bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐Term Effects of Nitrogen Fertilization on Soil Organic Nitrogen Availability
Authors: Vanotti M. B. , Leclerc S. A. , Bundy L. G.
Published: July 2010

Long‐term N fertilization affects soil organic N reserves, N mineralization potential, and crop response to applied N, but little information is available on the influence of short‐term N fertilizer (STN) management on soil organic N availability and crop response. This study was conducted to determine if STN changes soil N supplying capability to corn (Zea mays L.) after 3 yr of differential N fertilization on a Fayette silt loam soil (fine‐silty, mixed, mesic Typic Hapludalf) in Wisconsin. Various rates of N fertilizer (0–402 kg N ha−1) were applied to corn in 1983, 1984, and 1985, and their residual effects on corn response were evaluated in 1986. Soil profile No3‐N levels in spring 1986 were very low in all plots (48 ± 4 kg ha−1 [90 cm]−1), yet grain yields and N uptake were significantly increased by STN applications. Corn N uptake was linearly related to the total amount of N returned to soil in crop residues during the previous 3 yr. Increased organic N availability under high STN management was equivalent to a 78 kg N ha−1 rate, or 47% of the N fertilizer required for optimum crop yields. In aerobic incubations (40 wk) of spring 1986 soil (0–30 cm), STN additions increased N release only in the first few weeks. Kinetics of N mineralization were best described by a two‐component model in which the active fraction (NA) of soil organic N was highly correlated with corn N uptake (r = 0.88). Simulation of field conditions showed that 95% of NA is available before crop maturity. A phosphate‐borate buffer organic N availability index was significantly and consistently related to STN treatments. Relative increases in total soil organic N corresponded with the 3‐yr N balance between fertilizer additions and grain removals, and were about 10 times larger than mineralizable N. These results indicate that immobilization of excess mineral N into stable soil organic N during decomposition of crop residues should be considered in determining the environmental risk of N fertilization. Although labile organic N is a small fraction of the total fertilizer N contribution to soil N, its quantification should allow a more accurate assessment of crop N needs.
Pedogenesis of Cotiga Mound, a 2100‐Year‐Old Woodland Mound in Southwest West Virginia
Authors: Cremeens D. L.
Published: July 2010

Cotiga Mound, an Early Woodland mortuary mound constructed 2100 YBP, was sampled to evaluate diagnostic horizon development during a well‐defined, relatively short period of time. Five columns (profiles), three of which extended into the submound terrace soil, and one Giddings core of the terrace soil were sampled for particle‐size, pH, organic C, and micromorphology analysis. Six additional cores were collected to characterize the terrace soil. The mound was constructed of acid, silty material, in a manner that resulted in basketloading macrofabric consisting of long, sinuous, thin layers contrasting in color and texture. Pedogenesis destroyed the macrofabric and formed a solum in the upper 0.75 to 1.0 m of the mound. The solum consisted of a thin, dark A horizon; and intermittent, thin E horizon; and a variable B horizon. The B horizon was thickest at the mound crest, contained clay films on ped surfaces, and was designated Bt. On side slopes, the B horizon was thinner, lacked clay films, and was designated Bw. No B horizon was formed at the mound periphery. Clay distribution indices indicated that the Bt horizon was borderline cambic‐argillic, consistent with those typical of 2000‐yr‐old mid‐Atlantic alluvial soils. Clay films were sparsely distributed throughout the mound, indicating that clay accumulation mechanisms were largely inefficient in the 2100 yr. Mound soils were classified as Typic Dystrochrepts grading to Typic Hapludults at the mound crest. These soils are similar to floodplain soils mapped nearby. Submound terrace soils and adjacent terrace soils were classified as Humic Hapludults.
Effects of Dinitrogen‐Fixing Trees on Phosphorus Biogeochemical Cycling in Contrasting Forests
Authors: Zou Xiaoming , Binkley Dan , Caldwell Bruce A.
Published: July 2010

Phosphorus availability in soils is controlled by both geochemical and biological reactions. Dinitrogen‐fixing trees differ from non‐N2‐fixing trees in litter production and litter chemistry, and these differences may substantially alter soil P biogeochemistry. We examined the effects of two N2‐fixing tree species on labile P pools and potential P transformation rates and correlated these variables with soil acid phosphatase activity. Experimental treatments include stands of N2‐fixing red alder (Alnus rubra Bong.), conifers, and a mixture of both in Oregon, and plantations of N2‐fixing Albizia falcataria (L.) Fosberg, Eucalyptus saligna Sm., and a mixture of both in Hawaii. Data from Oregon indicated that red alder increased labile organic P (Po) levels and soil phosphatase activity. Soil labile Po concentrations in the red alder and mixed stands were twice those of the conifer stand. Labile inorganic P (Pi) pools and net P solubilization rates in soils under the mixed stand were two‐ to fivefold greater than in pure stands, suggesting that interactions between alder and conifers, rather than alder's effect, triggered changes in P geochemical reactions. In Hawaii, labile Po concentrations in both pure A. falcataria and mixed plantations were higher than in the pure E. saligna plantation. Soil acid phosphatase activity in the pure A. falcataria plantation was twice as high as that in the pure E. saligna plantation. However, labile Pi pools and P transformation rates did not differ among the three Hawaiian plantations. Our results suggest that N2‐fixing trees increase soil labile Po levels and soil phosphatase activities whereas their interactions with non‐N2‐fixing trees vary with species and may result in altering both geochemical and biological P transformations.
Absorbent Method for Measuring Solute Activities in Unsaturated Soils: Thermodynamics and Preliminary Experiments
Authors: Snyder V. A. , Martínez G. A. , Vázquez M. , Peña L. , Cavallaro N.
Published: July 2010

