bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption of Mercury(II) by Variable Charge Surfaces of Quartz and Gibbsite
Authors: Sarkar D. , Essington M. E. , Misra K. C.
Published: July 2010

The influence of pH, ionic strength, ligands (Cl, SO4, PO4), and metals (Ni and Pb) on the adsorption of Hg(II) by quartz and gibbsite was investigated to better understand the Hg(II) adsorption process and the impact of metals and ligands on this process. The triple layer model (TLM) was used to simulate Hg(II) adsorption on both surfaces. Mercury(II) adsorption from a 0.6 μM Hg(II) solution varies as a function of pH, increasing to an adsorption maximum with increasing pH before tailing off to a constant level at high pH values. The pH at which maximum Hg(II) adsorption occurs (pHmax ≈ 4.5) is comparable to the pKa (3.2) for the hydrolysis of Hg2+ to form Hg(OH)02 Further, the Hg(II) adsorption edge shifts to much higher pH values in the presence of 0.001 M and 0.01 M Cl, which also corresponds to the pH at which Hg(OH)02 is predicted to form. Only minor deviations in the degree of adsorption and the shape of the Hg(II) adsorption edge are influenced by ionic strength, suggesting the formation of inner‐sphere surface complexes. However, Hg(II) adsorption can only be successfully modeled with consideration of the formation of both an outer‐sphere surface complex [≡XO−–HgOH+] and an inner‐sphere surface complex [≡XOHg(OH)−2]. Swamping concentrations (0.01 M) of SO4 and PO4 reduced Hg(II) adsorption on quartz, a result of the predicted formation of Hg(OH)2SO2−4, Hg(OH)2H2PO−4, and Hg(OH)2–HPO2−4 aqueous species (the adsorption edge and pHmax were not influenced). The presence of SO4 also decreased Hg(II) retention by gibbsite, which was also attributed to the formation of the Hg(OH)2SO2−4 ion pair; however, the presence of PO4 increased Hg(II) retention by gibbsite, which was attributed to the formation of a phosphate bridge [≡AlOPO3Hg(OH)2−2]. Mercury(II) adsorption was decreased in the presence of 14 μM Pb and 48 μM Ni, and most noticeably in the quartz system. The adsorption of Hg(II), when in competition with Pb or Ni, could not be simulated by the TLM without the reoptimization of the Hg(II) outer‐ and inner‐sphere log Kint values. Intrinsic Hg(II) adsorption constants derived from single‐element systems could not be employed to simulate adsorption in multi‐element, competitive systems.
Effects of pH and Metals on the Surface Tension of Aqueous Humic Materials
Authors: Yates Leland M. , von Wandruszka Ray
Published: July 2010

Humic substances play an important role in the transport and fate of xenobiotic materials in the environment. Since most of the relevant interactions take place in aqueous media, it is of prime importance to understand the behavior of these natural polymers in solution. In this study, surface tension measurements were used to elucidate conformational and structural changes in dissolved humic and fulvic acids under different conditions of pH, ionic strength, and the presence of certain metal ions. The measurements showed that the amphiphilic character of the humic solutes, which determines their surface activity, varied significantly with pH and metal content. The charge of the metal ion added was found to have an important effect in rendering the humic material sufficiently amphiphilic to migrate to the surface. As cation concentrations were increased, the formation of micelle‐like humic structures led to the restoration of higher surface tensions. Measurements with materials of different molecular size indicated that these structures could arise from both intermolecular aggregation and intramolecular coiling. Kinetic measurements showed that the evolution of surface tension values in humic acid solutions followed a course that was consistent with the migration of metal ions within the humic structure. This is thought to involve the formation and subsequent disintegration of hydrophobic domains as the metal–humate interactions change during a period of hours.
Pseudomonas cepacia–Mediated Rock Phosphate Solubilization in Kaolinite and Montmorillonite Suspensions
Authors: Bar-Yosef B. , Rogers R. D. , Wolfram J. H. , Richman E.
Published: July 2010

Pseudomonas cepaciais known as a rock phosphate (RP) solubilizer in bioreactors and in soils. The objectives of this study were to determine the production rates of gluconic acid (GA, pKd3.41) and 2‐ketogluconic acid (KGA, pKd2.66) by the bacteria in the presence of clay minerals which prevail in soils, and the resulting rate and extent of orthophosphate (OP) release into the suspension solutions. Suspensions (1:40) of RP, RP + Ca–kaolinite (CaKL), RP + Ca–montmorillonite (CaMT), and RP + K–montmorillonite (KMT) were inoculated withP. cepaciaE37. The electrical conductivity (EC) and pH, and the OP, glucose, GA, KGA, Ca, and Al concentrations were determined in the suspension solutions as functions of time. In a given clay system, the rate‐limiting step in RP dissolution was the rate of GA release by the E37. This acid lowered the pH of all the clay suspensions to 2.7 to 2.8, which resulted in a pronounced increase in the OP concentration in solution, Cp. As glucose was depleted from the system, the KGA concentration increased with a concomitant lowering in pH to ≈2.5. At this pH, a sharp decline in Cp occurred, which was attributed to Al release by the alumosilicates, and formation of a new, stable Al–P or Fe–P solid phase. The E37 glucose oxidation efficiency (GOE) was considerably inhibited in CaKL as compared with CaMT or KMT. The GA and KGA adsorption by the clays or their Ca complexation did not play a role in the E37‐mediated RP solubilization.
Annual Course of Matric Potential in Differently Used Savanna Oxisols in Brazil
Authors: Lilienfein Juliane , Wilcke Wolfgang , Ayarza Miguel Angelo , do Carmo Lima Samuel , Vilela Lourival , Zech Wolfgang
Published: July 2010

