bluuebunny/crossref_metadata_2025 huggingface dataset:
Parent Materials and Stratigraphy of a Doline in the Valley and Ridge Province
Authors: Crownover S. H. , Collins M. E. , Lietzke D. A.
Published: July 2010

A variety of contrasting parent materials have been preserved within a ridgetop doline in the Valley and Ridge Province of eastern Tennessee. These materials, related to current and past slope processes, were differentiated based on morphologic properties. Matrix color and texture and the nature and content of chert fragments were particularly important in this discrimination. The doline rim was host to several distinct parent materials, including: (i) Copper Ridge residuum, (ii) mixed ancient alluvium and colluvium, and (iii) ancient toeslope colluvium. Mass wasting and fluvial processes emplaced these “ancient” materials, which currently have no source area, during the late Pliocene or early Pleistocene. The doline sideslopes contain parent materials composed of stacked layers of cherty colluvium that are late Pleistocene and Holocene in age. These colluvial deposits were derived from upslope residual and “ancient” toeslope colluvial soils via recent mass wasting. Parent materials in the doline center have a completely different morphologic character than upslope deposits. A silty material, possibly late‐Wisconsinan loess eroded into this doline during the Holocene, is devoid of chert fragments. These materials have been sorted and deposited by active slope wash and originated from either locally derived loess deposited on upper doline sideslopes, the A and E horizons of soils located upslope, or both. At 1.3 m these silty materials rest directly on a buried A horizon (2Ab) that has been radiocarbon dated to 9170 ± 140 years before present (YBP). Beneath this buried surface, alternating layers of thick noncherty and thin cherty silt loam materials represent cycles of late Quaternary landscape stability and instability.
Fallow Management and Overwinter Effects on Wind Erodibility in Southern Alberta
Authors: Larney Francis J. , Lindwall C. Wayne , Bullock Murray S.
Published: July 2010

Aggregate size distribution (ASD) is influenced by tillage and climate and greatly affects wind erodibility of soils. This study determined the effects of fallow management and winter effects on ASD in the chinook belt of Alberta. Geometric mean diameter (GMD), geometric standard deviation (GSD), and erodible fraction (EF) <0.84 mm were determined in fall and spring on five fallow systems on a Lethbridge clay loam soil (fine‐loamy, mixed, Typic Haploboroll). The fallow systems were (i) tillage only, (ii) minimum tillage (herbicides and tillage), and (iii) zero tillage (herbicides only). In fall, one‐way disk and heavy‐duty cultivator fallow treatments had GMD values about 1 mm higher than blade cultivator or zero tillage treatments. The 1989–1990 winter with 90 cm of snowfall, 67 d of snow cover, and 101 d with a mean 2‐cm soil temperature between +2 and −2°C resulted in greater aggregate breakdown than the 1988–1989 winter, which had 129 cm of snowfall, 104 d of snow cover, and 68 d with 2‐cm soil temperatures between +2 and −2°C. Estimates of initiating wind velocities for erosion, based on residue cover and EF, were 13.3 m s−1 for the tillage treatments, 13.7 m s−1 for the minimum tillage treatment, and 15.4 m s−1 for the zero tillage treatment. However, the minimum and zero tillage systems had EF values >60% at more sampling times than the tilled treatments, indicating that wind erosion problems may occur if the residue cover was jeopardized.
Fertilizer Nitrogen Uptake by Rice from Urea‐Ammonium Nitrate Solution vs. Granular Urea
Authors: Wilson C. E. , Wells B. R. , Norman R. J.
Published: July 2010