Characterizing the physico‐chemical environment in unsaturated soils has been difficult due to lack of methods for measuring solute activities at low soil water content. We describe a method where a thin sheet of insoluble and chemically nonreactive absorbent material is allowed to absorb water and solutes from the soil. Solute activities are inferred from the measured amounts of sorbed water and solutes and a generalized pressure membrane technique. Preliminary evaluations of the method used Whatman no. 42 filter paper as the absorbent. Air‐dry filter papers that had been impregnated with different known amounts of K2HPO4 were allowed to absorb water by equilibrating through the vapor phase with salt solutions of known water potential. Measured filter paper water contents and K2HPO4 molalities (mol sorbed K2HPO4 kg−1 sorbed water) related to water potential in a way consistent with theory. To examine general trends and variability of measurements in actual soil systems, filter papers were equilibrated with soil receiving different chemical pretreatments, at soil water matric potentials between −7 and −5400 J kg−1. Coefficients of variation for Ca, Mg, and K molalities in the filter papers were usually <20% for a given treatment. Predictably, cation molalities generally increased with decreasing soil water content. In CaSO4‐treated soil, however, Ca molalities decreased significantly, perhaps reflecting increased soil adsorption of CaSO4 at low water potentials. Adding Ca electrolytes to the soil generally increased K and Mg molalities, as expected from ion exchange.
Fate of l‐Phenylalanine in Soil and Its Effect on Plant Growth
Authors: Sarwar M. , Frankenberger, W. T.
Published: July 2010

Phenylacetic acid (PAA) is a deamination product of phenylalanine (PHE) applied to soil, which can have a positive physiological effect on plant growth and development. The objective of this study was to determine the factors limiting deamination of PHE when added to soils, determine the major pathway upon detection of metabolic intermediates, and assess the growth‐promoting effect on maize (Zea mays L.) of an exogenous application of PHE to soil. The highest activity of PHE deamination in soils occurred at pH 8.5 and on incubation temperature of 40°C. The soil assay used to determine these parameters was based on the amount of NH4‐N cleaved from l‐PHE when incubated for 48 h in the presence of toluene. A sigmoidal relationship was observed between NH4‐N and PHE concentration, indicating cooperative kinetics. Both phenylpyruvic acid and PAA were detected by high‐performance liquid chromatography (HPLC) following the addition of PHE to soil. A glasshouse experiment revealed that an exogenous application of PHE as a soil drench to established uniform seedlings of maize had a significant effect on vegetative growth parameters (shoot height, shoot fresh weight, internodal distance, uppermost leaf collar base distance, and leaf width). Since PAA is a well‐established plant growth regulator, it was concluded that this metabolic product derived from PHE in soil was responsible for the stimulatory growth effects in maize.
Sodic Calcareous Soil Reclamation as Affected by Water Chemical Composition and Flow Rate
Authors: Nadler A. , Levy G. J. , Keren R. , Eisenberg H.
Published: July 2010

Sodic soils exhibit poor physical conditions that adversely influence water and air movement, soil erodibility, and plant growth. This study investigated the efficiency of naturally occurring CaCO3 in reclaiming a sodic loess soil (Calcic Haploxeralf) with an exchangeable sodium percentage of 16. Soil columns (50 or 100 mm high) were leached with distilled water (DW), 1 dS m‐1 tap water (TW), or CO2‐enriched TW at a flow rate of either 11.5 or 50 mm h‐1. The effluent from the columns was collected continuously, and its chemical composition was analyzed. When DW was used, CaCO3 dissolution was the main source (85%) for replacing exchangeable Na. When TW was used, 80% of the (Ca2+ + Mg2+) for reclaiming the sodic soil came from the leaching solution. The slow water flow rate (11.5 mm h‐1) improved reclamation by ∼30%, probably due to the higher concentration of (Ca2+ + Mg2+) from CaCO3 and the longer time available for Ca2+ diffusion into soil aggregates. The CO2‐enriched TW was the most favorable treatment for CaCO3 dissolution and thus the most efficient for soil reclamation. Our results suggest that reclamation of sodic soils can be accomplished by means of the naturally occurring CaCO3 in the soil, providing management conducive for CaCO3 dissolution is used.
Soil Emissions of Nitric Oxide and Nitrous Oxide from No‐till Corn
Authors: Thornton Frank C. , Valente Ralph J.
Published: July 2010