Sustainable land use in periodically dry Brazilian savannas requires a water‐saving management. We hypothesized that the annual course of matric potentials (ψM) in very‐fine, isohyperthermic Anionic Acrustoxes of Pinus plantations (PI), degraded (DP) and productive pastures (PP), no‐till (NT) and conventional tillage (CT) cropping, and natural savanna (Cerrado, CE) differed significantly. On three plots in each of these land‐use systems water input and ψM at the 0.15‐, 0.30‐, 0.80‐, 1.2‐, and 2.0‐m depths was measured with tensiometers weekly between 27 Mar. 1997 and 28 Apr. 1998. Precipitation between 29 Apr. 1997 and 28 Apr. 1998 was 1562 mm, with only 210 mm in May to September, when ψM at the 0.15‐ and 0.30‐m depths decreased to less than −80 kPa in all systems; the lowest ψM at 2‐m depth was −57 kPa. During the monitored period, the PI soils had lower average ψM at the 0.8‐ to 2‐m depths (−60 kPa) than those in CE (−46), indicating higher rainfall interception losses and higher transpiration. In CT, average ψM values at the 0.8‐ to 2‐m depths (−29) were higher than in NT (−51) because of different crops and different soil management. Between June and November, ψM at the 2‐m depth in CE decreased to a lower value (−42) than in vegetation‐free CT (−22) and NT (−27). In DP and PP soils, ψMs were similar to those in CE soils at all depths. The estimated average water storage in the upper 2 m during the monitored period was: 565 mm (CT) > 553 (PP) > 541 (DP) > 537 (CE) > 526 (NT) > 479 (PI). Our results show that mainly the vegetation type and tillage practices control the annual course of matric potential in differently used savanna Oxisols.
A Climate Change Scenario for Carbon Dioxide and Dissolved Organic Carbon Fluxes from a Temperate Forest Soil Drought and Rewetting Effects
Authors: Borken W. , Xu Y.-J. , Brumme R. , Lamersdorf N.
Published: July 2010

Our objective was to assess the effect of changes in rainfall amount and distribution on CO2emissions and dissolved organic C (DOC) leaching. We manipulated soil moisture, using a roof constructed below the canopy of a 65‐yr‐old Norway spruce plantation [Picea abies(L.) Karst.] at Solling, Germany. We simulated two scenarios: a prolonged summer drought of 172 d followed by a rewetting period of 19 d and a shorter summer drought of 108 d followed by a rewetting period of 33 d. Soil CO2emission, DOC, soil matric potential, and soil temperature were monitored in situ for 2 yr. On an annual basis no significant influence of the droughts on DOC leaching rates below the rhizosphere was observed. Although not significantly, the droughts tended to reduce soil respiration. Rewetting increased CO2emissions in the first 30 d by 48% (P< 0.08) in 1993 and 144% (P< 0.01) in 1994. The CO2flush during rewetting was highest at high soil temperatures and strongly affected the annual soil respiration rate. The annual emission rate from the drought plot was not affected by the drought and rewetting treatments in 1993 (2981 kg C ha−1yr−1), but increased by 51% (P< 0.05) to 4813 kg C ha−1yr−1in 1994. Our results suggest that reduction of rainfall or changes in rainfall distribution due to climate change will affect soil CO2emissions and possibly C storage in temperate forest ecosystems.
Phosphorus Pools in Tree and Intercanopy Microsites of a Juniper–Grass Ecosystem
Authors: Kr a ¨ mer Susanne , Green Douglas M.
Published: July 2010

Gradients of soil‐nutrient distribution between trees and intercanopy areas are common in many semiarid woodland ecosystems. To test if microsites under and between canopies influenced P pool distribution in a semiarid woodland dominated by one‐seed juniper [Juniperus monosperma(Engelm.) Sarg.] and galleta grass [Hilaria jamesii(Torr.) Benth.], we compared inorganic, organic, and microbial P pools under trees and intercanopy areas of two Aridisols. Soils collected (5–15 cm depth) under eight tree canopies and in eight intercanopy areas from a Calciorthid and a Camborthid were subjected to a sequential P fractionation scheme. Soils and microsites were significant independent factors determining total soil P, which ranged fromto 1123 μg P g−1soilResin P was significantly influenced by the interaction of soils with microsite. Organic hydroxide P was the largest organic P fraction and exceeded or equaled the amount of resin P. It differed significantly between the Calciorthid at 10.1 μg P g−1soiland the Camborthid at 22.1 μg P g−1soil (SE = 1.6). Microsite and soil did not significantly affect microbial P, which ranged from 12.9 μg P g−1soilto 17.0 μg P g−1soilNutrients and microbial activity are usually concentrated under canopies in semiarid and arid ecosystems. This research shows that P pools distribution in the studied ecosystem did not follow this general pattern, and that soils may be more important in determining P pool distribution than microsites.
Evolution of CO2 during Birnessite‐Induced Oxidation of 14C‐Labeled Catechol
Authors: Majcher Emily H. , Chorover Jon , Bollag Jean-Marc , Huang P.M.
Published: July 2010