Granular urea is the primary N fertilizer source for rice (Oryza sativa L.) production in the southern USA. New cultivars respond to higher rates of N fertilizer applied preflood. Application of high rates often results in distribution problems when granular urea is used as the N source. Because liquid fertilizer sources can reduce distribution problems, this study was initiated to evaluate the efficiency of urea‐ammonium nitrate solution (UAN, 28‐0‐0) as a N source for rice. Each N fertilizer source was applied in three split applications at a rate of 84 kg N ha−1 just prior to flooding (preflood), 33.6 kg N ha−1 at 1.3‐cm internode elongation (IE), and 33.6 kg N ha−1 10 d after IE (IE + 10d) onto ‘Newbonnet’ rice that was seeded into microplots (0.58 m2). The fertilizer sources consisted of granular urea or UAN with either the urea, NH4, or NO3 labeled with 15N at each application time. At all three application times, the highest fertilizer N uptake occurred when granular urea was the N source. Application of granular urea resulted in 72.5% recovery of the fertilizer N in the plant compared with 52.6% recovery of the fertilizer N from UAN. Application of granular urea also resulted in significantly higher grain yields than UAN. Granular urea was superior to UAN as a N source for rice production due to the inefficient uptake of NO3‐N from the preflood application (9.8%). However, these data show that rice can efficiently utilize NO3‐N from applications made at IE or later (73.7% recovery).
Linear and Nonlinear Estimates of Fractal Dimension for Soil Aggregate Fragmentation
Authors: Rasiah V. , Perfect E. , Kay B. D.
Published: July 2010

Estimates of nonlinear parameters may vary with the fitting procedure (linear or nonlinear) used. The objectives of this study were to compare (i) values of the fractal dimension, D, and the constant, k, obtained using linear (defined D1 and k1) and nonlinear (defined Dnl and knl) fitting procedures and (ii) the sensitivity of D1, Dnl, k1, and knl to variations in cropping and tillage practices and soil properties. Using aggregate mass‐size distribution data, from five different soils under two cropping and two tillage systems, obtained after wet sieving, 90 values were obtained for each of D1, Dnl, knl, and kl. The nonexistence of a 1:1 relation between Dnl and D1 indicated that the population of Dnl was different from that of D1. A similar trend was observed between knl and k1. The standard error of the estimates of Dnl was less than that of D1. Soil properties and cropping and tillage systems accounted for 84% of the variability in Dnl, 87% of knl, 81% of D1, and 46% of k1. The estimates of Dnl are accurate and can be predicted with greater confidence than those obtained using the linear procedure.
One‐Dimensional Model to Evaluate the Performance of Wick Samplers in Soils
Authors: Rimmer Alon , Steenhuis Tammo S. , Selker John S.
Published: July 2010

Wick samplers have become a valuable device for collecting soil pore water samples from the unsaturated zone. However, one of the problems with wick samplers has been that water and solutes bypass the samplers. Little work has been done on the nature of soil‐wick interrelations. Based on an analytical solution for a layered soil profile, a steady‐state solution was developed to predict the pressure head in a wick‐soil continuum. The solution was also used to match wick properties to a given soil type in order to minimize the bypass flow. The results of this analysis show that for a good match between wick and soil types, (i) their capillary length (α−1) needs to be similar, and (ii) the ratio of their saturated hydraulic conductivities should be similar to the inverse ratio of their cross section for flow. Examples for wick type selection based on these two requirements are given for two soil types and two wick types. For sandy soils, the optimal wick length is 30 to 40 cm, while for silt loams, the optimal length is >100 cm. Sampling with wick samplers in coarse‐textured soils was found to be less disturbing of the soil pressure head and moisture profile than sampling in fine‐textured soils. Hydraulic properties of fine‐textured soils require a large sampling area in order to create an undisturbed zone above the wick sampler.
Nitrate Leaching under Furrow Irrigation as Affected by Crop Sequence and Tillage
Authors: Meek B. D. , Carter D. L. , Westermann D. T. , Wright J. L. , Peckenpaugh R. E.
Published: July 2010

