bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Hydraulic Conductivity of Unsaturated Soils with Thermocouple Psychrometers
Authors: Daniel David E.
Published: July 2010

A method of measuring the hydraulic conductivity of unsaturated soil using the instantaneous profile method with psychrometric probes to measure water potential is developed and described. Soil is compacted into cylindrical tubes, and the tubes are sealed and instrumented with thermocouple psychrometers. The soil is moistened or dried from one end of the tube. Psychrometers are read periodically. Hydraulic conductivity is computed from the psychrometer readings and the appropriate moisture characteristic curve for the soil and then plotted as a function of water potential, water content, or degree of saturation.

Hydraulic conductivities of six soils were measured at water potentials as low as −80 bar. The measured hydraulic conductivities and moisture characteristic curves were used along with the known boundary flux in a computer program to calculate the final water content profiles. Computed and measured final water content profiles agreed tolerably well.
Constant‐Flux Absorption of a Tritiated Calcium Chloride Solution by a Clay Soil with Anion Exclusion
Authors: Bond W. J. , Gardiner B. N. , Smiles D. E.
Published: July 2010

The distribution of water, tritium, and chloride was measured following horizontal constant‐flux absorption of a tritiated CaCl2 solution by a Ca‐saturated clay soil. Water contents throughout the soil were < 80% of saturation at all times. The position of the tritium front corresponded closely with the interface which would exist between the initial and the inflowing solutions if the former were completely displaced by the latter. There was therefore no evidence of immobile water in these experiments. The chloride front moved ahead of the tritium front and the measured chloride concentrations throughout the soil were less than the concentration of the inflowing solution, although all of the added chloride was recovered. The behavior of the chloride relative to tritium is accounted for by anion exclusion.

Tritium concentration profiles were accurately predicted using a theory described earlier. Difficulties were encountered, however, in extending this theory to the case of an excluded anion but an approximate predictive scheme is discussed. Areas for further work are outlined.
Improved Corrective Fertilizer Recommendations Based on a Two‐Step Alternative Usage of Soil Tests: I. Recovery of Soil‐Equilibrated Phosphorus
Authors: McLean E. O. , Oloya T. O. , Mostaghimi S.
Published: July 2010

The objective of these studies was to improve corrective fertilizer P recommendations using soil quicktest methodology which measures P‐fixation (buffering) tendencies of individual soils. Actual amounts of fertilizer P required to reach a selected sufficiency level of Bray‐1 available P were measured from the added P vs. available P relationship in 10 soils with a wide range in P‐fixation tendency. The new (universal) extractant of Mehlich was found to give approximately the same indication of P fixation as did Bray‐1, indicating that both P and K may be equilibrated together thereby eliminating one extraction. Regression analyses were made between the actual and variously computed amounts of P to reach sufficiency level based on constant fraction recovery, quicktest measured recovery (one‐step), and regression‐adjusted recovery (two‐step). This showed that most of the deviations between actual and computed values can be eliminated by this quicktest‐computed, regression‐adjusted procedure. Hence fertilizer recommendations evidently can be improved correspondingly. Relatively low correlation of Bray‐1 available P with yields of corn seedlings in this preliminary study appeared to be not the fault of the soil test but the effect of plant exploitation of the small aliquots of soils used.
Toxicity of Aluminum to Coffee in Ultisols and Oxisols Amended with CaCO3, MgCO3, and CaSO4·2H2O
Authors: Pavan Marcos A. , Bingham F. T. , Pratt P. F.
Published: July 2010

A greenhouse experiment was conducted with six acid soils from southern Brazil to investigate the effect of available Al on growth and mineral nutrition of coffee (Coffea arabica L.) seedlings. Coffee seedlings were grown for 7 months in pots containing soil treated with varying amounts of CaCO3 up to twice the lime equivalent, and amounts of MgCO3 and CaSO4·2H2O equal to the lime equivalent. Leaf samples were collected immediately before harvesting the seedlings and analyzed for Ca and Al. At this time, soil was collected from each pot and analyzed for exchangeable cations and soluble ions. The chemical composition of the soil solution was used as input data for a computer program (GEOCHEM) to chemically speciate Al in the soil solutions. Shoot and root weights were correlated with KCl‐exchangeable Al of soil, percent Al saturation of soil, the concentrations of total Al (Alt) and Al3+ (calculated), and the activity of Al3+ (calculated) in the soil solution. Growth reductions of the seedlings correlated best with the Al3+ activity value. The toxicity threshold for the Al3+ activity was approximately 4.0 × 10−6. Leaf Al concentrations likewise correlated best with Al3+ activity. Threshold leaf Al concentrations of approximately 62 and 100 µg/g, respectively, were observed for reduction in root and shoot growth.
Leaching of Fertilizer Ions in a Kaolinitic Ultisol in the High Rainfall Tropics: Leaching of Nitrate in Field Plots under Cropping and Bare Fallow
Authors: Arora Yogesh , Juo A. S. R.
Published: July 2010

Leaching and crop recovery of nitrogen (N) applied as calcium ammonium nitrate (CAN) to bare fallow and cropped plots were studied in a coarse‐textured, kaolinitic Ultisol under high rainfall conditions (mono‐modal). Maize (Zea mays) was planted in the first cropping season (March–July) and upland rice (Oryza sativa) in the second season (August–December). Rates of N applied to maize and rice were 150 and 90 kg/ha, respectively. Soil samples up to 120 cm in depth were taken at 4‐week intervals throughout the two growing seasons. Nitrate leached readily in the fallow and cropped plots. Liming (2 t/ha) shortened the initial time lag of nitrification, increased the nitrification rate, and, consequently, increased leaching of nitrate in both fallowed and cropped plots. During the first season, substantial amounts of NH4‐N persisted in the surface soil for over 4 weeks in plots that received CAN application.