Fertilized agricultural soils can be a significant source of emissions of NO and N2O into the atmosphere. This study was conducted to determine the influence of N rate on the emissions of these gases in a no‐till corn (Zea mays L.) crop grown in western Tennessee. The influence of N rate was assessed for a 210‐d period on replicated plots receiving 0, 140, and 252 kg N ha−1 (0N, 140N, and 252N) as ammonium nitrate (AN). Plots were located on a Routon silt loam (fine‐silty, mixed, thermic Typic Ochraqualf) at the West Tennessee Agricultural Experiment Station in Jackson, TN. Gas fluxes were measured by static chamber boxes located on plots. The measurement technique was automated and replicate chamber estimates were made eight times daily for the entire study period. Fertilizer application significantly affected both NO and N2O emission rates. The cumulative N2O‐N lost from the fertilizer treatments was from 10 to 20‐fold that of NO. On an areal basis, the 140N treatment emitted 4.23 kg N2O‐N and 0.19 kg ha−1 of NO‐N whereas the 252N treatment emitted 6.56 kg N2O‐N and 0.50 kg ha−1 NO‐N. Soil parameters of water‐filled pore space (WFPS), NO3− and NH4+, were correlated with N2O emissions but only soil NO3− was correlated with NO flux. Our data, and more recent data in the literature, suggest that N2O emissions from fertilized soil may be considerably higher than previously thought. Emissions of N2O were 2.6 to 3.0% of the fertilizer amounts applied. These higher emissions may, in part, explain some of the reason for the shortfall in the global N2O budget.
Mechanistic Modeling of Coupled Ammonium and Nitrate Uptake by Onions Using the Finite Element Method
Authors: Abbès C. , Parent L. E. , Robert J. L.
Published: July 2010

A two‐dimensional finite element model for predicting N uptake by onion (Allium cepa L. cv. ‘Norstar 210B’) was developed using variable space intervals in zones of high ionic gradient near the root surface and flexible grid size describing shrinkable subdomains of increasing root competition. The rationale included assumptions of the Cushman‐Barber model, the mobile layer concept, the type of elements, and the discrete variables of the system. The model can predict simultaneous NO3− and NH4+ uptake by coupling a nitrification model and plant‐specific Michaelis‐Menten kinetic paremeters. The model output was compared with measured N uptake based on ammonium sulfate and ammoniated peat (AP) applied to four soils (a silt loam, two sandy loams, and a sand) in a growth chamber. The observed N uptake was close to the predicted in all soils but one, where NH4+ uptake capacity was probably attained. Root growth rate was a sensitive parameter reducing N uptake from As compared with AP. The S‐shaped uptake curves were obtained for the silt loam and sandy loam soils receiving AP. Ammonium profiles were steep. Nitrate profiles were smoother. Nitrate was the dominant N form taken up even when NH4+ was the major available form. Total N uptake was smallest in the sand, which had a low moisture content and maintained a high NH4+ gradient, and the highest in the silt loam, which showed the smallest buffering capacity and the largest volumetric water content, both known to increase NH4+ and NO3− diffusivity.
The Effect of Raindrop Impact and Sheet Erosion on Infiltration Rate and Crust Formation
Authors: Morin Joseph , Van Winkel Jeannoux
Published: July 2010

Soil crust formation can result from the beating action of falling drops (structural crust) or the deposition of entrained eroded suspension in shell flow (deposional crust). To determine the relative importance of the two processes, an experiment was carried out with rainfall simulation under laboratory conditions. Clay soil exposed to the beating action of rain drops produced sheet erosion, which was deposited on a layer of clean sand downslope of the same continuous slope. The thin crust that was formed on the two parts of the slope, the clay and the sand, reduced the infiltration rates in time to values of 1 to 5 mm h−1. In comparison with the uniform clay slope, the main difference was the longer time needed to reach the low infiltration rates. Preventing the sand part from any rain impact beating extended the time needed to obtain the low infiltration rates that were nearly the same as those of the clay slope. The results provoke the question is the common theory of compacted crust by rain impact such an important factor?
Nitrogen Recovery by Corn from Nitrogen‐15 Labeled Wheat Residues and Intact Roots and Soil
Authors: Hubbard Victoria C. , Jordan Diann
Published: July 2010

Conservation tillage systems, which maintain crop residues on the soil surface, are becoming more widely used. Crop residues serve as ground cover to reduce soil erosion and act as a sink‐source for plant nutrients. A better understanding of the processes involved in crop residue decomposition and N release in these systems is needed to develop more efficient residue and fertility management practices. A greenhouse study was conducted to determine N availability to corn (Zea mays L.) from wheat (Triticum aestivum L.) residues and intact roots and soil as affected by residue placement. Tracer 15N was used to quantify the N recovered by corn from wheat residues and intact roots and soil. Wheat residues were either surface‐placed or incorporated in a Mexico silt loam (fine, montmorillonitic, mesic Udollic Ochraqualf) in pots with intact wheat roots. Residue placement significantly influenced the amount of 15N recovered by corn from wheat residues but not from intact roots and soil. Corn 15N recovery was significantly higher from incorporated residues than from surface residues; however, this was not reflected in the dry weight. Corn dry weight was 12% greater from surface residues than from incorporated residues. Higher yield from surface residues was attributed to a more constant optimum soil water content.
Availability of Residual Phosphorus in Manured Soils
Authors: Sharpley Andrew N.
Published: July 2010