Phenolic compounds undergo several transformation processes in soil and water (i.e., partial degradation, mineralization, and polymerization), many of which have been attributed primarily to biological activity. Results from previous work indicate that naturally occurring Mn oxides are also capable of oxidizing phenolic compounds. In the present study, 14C‐labeled catechol was reacted with birnessite (manganese oxide) in aqueous suspension at pH 4. The mass of catechol‐derived C in solid, solution, and gas phases was quantified as a function of time. Between 5 and 16% of the total catechol C was liberated as CO2 from oxidation and abiotic ring cleavage under various conditions. Most of the 14C (55–83%) was incorporated into the solid phase in the form of stable organic reaction products whereas solution phase 14C concentrations increased from 16 to 39% with a doubling of total catechol added. Polymerization and CO2 evolution appear to be competitive pathways in the transformation of catechol since their relative importance was strongly dependent on initial birnessite–catechol reaction conditions. Solid phase Fourier transform infrared (FTIR) spectra are consistent with the presence of phenolic, quinone, and aromatic ring cleavage products. Carbon dioxide release appears to be limited by availability of reactive birnessite surface sites and it is diminished in the presence of polymerized reaction products.
Regeneration of Earthworm Populations in a Degraded Soil by Natural and Planted Fallows under Humid Tropical Conditions
Authors: Tian G. , Olimah J.A. , Adeoye G.O. , Kang B.T.
Published: July 2010

Earthworm populations (predominantly Hyperiodrilus africanus and Eudrilus eugeniae) were sampled monthly for 1 yr during 1994 and 1995 in natural regrowth vegetation fallow (dominated by the natural fallow shrub Chromolaena odorata L.), planted fallow (the woody species Senna siamea Lam., Leucaena leucocephala Lam., and Acacia leptocarpa), and intercropped maize (Zea mays L.)–cassava (Manihot esculenta Crantz) established in 1989 in a degraded Alfisol (Oxic paleustalf) in southwestern Nigeria. Compared to leaves of Chromolaena (3.3% N), N concentrations were lower in those of Senna and Acacia, and higher in Leucaena Acacia and Leucaena had higher polyphenol relative to the natural fallow (2%). The lignin was lower in Leucaena than the natural fallow leaves (14%). For 65% of the sampling dates, earthworm numbers under all fallows were significantly higher than under continuous maize–cassava. The mean earthworm numbers (no. m−2) during the rainy season (April–October) decreased in the following order: Chromolaena (147), Senna (131), Leucaena (92), Acacia (80), and maize–cassava (14). Earthworm fresh weights in fallow plots were higher than in the maize–cassava plot, though this was significant for only 4 out of 11 sampling dates. Higher earthworm numbers and biomass in fallow plots were attributed to higher litterfall, lower soil temperature, and higher soil moisture. The mean earthworm numbers were directly correlated with the mean soil moistures (, P < 0.05) in fallow plots and N/polyphenol ratios of fallow litterfall (, P < 0.05). Increase in earthworm population by fallows led to an increase in leaf‐litter decomposition, soil organic matter, available P, and extractable cations and pH; and a decrease in soil bulk density and penetrometer resistance in the fallow plots.
Relationship of Map Unit Variability to Shrink–Swell Indicators
Authors: Thomas P.J. , Baker J.C. , Zelazny L.W. , Hatch D.R.
Published: July 2010

A study was conducted in the Culpeper Basin in northern Virginia to quantify soil shrink–swell indicators, to relate the indicators to soil properties, and to partition variability into map unit components. Five delineations in each of five map units were selected for study. Three profiles were sampled within each delineation to complete a nested sampling scheme. Three map units of smectitic, high shrink–swell soils with phase names of Haymarket silt loam, Jackland silt loam, and Waxpool loam, all 0 to 2% slopes, were selected. Also selected was a vermiculitic, high shrink–swell soil map unit named Kelly silt loam, 0 to 2% slopes, and a kaolinitic, a low shrink–swell soil map unit named Davidson clay loam, 2 to 6% slopes, eroded. The Bt horizons of Haymarket, Jackland, Waxpool, and Kelly were clayey and had high cation‐exchange capacities (CECs), liquid limits, and plasticity indices (PIs). Soils in the Davidson map unit also had high clay contents but had lower swell indices, liquid limits, PIs, and CECs than the other four map units. Shrink–swell indices and related soil properties exhibited high variability. However, the variability was partitioned within the delineations of each map unit. Each delineation within an individual map unit consisted of the same variability as map units with similar names. Swell indices in all five map units were correlated with liquid limit, clay content, and CEC. However, individual map units exhibited differing relationships. Liquid limit and clay content were the best predictors of swell index in the Haymarket, Jackland, and Waxpool map units, whereas clay content was the best predictor in the Kelly and Davidson map units. Cation‐exchange capacity was weakly correlated with swell index in all five map units.
Diurnal and Seasonal CO2–C Flux from Soil as Related to Erosion Phases in Central Ohio
Authors: Bajracharya R. M. , Lal R. , Kimble J. M.
Published: July 2010

