bluuebunny/crossref_metadata_2025 huggingface dataset:
Runoff and Erosion in a Piñon–Juniper Woodland Influence of Vegetation Patches
Authors: Reid Kevin D. , Wilcox Bradford P. , Breshears David D. , MacDonald Lee
Published: July 2010

In many semiarid regions, runoff and erosion differ according to vegetation patch type. These differences, although hypothesized to fundamentally affect ecological processes, have been poorly quantified. In a semiarid piñon–juniper woodland [Pinus edulis Engelm. and Juniperus monosperma (Engelm.) Sarg.] in northern New Mexico, we measured runoff and erosion from the three patch types that compose these woodlands: Canopy patches (those beneath woody plants), vegetated patches in intercanopy areas, and bare patches in intercanopy areas. The bare intercanopy patches exhibited the highest rates, followed by vegetated intercanopy patches and then by canopy patches. Large convective summer storms, though relatively infrequent, generated much of the runoff and most of the sediment; prolonged frontal storms were capable of generating considerable runoff but little sediment. A portion of the runoff and most of the sediment generated from bare intercanopy patches was redistributed downslope, probably to adjacent vegetated intercanopy patches, demonstrating connectivity between these two patch types. Our results indicate that there are significant and important differences in runoff and sediment production from the three patch types; that bare intercanopy patches act as sources of both water and sediment for the vegetated intercanopy patches; and that the transfer of water and sediment at small scales is both frequent enough and substantial enough to be considered ecologically significant.
Parent Material Influence on Sulfate Sorption in Forest Soils from Northwestern Spain
Authors: Arbestain M. Camps , Barreal M. E. , Mac ı ´ as F.
Published: July 2010

Sulfate sorption by forest soils decreases the potential detrimental effect of S deposition on cation leaching. Twenty‐four soils from the 3416‐km2 area surrounding two lignite‐fueled power‐generating plants in NW Spain were studied to relate SO2−4 sorption to soil properties and ultimately to the parent material. The area contains a variety of parent materials, and has a wide range of acidic soils (Haplumbrepts, Fulvudands, and Kanhaplohumults). Total annual precipitation ranges from 1100 to 1900 mm yr−1 and mean annual temperature is 12°C. Sulfate sorption was studied by adding either 0.4 or 1.6 mM SO2−4 solutions to soils. Sorption decreased in the following order: amphibolite > biotitic schist > granite > phyllite and was positively related to Al extractable with sodium hydroxide, oxalate, and pyrophosphate, and to Fe extractable with dithionite‐citrate and oxalate, which were high in soils derived from basic materials. Organic matter apparently had counteracting effects on SO2−4 sorption. First, sorption was important in surface horizons with pH‐NaF ≥9.7, mainly due to the presence of Al–humus complexes, which often give these soils an andic character. Second, sorption was specially low in surface horizons of soils derived from acidic materials with pH‐NaF <8.0, which may be attributed to competition between SO2−4 and organic acids for sorption sites, in addition to the low content of reactive surfaces. Sorption was positively related to soil pH due to the positive relation between Fe and Al oxy‐hydroxides and basic materials. These results suggest the need to take into account the influence of parent material on SO2−4 sorption in assessing the sensitivity of soils to S deposition.
Equifinality and the Problem of Robust Calibration in Nitrogen Budget Simulations
Authors: Schulz Karsten , Beven Keith , Huwe Bernd
Published: July 2010

Recent trends in predicting N dynamics of agricultural catchments have led to the development of increasingly complex simulation models. However, the parameter calibration of these models is often limited by the availability and temporal resolution of appropriate measurement data. This study addressed the problem of evaluating the predictive uncertainty of a simple N budget simulation model when applied across a winter period by using the Bayesian Generalized Likelihood Uncertainty Estimation (GLUE) methodology. Within a Monte Carlo simulation analysis, it was shown that parameter equifinality was obtained across wide areas of the model parameter space. Equifinality is used here in the sense that many different parameter combinations will produce similar good simulation results with respect to available calibration data. The GLUE methodology assigned a likelihood weight to each acceptable simulation from where uncertainty bounds for the predicted amounts of mineral N in a soil profile and for N drainage fluxes were calculated. It was demonstrated that the equifinality of different parameter sets results in large uncertainty in the predictions. This study also suggested that introducing more complexity into the process description is very unlikely to allow this uncertainty to be constrained.
Carbon Dynamics of Surface Residue– and Root‐derived Organic Matter under Simulated No‐till
Authors: Gale W. J. , Cambardella C. A.
Published: July 2010

No‐till practices have the potential to increase soil organic C, but little is known about the relative contribution of surface residue and roots to soil organic C accumulation. In a simulated no‐till experiment, we studied the fate of 14C‐labeled surface residue and in situ roots during a 1‐yr incubation. Soil samples collected during the incubation were chemically dispersed and separated into five particle size and density fractions. The organic C, 14C, and total N content of each fraction was determined. Alkali traps were used to measure 14C losses due to respiration. After 360 d, 66% of the 14C contained in the surface residue on Day 0 had been respired as 14CO2, 11% remained in residue on the soil surface, and 16% was in the soil. In comparison, 56% of the root‐derived 14C in the soil was evolved as 14CO2 and 42% remained in the soil. The large (500–2000 μm) and small (53–500 μm) particulate organic matter (POM) fractions together contained 11 to 16% of the initial root‐derived 14C in the soil. In contrast, POM contained only 1 to 3% of the inital surface residue–derived 14C. These data show clear differences in the partitioning of surface residue– and root‐derived C during decomposition and imply that the beneficial effects of no‐till on soil organic C accrual are primarily due to the increased retention of root‐derived C in the soil.
On Diffusion in Fractal Soil Structures
Authors: Anderson Alison N. , Crawford John W. , McBratney Alex B.
Published: July 2010