Splitting of N from one to three applications reduced the leaching loss from 53 to 28% of applied N. The limed plots with single application of N lost the largest amount of N through leaching. Splitting of N into two applications significantly increased grain yield of maize and rice. Further splitting into three splits increased the yield of rice only. Percentages recovery of applied N by maize were 22, 35, and 41% and 31, 39, and 61% by rice for one application, two and three splits, respectively. With one application of N during each cropping season, bare fallow retained 37% of the total applied N (240 kg N/ha) within the 0‐ 120‐cm depth at the end of the second cropping season.
Formation of an Oxisol‐Ultisol Transition in São Paulo, Brazil: I. Double‐Water Flow Model of Soil Development
Authors: Moniz A. C. , Buol S. W.
Published: July 2010

This study of Oxisol‐Ultisol transitions on hill slopes in transported material with oxic properties allowed the development of a double‐water flow model explaining the formation of soil structure that occurs during the soil development. According to this view, Ultisols form from Oxic materials through the action of both lateral‐ and base‐water flow, integrated in the landscape.

In the sites studied both argillic and oxic horizons are formed from the same parent material. Oxisols are formed in thick colluvium on nearly level surfaces where the lateral‐water flow is not developed and the base‐water flow is too deep to affect the solum.

The argillic horizon of the Ultisols on the slopes below the Oxisols is hypothesized to form inside a layer having blocky structure initiated by saturation ⇆ desiccation‐induced compression.

The formation of the compressed layer is controlled by the geomorphology, which promotes the formation of the lateral‐water flow as the relief becomes steeper, as well as by the degree of vertical textural anisotropy.
Formation of an Oxisol‐Ultisol Transition in São Paulo, Brazil: II. Lateral Dynamics of Chemical Weathering
Authors: Moniz A. C. , Buol S. W. , Weed S. B.
Published: July 2010

Depending on the mineralogical nature of the parent material and underlying rock, Fe, Mn, Si, and bases are concentrated downslope as a result of lateral‐ and/or base‐water flow action. Dissolution at the rock‐saprolite interface is an important supplier of those elements, which are transported by the base‐water flow affecting mainly the soils in the footslope.

Chemical weathering does not always proceed in the same direction. The alternate process of desilication‐resilication occurs horizontally downslope along the toposequence. This approximately corresponds to Walther's Law of Succession of Facies. The lateral resilication process is important in tropical regions because it counterbalances the allitization process and explains the occurrence of relatively less weathered clay minerals on lower slope positions in the soilscape.
Mineralogy and Iron Characterization of Plinthitic Soils on Alluvial Landforms in Venezuela
Authors: Daugherty L. A. , Arnold R. W.
Published: July 2010

The iron oxides and clay mineralogy were characterized for several soils of Venezuela which contain plinthite and pseudo‐plinthite. Molar ratios of SiO2/Al2O3 (Ki ratios) of the plinthite and pseudo‐plinthite zones range from below 2 to above 4 suggesting a wide range in mineral composition. Cation exchange capacity for these zones ranged from 14.6 to 65.6 meq/100 g of clay suggesting that these mottled zones are not always associated with low activity clays. Kaolinite dominated the clay minerals. Montmorillonite was identified in a few pedons.

Goethite was the dominant iron oxide present in the plinthite. The percentage of iron was determined by extracting the soil with citrate‐bicarbonate‐dithionite and by extracting with ammonium oxalate. These two extractions were ratioed (OX/CBD) yielding values of >0.05 for pseudo‐plinthite and values of <0.05 for plinthite in most cases. Soils with plinthite contained most of the iron in the sand‐ and silt‐size fraction following one drying cycle while soils with pseudo‐plinthite contained most of the iron in the clay‐size fraction.
Runoff and Soil Loss in Trinidad under Different Crops and Soil Management
Authors: Gumbs F. A. , Lindsay J. I.
Published: July 2010

Erosion caused by some of the farming practices on the major soil type (Orthoxic Tropudult) in the northern mountain range in Trinidad was assessed by measuring the runoff and soil loss from maize (Zea mays L.) and cowpea (Vigna unguiculata L. Walp) plots on 11, 22, and 52% slopes with and without tillage during the wet seasons in 2 consecutive years. The total rainfall for each of the three periods over which the experiments were conducted was 38.8, 22.4, and 82.5 cm, respectively.

At the lower levels of rainfall there was generally a significant increase in soil loss (but not runoff) from the bare plots with an increase in slope from 11 to 22 to 52%; but a nonsignificant increase in both runoff and soil loss from the cropped plots. At the higher rainfall level, there were significant increases in soil loss from the bare and both of the cropped plots with an increase in slope from 11 to 22% only.