The CO2–C flux from soil is an important part of the global C cycle, whose dependence on erosion is as yet largely unknown. We hypothesized that the magnitude of diurnal and seasonal C flux is related to soil erosion phase and is influenced by soil water and temperature regimes. The CO2–C flux from the surface of a Miamian silt loam soil (fine, mixed, active, mesic Oxyaquic Hapludalf) in central Ohio was monitored using the static chamber method. Gas samples were collected four times daily (at 0900, 1200, 1500 and 1800 h) at ≈2‐wk intervals between July 1995 and June 1997. The CO2evolved from the soil surface varied significantly among seasons ranging from 0 g C m−2d−1in the winter to ≈1.6 g C m−2d−1during the summer. Soil erosion phase had no direct effect on C flux from the soil, although depositional areas had 20 to 25% higher water content than other phases, while severely eroded and depositional areas generally had higher soil temperatures than slightly and moderately eroded phases. Soil C flux exhibited diurnal variations with high values differing from lows by as much as 0.04 g C m−2h−1Peak flux rates as high as 0.082 g C m−2h−1occurred during the mid afternoon during the spring, summer, and autumn seasons. Soil C flux was significantly correlated with soil temperatureand air temperaturebut not with soil moisture content.
Mechanisms of Residue Mulch‐Induced Cereal Growth Increases in West Africa
Authors: Buerkert Andreas , Bationo Andre´ , Dossa Komlan
Published: July 2010

The use of crop residues (CR) has been widely reported as a means of increasing crop yields across West Africa. However, little has been done to compare the magnitude and mechanisms of CR effects systematically in the different agro‐ecological zones of the region. To this end, a series of field trials with millet (Pennisetum glaucumL.), sorghum [Sorghum bicolor(L.) Moench], and maize (Zea maysL.) was conducted over a 4‐yr period in the Sahelian, Sudanian, and Guinean zones of West Africa. Soils ranged in pH from 4.1 to 5.4 along a rainfall gradient from 510 to 1300 mm. Treatments in the factorial experiments were three CR rates (0, 500, and 2000 kg ha−1) and several levels of phosphorus and nitrogen. The results showed CR‐induced total dry matter (TDM) increases in cereals up to 73% for the Sahel compared with a maximum of 16% in the wetter Sudanian and Guinean zones. Residue effects on weakly buffered Sahelian soils were due to improved P availability and to a protection of seedlings against wind erosion. Additional effects of CR mulching on topsoil properties in the Sahel were a decrease in peak temperatures by 4 °C and increased water availability. These mulch effects on soil chemical and physical properties strongly decreased from North to South. Likely explanations for this decrease are the decline of dust deposition and wind erosion hazards, the higher soil clay content, lower air temperature, and a faster decomposition rate of mulch material with increasing rainfall from the Sahel to the Sudanian and Guinean zones.
Nitrogen Availability through a Coarse‐Textured Soil Profile in the Shortgrass Steppe
Authors: Dodd M. B. , Lauenroth W. K. , Burke I. C.
Published: July 2010

We conducted a study of N resources in a loamy sand soil in the shortgrass steppe of northeastern Colorado, on a site dominated by both shrubs and grasses. Our objective was to determine whether the soil N resources were more evenly distributed with depth than is typical for this environment, thereby helping to explain the coexistence of the two plant life forms. We measured total soil C and N, potential net N mineralization, and in situ available inorganic N (using ion exchange resin bags) through the soil profile to a depth of 150 cm. All three measures confirmed that available N was greatest in the surface soil layers (0–10 cm) and decreased substantially with depth. A supplemental watering treatment was imposed on the soil during the spring of 1996 to examine N‐leaching potential. The water addition increased soil water content and available NO−3to a depth of 60 cm, indicating that NO−3leaching might occur on this soil type under favorable conditions. To confirm this assertion, we used two simple models to examine the impact of increased soil moisture on in situ mineralization and solute transport processes. The results indicated that NO−3leaching could better account for the observed patterns in available N. This process, by contributing to a more even distribution of resources through a coarse‐textured soil profile, could be important for improving the competitive status of shrubs in an otherwise grass‐dominated ecosystem.
Vertical Hydraulic Gradient and Run‐On Water and Sediment Effects on Erosion Processes and Sediment Regimes
Authors: Zheng Fen-li , Huang Chi-hua , Norton L. Darrell
Published: July 2010

During rainfall events, runoff water carries sediment downslope. It has been hypothesized that the detachment potential of the runoff water would decrease as the sediment content is increased until a sediment transport capacity, Tc, is reached and the excessive amount of sediment beyond Tc would then be deposited. Translating this concept to a hill slope setting implies that water and sediment from up‐slope areas would affect erosion processes on a downslope segment. However, there are few experimental data to support this hypothesis or the run‐on water and sediment transport capacity effect. A dual‐box system, consisting of a 1.8‐m‐long sediment feeder box and a 5‐m‐long test box, was used to quantify run‐on water and sediment effects. The test box has holes at the bottom for controlling the vertical hydraulic gradient. Experimental variables were rainfall intensity, slope steepness, near‐surface hydraulic gradient, and run‐on sediment concentration. Results demonstrated that under free soil drainage conditions, a decrease in run‐on sediment content caused a corresponding increase in downslope sediment detachment, resulting in a relatively constant sediment delivery from the test box. Under artesian seepage conditions, sediment deliveries were three to six times greater than those under drainage conditions and decreased as the erosion event progressed, possibly because of a reduction in soil erodibility. Sediment detachment by the run‐on water increased as either slope or rainfall intensity was increased or when the surface was changed from a drainage to a seepage condition. These results demonstrated that the sediment delivery reached a dynamic equilibrium and the dual‐box system can be used to study erosion processes similar to those occurring on a hill slope. A process‐based erosion model needs to account for surface hydraulic conditions and the associated erosion processes and their interactions.
Nitrogen and Water Interactions in Subsurface Drip‐Irrigated Cauliflower II. Agronomic, Economic, and Environmental Outcomes
Authors: Thompson Thomas L. , Doerge Thomas A. , Godin Ronald E.
Published: July 2010