Fractal models of soil structure can be used to predict the scaling properties of associated transport coefficients. For gas diffusion, the structure of the soil pore space is relevant, while the structure of the solid matrix is most implicated in heat conduction. In fractal soil structures, the magnitude of the relevant diffusivities can be written in the generic form , where D(r) is a length‐dependent diffusion coefficient, A is the normalization coefficient, r is the Pythagorean length, and ϕ is a structure‐dependent constant. The dependence of ϕ on structure has been described elsewhere; however, the influence of structure on the magnitude of A has not been previously elaborated. Here, we determine the functional dependence of A on the structural parameters of the soil. The heterogeneity and connectivity, as quantified by the mass fractal dimension (Dm) and spectral dimension (d), respectively, and porosity are estimated from sections of undisturbed soil cores. For these soil structures, we demonstrate that the magnitude of the thermal and gas diffusivities is more sensitive to the porosity than to the scale dependency inherent in fractal structures. A methodology is developed and applied to rank the predicted thermal and gas diffusivities for the soil structures studied.
An Expansive Soil Index for Predicting Shrink–Swell Potential
Authors: Thomas P. J. , Baker J. C. , Zelazny L. W.
Published: July 2010

Soil properties indicative of shrink–swell potential were studied for 12 soils encompassing several parent materials in Virginia. Soils are rated from moderate to very high shrink–swell potential. The mineralogy classes, soil series, and (parent materials) examined include: smectitic—Iredell (hornblende gneiss), Jackland and Waxpool (diabase); vermiculitic—Kelly (thermal shale); kaolinitic—Cecil (granite gneiss) and Davidson (diabase); and mixed—Carbo and Frederick (limestone), Craven and Peawick (Coastal Plain sediments), and Mayodan and Creedmoor (Triassic sandstones). Soil properties measured were swell index, coefficient of linear extensibility (COLE), particle‐size distribution, cation‐exchange capacity (CEC), liquid limit, plasticity index (PI), and clay mineralogy. Soils with estimated high or very high shrink–swell potential were clayey, with clay contents exceeding 60%. These expansive soils also exhibited high CEC (>15 cmolckg−1soil), high liquid limits (>70), and appreciable swelling 2:1 mineral content (>15% montmorillonite + 1/2 vermiculite on whole‐soil basis). An expansive soil rating system, termed the Expansive Soil Index (ESI), was developed using the soil properties most correlated with shrink–swell potential. The sum of swelling 2:1 minerals, swell index, liquid limit, and CEC gave ESI ratings for each soil series. The higher the ESI, the greater the shrink–swell potential. Where less‐detailed information is required, such as for initial feasibility studies, an ESI consisting of liquid limit and CEC is recommended. Finally, the soils were grouped into risk categories based on parent material to allow for classification of similar soils into the ESI rating system. Soils with restricted drainage formed from mafic rocks, carbonate parent material, and metamorphic shales are at high risk for expansive soil behavior.
Corn Residue Retention by a Combination Chisel Plow
Authors: Hill Peter R. , Stott Diane E.
Published: July 2010

Using combination chisel plows in corn (Zea mays L.) residue can reduce surface residue cover to below levels that will protect the soil against erosion. Equipment operation and setup changes can alter the residue amount incorporated into soil. We evaluated the operational effects of using a combination chisel plow, equipped with coulter gangs, on corn residue cover on two silt loam soils. Variables included timing of chiseling, point selection, speed and depth of chiseling, and coulter‐gang engagement. Chisel plowing left 21 to 46% residue cover in the fall, and 13 to 33% residue cover in the spring. Differences were negated when overwintering losses after fall chiseling were considered. Only three of the eight spring chiseling treatments left >30% residue cover: (i) the DMI Tiger‐C point with coulter‐gang engagement, (ii) the DMI Tiger‐C point without coulter‐gang engagement, and (iii) the 406‐mm sweep with gang engaged. Ranking of residue‐retention coefficients for the chisel points was as follows: 406‐mm low‐crown sweep (0.42–0.53) ≈ DMI Tiger‐C specialty point > 51‐mm chisel point (0.33–0.40) > 102‐mm twisted shovel (0.17–0.25). Depth of chiseling did not affect residue retention. Slowing the speed of operation from 6.4 to 3.2 km h−1 (resulting in 27–42% increased residue retention) had more effect than slowing from 9.6 to 6.4 km h−1 (19–24%). Primary tillage of corn residue using a combination chisel plow can provide adequate (>30%) soil surface protection from erosion processes. Residue‐cover levels following secondary tillage and planting operations will likely fall below 30%.
Performance of Soil Condition Indicators Across Taxonomic Groups and Land Uses
Authors: Schipper L. A. , Sparling G. P.
Published: July 2010