The effect of tillage of the 22% slope on runoff and soil loss seems to have depended on the level and distribution of the rainfall and on the crop type. When rainfall is low, no‐tillage does not significantly affect runoff or soil loss, but it significantly (P = 0.05) reduces soil loss from bare plots if there are intense storms. At the highest rainfall level, no‐tillage still resulted in high soil losses (28 to 55 t/ha) and maize and cowpea (particularly maize) were less effective than at lower rainfall in reducing soil loss. Because of the high level of rainfall experienced in these hills the bare soil should not be exposed in the wet season and the clean cultivation of maize and cowpea in the wet season should not be recommended for slopes >11%.
Hydraulic Conductivity of Soil as Determined from Cumulative Runoff
Authors: Schroeder S. A. , Foster G. R. , Moldenhauer W. C. , Mannering J. V.
Published: July 2010

Hydraulic conductivity measurements using a Purdue sprinkling infiltrometer were performed on plots with the resultant data of cumulative runoff vs. time analyzed to determine values of hydraulic conductivity through the use of a cumulative runoff equation based on an infiltration equation proposed by Swartzendruber. Comparisons made with a differentiated form of an infiltration equation by Swartzendruber and Youngs (similar to the form of Philip's) or Swartzendruber's proposed infiltration equation were not, generally, greatly different. Additions of random errors in the data through computer simulation also did not change the resultant hydraulic conductivity values in the cumulative runoff method very much from the original data's determined hydraulic conductivity values. Thus using cumulative runoff versus time to determine hydraulic conductivity has shown to be reliable.
Effect of Soil pH on Adsorption of Lead, Copper, Zinc, and Nickel
Authors: Harter Robert D.
Published: July 2010

Lead, copper, nickel, and zinc adsorption by and desorption from pH‐adjusted soils has been studied. Surface and subsurface horizon samples of two soils were equilibrated with varying amounts of Ca(OH)2 prior to metal addition. The amount of all four metals retained was dependent upon pH of the soil sample, with retention dramatically increasing above pH 7.0 to 7.5. With the exception of Ni, at least 70 to 75% of the retained metal was extractable in 0.01N HCl. Nickel was somewhat less extractable, with that sorbed by the highest pH soils being the least extractable. Based on subsequent extractability, the soils used appeared to have specific adsorption sites for Pb, Ni, and Cu but little or none for Zn. These studies cast some doubt on the concept of pH management for immobilizing heavy metals placed on the land in that sorbed metals were substantially extractable by 0.01M HCl, which has been used to estimate plant availability of soil ions.
Evaluation of Irrigation‐Nitrogen Management Practices for Celery using Continuous‐Variable Irrigation
Authors: Stark J. C. , Jarrell W. M. , Letey J.
Published: July 2010

The interaction between N source and irrigation rate and the resultant effects on NO‐3 leaching were characterized for celery, using a modified line‐source sprinkler system which applied water across fertilizer plots at rates varying from replacement of evapotranspiration (ET) to 1.8 ET. Nitrogen, as (NH4)2SO4 (AS), was applied at a rate of 300 kg/ha in split applications (AS300); sulfur‐coated urea (SCU) was applied alone at 300 kg N/ha (SCU300), all preplant, or in a combination with 150 kg N/ha SCU preplant and 150 kg N/ha AS sidedressed (SCU150AS150). Plants with the AS300 and SCU300 treatments removed significantly less N at the lowest irrigation rate than those with the SCU150AS150 treatment, but this difference was not observed at high irrigation rates. All three N treatments produced large accumulations of NO‐3 beneath the root zone which increased with increased leaching. Yields from the fertilized treatments were significantly higher at all irrigation levels than yields from unfertilized plots, but were not different from each other. Yields also did not vary substantially across the range of irrigation rates, indicating that deep percolation of water and NO‐3 can be minimized through improved irrigation management without reducing celery yield.
Phosphorus and Potassium Fertilization of Irrigated Alfalfa on Calcareous Soils: I. Soil Test Maintenance Requirements
Authors: Fixen P. E. , Ludwick A. E.
Published: July 2010

Field experiments with irrigated alfalfa (Medicago sativa L.) were established in far eastern Colorado on a Keith soil and in far western Colorado on a Ravola soil in 1976. Concentrated superphosphate was applied at rates of 25 and 50 kg P/ha annually for 3 years or 75 kg P/ha in a single application at seeding. Muriate of potash was applied at rates of 140 and 280 kg K/ha annually for 3 years or 420 kg K/ha in a single application at seeding. Soil profile changes in NaHCO3‐P and exchangeable K were determined. At a location having low to medium available‐P status (crop response to P expected), 2.2 times the P removed by the alfalfa was required to maintain the initial NaHCO3‐P level. At a location with medium to high available‐P status (no P response expected), only 1.4 times the removed P was required for maintenance. The two locations required a fertilizer K rate of 0.75 and 0.22 times the K removed by alfalfa uptake to maintain their respective initial exchangeable‐K levels. The low maintenance requirement of the latter soil was apparently due to the K minerals present which buffered the exchangeable K near 100 mg·kg−1.
Phosphorus and Potassium Fertilization of Irrigated Alfalfa on Calcareous Soils: II. Soil Phosphorus Solubility Relationships
Authors: Fixen P. E. , Ludwick A. E. , Olsen S. R.
Published: July 2010