In many areas with confined animal operations, continual manure application has increased soil P above amounts sufficient for optimum crop yields. In these areas, it is of economic and environmental importance to determine how long high‐P soils will remain above crop sufficiency and identify soils where P contents would decrease most rapidly under similar management conditions. Thus, the surface 5 cm of 23 high‐P soils (85–419 mg kg−1 Mehlich‐3 P) in Oklahoma and Texas, which had received beef feedlot, poultry, or swine manure (90–1880 kg P ha−1 yr−1 for up to 35 yr) were successively extracted with Fe‐oxide‐impregnated paper strips to investigate residual soil P availability. A decrease in strip P with successive extractions followed the equation: Strip P = a(extraction number)−b (r2 of 0.88‐0.98). The rate of P release to strips (exponent b) decreased more rapidly as soil P sorption saturation increased (R2 of 0.79). Phosphorus saturation also accounted for 85% of the variation in the total amount of P released to strips from manured soils in 15 successive extractions (51–572 mg kg−1). Fractionation of soil P before and after strip extraction showed bicarbonate inorganic P contributed most of the P released to strips (46%). The above equation also described soil P release in several published field studies (r2 of 0.77–0.98). Thus, successive strip extraction of soil has the potential to describe soil factors controlling the availability of residual P and identify soils where high P contents may be less buffered and, thus, decrease more rapidly than others under similar management conditions.
Sandy Wet Spodosols: Water Tables, Chemistry, and Pedon Partitioning
Authors: Evans C. V. , Mokma D. L.
Published: July 2010

Spodosols are notably difficult to classify in terms of moisture regime, presumably because redox colors are masked by spodic colors, or perhaps because the absence of structure in sandy Spodosols is a hindrance to detection of redox features. Some views of Spodosol pedons as a series of compartments raise the possibility that some portions of the spodic pedon are simply more responsive than others to saturation parameters. This study attempts to determine whether compartmentalization within Spodosol pedons results in differentiation of soil response to saturation and water table fluctuation. Water table and chemical data were compiled from 16 Aquod pedons. Pyrophosphate‐extractable Fe and Al, oxalate‐extractable Fe and Al, and dithionite‐extractable Fe and Al were determined for all soils; organic C was also determined for at least Bh, Bhs, and Bs horizons, and oxalate‐extractable Si and the optical density of the oxalate extract (ODOE) were also determined for eight of the pedons. Comparisons of chemical data to saturation and water table fluctuation indicated that spodic horizon chemistry was unresponsive to both saturation duration and water table fluctuation. Chemistry of E horizons was most responsive to water table fluctuation, while Al and Si levels of C horizons were more sensitive to saturation and water table fluctuations. Thus, due to compartmentalization of Spodosol pedons, interpretations of saturation and water table fluctuation can be most effectively made from the chemistry of C and E horizons, respectively. The B horizon chemistry was not a good indicator of saturation duration or of water table fluctuation patterns.
Kinetics of Phosphate Rock Dissolution in Acidic Soil Amended with Liming Materials and Cellulose
Authors: He Z. L. , Baligar V. C. , Ritchey K. D. , Martens D. C. , Kemper W. D.
Published: July 2010

Phosphate rock (PR), coal combustion by‐product (CCBP), lime‐stone, and organic materials are promising amendments for low P, acid soils, and two or more of the amendments are commonly applied to improve crop yields in acid soil. However, the interactions between these amendments in acid soil are not fully understood. The effects of CCBP, limestone, and cellulose application on dissolution of North Carolina phosphate rock (NCPR) in an acid Lily loam (fine‐loamy, siliceous, mesicTypic Hapludult) from West Virginia were examined in an incubation study. Based on the ΔP‐NaOH estimation method, ≈ 30% of the added NCPR was dissolved after 60 d of incubation. The NCPR dissolution decreased drastically with increasing rate of CCBP, particularly when it was applied together with limestone, whereas cellulose addition tended to enhance NCPR dissolution. Dissolution of NCPR was well described by first‐order, Elovich, and Langmuir kinetic equations. The average r2 values between the experimental data of NCPR dissolution and the three models were 0.829*, 0.851**, and 0.930**, respectively, for 17 soil samples with and without amendments. Half‐life (t1/2) from the first‐order reaction could be employed as a simple measure of the NCPR dissolution rate. Constants A and b derived from the Elovich equation were related to the initial and average dissolution rate of NCPR. The potential maximum dissolution of PR from the Langmuir equation provided an estimate of the dissolution extent of NCPR. All four kinetic parameters, particularly t1/2 and A, were closely correlated with CCBP application rates. These parameters appeared useful in evaluating the effects of CCBP application on NCPR dissolution in the acid soil and might also be applicable to predicting PR dissolution for a wide range of soils with different properties.
Mechanisms of Negative Impacts of Three Forest Treatments on Nutrient Availability
Authors: Harrison Robert B. , Gessel Stanley P. , Zabowski Darlene , Henry Charles L. , Xue Dongsen , Cole Dale W. , Compton Jana E.
Published: July 2010