Information on soil conditions in New Zealand is needed to assess soil quality at a national scale. We tested a standard set of 16 primary indicators at 29 sites (0–10 cm depth) across nine soil great groups with matched examples of indigenous forest, plantation forest, pastures, and crops. Soils under indigenous forest were acidic (pH 5.5–5.7), low in Olsen P (5–14 μg cm−3), with high microbial C (814–1228 μg cm−3), respiration (1.1–1.4 μg C cm−3 h−1), total C (31.8–52.9 mg cm−3), macroporosity (9.6–11.7% v/v), and total available water (29.2–31.5% v/v). Plantation forest soils had generally similar characteristics. Pasture soils were less acidic (pH 5.3–6.9) than forest soils, but with more available P (5.5–43.0 μg cm−3), higher total C (30.7–141.5 mg cm−3), total N (2.7–9.0 mg cm−3), and mineralizable N (68–175 μg cm−3). The physical condition was similar to forest soils. Cropped soil had low total C (20–34 mg cm−3), microbial C (160–956 μg cm−3), respiration (0.29–1.33 μg C cm−3 h−1), and total available water (6.7–30.1% v/v), but high pH (5.8–7.2), Olsen P (11.2–199 μg cm−3), and bulk density (0.96–1.3 g cm−3). Principal component analysis identified outlier sites and grouped land uses independently of soil great groups. Some indicators were less useful because of high variability (unsaturated hydraulic conductivity), correlation to other indicators (microbial C) or interpretation difficulties (respiration). Overall, the standardized approach provided useful information about soil conditions on a national scale.
Soil Water Evaluation Using a Hydrologic Model and Calibrated Sensor Network
Authors: Hymer D. C. , Moran M. S. , Keefer T. O.
Published: July 2010

Studies show that it may be possible to combine satellite‐derived soil water maps with soil–vegetation–atmosphere transfer (SVAT) models to obtain spatially distributed, temporally continuous information on vadose zone water contents. However, before this method can be instituted, it is essential to determine the ability of a SVAT model to simulate vadose zone soil water contents. A study was designed to evaluate the simultaneous heat and water (SHAW) model by comparing its soil water predictions with measured soil water contents collected by electrical resistance sensors (ERS) during the Monsoon ′90 multidisciplinary field experiment. ERS collected hourly soil water measurements at 5‐, 15‐, and 30‐cm depths in a shrub‐dominated site [Larrea tridentada (Sessé & Moc. ex DC.) Coville] with large bare interspace areas. Data collected by the ERS were calibrated to time domain reflectometer (TDR) sensor measurements placed adjacent to the ERS using an in situ calibration technique. Results indicated that the SHAW model overestimated soil water at each depth by 0.02 m3 m−3 under bare soil and underestimated soil water at each depth under shrub cover by 0.02 m3 m−3 The ability of the model to simulate ERS water content values gives it the potential to be periodically updated with remotely sensed data to predict vadose zone soil water content over large areas at high temporal resolutions.
Pedotransfer Functions for the Estimation of Soil Water Retention in Brazilian Soils
Authors: Tomasella Javier , Hodnett Martin G. , Rossato Luciana
Published: July 2010

Various studies have shown that micro‐aggregated, strongly weathered tropical soils have different water retention properties than temperate‐region soils because of differences in mineralogy and weathering history. Hence, pedotransfer functions (PTFs), derived from data from temperate‐region soils (temperate PTFs) have limitations when applied to tropical soils. In the absence of PTFs specifically for tropical soils, temperate PTFs are being applied worldwide in global climate modeling exercises, regardless of their textural validity. We derived a PTF to predict the water retention parameters of the van Genuchten (1980) equation using data from more than 500 Brazilian soil horizons. A modified approach was adopted: Multiple regression was used to derive coefficients that relate the van Genuchten parameters to basic soil data, followed by re‐optimization of those coefficients by fitting the individual water content estimations to the measured data simultaneously. Pedotransfer functions were developed for four levels of availability of basic soils data and validated using independent data from 113 Brazilian soil horizons. Water retention curves were better predicted by the new PTFs than by two temperate PTFs tested: The root mean square deviation (RMSD) ranged from 3.78 to 5.84, compared with 9.08 and 10.44, respectively. The new PTFs performed better even when the comparison was restricted to the range of textural validity of the temperate PTFs. For the proposed PTF, RMSDs increased with increasing silt content, but decreased for the temperate PTFs. This reflects the differences in silt content between temperate and strongly weathered tropical soils.
Water Use and Yield of Limited‐Irrigated and Dryland Corn
Authors: Norwood Charles A.
Published: July 2010