Water × N rate experiments were conducted on subsurface drip‐irrigated cauliflower (Brassica olearaceaL. var.botrytisL.) during three winter growing seasons in southern Arizona. A range of water and N rates were selected to permit the calculation of appropriate water × N production functions. The objectives were to (i) determine the effects and interactions of irrigation water and N inputs on crop N uptake, residual soil NO3–N, N‐use efficiency, and unaccounted fertilizer N, and (ii) evaluate agronomic, economic, and environmental production criteria during three growing seasons. Spatial analysis was used to identify overlap of acceptable zones of marketable yield, net return, and unaccounted fertilizer N within each growing season. Acceptable yields and net return were defined as ≥95% of the maximum predicted response within the range of the treatments; acceptable unaccounted fertilizer N was defined as ≤40 kg ha−1Net returns and aboveground plant biomass N were significantly affected (P< 0.01) by N rate and in 2 yr by irrigation. There were also significant irrigation treatment × N rate interactions for net returns and biomass N. Residual soil NO3–N concentrations increased with N rate and decreased with soil water tension (SWT). Average amounts of residual soil NO3–N (0–0.9 m) for the highest N rate during the three seasons were 317, 296, and 180 kg ha−1for the low, medium, and high irrigation treatments, respectively. Unaccounted fertilizer N was significantly affected (P< 0.05) by irrigation treatment, N rate, and irrigation treatment × N rate interactions each year. Overlap of acceptable zones of marketable yields, net returns, and unaccounted N was achieved in one of the three years. The single combination of SWT and N rate that came closest to producing optimal or near‐optimal agronomic, economic, and environmental outcomes in all three years was 10 to 12 kPa and 350 to 400 kg N ha−1
Unstable Water Flow in a Layered Soil I. Effects of a Stable Water‐Repellent Layer
Authors: Carrillo M. L. K. , Letey J. , Yates S. R.
Published: July 2010

The development of preferential water flow in a soil profile can cause accelerated movement of pollutants to the groundwater thus reducing groundwater quality. This study investigated the effects of a stable water‐repellent soil layer on the development of unstable water flow in a homogenous profile. Stable water‐repellent soil is defined as one whose degree of water repellency does not change with time after contact with water. The effects of water entry pressure (hp), water‐repellent layer depth (L) and depth of ponded water at the soil surface (ho) on the development of unstable flow were investigated using homogenous coarse sand packed into a specially built rectangular chamber. The hydraulic conductivity of the water repellent soil was also measured as a function of hp and ho in a separate experiment using the constant head method. The hydraulic conductivity and the water content of the water repellent soil increased as ho/hp increased. No water penetrated the water repellent layer for values of (ho + L)/hp < 1, unstable flow developed for values between 1 and 1.5 and a stable front developed for values > 1.5. The conclusion is that stable flow occurred when the water flux through the water repellent layer exceeded the saturated hydraulic conductivity of the underlying wettable layer. The water flux through the water repellent layer was a function of the hydraulic conductivity of the water repellent layer which increased as ho/hp increased.
Infiltration in Homogeneous Sands and a Mechanistic Model of Unstable Flow
Authors: Geiger Steven L. , Durnford Deanna S.
Published: July 2010

One‐dimensional infiltration experiments were conducted to study the mechanics of unstable flow in homogeneous soils under non‐ponding infiltration. A mechanistic model is presented which explains soil water pressure gradients that are characteristic of stable and unstable flow in homogeneous soils and is based on a dynamic soil water entry pressure, the Darcy‐Buckingham flux equation, and hysteretic moisture retention functions. Infiltration experiments were conducted with five sand samples under applied fluxes of 2, 5, 20, and 50% of their saturated hydraulic conductivity. Soil water pressures were measured at fixed depths following passage of the wetting front. A trend of decreasing soil water pressure over time following passage of the wetting front is not predicted by Richards' equation and produces unstable flow. Under air‐dry initial soil water conditions, soil water pressures were unstable for all fluxes in the three coarser sands. In the two finer sands, unstable flow occurred at infiltration rates of 20 and 50% of their respective saturated hydraulic conductivities but stable flow occurred at lower fluxes. Soil water pressure measured just behind the wetting front was found to be an increasing function of applied flux and average grain size of the media for infiltration with air‐dry initial soil water content. Additional tests showed that systems that produced unstable flow under air‐dry initial soil water contents exhibited stable flow during infiltration with initial soil water contents that were greater than air dry.
Stability of Structural Form during Infiltration Laboratory Measurements on the Effect of De‐inking Sludge
Authors: Nemati M. R. , Caron J. , Gallichand J.
Published: July 2010