Alfalfa (Medicago sativa L.) was established at two field locations in Colorado in 1976 and triple superphosphate applied at rates of 25 and 50 kg P/ha annually or 75 kg/ha in a single application at seeding. The initial P applications were incorporated while subsequent applications were topdressed. Soil profile changes in NaHCO3‐extractable P and in P solubility measured in 0.01M CaCl2 were determined over a three‐year period. The resulting calcium hydroxide and monocalcium phosphate potentials were related to known solubility products for distinct P mineral phases including octacalcium phosphate (OCP) and β‐tricalcium phosphate (TCP). Octacalcium phosphate controlled solution P if the NaHCO3‐extractable P rose above 35 mg·kg−1 while TCP or a similar mineral phase dominated P intensity in the range of 10 to 25 mg·kg−1. Relating these potentials to the changing NaHCO3‐P levels indicated that considerable Ca8H2(PO4)6·5H2O, octacalcium phosphate (OCP), accumulated in one soil. Solubility data from both soils also indicated significant buffering of soil P on or near the solubility isotherm of β‐Ca3(PO4)2, tricalcium phosphate.
The Kinetics of Gibbsite Dissolution in Nitric Acid
Authors: Bloom P. R.
Published: July 2010

The kinetics of dissolution of two synthetic gibbsite preparations was studied in nitric acid solutions with pH values that ranged from 1.5 to 3.3. Dissolution rates were determined at 298 K for both gibbsites and additional rate experiments were conducted at 313 K and 328 K with one of the gibbsites. Dissolution was controlled by reactions at the solid‐solution interface and not by diffusion. The rate of reaction did not increase monotonically with H+ activity; rather, there was a minimum rate of about pH = 2.25. Two different mechanisms with different rate‐controlling steps were suggested. At pH < 2.1 the rate‐controlling step was probably protonation of positively charged surface sites while at pH > 2.4 the rate‐controlling step was probably water attack of surface Al.
The Effect of Suspended Solids in Wastewater on Soil Hydraulic Conductivity: I. Suspended Solids Labelling Method
Authors: Vinten A. J. A. , Mingelgrin U. , Yaron B.
Published: July 2010

A method for labelling suspended solids in sewage effluent with 14C‐DDT [1,1,1, trichloro‐2,2‐bis(p‐chlorophenyl)ethane] is presented. The method allows the vertical distribution of deposited solids in a soil, following leaching with effluent, to be determined. A simple physical model which describes transport of labelled suspension through the soil is developed. This enables the conditions necessary for successful utilization of the method to be defined. Procedures for the estimation of the parameters required for the model are presented and the application of the method is demonstrated for two soils. It is shown that the method for tracing the fate of suspended solids is valid, as long as the label is sufficiently strongly adsorbed on suspended solids. It is also required that the rate of desorption of label from suspended solids be low compared with the residence time of mobile suspended solids in the soil.
Leaching Characteristics of a Stony Desert Soil
Authors: Russo David
Published: July 2010

The leaching characteristics of a stony desert soil were studied. The functional relationships between pressure potential head and gravimetric water content for the different soil layers were determined in the laboratory under drying conditions using samples in which the stony fractions (> 2 mm) were excluded. These gravimetric water content values were converted to field volumetric water contents, using the field‐measured values of the field bulk density and the stone fraction (on a mass basis). For a given pressure potential head, volumetric water content decreased with depth. Unsaturated soil hydraulic conductivity functions for the different soil depths were determined by the transient drainage profile method, using tensiometers and the appropriate soil water characteristics functions. The saturated hydraulic conductivities were estimated from the steady‐state infiltration rate and the appropriate hydraulic head gradients. Measured saturated hydraulic conductivity values decrease with soil depth while for a given pressure potential head, the unsaturated hydraulic conductivity increases with depth. A leaching experiment was conducted in the field, by operating a sprinkler system at a rate of 7.6 mm/h. The time variations of the electrical conductivity (EC) of the soil solution as well as the concentrations of Na+, Ca2+, Mg2+, Cl‐, and SO2‐4 were recorded by extracting soil solution samples from four soil suction probes located at a depth of 0.45 m and spaced 12 by 12 m apart. The initial average EC of 165 dS/m was reduced to 7.5 dS/m as 800 mm of water were applied to the soil. This final value of the EC of the soil solution is three times higher than the EC of the irrigation water, as a result of the presence of gypsum and relatively high ESP in the solid phase of the soil profile. Measured values of the EC of the soil solution were used to estimate the value of the dispersivity for longitudinal dispersion, λ. The resulting λ = 2.91 cm is in relatively good agreement with published field data of λ for another soil, but is much smaller than the value of the equivalent field‐scale dispersivity calculated for two different soils.
Effect of Soil Properties on the Kinetics of Phosphorus Desorption
Authors: Sharpley A. N.
Published: July 2010

Relationships between the constants of a semilogarithmic modified Elovich and a logarithmic equation describing the kinetics of soil P desorption and physical and chemical properties of 60 soils, collected from throughout the USA, and volcanic ash were investigated. These relationships are needed for application of the equations to modeling soluble P transport in runoff from agricultural watersheds. The constants of the semilogarithmic equation (a and b) were significantly related to the extractable Al and CaCO3 content of acidic and basic calcareous soils, respectively. For the logarithmic equation, constants (K, α, and β) were related to the ratio of Fe‐ or clay‐organic C content of the acidic soils and CaCO3‐ or clay‐organic C content of the basic calcareous soils. It is suggested that these ratios represent an index of interactive specific surface area involved with P adsorption‐desorption for a given soil. In contrast to the logarithmic equation, constants of the modified Elovich equation varied with soil P status and water‐to‐soil ratio. Thus, the former equation may have a wide application to describing soil P desorption in water quality models.
Particle‐size Fractions and their Use in Studies of Soil Organic Matter: II. Cultivation Effects on Organic Matter Composition in Size Fractions
Authors: Tiessen H. , Stewart J. W. B.
Published: July 2010