Corn (Zea mays L.) is grown on more irrigated hectares than any crop in the Great Plains. Much of this area is irrigated from the Ogallala aquifer, which is being depleted in some areas, particularly in the central and southern portions of the region. Research was conducted at Garden City, KS, from 1994 through 1997 to evaluate the effects of various combinations of irrigation, N rate, and plant population on water use and yield of corn and to determine if limited irrigation is a viable alternative to returning irrigated hectares to dryland in an area of declining groundwater. Treatments were zero, one, two, and three irrigations, each consisting of 150 mm of water, applied to corn grown with conventional tillage (CT) and no tillage (NT). Appropriate N rates and plant populations were used with each irrigation treatment to give the management systems S0, S1, S2, and S3. The single irrigation was at tassel (VT) and the two irrigation treatment was at VT and at the dough stage of grain fill (R4). Corn irrigated three times received a vegetative irrigation at the 9 to 10 leaf stage (V9) plus irrigations at VT and R4. Management system S1 increased yield by an average of 1.76 Mg ha−1 or 29%. On average S2 and S3 increased yields an additional 11 and 13%, respectively. No till increased yield and water‐use efficiency (WUE) in 2 of 4 yr. On average NT increased yield by 0.56 Mg ha−1, and WUE by 0.96 kg ha−1 mm−1 . Conclusions are that corn will produce adequate yields with one or more irrigations; thus, limited irrigation combined with proper fertility and plant population is a viable alternative to dryland in an area of declining groundwater.
Changes in Soil Phosphorus and Nitrogen During Slash‐and‐Burn Clearing of a Dry Tropical Forest
Authors: Giardina C. P. , Sanford R. L. , Døckersmith I. C.
Published: July 2010

Slash‐and‐burn clearing of forest typically results in an increase in soil nutrient availability. Throughout the tropics, ash from consumed vegetation has been accepted as the primary nutrient source for this increase. In contrast, soil heating has been viewed as a secondarily important mechanism of nutrient release. Through the use of multiple burn plots and intensive pre‐burn and post‐burn sampling of mineral soil, this study quantified changes in total P and N, P fractions, and KCl‐extractable N in soil during the slash‐and‐burn conversion of a Mexican dry forest to agriculture. Slash burning resulted in large transformations of non‐plant‐available P and N in soil into mineral forms readily available to plants. Anion‐exchange resin, NaHCO3‐extractable P, and KCl‐extractable N in soil increased by 37 kg P ha−1 and 82 kg N ha−1 Organic and occluded P (sequentially extracted with NaOH, sonication + NaOH, and NaOH fusion) and organic N (total N minus KCl‐extractable N) decreased after burning by 25 kg P ha−1 and 150 kg N ha−1 Immediately after burning, ash from consumed aboveground biomass contained 11 kg P ha−1 and 27 kg N ha−1, of which 55 and 74%, respectively, were quickly transported off the site by wind. At this dry forest site, soil heating had a much larger influence on soil P and N availability than inputs of ash.
Water Flow in Unsaturated Soil Below Turfgrass Observations and LEACHM (within EXPRES) Predictions
Authors: Roy J. W. , Parkin G. W. , Wagner-Riddle C.
Published: July 2010

In cropped soils, water sustains the plants, affects the transport of nutrients within the root zone, and controls the leaching of nutrients and chemicals to ground water. The objectives of this study were (i) to investigate the effects of turfgrass on water flow in sandy loam soil during the growing season using field lysimeters, and (ii) to test the abilities of the models EXPRES and LEACHN with free‐drainage and lysimeter bottom‐boundary conditions, respectively, to simulate water movement in the lysimeters. Twelve field lysimeters were packed with a three‐horizon profile, topped with Kentucky bluegrass (Poa pratensis L.) sod, and monitored for 2 yr. Saturated hydraulic conductivity, measured on cores, was much greater and more variable for turf than soil. The moisture‐retention curve for turf also had a much steeper drop in water content at low applied negative head than soil. The lysimeters became very dry during the summer, and only drained during the spring and autumn. The model EXPRES generally predicted water flow well, but had some difficulty with water redistribution during the drying periods (gravity drainage and evapotranspiration). In general, with the free‐drainage bottom‐boundary condition, EXPRES predicted more drainage and less drying during the summer than was observed. Under conditions of little to no irrigation, the free‐drainage condition over‐predicted and the lysimeter condition under‐predicted the total amount of measured drainage. Model predictions of drainage under heavily irrigated conditions were similar for both bottom‐boundary conditions.
Preferential Solute Flow in Intact Soil Columns Measured by SPECT Scanning
Authors: Perret Johan , Prasher S. O. , Kantzas A. , Hamilton K. , Langford C.
Published: July 2010

Single photon emission computed tomography (SPECT) is an imaging technique that is widely used in medical diagnosis. This technique has never been applied to soils. The objective of this study was to investigate the capabilities of SPECT scanning for visualizing preferential flow in soil. This paper describes the principle of SPECT scanning and its application to tracer breakthroughs in four large undisturbed soil columns (800‐mm length × 77‐mm diam.). This new approach allows real‐time analysis of flow patterns of radioactive tracers in 2‐D using planar imaging, and in 3‐D using the tomographic capabilities of the SPECT scanner. Not only does SPECT scanning provide qualitative data, but it also allows for the quantification of a tracer's spatial distribution. Our results characterized preferential flow very clearly in soil columns. SPECT scanning opens up new avenues for 2‐D and 3‐D tracer studies in porous media such as soils.
Comparison of Tension Infiltrometer, Pressure Infiltrometer, and Soil Core Estimates of Saturated Hydraulic Conductivity
Authors: Reynolds W. D. , Bowman B. T. , Brunke R. R. , Drury C. F. , Tan C. S.
Published: July 2010