An adequate understanding of the mechanisms involved in the structural stabilization of soil by different sources of organic matter is needed to help design management strategies aimed at maintaining a stable soil structure. The objective of this study was to identify mechanisms involved in soil structure stabilization by paper sludge application, either by increasing the soil resistance to external stresses (aggregate stability) or by decreasing the magnitude of the external stresses (diminution of the wetting rate). A laboratory study was conducted on three different soil types with application of paper sludge at three rates (8, 16, and 24 dry t ha−1). The mean weight diameter, bulk density, hydraulic conductivity, and water retention properties were measured before and after a wetting event. The results indicate that most of the changes in physical properties resulting from rapid wetting took place at the soil surface (0–50 mm) and the magnitude of these changes gradually decreased down to a depth of 150 mm. Paper sludge application significantly improved the stability of 1‐ to 4‐mm aggregates to the destructive action of wetting in all three soil types. Paper sludge application increased porosity at potential > −2 kPa, which resulted in higher hydraulic conductivity values (up to 88%) and a smaller increase in soil bulk density (down to 67%) relative to a control following rapid wetting. The wetting rates observed during the wetting event were similar regardless of the treatment, because the increase in the water potential at the wetting front was compensated for by an increase in hydraulic conductivity with increasing rates of sludge application.
Exact solution for horizontal water redistribution by general similarity
Authors: Shao Mingan , Horton Robert
Published: July 2010

This paper presents an exact solution to horizontal water redistribution by using general similarity theory. A power function of soil water diffusivity is used to derive the exact solution. The similarity solution contains initial wetted length, amount of water present, and coefficients of water diffusivity. A similarity solution for a step function initial condition is compared with a corresponding numerical solution. Error analysis indicates that the maximum global error in water content is within 2%. The general similarity theory provides an approach that exactly solves horizontal water redistribution with a variable first‐type boundary of a specific form of time dependence and initial conditions; the Boltzmann transformation case is restricted to a horizontal infiltration problem with constant first‐type boundary and initial conditions.
Water‐Budget Evaluation of Prairie and Maize Ecosystems
Authors: Brye K. R. , Norman J. M. , Bundy L. G. , Gower S. T.
Published: July 2010

Annual monitoring of water‐budget components is useful for comparing the fate of water inputs among ecosystems. Land‐use changes from natural prairies to managed agroecosystems alter water‐budget components. Weekly hydrological budgets for a restored natural prairie and maize (Zea mays L.) agroecosystems (no‐tillage and chisel‐plow) were constructed for 132 consecutive wk between June 1995 and January 1998. Precipitation, drainage, soil water–storage changes, and snow‐cover changes were measured on Plano silt loam soil (fine‐silty, mixed, superactive, mesic Typic Argiudoll) at agricultural and prairie sites. Compared with the maize ecosystems, the prairie maintained greater soil water contents deeper in the soil profile (0.8–1.4 m), somewhat larger evapotranspiration (Et), and significantly less drainage because of considerable interception of precipitation by a residue layer. Soil water storage in the no‐tillage maize setting was more similar to the prairie, while Et, net primary productivity, and drainage were more comparable to the chisel‐plow agroecosystem. Total drainage measured with equilibrium‐tension lysimeters was 199 mm of water (coefficient of variation [CV] = 5.7%) for the prairie ecosystem, 563 mm of water (CV = 13.6%) for the no‐tillage maize ecosystem, and 793 mm of water (CV = 18.5%) for the chisel‐plow maize ecosystem. Residue interception for the prairie was 477 mm, compared with 681 mm of precipitation during the growing season of 1997, which contributed to lower prairie drainage. The combination of similar productivity, higher soil water contents, and less drainage than the chisel‐plow ecosystem suggests that a no‐tillage ecosystem is more sustainable than the chisel‐plow agroecosystem in terms of reducing potential adverse environmental impacts associated with soil water movement.
Response of Surface Horizons in an Oak Forest to Prescribed Burning
Authors: Phillips D. H. , Foss J. E. , Buckner E. R. , Evans R. M. , FitzPatrick E. A.
Published: July 2010

The reduction of forest floor ground cover and litter layers by prescribed fires may alter the morphology (field and micro) and physical properties of surface horizons. This study determined long‐term (35 yr) changes in surface horizon bulk density, organic matter concentration and content, and morphology in response to periodic (5 yr) and annual (1 yr) prescribed fires. Soils were fine‐silty, siliceous, thermic Glossic Fragiuldults, supporting mixed oak vegetation in middle Tennessee. Upper mineral soils (0‐ to 2‐cm and 0‐ to 7.6‐cm depths) were sampled and detailed field descriptions made. Periodic and control plots had a thin layer of Oi, Oe, and Oa horizons 5 yr after the 1993 burn, whereas on annual burn plots a 1‐ to 2‐cm charred layer was present. Significant reductions in organic matter concentration and mean thickness of the A horizon were found from burning (A horizons thicknesses were 6.4, 4.6, and 2.9 cm in control, periodic, and annual plots, respectively). Periodic burns did not significantly alter the organic matter and bulk density of the upper 7.6 cm of mineral soil; however, annual burns did result in significantly higher bulk densities (1.01, 1.07, and 1.29 Mg m−3 in control, periodic, and annual plots, respectively) and lower organic matter concentrations and contents. Microscopic investigations confirmed that compaction was increased from annual burning. Thin sections also revealed that the granular structure of the A horizons in control and periodic plots resulted from bioterbation of macro and mesofauna, fungi, and roots. Long‐term annual burning greatly affected surface soil properties, whereas periodic burning on a 5‐yr cycle had only limited effects.
Minirhizotron installation in sandy, rocky soils with minimal soil disturbance
Authors: Phillips Donald L. , Johnson Mark G. , Tingey David T. , Biggart Craig , Nowak Robert S. , Newsom Jon C.
Published: July 2010

