulgaris L.), and corn (Zea mays L.) on Zn availability to subsequent crops grown on a Portneuf silt loam (Durixerollic Calciorthids, coarse silty, mixed, mesic). The sugarbeet and corn plant tops and sugarbeet roots were removed, and 11.2 kg Zn ha−1 was applied on one‐half of each plot before fall plowing 25‐cm deep. Beans, sweet corn, or potatoes (Solanum tuberosum L.) were planted the following spring. Whole plant samples of beans and sweet corn and potato stems, leaflets, and petioles were sampled for chemical analyses during the growing season. All bean plants were Zn deficient when grown after fallow or sugarbeets but not after corn or where Zn fertilized. Potatoes and sweet corn did not show any Zn deficiency symptoms or any growth responses to Zn fertilization. The average zinc concentration in beans (vegetative development stage, V3) following corn was 20.5 mg kg−1 compared with 12.5 mg kg−1 following fallow or sugarbeets without Zn fertilization. The average Zn uptake by beans (V3) following corn was 1.3 g ha−1 compared with 0.6 g ha−1 after fallow or sugarbeets without Zn fertilization. The Zn uptake after corn was even greater than where 11.2 kg Zn ha−1 was applied to fallow or sugarbeets (1.3 vs. 0.9 g Zn ha−1). Enhanced Zn availability following corn persisted throughout the growing season and into a second bean crop, although at a decreased level. Similar trends occurred with potatoes and sweet corn. Soil DTPA‐extractable Zn was not significantly different after fallow, sugarbeets, or corn. These results indicate that Zn deficiency in sensitive crops may be alleviated or prevented depending upon the preceding crop grown, and that factors not measured by DTPA can significantly influence Zn availability.
Use of Rayleigh Scatter for Determining X‐ray Mass Absorption Coefficients
Authors: Beavers A. H. , Olson Ken R.
Published: July 2010

X‐rays impinging upon matter are both scattered and absorbed. As the mass absorption coefficient (µM) of the soil sample increases more x‐rays are absorbed and less are scattered. X‐ray absorption is directly related to the atomic number of the element present and the scatter is inversely related to the atomic number of the elements making up the sample. Since some x‐ray tubes, such as W, have severe limitations using the Lα Compton scatter for determining (µM), we have found that the Rayleigh (unmodified) x‐ray scatter is as precise as the Compton scatter (MoKα) and has many advantages. Any x‐ray tube can be used and the Rayleigh scatter is linear with respect to (µM) over a range of two theta settings, making possible the determination of both µM and the true background from one measurement. X‐ray mass absorption coefficient µM can be used to characterize the homogeneity and changes of soil with depth. Each soil studied had a characteristic line expressing the relationship between mass absorption coefficient and soil depth. The maximum value of µM appeared to reflect the maximum of soil mass including weathering productions such as clay, Fe, and bases. For all soils, the maximum value of µM appeared to be one or two subhorizons below the maximum clay and cation exchange capacity values. The subsoil tends to have a higher capacity to absorb x‐rays than either the topsoil or parent material.
A Method to Verify the Presence of a Trend in Studying Spatial Variability of Soil Temperature
Authors: Davidoff B. , Lewis J. W. , Selim H. M.
Published: July 2010

A method for estimating the drift function and assessing the significance of possible trends in spatial observations was developed. This method takes as many data points as possible within each lag distance, is less sensitive to “outliers,” and nearly all observations obtained by it have their contribution in calculating the drift function. Our method, as well as the “cancellation method,” were examined on temperature data collected at a depth of 0.05 m at 0.68‐m intervals along an 80‐m long transect. Tests based on the cancellation method falsely indicated the presence of a significant trend in the temperature data. No trend was indicated by our method, which has more statistical validity than the cancellation method. The decision to detrend or not has a marked impact on the interpretation of the data as attested to by the semivariograms and autocorrelograms of the original and detrended data. Detrending of the data resulted in a loss of information about the spatial dependence of temperature observations.
Boron Adsorption on California Soils
Authors: Goldberg Sabine , Glaubig R. A.
Published: July 2010

Boron adsorption on 15 arid zone soil samples was investigated both as a function of equilibrium B concentration (0–100 g m−3) and as a function of solution pH (5.5–11.5). Boron adsorption as a function of equilibrium B concentration could be described by the Freundlich adsorption isotherm over the entire concentration range studied and by the Langmuir adsorption isotherm over a limited concentration range. Boron adsorption increased from pH 5.5 to 8.5, exhibited a peak in the pH range 8.5 to 10, and decreased from pH 10 to 11.5. The adsorption maximum was highly correlated with both specific surface area and clay content. It was assumed that B adsorbs by ligand exchange with hydroxyl groups at the edges of clay particles and Al and Fe oxide minerals. The constant capacitance model was able to describe B adsorption on the soil samples. While the fit was generally good, the chemical significance of one of the surface complexation constants is uncertain for a few soil samples. An average set of surface complexation constants could be used to predict B adsorption on most of the soil samples studied.
Role of Soil Organic Matter in the Effect of Acid Rain on Nitrogen Mineralization
Authors: Stroo Hans F. , Alexander Martin
Published: July 2010