Saturated hydraulic conductivity (KSAT) is an important soil property that is difficult to measure. Positive‐head tension infiltrometer (TI) and single‐ring pressure infiltrometer (PI) techniques show promise for measuring KSAT, but there have been few field tests or comparisons with other methods. The TI, PI, and classical undisturbed soil core (SC) methods for measuring KSAT were compared on single‐grain sand, structured loam, and cracking‐clay loam soils under conventional tillage (CT), no‐tillage (NT), and native woodlot (WL) managements. Of the 27 between‐method correlations (3 methods × 3 soils × 3 managements), only four were significant (P < 0.05). The TI method yielded lower KSAT values under high‐permeability conditions (KSAT ≥ 10−4 ms−1) relative to the other methods, as evidenced by lower geometric mean KSAT (KGM), lower maximum KSAT (KMAX), and lower minimum KSAT (KMIN) values. The 0.10‐m diam. by 0.10‐m‐long SC method cores may have been too small to yield representative estimates of KSAT in the cracking‐clay loam and in the NT and WL managements of the sand and loam, as indicated by high coefficients of variation (CVs), inconsistent KGM values, or high KMAX values relative to the other methods. Erratic KMAX and KMIN values, along with high CVs, suggest that the 0.10‐m‐diam. PI ring may have been too small to adequately sample the cracking clay loam soil under CT and NT management. Further work appears warranted for developing KSAT measurement methods, interpreting KSAT results, and determining appropriate KSAT methods for various soil types and conditions.
Evaluation of a Simple Method for Estimating Solute Transport Parameters Laboratory Studies
Authors: Lee Jaehoon , Jaynes Dan B. , Horton Robert
Published: July 2010

A two‐domain, physical nonequilibrium solute transport model has been used to describe the transport and fate of solute in soil. The model contains the parameters θim (immobile water content) and α (mass transfer coefficient) which must be determined for a soil before applying the transport model. A simple field method that can estimate both θim and α without measuring extensive breakthrough curves (BTCs) has been presented. The purpose of this paper was to test in laboratory soil columns the simple method of estimating parameters by comparing to the conventional BTC analysis method of parameter estimation. The experiments involved 12‐cm‐long and 4‐cm‐diam. columns packed with five different soil materials. The BTCs were performed on each column using a sequential application of four fluorobenzoate tracers. Each tracer was applied for a different length of time. The soil columns were sectioned at the end of the BTC experiments. The simple method gave results of θim and α based upon the sectioned soil samples, and the BTC analysis gave results of θim and α based upon effluent concentrations. The estimates by the two different methods were from the same experiments. Most of the estimated α values using the simple method were within the 95% confidence interval (CI) of the BTC estimates. For 7 of 10 soil columns, the estimates of immobile water fraction, θim/θ, from the simple method were within the 95% CI of the estimates of θim/θ obtained from BTC data. Breakthrough curves calculated using the θim and α values estimated by the simple method were similar to observed BTCs. The simple method provides estimation of θim and α from easy to obtain soil samples in field and can be used as a first approximation to apply the analytical BTC method.
Spatial Variability of Solute Leaching
Authors: de Rooij Gerrit H. , Stagnitti Frank
Published: July 2010

Soil heterogeneity, soil structure, and fingered flow affect solute leaching from the vadose zone to the ground water. Recently, the spatial variation of cumulative solute fluxes at a given depth was characterized by fitting the two‐parameter beta distribution to sorted amounts of solute leaching at different sampling points. We tested this parameterization on data from a chloride tracer experiment performed on a monolith lysimeter, below which drainage was collected from 300 compartments with a combined area of 0.75 m2. The effect of total sampling area, sample size, and the number of samples and their spatial distribution (random locations vs. clustered) on the fitted parameters was examined. Sixteen or more sampling locations of 25 cm2 each (5% of the total area) resulted in adequate representation of parameter values. Increasing the sample size underestimated the degree of heterogeneity. We therefore recommend that the fitted parameter values of the beta distribution be reported together with the sample size. In solute‐transport experiments, collecting many small samples will give more accurate results than taking fewer but larger samples.
Dye Tracing and Image Analysis for Quantifying Water Infiltration into Frozen Soils
Authors: Stadler Daniel , Sta¨hli Manfred , Aeby Philipp , Flu¨hler Hannes
Published: July 2010

New methods are needed to quantify infiltration into frozen soil, an important issue for agricultural management in northern latitude regions. A dye tracer method that uses digital image analysis and fluorescence imaging is presented for visualizing and quantifying flow pathways in frozen soils. The method was applied to three soil columns in a cold chamber. Two of them were packed with sand and the third was an undisturbed soil monolith. After complete freezing to −5°C, the columns were irrigated at above‐freezing temperatures before they were vertically and horizontally sectioned to analyze pictures of the stained profiles and cross‐sections. Image analysis was done for either the visual or fluorescent spectral ranges of three different tracers. Small samples were taken from the profiles to calibrate the dye tracer concentration. This was achieved by means of second‐order polynomials of the R, G, and B values from the corresponding areas of the pictures with coefficients of determination of 0.92 to 0.99. This method results in concentration maps with a high spatial resolution reflecting the infiltration pattern. The experiment confirmed current hypotheses of infiltration mechanisms into frozen soil in that the infiltrability of the initially wet sand was restricted, whereas in the undisturbed soil monolith, the dye solution infiltrated through preferential pathways which were air filled at the time of freezing.
Determining Soil Water Flux and Pore Water Velocity by a Heat Pulse Technique
Authors: Ren T. , Kluitenberg G. J. , Horton R.
Published: July 2010