Many forest management treatments are directly aimed at maintaining or enhancing forest productivity. There may also be secondary effects that detract from this goal. We discuss three case studies in Washington state in which several mechanisms may have led to adverse secondary impacts. In the first study, pulp and paper (PII) sludges were mixed into soil and growth of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco], noble fir (Abies procera Rehder) and western white pine (Pinus monticola Douglas ex D. Don) was monitored. There was a significant negative correlation of height and diameter growth and C/N ratio for Douglas‐fir and western white pine (0.05 level). In a second study, effects of 50 yr of red alder (Alnus rubra Bong.) and Douglas‐fir growth on soil chemistry and stand productivity were compared. When the 50‐yr‐old stands were cut and red alder was established by planting into the soil of the former Douglas‐fir and red alder forests, lowered available P in the soil of the previous red alder stand was observed. In a third study, high rates of low C/N ratio organic matter (300 Mg ha−1) were added in municipal biosolids (N amount about 8000 kg ha−1) to Douglas‐fir and grand fir [Abies grandis (Dougl.) Forbes] plantations. Excess organic N in the biosolids apparently mineralized, nitrified, and contributed to soil acidification and accelerated cation leaching. Severe Mg deficiency (0.25 g kg−1 in biosolids‐treated vs. 0.93 g kg−1 in untreated area) might be the cause of observed foliar chlorosis and poor growth rates.
Importance of Soil and Role of Ecosystem Disturbance for Sustained Productivity of Cool Temperate and Boreal Forests
Authors: Kimmins J. P.
Published: July 2010

Human population growth places increasing demands on the world's forests. Sustaining these forests will depend to a considerable extent on sustaining soil structure and function. Traditional scientific concerns about sustaining timber production focused largely on soil fertility, but recent interest has focused attention on the plant and animal community and on “biodiversity”. Neither of these approaches is satisfactory on its own. They should be replaced with an ecosystem analysis approach that includes the biotic and abiotic components. The most fundamental issue in sustainable forest management is the long‐term productive capacity of individual sites, which is determined to a considerable extent by the availability of soil resources. Understanding the sustainability of site productivity requires knowledge of the determinants of leaf area and its photosynthetic efficiency, and of the allocation of net production. Keys that determine production ecology in boreal and cool temperate forests include low soil temperature, slow rate of litter decomposition and the resultant character of the forest floor, and, in some areas, impeded soil drainage; these lead to limitations on nutrient availability. Natural disturbance influences these factors and thereby plays a vital role in maintaining productivity and several measures of biological diversity. Without stand‐replacing disturbances, closed forest may not be the climax vegetation in many western and northern Canadian landscapes. While forests and soils should be protected from “damage”, sufficient disturbance should be sustained to respect the disturbance‐related ecology of these forests. Ecological site classification and use of ecosystem‐level management simulation models are important for the design of appropriate disturbance regimes.
Boron Sorption and Release by Allophane
Authors: Su Chunming , Suarez Donald L.
Published: July 2010

To predict B behavior in soils and its influence on plants, it is crucial to understand the mechanisms of B sorption by mineral phases. Because B reacts with clay minerals and Al and Fe oxides, it should also sorb to poorly crystalline aluminosilicates such as allophane. Boron sorption, with and following allophane precipitation, was studied in batch experiments. Solutions containing AlCl3 and Na2SiO3 (concentrations <47 mM with Al/Si molar ratio of 1:1) and B(OH)3 (0, 4.4, and 32 mM) were mixed and titrated to pH 8.0 with 1 M NaOH at two rates (1 and 5 mL min−1) at 23°C, then incubated at 23 and 90°C for 5 d. More B was removed from solution when B was present during allophane precipitation than when B of an equal concentration was reacted with freshly precipitated allophane. In addition, more B was removed when allophane was formed by slower mixing at a slower titration rate, with higher initial B concentration, and incubated at lower temperature. More B was released by repeated washing with dionized water from allophane precipitated in the presence of B(OH)3 than from allophane reacted with B(OH)3. Boron sorption was investigated with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Adsorbed B was both trigonally and tetrahedrally coordinated, with the former being predominant. Boron reacted with allophane precipitate was surface sorbed. Corprecipitated B occurred only in tetrahedrally coordinated positions, presumably by substituting for Si in the tetrahedral layer. The structurally coprecipitated B is expected to be more resistant to release than the adsorbed B.
Effects of Soil Type and Water Flux on Solute Transport
Authors: Vanderborght J. , Vanclooster M. , Mallants D. , Feyen J. , Gonzalez C.
Published: July 2010

Prediction of solute transport in soils requires appropriate transport models and model parameters. The most suitable solute transport model and its parameters are likely to depend on both soil type and water flux. This dependency was investigated by means of transport experiments that were carried out in three different soils (Plaggept, Hapludalf, and Glossudalf) for two water application rates (0.5 and 1.0 cm d−1). Solute concentrations were measured during the transport experiment at six different depths in undisturbed soil monoliths (1.0‐m length, 0.8‐m i.d.) using time domain reflectometry (TDR). For each depth, parameters of two solute transport models, (i) the convective lognormal transfer function (CLT) model assuming stochastic‐convective solute transport or no solute mixing and (ii) the convective‐dispersive (CDE) model assuming complete solute mixing, were derived. The transport in the Plaggept and Hapludalf soil was better modeled as a stochastic‐convective process. Furthermore, solute transport in these two soils was very heterogeneous, resulting from considerable differences in local advection velocity. In the Glossudalf soil, solute transport was more homogeneous and characterized as a convective‐dispersive process. The heterogeneity of solute transport in both Plaggept and Hapludalf soils increased with the applied water flux. This increase was more pronounced in the Hapludalf soil, as the higher water flux resulted in a larger contribution of macropores to flow and transport of solutes.
Simulating Impact of Funnel Flow on Contaminant Sampling
Authors: Ju S.‐H. , Kung K.‐J. S. , Helling C. S.
Published: July 2010