Losses of carbon, nitrogen, and phosphorus from soil particle‐size fractions during cultivation were examined and their implications on the nutrient‐supplying potential of soils is discussed. Particle‐size fractions were obtained by ultrasonic dispersion in water from three north American grassland soils (Cryoborolls) of different textures. Soils that had been cultivated under small grain‐fallow rotations for between 4 and 90 years were compared with similar soils under native prairie. Four years of cultivation of a Blaine Lake silt loam resulted in an extensive depletion of organic matter associated with particles > 50 µm (43% of the initial C lost). This was considered a result of physical disintegration which led to accumulation of these materials in finer particle‐size fractions. With continued cultivation this accumulated material was slowly transformed within the system, accompanied by net losses of 34% C and 29% N from the total soil over 60 years. Reductions in organic P content amounted to 20% and were accompanied by slight increases in inorganic P content.

Fine clay (< 0.2 µm) associated organic matter was rapidly depleted during the first 60 years but showed little change thereafter, reaching a new equilibrium level at approximately one‐half its original C content. Losses of fine silt (5 to 2 µm) and coarse clay (2 to 0.2 µm) associated organic materials were substantially less, and the proportion of total soil organic matter in these forms increased with time of cultivation. The relative abundance of these biologically resistant, more humified materials in cultivated soils indicated that the remaining organic matter may have a reduced capability for supplying nutrients by mineralization. The continuing, slow mineralization of these more resistant organic matter fractions of the Blaine Lake soil after 90 years of cultivation suggests that organic matter losses may not level off further in the near future. In addition, losses of organic matter from the B horizon were evident after 60 and 90 years. Organic matter losses during 65 years cultivation of a coarser sandy loam soil showed a similar distribution and magnitude across size fractions, while a heavy clay soil was characterized by a greater stability of the silt and clay associated organic matter, which lost only 10% C during 70 years of cultivation.
In‐Situ Determination of Soil Hydraulic Properties during Drainage
Authors: Dane J. H. , Hruska S.
Published: July 2010

In‐situ soil water retention and hydraulic conductivity relations were determined for two soils from knowledge of initial and boundary conditions and water content profiles during drainage. Empirical relations were assumed for each soil between volumetric water content (θ) and soil water pressure head (h), and between hydraulic conductivity (K) and θ. Assigning values to the parameters in these relations made it possible to solve the general water flow equation for the same initial and boundary conditions as encountered in the drainage experiments. Calculated water content profiles were compared with measured water content profiles at corresponding times. Differences in measured and calculated θ values provided information for changes to be made in the parameters. This procedure was repeated until a satisfactory agreement was found and the determined relations apparently represented the soils in question.
Diffusivity and One‐Dimensional Absorption Experiments
Authors: Clothier B. E. , Scotter D. R. , Green A. E.
Published: July 2010

Profiles of normalized volumetric soil water content, Θ, during one‐dimensional absorption are often found to provide a unique profile in terms of the Boltzmann similarity variable, λ. Traditionally, λ(Θ) data have been used to obtain the diffusivity‐water content function D(Θ) by the method of Bruce and Klute. This paper highlights the well‐known inadequacy of this method, and outlines a procedure for deriving D(Θ) by the fitting of a mathematical function to the primary experimental data set, namely λ(Θ). An analytical expression for D(Θ) scaled by sorptivity is provided. A function of the form (1‐Θ)p is shown to fit the λ(Θ) of a fine sand adequately and provide a D(Θ) function that accommodates the soil water diffusivity measured using other methods at near‐saturation.
Kinetics of Oxidation of Arsenite by Various Manganese Dioxides
Authors: Oscarson D. W. , Huang P. M. , Liaw W. K. , Hammer U. T.
Published: July 2010

Three Mn dioxides—birnessite, cryptomelane, and pyrolusite—were examined for their ability to deplete the concentration of As(III), a highly toxic pollutant, in solution. The depletion [oxidation of As(III) to As(V) and sorption of As(III)] of As(III) by all three Mn dioxides follows first‐order kinetics. The rate constants for the depletion of As(III) by birnessite and cryptomelane at 298 K are 0.267 and 0.189 h−1, respectively. On the other hand, the depletion rate of As(III) by pyrolusite is much slower: the rate constant at 298 K is 0.44 × 10−3 h−1. This difference in the rate of depletion is largely attributed to the crystallinity and specific surfaces of the Mn dioxides. Pyrolusite is highly ordered and has a low specific surface of 0.8 hm2/kg (7.9 m2/g); conversely, birnessite and cryptomelane are poorly crystalline and have relatively high specific surfaces of 27.7 and 34.6 hm2/kg (277 and 346 m2/g), respectively. The energies of activation for the depletion of As(III) by the Mn dioxides range from 26.0 to 32.3 kJ/mol. The reaction appears to be predominantly diffusion‐controlled. The ability of the Mn dioxides to sorb As(III) and As(V) appears to be related to the specific surface and the point‐of‐zero charge of the oxides. The data indicate that, after the systems have reached equilibrium with respect to the sorption of total As, the depletion of As(III) by the oxides is still progressing. This is apparently because of the one‐to‐one relationship between the amount of As(III) depleted and the amount of As(V) appearing in solution.
Regulation of Invertebrate Grazers as a Means to Enhance Biomass and Nitrogen Fixation of Cyanophyceae in Wetland Rice Fields
Authors: Grant Ian F. , Tirol Agnes C. , Aziz Taufiqul , Watanabe Iwao
Published: July 2010