The effect of soil organic matter on the influence of acid rain on microbial processes was studied in columns containing samples from the O horizons of two forest soils and mixtures of those horizons with sand. Simulated acid rain at pH 3.5 reduced the percentage of inorganic N present as NO‐3 when the organic matter level was below about 0.1 g/g soil, and the percentage decreased with decreasing organic matter levels. The effects of acid rain on N mineralization and NO‐3 formation in Adams (Typic Haplorthods) soil were similar. Nitrogen mineralization was increased in Croghan (Aquic Haplorthods) soil by simulated acid rain when the organic matter content was high, and the degree of stimulation decreased with lower organic matter levels. Dissolved organic C levels were initially decreased by treatment with simulated acid rain in all soil mixtures, but the amounts in soil solutions from acid rain‐treated soils recovered with time to similar or greater levels than in the control soils. The recovery was more rapid in Croghan than Adams soil. Increasing organic matter contents in soil mixtures also decreased the magnitude and duration of acid rain‐induced changes in pH of soil solution and levels of dissolved organic C.
Effects of Land Clearing and Subsequent Management on Soil Physical Properties
Authors: Alegre J. C. , Cassel D. K. , Bandy D. E.
Published: July 2010

Large scale, mechanized land clearing is common in the humid tropics even though little attention has been given to defining and solving soil problems that may be created. The purpose of this study was to evaluate various combinations of land clearing method, burning of vegetation, post clearing tillage, and soil management on soil physical properties of a forested Ultisol in the Amazon basin. Land clearing methods used were (i) slash, (ii) bulldozer clearing with a straight blade, and (iii) bulldozer clearing with a shear blade. Specific effects associated with clearing were mechanization, bulldozer blade type, burning, disking, and chiseling. Post clearing soil management systems isolated effects of bedding, liming, and fertilization. Soil physical properties were measured before clearing and 14, 29, and 98 weeks after clearing. Compaction increased bulk density (ρb) of the 0‐ to 15‐cm depth for all clearing methods, but ρb of the 15‐ to 25‐ depth increased by 0.1 Mg m−3 only for the bulldozer cleared treatments. Soil texture of the 0‐ to 15‐cm depth was not altered by land clearing. Gravimetric water content at soil matric potentials < −2 kPa was greatest for the straight blade cleared soil. The infiltration rate 14 weeks after clearing decreased 37, 96, and 90% for soil cleared by slash, straight blade, and shear blade, respectively, as compared to initial conditions. Chisel plowing and disking the newly cleared land increased the infiltration rate compared with straight blade without chiseling. Detrimental changes in soil physical properties caused by clearing were minimized when post clearing management practices of bedding, fertilization, and liming were adopted.
Concurrent Sorption of Phosphate and Zinc, Cadmium, or Calcium by a Hydrous Ferric Oxide
Authors: Kuo S.
Published: July 2010

Concurrent sorption of phosphate and Zn, Cd, or Ca by a hydrous Fe oxide sample was investigated by enclosing sparingly‐soluble Zn‐phosphate, Cd‐phosphate, or Ca‐phosphate in dialysis tubings and equilibrating with the oxide up to 2 yr in 0.1 mol L−1 NaNO3 solution at room temperature (296 ± 2 K). The ability of the oxide to concurrently sorb phosphate and Zn, Cd, or Ca was evident from their amounts present in the oxide, as well as from x‐ray analysis and microprobe mapping of the elements sorbed on Fe‐oxide particles. The selectivity of the oxide for the metals increased int he order Ca < Cd < Zn, and was apparently not affected by the absolute amounts of phosphate sorbed. No obvious complementary effect of metal sorption on phosphate sorption, or vice versa, was observed. Aging the oxide up to 1 or 2 yr in the presence of metal and phosphate adversely affected only the sorption of Ca but not the sorption of Zn, Cd, or phosphate. Therefore, it is likely that the affinity determines whether or not a sorbate, once sorbed, can be excluded from the oxide undergoing aging or changes in its crystallinity. Two simplified equations were tested for their ability to fit the sorption of the metals and phosphate by the oxide, with sorbate concentration, pH, and available sites as dependent variables. The good fit of Zn, Cd, and phosphate sorption data to the equations suggests that phosphate and the metal are being sorbed on specific sites.
The Effect of Adsorption on Sulfate Leaching
Authors: Bolan N. S. , Scotter D. R. , Syers J. K. , Tillman R. W.
Published: July 2010