A method is presented for measuring soil water flux density (J) with a thermo‐TDR (time domain reflectometry) probe. Constant heat input during a small time interval (15 s) is used to emit a heat pulse from a line heat source. Asymmetry in the thermal field near the heat source is quantified by computing the maximum dimensionless temperature difference (MDTD) between upstream and downstream locations. Heat transfer theory was used to relate MDTD to J A thermo‐TDR probe was used to obtain measurements of MDTD in water‐saturated soil materials of different textures (sand, sandy loam, and clay loam) with imposed water flux densities ranging from 1.16 × 10−5 to 6.31 × 10−5 m3 m−2 s−1 A nearly linear relationship between measured MDTDs and fluxes was observed for all soil materials. Measured and predicted MDTDs agreed well for flow experiments in sand. Greater discrepancies were observed for flow experiments in sandy loam and clay loam. Despite the lack of universal agreement between measured and predicted MDTDs, the experimental results indicate that the proposed method may provide a useful means of measuring J The method presented herein improves upon earlier methods by reducing distortion of the water flow field and minimizing heat‐induced soil water redistribution. Because the thermo‐TDR probe can be used to make TDR‐based measurements of volumetric water content (θ), the proposed method also may permit measurement of pore water velocity (J/θ).
Modified sessile drop method for assessing initial soil–water contact angle of sandy soil
Authors: Bachmann J. , Horton R. , van der Ploeg R. R. , Woche S.
Published: July 2010

Existing methods for determining the soil–water contact angle as a measure of water repellency are either indirect, cumbersome, or time‐consuming. Our objective was to develop a method that is simpler than existing procedures and that still yields accurate results. The proposed method represents a modified sessile drop method for measuring the initial contact angle of powdered or granular material. The measurements are made by placing a layer of uniform soil particles onto adhesive tape, adding droplets of deionized water, and reading off the contact angle at the three‐phase boundary line with a goniometer‐fitted microscope immediately after placing the drops on the soil sample. Sieved soil fractions <63 μm, 63 to 100 μm, and 100 to 200 μm were used to ensure particle layer uniformity. The method was tested on 10 samples from different depths of a sandy soil profile. The contact angles measured on these soil fractions were compared with the water drop penetration time (WDPT) test and the capillary‐rise method. The contact angles of the fractions <63 μm and 63 to 100 μm compared reasonably well with those measured with the capillary‐rise method and their rank order agreed in general with that of the WDPT test. We conclude that the new method appears to be promising for the simple, rapid, and reproducible determination of the contact angle of sandy soils. The sessile drop method can be used in a wider range of water repellency conditions compared with either the capillary‐rise or the WDPT method.
Nitrite Fixation by Humic Substances Nitrogen‐15 Nuclear Magnetic Resonance Evidence for Potential Intermediates in Chemodenitrification
Authors: Thorn K. A. , Mikita M. A.
Published: July 2010

Studies have suggested that NO−2, produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic matter to form trace N gases, including N2O. To gain an understanding of the nitrosation chemistry on a molecular level, soil and aquatic humic substances were reacted with 15N‐labeled NaNO2, and analyzed by liquid phase 15N and 13C nuclear magnetic resonance (NMR). The International Humic Substances Society (IHSS) Pahokee peat and peat humic acid were also reacted with Na15NO2 and analyzed by solid‐state 15N NMR. In Suwannee River, Armadale, and Laurentian fulvic acids, phenolic rings and activated methylene groups underwent nitrosation to form nitrosophenols (quinone monoximes) and ketoximes, respectively. The oximes underwent Beckmann rearrangements to 2° amides, and Beckmann fragmentations to nitriles. The nitriles in turn underwent hydrolysis to 1° amides. Peaks tentatively identified as imine, indophenol, or azoxybenzene nitrogens were clearly present in spectra of samples nitrosated at pH 6 but diminished at pH 3. The 15N NMR spectrum of the peat humic acid exhibited peaks corresponding with N‐nitroso groups in addition to nitrosophenols, ketoximes, and secondary Beckmann reaction products. Formation of N‐nitroso groups was more significant in the whole peat compared with the peat humic acid. Carbon‐13 NMR analyses also indicated the occurrence of nitrosative demethoxylation in peat and soil humic acids. Reaction of 15N‐NH3 fixated fulvic acid with unlabeled NO−2 resulted in nitrosative deamination of aminohydroquinone N, suggesting a previously unrecognized pathway for production of N2 gas in soils fertilized with NH3
Characterization of Organic Matter in Soils by Thermochemolysis Using Tetramethylammonium Hydroxide (TMAH)
Authors: Chefetz Benny , Chen Yona , Clapp C. Edward , Hatcher Patrick G.
Published: July 2010