Soil‐solution sampling methods developed more than 50 yr ago are still routinely used to monitor the fate of contaminants in unsaturated soils. The measured results, expressed as a function of depth or time, are called breakthrough curves (BTC). In this paper, BTC from limited samples are called SBTC, while ABTC are the BTC from the entire soil profile and MBTC are mass‐flux‐based BTC. Conventionally, assumptions have been that: (i) ABTC and MBTC are identical; and (ii) SBTC would accurately indicate MBTC when enough samples are collected. In soil with preferential flow paths, such assumptions may be invalid. The objectives of this study were to: (i) determine whether increasing the total number of samples would make SBTC an accurate indicator of contaminant loading; (ii) determine whether ABTC and MBTC are identical; and (iii) explore how to obtain representative MBTC with only a limited number of samples. Numerical simulations were conducted in three sets of four, two‐dimensional hypothetical profiles with inclined layers that could trigger funnel‐type preferential flow paths. Soil‐solution samplers at four different spacings were placed at four depths in each profile. Simulated results indicate that ABTC always significantly underestimate MBTC. By increasing the total number of randomly located samples, SBTC will never accurately indicate MBTC. The SBTC could be modified to better estimate MBTC when preferential weight is assigned according to the local water flux.
Determining Nitrogen‐15 in Ammonium by Producing Nitrous Oxide
Authors: Laughlin R. J. , Stevens R. J. , Zhuo S.
Published: July 2010

Standard procedures for determining 15N in the NH4+ fraction of 2 M KCl soil extracts convert NH4+ to N2 prior to isotope‐ratio mass spectrometry. We developed a new gas‐phase method for determining 15N in NH4+ by producing N2O. Producing N2O means that atmospheric contamination by N2 at natural abundance is not a problem. The method is more sensitive than other methods at lower enrichments, and as accurate and precise as other methods. Nitrous oxide is produced as a by‐product during the oxidation of NH4+ by alkaline OBr−. The reaction is catalyzed by Cu2+ and is pH‐dependent. The best practical conditions for producing N2O were when the NH3‐absorbing solution contained 0.005 M H2SO4 with 0.5 mM CuSO4, and when the molarity of the NaOH in the NaOBr was 10 M. Background N (0.20 µmol test−1) significantly diluted the theoretical enrichments for amounts of N <10 µmol test−1. Corrected enrichment values were accurate for amounts of NH4+‐N ≥1 µmol test−1. For amounts of NH4+‐N ≥1 µmol test−1, precision was determined with a CV of 5.6% at 0.10 atom % excess and with a CV of 0.3% at 10.00 atom % excess. The method is suitable for any matrix and has the potential for better performance if the background contamination could be lowered.
Parameterizing Temporal Changes in Aggregation in a Sludge Amended Soil
Authors: Rasiah V. , Biederbeck V. O. , Curtin D. , Zentner R. P.
Published: July 2010

Statistical comparison of the changes in aggregate size distributions (ASD) with time among treatments in a given soil or among soils is difficult. The objective of this study was to compare the use of fractal dimension (D), geometric mean diameter (GMD), and alpha (α) parameters as indices to characterize the temporal changes in ASD of a soil subsequent to the incorporation of an oily waste sludge. Soil samples for dry and wet aggregate size distribution (DASD and WASD, respectively) measurements were collected from a loamy sand during a 4‐yr period following sludge incorporation. Sludge incorporation produced a continuous oil content, i.e., 0, 1.0, 1.5, 3.0, and 7.0%, variable in the soil (by mass). The wind erodible fraction (WEF; <0.84 mm) in the sludge treated plots decreased from 80 to 38% but increased with time to 78% 4 yr later. The reduction in WEF was reflected as gains in larger size fractions which decreased with time. The 4.76‐ to 8‐mm water stable aggregates in the sludge treated plots increased from 10 to 80% but decreased with time to 40% 4 yr later. An opposite trend was observed for smaller size aggregates. After sludge incorporation, the D for DASD and WASD decreased with increasing oil content and increased with time. An opposite trend was observed for GMD and α. Initial oil content and time of sampling accounted for 91% of the variability in DASD characterized by GMD, 89% by D, and 60% by α. Initial oil content and time accounted for 78% of the variability in WASD characterized by D and 67% by GMD. Our results indicate that the temporal changes in DASD can be characterized equally well by GMD and D and the changes in WASD by D.
Forest Management Effects on Surface Soil Carbon and Nitrogen
Authors: Knoepp Jennifer D. , Swank Wayne T.
Published: July 2010

Changes in surface soil C and N can result from forest management practices and may provide an index of impacts on long‐term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south‐ and one north‐facing, undisturbed since the 1920s; a white pine (Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole‐tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for ≈15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south‐facing and decreased on the north‐facing watershed. The pattern for total N was similar. Total N decreased significantly on the north‐facing but was stable on the south‐facing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20‐yr period. Soil C and N concentrations generally declined the first year following whole‐tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long‐term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long‐term treatment impacts.
Soil Microbial Biomass and Mineralizable Carbon of Water‐Stable Aggregates
Authors: Franzluebbers A. J. , Arshad M. A.
Published: July 2010