Movement of sulfate (S) through repacked columns of soil with high and low S adsorption capacity was studied in the laboratory. Differences in movement could be explained by the shape of adsorption isotherms which were determined from batch‐type experiments. 35S was found to be a suitable tracer to study the movement of applied 35S. For step‐function changes between 0, 3.12, and 6.24 mol m−3 in the concentration of the applied S solution, different breakthrough curves (BTC) were found for the rising and falling limbs. Also the higher the concentration of S in the applied solution, the earlier the added S appeared in the effluent. The BTC obtained agreed well with those calculated from numerical solution of the dispersion‐convection equation, assuming a Freundlich adsorption isotherm and instantaneous reversible adsorption. However, after leaching of a pulse of S added to the surface soil, the observed S distributions in soil columns were not well described by theory. The discrepancies were largest when the soil containing the added pulse of S was incubated prior to leaching. Possible reasons for this lack of agreement are discussed.
Alteration of Sulfur‐34 Natural Abundance in Soil by Application of Feedlot Manure
Authors: Chae Yeh Moon , Krouse H. Roy
Published: July 2010

The 34S/32S abundance ratios (δ34S) of four forms of S present in cattle feedlot manure and at various depths in profiles of a soil receiving different rates of manure were determined. Whereas the δ34S values for all S forms in manure were similar (−2.8–3.6) they differed markedly among different forms of soil S (+1.6 for Raney Nireducible S to +6.2 for HI‐reducible S). Effects of manure applications on the isotopic composition of S were observed for most S forms only at the soil surface or in shallower horizons. In contrast, the δ34S values and concentrations of C‐bonded S indicated penetration of manure S down to or near the water table, particularly in the profile which had received a high rate of manure application. The NO‐3‐‐N distribution in the soil profiles showed that manure NO‐3‐‐N had also moved down below the water table. Therefore, it is concluded that C‐bonded S is the best form for tracing the down‐ward movement in soils of S‐bearing compounds in manure.
Calcium Carbonate Supersaturation in Soil Solutions of Calciaquolls
Authors: Inskeep William P. , Bloom Paul R.
Published: July 2010

We found that soil solutions of Calciaquolls in western Minnesota were up to 40‐fold oversaturated with respect to pure calcite. Selective dissolution of soil calcites and x‐ray diffraction showed that the Mg content of these calcites ranged from 1 to 10 mole % MgCO3. This amount of Mg substitution cannot explain the degree of oversaturation observed in the soil solutions. X‐ray peak broadening and scanning electron microscopy (SEM) was used to determine the size and shape of soil calcites. The mean size of soil calcite crystallites was approximately 0.04 to 0.09 µm. Surface energy relationships predict that soil calcites of this size would have solubility products (−log Ksp) near 8.3, not low enough to explain the observed supersaturation. Energy dispersive analysis of x‐rays (EDAX) and SEM observations of these samples showed that the larger soil calcites (0.5–20 µm) were irregularly shaped and did not exist as independent crystals, and were associated with other aluminosilicate solid phases. Soil suspensions of Calciaquolls prepared at 10‐fold oversaturation remained oversaturated for 40 d. Adding pure calcite seeds to soil suspensions and soil solution supernatants induced some precipitation, but the solutions remained oversaturated, attaining CaCO3 ion activity products (−long IAP) ranging from 7.6 to 7.9. These results suggest that the metastable condition of supersaturation is a result of inhibition of the calcite precipitation process by water‐soluble organic components, which are adsorbed and block potential crystal growth sites.
Agronomic Effectiveness of Bayovar Phosphate Rock in Soil with Induced Phosphorus Retention
Authors: Hammond L. L. , Chien S. H. , Easterwood G. W.
Published: July 2010

A greenhouse experiment was conducted with soil from the A horizon of an acid Mountview silt loam (Typic Paleudult) to measure the relative influence of soil P retention capacity on P availability from Bayovar (also known as Sechura) phosphate rock (Peru) with that from triple superphosphate (TSP). The P retention capacity of the soil was adjusted by application of variable quantities of freshly prepared amorphous Fe gel. The P sources were incorporated into the treated soil at rates to supply 0, 150, and 300 mg total P kg−1 soil. Corn (Zea mays L.) was grown as a test crop. The Fe gel treatments significantly increased the P retention capacity of the soil and resulted in significant reductions of both dry matter production and P uptake with both P sources. The effectiveness of the phosphate rock, however, tended to decline to a greater extent than that of TSP with increasing P retention capacity. These results suggest that, contrary to popular opinion, the effectiveness of phosphate rock relative to soluble P fertilizer may be less on soils with high P retention capacity than on soils with the same pH but with lower P retention capacity for short‐term crops such as corn.