Tetramethylammonium hydroxide (TMAH) thermochemolysis–gas chromatography/mass spectrometry (GC/MS) was employed to study the chemical structure of soil organic matter sampled from a soil plot in which corn (Zea mays L.) was farmed continuously for 15 yr. The chromatograms exhibited peaks related to compounds derived from lignin, fatty acid methyl esters (FAMEs), non‐lignin aromatic structures, and heterocyclic N compounds. The dominant lignin‐derived peaks in the TMAH thermochemolysis–GC/MS chromatograms were mainly derivatives of p‐hydroxyphenyl and guaiacyl structures, suggesting a non‐woody (grass) lignin type. With depth, the ratio of syringyl to guaiacyl compounds (S/G) decreased, suggesting a preferential degradation of the syringyl units by microorganisms. Fatty acid methyl esters of varying C‐chain length (C7 to C27) were identified in the soil chromatograms. Both TMAH–GC/MS and 13C‐NMR (nuclear magnetic resonance) data suggested a relative increase of long‐chain fatty acids with soil depth (or degree of humification), suggesting a refractory nature for these compounds. The heterocyclic N compounds yielded from the TMAH thermochemolysis were mainly pyrroles, pyridines, and pyrazoles. In addition, low levels of methylated amino acids (phenylalanine, leucine, and valine) were detected. The presence of the amino acids in the bottom layer of the soil suggests a preservation mechanism. The changes identified in the chemical components provide clues as to the nature of the humification processes in the soil profile and also yield information on the nature of the sources of soil organic matter.
Spatial Distribution of Soil Carbon and Nitrogen Pools under Grazed Tall Fescue
Authors: Franzluebbers A. J. , Stuedemann J. A. , Schomberg H. H.
Published: July 2010

Cattle (Bos taurus) behavior may be an important variable controlling the spatial distribution of soil C and N pools in long‐term, grazed pastures. Shade and water sources are more frequented areas of a pasture that can also serve as camping areas where excreta are deposited. We sampled a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) under tall fescue (Festuca arundinacea Schreb.) at distances of 1, 10, 30, 50, and 80 m from permanent shade or water sources at the end of 8 and 15 yr of grazing. To a depth of 75 mm, soil bulk density was 1.15 Mg m−3 at 1 m and averaged 1.00 Mg m−3 at other distances from shade or water. To a depth of 300 mm, soil organic C was 4.6 kg m−2 at 1 m, 4.3 kg m−2 at 10 m, and ≈4.0 kg m−2 at distances of 30, 50, and 80 m from shade or water. Particulate organic C averaged 1.53 kg m−2 at distances of 1, 10, and 30 m and 1.30 kg m−2 at distances of 50 and 80 m from shade or water. Soil microbial biomass C, basal soil respiration, and net potential N mineralization were also greater nearer shade or water than farther away. Although lateral distribution effects were most dramatic at a depth of 0 to 25 mm, similar effects were observed even at a depth of 150 to 300 mm. Long‐term cattle grazing in relatively small paddocks (0.7–0.8 ha) with permanent shade and water sources resulted in significant lateral and vertical changes in soil organic C and N pools.
Erosion Effects on Carbon Dioxide Concentration and Carbon Flux from an Ohio Alfisol
Authors: Bajracharya R. M. , Lal R. , Kimble J. M.
Published: July 2010

Carbon dioxide concentrations in soil both reflect and influence soil biological activity and C flux to the atmosphere. We hypothesized that erosion affects CO2concentration and C flux from the soil surface because of its effects on soil temperature and water regimes. The soil air concentrations of CO2and corresponding temperature and water contents were monitored on slight (SLI), moderate (MOD), severe (SEV), and depositional (DEP) phases at 2‐wk intervals between May 1996 and June 1997. The ambient soil CO2concentration and CO2–C flux were determined using gas chromatograph analyses. Seasonal patterns in soil air CO2concentrations (ranging from a winter low of 0.56 mL L−1to a summer high of 20.90 mL L−1) predominated over more subtle differences (20–80% variation) due to erosion phase effects. Significantly greater (by 12–37%) CO2concentrations for SEV and MOD phases over SLI and DEP were observed mainly during the summer. The effects of the erosion phase on soil CO2concentrations appeared to be indirect through its impacts primarily on soil temperature and, presumably, soil biological activity. Soil air CO2concentrations were significantly correlated with soil temperature (R2= 0.61) and CO2–C (R2= 0.65) flux from the soil surface but not with soil water content. Both linear and second‐order polynomial regression equations using soil temperature predicted soil CO2concentration.
Influence of Time on Soil Response to No‐Till Practices
Authors: Rhoton F. E.
Published: July 2010

The number of growing seasons required for no‐till practices to improve soil properties should be considered before changing management systems. To evaluate this time factor, an 8‐yr tillage study was conducted on a Grenada silt loam (fine‐silty, mixed, active, thermic Glossic Fragiudalfs) using cotton (Gossypium hirsutumL.), grain sorghum [Sorghum bicolor(L.) Moench]–corn (Zea maysL.), and soybean [Glycine max(L.) Merr.]–wheat (Triticum aestivumL.) as test crops. Soil samples were characterized for soil organic matter (SOM), pH, exchangeable Ca and Mg, extractable P, K, Fe, Mn, Cu, and Zn, aggregate stability (AS), water dispersible clay (WDC), total clay (TC), and modulus of rupture (MR) at time 0, 4, and 8 yr. Within 4 yr, no‐till (NT) resulted in statistically significant (P≤ 0.05) differences compared to conventional tillage (CT). The surface 2.5 cm of the NT treatments had higher levels of SOM, exchangeable Ca, and extractable P, Mn, and Zn, but lower extractable K, Fe, and Cu. Tillage had no effect on exchangeable Mg and pH. No‐till also resulted in higher AS, and lower MR, WDC, and TC in the top 2.5 cm, relative to CT. The differences in soil properties between tillage treatments were essentially independent of crop. Instead, the results are controlled by relative amounts of SOM and clay, and the extent to which these properties change with time. Undoubtedly, NT practices can improve several fertility and erodibility‐related properties of this soil within 4 yr, and enhance its sustainability.
Phosphorus Enrichment Affects Litter Decomposition, Immobilization, and Soil Microbial Phosphorus in Wetland Mesocosms
Authors: Qualls Robert G. , Richardson Curtis J.
Published: July 2010