Biophysical alterations of agricultural soils following adoption of zero tillage (ZT) deserve investigation in order to better understand the processes of soil organic C (SOC) sequestration and turnover. We determined the vertical distribution of soil microbial biomass C (SMBC), C mineralized in 24 d under standard conditions, and basal soil respiration (BSR) in five water‐stable aggregate classes. Four soils (loam, silt loam, clay loam, and clay) from the Peace River region of northern Alberta and British Columbia were sampled following 4 to 16 yr under comparison of conventional shallow tillage (CT) and ZT. Macroaggregates (>0.25 mm) had greater SMBC, more C mineralized in 24 d, and higher BSR than microaggregates at a depth of 0 to 50 mm. Differences between macro‐ and microaggregates in these properties decreased with soil depth. Carbon mineralized in 24 d and SMBC were 9 ± 9% greater (mean of four soils ± standard deviation among soils) under ZT than under CT in macroaggregates, but were 6 ± 11% lower in whole soil due to lower amounts in microaggregates under ZT than under CT. Macroaggregate‐protected SOC to a depth of 200 mm was 6.7 ± 1.9 g m−2 under CT and 9.8 ± 2.6 g m−2 under ZT. Soil organic C in macroaggregates, which had high concentrations of active pools of SOC, appeared to have been shunted into the more stable microaggregate fraction after disturbance with CT. Unlike in temperate, humid climates, decomposition of SOC during the passage from macro‐ to microaggregates may have been limited by the frigid, semiarid climate.
Monitoring Near‐Surface Soil Water Storage in Turfgrass using Time Domain Reflectometry and Weighing Lysimetry
Authors: Young M. H. , Wierenga P. J. , Mancino C. F.
Published: July 2010

Monitoring near‐surface soil water content with time domain reflectometry (TDR) could improve our understanding of water movement in a daily irrigated crop. But, TDR field validation is needed using weighing lysimeters to assess actual changes in soil water storage. In this study, we test the hypothesis that vertically installed TDR probes can be used to measure evapotranspiration (ET) in a full‐cover turfgrass environment. This was done by directly comparing changes in soil water storage measured with TDR against changes in mass measured with weighing lysimeters. The TDR probes (200, 400, 600, and 800 mm long) were installed vertically in two weighing lysimeters. The TDR water content and lysimeter mass determinations were made every 30 min for a 28‐d period during daily irrigation intervals, and during a 6‐d irrigation interval. Average water contents increased with increasing probe length; e.g., 600‐ and 800‐mm probes yielded average water contents of 18.1 and 18.5%, vs. 14.8% for the 200‐mm probe. These differences reflect the lack of transpirational uptake from deeper soil layers. All TDR probes underestimated water added and lost compared with the lysimeter during daily irrigation, with shorter probes exhibiting larger differences than longer probes. However, when the irrigation interval was increased to 6 d, the longer TDR probes were more suited to measuring water loss; for example, the 200‐, 400‐, 600‐, and 800‐mm probes measured 40, 77, 78, and 96% of the water loss recorded by the lysimeter, which only records ET. This shows that increasing amounts of water were taken up from deeper layers as the soil dried.
Time‐Dependent Changes in Pedogenic Processes on Marine Terraces in Coastal Oregon
Authors: Langley‐Turnbaugh S. J. , Bockheim J. G.
Published: July 2010

Very little is known regarding soil‐forming processes on marine terraces along the Pacific Coast. This study examined a soil chronosequence on an elevated marine terrace sequence in south‐coastal Oregon in order to investigate changes in soil‐forming processes with time. The soils range in age from 80 000 to >500 000 yr, and with increasing age classify as Inceptisols, Spodosols, and Ultisols. Relevant pedogenic processes were studied using morphological properties; extractable Fe, Al, and Si; dissolved Fe, Al, and Si in soil solution; and micromorphology. Podzolization and in situ weathering of silt to clay are the dominant and contemporary processes on the young and intermediate‐aged terraces, and argilluviation and clay neoformation are dominant processes on the older terraces. Evidence for podzolization includes organically complexed Fe and Al that peak in Bs horizons and mineral grains coated by Fe as evidenced in thin section. In addition, up to 93% of the Fe and Al in solution in the E horizons is retained in the Bs horizons. In situ weathering of fine silt in the younger soils is indicated by irregular depth trends in fine silt/total silt ratios. Argilluviation is manifested by clay films observed in the field and in thin section, which increase in thickness and abundance with time. Evidence for clay neoformation includes the retention of up to 54% of dissolved silica in the Bt horizons of the older soils. Podzolization and in situ weathering decrease in importance with time, and argilluviation and clay neoformation become increasingly more significant.
Hydraulic Characteristics of Organomodified Soils for Use in Sorptive Zone Applications
Authors: Rakhshandehroo G. Reza , Wallace Roger B. , Voice Thomas C. , Boyd Stephen A.
Published: July 2010