We developed and demonstrated the utility of a technique for installing minirhizotron tubes in sandy, rocky soils where more traditional installation methods are inadequate. The method uses a pneumatic rock‐drill alternately to drill and drive drill casing into the soil. Soil particles and drilling debris are removed from the casing as it is installed. The minirhizotron tube is inserted into the drill casing and the casing is withdrawn. A pneumatic screw‐drive guide system powers the downward and upward movement of the rock‐drill and controls the angle of installation. Working from a platform suspended from a center‐pivot elevated catwalk minimized soil disturbance. Soil contact and root ingrowth around the minirhizotron tubes were very satisfactory. This method, while fairly labor intensive, allows minirhizotron studies of root dynamics in sandy, rocky soils where they would otherwise not be possible. Also, there is much less soil compaction and disturbance than traditional installation techniques entail.
Hydraulic Conductivity of an Allophanic Andisol Leached with Dilute Acid Solutions
Authors: Ishiguro M. , Nakajima T.
Published: July 2010

When the soil contains a substantial amount of pH‐dependent charges, pH strongly influences hydraulic conductivity. Adverse effects of acid rain and chemicals on soils have been observed, but few studies have focused on hydraulic conductivity change due to pH. Changes to the saturated hydraulic conductivity (K) of allophanic andisol (volcanic ash soil), which has a substantial amount of pH‐dependent charges, during dilute acid leaching were examined in this study. K was determined at a constant hydraulic gradient in soil columns. Influent solutions of HNO3 and H2SO4 were prepared at pH 3 and 4. Tensiometer pressure potential and pH distribution in the soil columns were measured. Clay dispersion was measured by optical transmission and soil buffer capacity was evaluated from acid titration curves. K decreased during HNO3 leaching but increased during H2SO4 leaching. Because of the high buffer capacity of the soil, the influence of acid leaching on the soil structure was significant only at the soil surface. Soil dispersion was observed only in HNO3 solution. No dispersion was observed in H2SO4 solution because of the strong specific adsorption of SO2−4 The swelling and dispersion of the soil at the surface layer caused the decrease in K during HNO3 leaching, while these processes were prevented in H2SO4 leaching.
Perturbation of Taranakite Formation by Ferrous and Ferric Iron under Acidic Conditions
Authors: Zhou J. M. , Liu C. , Huang P. M.
Published: July 2010

Taranakite is an important reaction product of monoammonium phosphate fertilizer with soils. Its formation affects the transformation of nutrients in soils. The effect of different molar ratios of Fe(II)/Al and Fe(III)/Al on the formation of taranakite at pH 4.0 was investigated in this study. The results show that Fe(II) ion significantly perturbed the formation of taranakite at the Fe/Al molar ratio of 1.2 When the Fe/Al molar ratio was increased to 2.5, the formation of taranakite was completely inhibited by Fe(II), whereas, under the same condition, some crystalline taranakite was still observed in the Fe(III) system. Although Fe(III) had less effect on the crystallization of taranakite than Fe(II) at lower Fe/Al molar ratios, it also completely inhibited the formation of taranakite at the molar ratio of Fe(III)/Al ≥ 5. The solid products formed in the Fe(III) or Fe(II) system contained a substantial amount of Fe(III) and a much higher proportion of phosphate than that was required for the formation of NH4–taranakite. As indicated by the solution phase analysis at the end of the experiment, more Fe ions were present in the solution in the Fe(II) system, compared with the Fe(III) system, to perturb the nucleation and crystallization of taranakite. Since iron is a very common element in soil, taranakite formation may be perturbed in soils with high Fe content, especially under reduced and acidic conditions.
Interaction of Carbonate and Organic Anions with Sulfate and Selenate Adsorption on an Aluminum Oxide
Authors: Wijnja H. , Schulthess C. P.
Published: July 2010

The presence of anionic cosolutes often influences anion adsorption on soil mineral surfaces. The possible effect of common solutes, such as CO3 species, on the adsorption of other anions on metal (hydr)oxides is poorly understood. Accordingly, we determined the effect of CO3, formate, acetate, oxalate, and citrate on the adsorption of SO4 and SeO4 on Al oxide. Carbonate markedly promotes the adsorption of SO4 and SeO4 between pH 6 and 8. The maximum effect occurs at relatively low CO3 concentrations (0.3 mM) and the promotive effect decreases with further increase in CO3 adsorption. Formate and acetate also promote adsorption of SO4 and SeO4, while oxalate and citrate have a competitive effect, especially at lower pH values. Based on existing Fourier transformed infrared (FTIR) spectroscopic data and new electrophoretic mobility data, CO3 may promote the adsorption of other oxyanions by forming extra reactive protonated sites that exist with the adsorbed CO3 Acetate and formate presumably interact through the same mechanism. This promotive mechanism was ineffective in the case of adsorption of a high affinity anion such as PO4 Finally, the adsorptive properties of Al oxide, as we know it from simple model systems, can significantly be altered in soils, where CO3 and organic anions are ubiquitous solutes. For example, the adsorption maximum of SO4 > SeO4 became in the presence of CO3
Estimating Earthworm‐Influenced Soil Structure by Morphometric Image Analysis
Authors: VandenBygaart A. J. , Fox C. A. , Fallow D. J. , Protz R.
Published: July 2010