Like many wetland ecosystems, areas of the northern Everglades of Florida, USA, have been influenced by P eutrophication. Our objective was to determine if P enrichment of water influences the litter decomposition rate and nutrient immobilization by litter and, further, to determine the quantitative relationship of these responses across a range of P concentrations in surface water. In addition, we determined whether P additions rapidly elevated microbial biomass P in the soil. In order to isolate the effects of P enrichment, we placed bags containing cattail (Typha domengensis Crantz) and sawgrass (Cladium jamaicense Pers.) litter into two sets of experimental channels into which controlled inputs of five different phosphate concentrations were added continuously. After 1 yr of incubation, litter was analyzed for C, P, N, Cu, Ca, and K content. Loss of C at the end of 1 yr increased linearly with increasing average PO4 content in the channels with a similar slope for both species of litter. Immobilization caused an absolute increase in P content of the litter up to approximately ninefold across the range of water P concentrations, while immobilization of N, Ca, and K did not vary with water P concentrations. During decomposition, litter exhibited a net uptake of Cu (a nutrient potentially limiting plant growth on peat soils). The microbial biomass P was up to nine times higher in the surface soil of the most enriched channel compared with the control, but this elevation in concentration was restricted to the upper 12 cm of soil.
Surface Roughness Effects on Soil Albedo
Authors: Matthias A. D. , Fimbres A. , Sano E. E. , Post D. F. , Accioly L. , Batchily A. K. , Ferreira L. G.
Published: July 2010

Knowledge of how surface roughness influences the reflectance of sunlight from cultivated soils is useful in various applications, such as estimating albedo values used as inputs to soil temperature models and erosion models. The albedos of two soils were studied for dry and wet surfaces with four different roughness conditions, changed from a reference smooth soil surface. The soils were the Gila fine sandy loam [coarse‐loamy, mixed (calcareous), thermic Typic Torrifluvent] (Ap horizon), 10YR 6.0/3.2 dry and 10YR 4.1/3.3 wet, and the Pima clay loam [fine‐silty, mixed (calcareous), thermic Typic Torrifluvent] (Ap horizon), 10YR 5.2/2.3 dry and 10YR 3.3/2.3 wet. Albedo measurements were made during selected mornings with clear skies in 1995 and 1996. The mean albedos of reference smooth surfaces (<2 mm sieved soil) were 0.279 and 0.155 for dry and wet Gila soil and 0.221 and 0.114 for dry and wet Pima soil. Four tillage conditions were studied: rough plow, disk, disk–disk, and seedbed. Tillage direction was north–south in 1995 and east–west in 1996. The goodness of fit of linear relationships determined between mean albedo and surface roughness, measured with a roughness meter and reported as the root mean square deviation, were relatively high; however, the slopes for the regression equations were different for the two soils and the two moisture conditions. The different slopes indicate that the sensitivity of albedo to surface roughness was highest for the most reflective surface (dry Gila soil) and lowest for the least reflective surface (wet Pima soil). The albedos were on average 27, 18, 10, and 8% lower for dry and wet rough‐plow, disk, disk–disk, and seedbed treatments, respectively, as compared with the albedo of the reference smooth soil. These reduction percentages can be used as a general guide to estimate the albedos of tilled soils similar to the Gila and Pima soils studied here.
Soluble Organic and Inorganic Nutrient Fluxes in Clearcut and Mature Deciduous Forests
Authors: Qualls R. G. , Haines B. L. , Swank W. T. , Tyler S. W.
Published: July 2010

The mechanisms by which forest ecosystems retain or lose soluble inorganic nutrients after disturbance are well known, but substantial amounts of soluble organic nutrients may also be released from cut vegetation. Our objective was to compare the leaching of dissolved organic and inorganic nutrients in cut and mature forest stands and to develop hypotheses about factors controlling the retention of soluble organic nutrients after disturbance. Solution chemistry was measured for 2 yr after clearcutting a small area in the surrounding undisturbed deciduous forest on a reference watershed at the Coweeta Hydrologic Laboratory in the Appalachian Mountains. Concentrations of dissolved organic C (DOC) and N (DON) in slash leachate were 2.6 to 3.2 times the concentrations in throughfall from undisturbed forest. Concentrations in forest floor, A horizon, and B horizon solutions from cut plots were 1.2 to 3.8 times those from undisturbed forest. Dissolved organic P (DOP) concentrations in cut plots were 3.1 and 3.6 times those of uncut plots in solutions from slash and forest floor, respectively, but did not differ in mineral soil. Fluxes of DOC, DON, and DOP in all strata were greater in cut plots than uncut plots. Fluxes of DON were greater than those of ammonium plus nitrate N in all strata of both cut and uncut plots. We hypothesize that the well‐recognized retention mechanisms for inorganic nutrients combine with equilibrium adsorption of dissolved organic matter to efficiently buffer against leaching of both soluble inorganic and organic nutrients after clearcutting.