The effect of invertebrate grazing on the growth and N fixation of blue‐green algae (Cyanophyceae) in flooded rice soils was investigated by depressing grazer populations. Grazers were controlled with commercial pesticides and seeds of neem (Azadirachta indica). Algal N fixation and standing biomass were estimated by acetylene‐reduction activity and chlorophyll a measurements. Suppression of ostracod (Ostracoda) grazing by Pertbane or neem seeds tripled blue‐green algal biomass and increased N fixation rates 10‐fold. In the absence of ostracods, free living blue‐green algae multiplied rapidly early in the rice cultivation cycle to be succeeded by chlorophytes. Carbofuran was not an effective control measure. Suppression of molluscan grazing had little effect. The population of tubificids (Tubificidae) was higher in the plots where algal growth was stimulated than in other plots. Total rice grain N was increased up to 37% when grazing was arrested.
Soils on Terraces Along the Cauca River, Colombia: II. The Sand and Clay Fractions
Authors: Alexander E. B. , Holowaychuk N.
Published: July 2010

Microscopic examination and elemental analyses of the sand fractions of the terrace soils show that their compositions are too variable to infer anything very noteworthy about the relative rates of primary mineral weathering. However, the parent materials are sufficiently uniform to reveal a relatively continuous progression of notable changes in clay mineralogy from floodplain through the age sequence of terrace soils. Mica, chlorite, vermiculite, smectite, and kaolinite are present in appreciable quantities in the floodplain soils and mica is present in the sand fractions of all terrace soils, but of these only kaolinite is present in more than minute amounts in the sola of any terrace soils. The quantities of 14A minerals with interlayer Al are greatest in the sola of the youngest terrace soils, but they persist in somewhat reduced quantities throughout all except in the subsoil on the highest terrace. Both amorphous aluminosilicates and gibbsite reach maximum concentrations in the lower terrace soils, thence their quantities decline with increasing age. The Feo/Fed ratio has a similar age trend but peaks sooner, at 0.53 in the higher floodplain soil, and thence decreases steadily with soil age to < 0.01 in the clay fraction of the highest terrace soil. Kaolinite is the major constituent of clay in the sola of all terrace soils. It increases with soil age to approximately 60% of the clay fraction in the highest terrace soil.
Effect of Synthetic Conditioners on Soil Water Retention, Hydraulic Conductivity, Porosity, and Aggregation
Authors: Nimah M. N. , Ryan J. , Chaudhry M. A.
Published: July 2010

Recent attention has been focused on the use of synthetic soil conditioners in the modification of soil water relationships especially in arid regions. Soils of extremes in texture—either sands or clays—present problems in this regard. In this laboratory study, Hygromull (a urea formaldehyde) and Agrosil LR and Agrosil S (amorphous sodium hydrosilicates) were evaluated on soils of different textures. Available water content was increased by Hygromull and Agrosil LR. Saturated hydraulic conductivity of the clay soils was improved by Hygromull, while that of the sandy soil was reduced by Agrosil LR. Hygromull increased porosity of all soils but, unlike Agrosil LR, had no effect on aggregation. In contrast, Agrosil S had no effect on any property studied. Notwithstanding the attributes of these conditioners, their acceptance in commercial farming in dry regions will depend on the outcome of field trials and economic considerations.
A Buried Pipe System for Controlling Erosion and Sediment Loss on Irrigated Land
Authors: Carter D. L. , Berg R. D.
Published: July 2010

A new system comprised of a buried pipe, with riser inlets from the surface at intervals, along the lower end of furrow‐irrigated fields was designed, installed, and evaluated on 21 fields to determine its effectiveness as an erosion and sediment loss control system for irrigated land. The system utilizes small sediment collection ponds with the riser inlets from the buried pipe serving as overflow outlets for the ponds. This system corrects convex‐shaped field ends caused by erosion and solves an energy related erosion problem common on furrow‐irrigated land. During the first season, these system removed from 80 to 95% of the sediment from runoff water and collected from 4.1 to 40.5 Mg ha−1 from 12 fields on irrigated land where detailed data were collected. All systems performed without problems and all convex end problems except one were corrected the first season. After the convex ends are corrected, the system continues to reduce sediment loss. This new system eliminates the tailwater ditch, puts more land into crop production, reduces weed problems, and prevents the usual problems associated with a wet tail‐water ditch. The buried pipe erosion and sediment loss control system is a major advance in the control of erosion and sediment loss on irrigated land.
Forest Floor, Soil, and Vegetation Responses to Sludge Fertilization in Red and White Pine Plantations
Authors: Brockway Dale G.
Published: July 2010