Earthworms have a profound influence on soil processes. However, there is generally a lack of adequate means by which to assess the influence of earthworms on soil structure. Not until quantitative methods on undisturbed soil samples are developed will there be any adequate measure of the influence of earthworms on soil structure. This paper describes an extension of an image‐analysis method developed for the quantitative determination of the influence of earthworms on soil structural properties. Mammillated vughs are most likely developed by the burrowing of soil macrofauna, in particular earthworms. A learning set of mammillated vughs was compiled with pores taken from a soil developed solely through the channeling and casting of earthworms. This learning set was used to classify soil blocks taken from a no‐till and conventionally tilled treated soil. The results indicated that the no‐till soils had more than twice the number of mammillated vughs >1000 μm in diameter. This was attributed to the larger earthworm population in the no‐till soils, coupled with the change in morphology or destruction of some of the mammillated vugh features caused by disturbance in the conventionally tilled soil. This method should allow for a more effective means to evaluate the influence of earthworms on soil properties within any given soil profile.
Soil–Landform Relationships on a Loess‐Mantled Upland Landscape in Missouri
Authors: Young F. J. , Hammer R. D.
Published: July 2010

Soil survey users are requesting statistically valid distributions of soil attributes that are important for management and land use. The hypothesis that many soil attributes vary predictably with landscape positions was tested with 257 pedons from point transects in a 40‐ha upland Missouri setting. The effect of landscape position on the central tendencies of selected soil properties was examined. Most soil properties were similar between ridge and shoulder positions. Differences were minimal within the backslope. Backslopes differed from ridges and shoulders, with more argillic horizon clay, thinner epipedons, and less organic C, lower pH and base saturation, and less silt on a clay‐free basis. Color patterns suggest that backslopes are wetter than ridges and shoulders, with more redoximorphic activity and organic matter accumulation on ped faces. Differences among the ridge–shoulder pedons and backslope pedons may be caused by differing hydrologic patterns as a result of interactions between topography and the underlying glacial till.
Biotic and Abiotic Nitrogen Retention in a Variety of Forest Soils
Authors: Johnson D. W. , Cheng W. , Burke I. C.
Published: July 2010

Nitrogen (N) immobilization in sterilized (abiotic) and non‐sterilized (biotic) O and A horizons was studied to determine the relative importance of biotic and abiotic processes in N retention in forest ecosystems. We collected samples from a variety of forest locations in Washington, Nevada, California, Tennessee, and North Carolina with differing soil types, vegetation, N status, and soil acidity. Included among these sites were adjacent stands of N2‐fixing and non‐N2‐fixing species and sites of differing N status due to slope position at a given location. We treated O and A horizon samples from each site with (15NH4)2SO4; sterilization was achieved by adding HgCl2, which proved to be highly effective. We found significant levels of both abiotic and biotic N immobilization in all soils. Biotic N immobilization was much greater in the N‐poor sites in California and Nevada than in the other sites and was inversely related to N concentration overall. Biotic immobilization was directly related to pH and base saturation among all sites, but we hypothesize that these correlations resulted from a correlation between those parameters and N concentration. Abiotic N immobilization varied less than biotic N immobilization across sites and was unrelated to N concentration or pH. The percentage of total N immobilization as abiotic N immobilization varied considerably (from 6–90%), and was positively correlated with N concentration. These results suggest that abiotic N immobilization can be a significant process in a variety of soil types. Across soil types with increasing N saturation, biotic N immobilization decreases and abiotic N immobilization accounts for a greater proportion of total N immobilization.
Predicting the Gas Diffusion Coefficient in Repacked Soil Water‐Induced Linear Reduction Model
Authors: Moldrup P. , Olesen T. , Gamst J. , Schjønning P. , Yamaguchi T. , Rolston D.E.
Published: July 2010

Investigations of gas transport and fate processes in packed soil systems require knowledge of the gas diffusion coefficient, DP, as a function of air‐filled porosity, ϵ. On the basis of the literature, data from six studies over the porosity range of 0.1 to nearly 1.0, it is reconfirmed that the Marshall (1959) model better predicts DP(ϵ) in completely dry, repacked porous media than do the Penman (1940) and Millington (1959) models. The smaller DP value in wet soil, as compared with dry soil at the same air‐filled porosity, is accounted for by introducing a water‐induced linear reduction (WLR) term, equal to the ratio of air‐filled porosity to total porosity, in the DP(ϵ) model. By adding the WLR term in each of the three DP(ϵ) models for dry porous media, the so‐called WLR(Marshall), WLR(Penman), and WLR(Millington) DP(ϵ) models for wet soil are developed. To test the three WLR models, DP was measured at different soil‐water contents in six differently textured (6–38% clay) repacked soils. The WLR (Marshall) model accurately and best described DP(ϵ) for all six soils and additional soils from the literature. All three WLR models performed better than previous DP(ϵ) models. This study implies that the smaller DP in a wet soil, which is due to water‐induced changes in air‐filled pore shape and pore connectivity, can be described by a simple, linear function of relative air‐filled porosity. The WLR(Marshall) model represents a conceptual and accurate model to predict DP(ϵ) in sieved, repacked soil.