The sorption capabilities of subsoils for organic contaminants can be enhanced by modification of soil clays with cationic surfactants. The use of these organomodified soils to establish permeable sorptive zones has been suggested as a potential means for attenuating the migration of contaminant plumes. The hydraulic feasibility of sorptive zones was evaluated by measuring the hydraulic conductivities and porosities of both modified and unmodified soils at different effective stresses when permeated with water. Samples with 6, 12, 18, and 24% fines content were prepared and batch treated with hexadecyltrimethylammonium (HDTMA) to 80% of their cation‐exchange capacities. Under the first load (24 kPa), all treated soils showed higher conductivities and similar or higher porosities than untreated ones. Higher loads decreased the difference in porosity between treated and untreated soils while increasing the difference between their conductivities. At the highest load (766 kPa), treated samples were 5 to 124 times more conductive than untreated ones depending on their clay contents. Differences in conductivities were explained in terms of the role of treated and untreated clays in controlling initial effective pore size and its change during consolidation. Creation of organomodified sorptive zones by batch soil processing is shown to be hydraulically feasible as evidenced by a marked increase in the conductivities of all treated samples compared with untreated ones. In addition, an increase in the sorptive capacity of the zone could potentially be achieved, without experiencing a loss in conductivity, by increasing the clay content during modification.
Infiltration and Redistribution of Perchloroethylene in Stratified Water‐Saturated Porous Media
Authors: Hofstee C. , Dane J. H. , Walker R. C.
Published: July 2010

Although infiltration, redistribution, and drainage of dense nonaqueous‐phase liquids (DNAPLs) in water‐saturated soils and aquifers are known to be sensitive to stratifications of the solid phases of the porous media, little experimental evidence is available to explain the behavior of DNAPL movement. To improve our understanding of DNAPL movement under these conditions, physical simulations were conducted with various perchloroethylene (PCE) spills in initially water‐saturated, stratified porous media in nominally one‐dimensional glass columns and in an intermediate scale, nominally two‐dimensional laboratory flow container. The columns and flow container were packed with two distinct layers of coarse sand, with a fine sand layer in between. Volumetric water and DNAPL contents, as well as bulk densities, were determined with a dual‐energy gamma radiation system. To obtain additional information required for the explanation of the displacement processes, in‐ and outflow rates of water and PCE were measured during each experiment. In the sand columns, PCE accumulated on top of the fine layer, while in the flow container, considerable lateral movement was observed just above the fine sand layer. In general, these phenomena were attributed to the small conductivity values of the fine layers relative to those of the coarse layers rather than to displacement pressures not being exceeded. Overall our results suggest that in field situations, continuous PCE spills are more likely to penetrate horizontal fine layers than short intermittent spills.
Modeling Soil Water Balance of a Maize‐Sorghum Sequence
Authors: Maraux F. , Lafolie F.
Published: July 2010

Modeling plant‐soil‐water interactions for long periods of time is important for crop management strategies. Because it is difficult to assess soil hydraulic properties, mechanistic models are rarely used for simulating soil water balance. Models less complicated with respect to soil water flow are more often used. Although simple water balance models are easy to use, however, they do not always provide good approximations of plant transpiration and soil‐water status. Our objectives were to test the ability of a model, mechanistic with respect to soil‐water flow and empirical for soil‐plant and plant‐atmosphere interactions, to predict soil‐water balance components for long periods of time when input parameters are measured or estimated independently. A data set gathered in Nicaragua during several months was used for this purpose. Soil hydraulic properties were measured independently and parameters taken from the literature were used for plant processes modeling. The model predicted reasonably well the soil‐water balance for a maize (Zea mays L.)‐sorghum [Sorghum bicolor (L.) Merr.] sequence and for a grass sod. Periods of crop water stress were also correctly reproduced. Adjusting some plant parameters slightly increased the goodness of the predictions. Results indicated that plant water uptake was not well predicted when topsoil layers were dry and deep soil layers wet. In addition, the model predicted the upward water flux into the root zone and its important contribution to plant water uptake. During drought periods, the upward water flux reached 2 mm d−1 while the actual evapotranspiration of the crop was between 2 and 4 mm d−1.
Soil Water Dynamics Using Multisensor Capacitance Probes in Nontraffic Interrows of Corn
Authors: Starr J. L. , Paltineanu I. C.
Published: July 2010

Water is often the primary factor limiting plant growth, and it is the primary agent for moving plant nutrients and pesticides to streams and groundwater. This study was conducted to assess the capabilities of recently developed multisensor capacitance probes and monitoring systems to measure the dynamics of soil water content under long‐term field‐scale conditions, and to quantify in real time the spatial variation of soil water content under plow‐tillage (PT) and no‐tillage (NT) corn (Zea mays L). Probes were placed at eight nontraffic interrow locations, with cable lengths ranging from 25 to 125 m, on a 0.5‐ha field site. The capacitance sensors were centered at four soil depths and readings were taken every 10 min by the data‐logging system. Real‐time dynamics of soil water change following 82 mm of rainfall in the spring were used to identify the apparent water‐holding capacity within the sensor depths (5–55 cm) under NT as 171 mm and 155 mm under PT. Rates of soil water loss with a full canopy of corn were 90% of high evapotranspiration (ET) demand. Breaking points were observed and calculated between high and low rates of soil water loss, under full canopy and high ET demand. Changes from high to low rates of soil water loss were more evident in PT plots (62% reduction) than in NT plots (46% reduction). At the end of three drying cycles during the growing season, there was an average of 37 mm more water (5–55‐cm soil depth) under NT than PT. The multisensor capacitance probes proved to be highly sensitive and robust for field‐scale, real‐time, soil water research.