An undigested, nutrient‐enriched papermill sludge applied to a 40‐year‐old red pine (Pinus resinosa Ait.) plantation at rates of 4, 8, 16, and 32 Mg/ha resulted in nitrogen application rates of 282, 565, 1130, and 2260 kg/ha. An anaerohically digested municipal sludge applied to a 36‐year‐old red pine and white pine (Pinus strobus L.) plantation at rates of 4.8, 9.7, and 19.3 Mg/ha resulted in nitrogen applications of 287, 578, and 1160 kg/ha. Both sludges produced significant forest floor increases in total salt, pH, and concentrations of nitrogen and phosphorous. The municipal sludge applications also resulted in increased levels of trace elements and heavy metals. Accelerated humification developed along the interface between the sludge layer and the accumulated forest litter. Movement of nutrients from the forest floor into the soil was generally limited to nitrate, ammonia, and total phosphorus leaching into the upper soil layers. Very small fluctuations in nutrient levels occurred in the soil below 15 cm. Understory nitrogen and phosphorus levels increased in treated plots on both sites while cadmium increased on plots treated with municipal sludge. Understory hiomass increases of up to 132% over controls were measured on sludge‐treated plots. No metal toxicity symptoms were observed and sludge‐treated understory vegetation remained green later into the growing season well after that on untreated plots had begun to discolor and approach dormancy. Overstory foliar nitrogen concentrations increased on sludge‐treated plots, improving the N:P ratio in the pines. Increases in fasicle dry weight and needle length were noted in sludge‐treated red pine, as were increases in radial growth in white pine. Evidence two growing seasons following sludge fertilization indicated an increased canopy weight, thus an enhanced potential for photosynthesis.
Characterizing Unsaturated Hydraulic Conductivity of Western Kentucky Surface Mine Spoils and Soils
Authors: Ward Andy , Wells L. G. , Phillips R. E.
Published: July 2010

A large‐scale laboratory infiltrometer system was used to determine infiltration characteristics of “reconstructed” surface mine spoil and soil horizons. Soil water characteristic curves were determined using the Brooks‐Corey and the Gardner procedures and developed based on desorption tensiometer data. Unsaturated hydraulic conductivity values were determined using the “plane of zero flux” procedure and compared with predictions resulting from models described by Campbell, Burdine, and Mualem for situations involving reconstructed soil and spoil materials. There was generally good agreement between the models and excellent agreement between Campbell's predictions and plane of zero flux results. Both the Gardner equation and the Brooks‐Corey equation gave good estimates of the soil water characteristic curves for the materials. The physical significance of the parameters θr and ψe, when determined by statistical procedures, appears very questionable. In this study, the final steady‐state infiltration rate appeared to be a good estimate of the hydraulic conductivity at apparent saturation.
Relationship of Marsh Elevation, Redox Potential, and Sulfide to Spartina alterniflora Productivity
Authors: DeLaune R.D. , Smith C. J. , Patrick W.H.
Published: July 2010

Data presented suggests that the short height form of Spartina alterniflora observed in inland areas of Louisiana Gulf Coast marshes is caused by toxic concentrations of sulfide, a result of slightly lower elevation and subsequently lower sediment redox potential than the adjacent productive streamside marsh. It is speculated that sulfide may limit growth by preventing nitrogen uptake and root development. Total sulfide concentrations as high as 250 µg g−1 of sediment and free sulfide concentrations in the order of 150 µg g−1 were found in the inland sediment. The inland sediment contained higher NH+4‐N concentrations at depth than the streamside sediment. The higher NH+4‐N concentrations closely paralleled the increasing sulfide concentrations and was inversely related to rooting depth. Maximum NH+4‐N concentrations of 60 and 16 µg N g−1 of dry soil was observed in the inland and streamside sediment, respectively. Redox potential was higher at the surface sediment of the more productive streamside marsh compared to the adjoining inland marsh. The higher redox potential is mainly due to the higher elevation of the streamside area that permitted greater drainage. This in turn allowed the development of more oxidized sediment containing lower sulfide levels. Observed differences in salinity and plant‐dissolved nutrients were not great enough to restrict plant growth.
Runoff Farming for Growing Christmas Trees
Authors: Fink D. H. , Ehrler W. L.
Published: July 2010

Runoff farming was used to grow two species of conifers [Quetta pine (Pinus eldarica) and Arizona cypress (Cupressus arizonica)] in a semiarid climate on a sandy soil treated with wax and a clay soil treated with sodium chloride salt. The treated runoff‐contributing areas were varied in length to provide a water supply estimated initially to be two, three, and four times the normal 300‐mm annual precipitation. Twenty‐five trees were planted per species per site per water‐level treatment for a total of 300 trees. Thirty‐seven percent of them (110 trees) were harvested after only three growing seasons. Eighty‐nine percent (67 trees) of the Arizona cypress on the sand‐wax site were marketable, and the remaining 43 trees were from the other three species/site locations. Large differences in tree growth existed among the four species/site locations. The best trees were the cypress grown on the sand‐wax site. Most of the cypress on the clay‐salt site were 1 to 2 years behind those at the sand‐wax site. The Quetta pines grew best on the clay‐salt site where 24% were marketable in 3 years, with most of the remaining projected to be marketable by year four. The pines grew poorly on the sand site suffering > 50% mortality on the two lower water treatments. Only the cypress on the sand‐wax site showed a significant statistical difference in tree growth as related to water level. Runoff farming shows promise of becoming a practical and practicable method for growing Christmas trees and many other crops in arid and semiarid lands where water is scarce.
A Mathematical Model of Soil Erosion and Deposition Processes: I. Theory for a Plane Land Element
Authors: Rose C. W. , Williams J. R. , Sander G. C. , Barry D. A.
Published: July 2010

The paper describes a new mathematical model of soil erosion and deposition on a plane land element. The model makes use of an approximate analytic theory of runoff on a plane assuming kinematic flow. Rates of the following simultaneously occurring erosion/deposition processes are represented mathematically: rainfall detachment, sediment deposition, and soil entrainment by overland flow. The concept of stream power is used in representing the entrainment process. The form of analysis reduces the first‐order partial differential equation expressing conservation of mass of sediment to an ordinary differential equation, which can thus be solved analytically. This solution gives sediment concentration at any time as a function of distance down the plane in terms of four defined soil factors, the slope of the land, two separate cover factors, and the rainfall and runoff rates. The product of water flux and sediment concentration gives sediment flux at any time and position on the plane.
Effect of Crop Residue, Tillage‐Induced Roughness, and Runoff Velocity on Size Distribution of Eroded Soil Aggregates
Authors: Cogo N. P. , Moldenhauer W. C. , Foster G. R.
Published: July 2010

The percentages of eroded soil aggregates over 10 size classes ranging from 0.002 to 2.0 mm in diameter as affected by crop residue cover, tillage‐induced roughness, and water flow velocity were investigated under field conditions using simulated rainfall. The soils used were a 4.5% slope Russell silt loam and a 6.5% slope Martinsville loam. With no vegetation present, the smallest eroded aggregates came from a chisel‐plowed surface while the largest came from chisel‐ and moldboard‐plowed surfaces which had been disked. A no‐till treatment gave intermediate values. The D50 size (the aggregate size which 50% of the aggregates exceed) in the absence of soil cover was 0.033, 0.032, 0.020, and 0.011 mm for chisel plow plus disk, moldboard plow plus disk, no‐till and chisel plow, respectively. When soil was covered by residue, the size distribution of the eroded aggregates was not greatly different among the tillage treatments. The D50 size was reduced in this case to about 0.012 mm for all tillage systems. For no‐till, the percentage of the eroded aggregates > 0.05 mm decreased exponentially (r2 = 0.85) with an increase in residue cover. Under chisel plowing residue was not effective in reducing the quantity of larger aggregates in the runoff. An increase in flow rate caused an increase in water flow velocity which, in turn, caused a linear (r2 = 0.94) increase in the percentage of the eroded aggregates > 0.05 mm, for chisel plowing. The results from this study were explained in terms of sediment trapping capacity of the soil surface, as well as runoff transport capacity.
Accuracy of Several Immiscible Displacement Liquids
Authors: Kittrick J. A.
Published: July 2010

Equilibrium solutions were displaced from moist samples of gibbsite and calcite of known stability using four different immiscible liquids, carbon tetrachloride, tetrachloroethylene, FC70 (a fluorocarbon), and 1,1,1‐trichloroethane. All four immiscible liquids permitted accurate solution analyses for gibbsite in the pH range near 4. In the pH range near 8.3, 1,1,1‐trichloroethane significantly decreased the pH of solutions displaced from calcite. All solutions in this pH range required protection from CO2 variations. Tetrachloroethylene and FC70 permitted accurate analyses of displaced solutions and are less toxic than CCl4.
Calcium‐Magnesium Exchange on Wyoming Bentonite in the Presence of Adsorbed Sodium
Authors: Sposito Garrison , Jouany Claire , Holtzclaw Kenneth M. , LeVesque C. S.
Published: July 2010

The exchange of magnesium for calcium at 298 K on Wyoming bentonite was investigated in a 50 mol m−3 perchlorate background maintained at pH 7. The charge fraction of Na+ in the aqueous solution phase was controlled at the values of 0.74 or 0.87 during the exchange experiments, resulting in average exchangeable sodium percentages (ESP) of either 16 or 36% on the clay. The Vanselow selectivity coefficient for Ca → Mg exchange was equal to 1.0 and was independent of exchanger composition at both ESP values. This result implied that, under the conditions of the exchange experiments, the clay exhibited equal affinities for Ca2+ and Mg2+ regardless of the quantity of adsorbed sodium present.
Competitive Complexation of Cd(II) and Cu(II) by Water‐Soluble Organic Ligands and Na‐Montmorillonite
Authors: Inskeep William P. , Baham John
Published: July 2010

Water soluble extracts obtained from a coniferous forest litter layer (FLLE), dried Chicago sludge (CSE), and a peat soil (PE) were used as a source of organic ligands to study the influence of metal complexation on the adsorption of Cd and Cu by Na‐montmorillonite. Adsorption of 50 to 0.1µM CdT and CuT by Na‐montmorillonite (2 g L−1) was measured in the presence of the FLLE (1.8 mM total carbon) over a pH range of 4 to 8.5 after a 2‐h equilibrium period under humidified N2 gas. Equilibrium activity measurements for Cd2+ and Cu2+ were made with ion selective electrodes for experiments at 50 and 10 µM total metal (MT). After accounting for inorganic complexation, the amount of Cd complexed with organic ligands in the FLLE was much lower than that for Cu. Multiple regression equations where pMads (metal adsorbed) was tested as a function of pH and pMTS (total soluble metal concentration) showed that Cu adsorption decreased with increased pH values in contrast to adsorption in the absence of FLLE. Conversely, the adsorption of Cd was only slightly affected. Adsorption of 10 µM CuT in the presence of CSE and PE showed similar effects on adsorption, revealing the importance of water soluble complexing ligands in controlling Cu speciation.