The potential for NO3‐N leaching after alfalfa (Medicago sativa L.) in irrigated crop production depends on cropping sequence and tillage practices. A 2‐yr field experiment in south‐central Idaho compared the NO3‐N leached following alfalfa of a conventional tillage bean‐bean (Phaseolus vulgaris L.) rotation with a silage corn (Zea mays L.)‐winter wheat (Triticum aestivum L.) rotation in a conventional tillage or no‐till system. Nitrate leaching was determined by: (i) sampling the soil solution below the root zone (1.2 and 1.5 m) using ceramic‐tipped samplers and calculating the N movement from the water balance, and (ii) measuring the change in soil NO3‐N at 1.35 to 4.5 m from soil samples taken in the fall and spring to 4.5 m. During the second growing season, average soil solution NO3‐N concentrations (below the root zone) were 28, 4, and 10 mg L−1 for the bean‐bean, corn‐wheat no‐till, and corn‐wheat tilled treatments, respectively. The soil NO3‐N in 1.35 to 3.3 m at the end of the study was 80 kg N ha−1 higher for the bean‐bean treatment than for the corn‐wheat treatments. The NO3‐N that moved below 1.35 m during the 2 yr was 53 kg ha−1 higher for the bean‐bean than for the corn‐wheat treatments. The soil NO3‐N in the 1.35 to 3.3 m depth after 2 yr was 21 kg ha−1 higher for the corn‐wheat under conventional tillage than under the no‐till system.
Construction and Installation of Acrylic Minirhizotron Tubes in Forest Ecosystems
Authors: Kloeppel Brian D. , Gower Stith T.
Published: July 2010

Glass tubing has been the traditional material used when constructing minirhizotrons for studying fine root dynamics in managed and natural terrestrial ecosystems. However, we have found that rocky soils, swelling smectite clays, large structural roots, and freezing soils frequently have broken glass minirhizotrons. We have developed a system to construct and install durable acrylic minirhizotrons. Acrylic tubing costs 42% less than glass and requires only 13% of the preparation time, resulting in a 121% savings vs. glass. The major time‐saving device is a unique spring‐loaded etching trough that places accurate, evenly spaced circles along the length of the tube in minutes. The design can be easily modified for many applications. Preliminary results in a mixed western larch (Larix occidentalis Nutt.)‐lodgepole pine (Pinus contorta var. latifolia Engelm.) forest in western Montana indicate that the acrylic minirhizotrons are durable, the etching is visible, and the system can be used to examine fine root phenology.
Clay Differentiation in Aridisols of Northern Mexico
Authors: Ducloux J. , Petit S. , Decarreau A. , Delhoume J. P.
Published: July 2010

Aridisols with smectite B horizons are usually classified as Argids although the argillic characters may not always be present. In the Chihuahuan Desert of northern Mexico, some Aridisols have clayey horizons that do not seem to result from clay illuviation. Our purpose was to determine the origin of the clay enrichment and the mineralogical relationships between the parent materials and the B horizons. The study area is the Mapimi Playa, derived from a lutite lagoonal sediment parent material. A soil sequence from Orthids to Argids was identified. Four profiles were analyzed. The particle‐size distribution was determined by the sedimentation and centrifugation methods. The clay fractions were studied by x‐ray diffraction and peak decomposition, infrared spectroscopy, and chemical analyses. Soil water extracts were analyzed with an absorption spectrometer. From the Orthids to the Argids, clay enrichment in B horizons is controlled by the <0.2‐µm clay size fraction and small amounts of palygorskite. The B horizons contain prominent smectite, which has more Mg than the lutite smectite (parental material). The existence of the AIMgOH infrared vibrations in the soil clay suggests the neogenesis of a smectite different from the lutite smectite. The composition of the soil water extract suggests that Mg‐smectite and palygorskite may form in Mapimi soil profiles. The Argids of Mapimi Reserve result principally from clay neogenesis under current climatic conditions.
Small Spatial Scale Soil Water Content Measurement with Time‐Domain Reflectometry
Authors: Amato M. , Ritchie J. T.
Published: July 2010

Plants growing on stored soil water often exhibit symptoms of water deficit even though a relatively large quantity of soil water is available for uptake where roots are present in the subsoil. To explore the possibility that this less effective absorption phenomenon was related to nonuniform root distribution or root clumping around soil peds, we examined the suitability of time‐domain reflectometry for measuring soil water content distribution on a small spatial scale. Measurements were made on clay loam and sandy clay soils with 21‐mm‐long parallel balanced transmission lines and compared with gravimetric water content measurement. Water content values ranged from oven dry to saturation. To quantify the error in propagation time measurement using short transmission lines, measurements were made in air using rod lengths ranging from 10 to 150 mm. The coefficient of variation was quite high (2.8–7.3%) for times shorter than 100 ps for air‐dry soil. In this case, the technique proved less reliable. For longer times, corresponding to higher water contents, the coefficient of variation was <3%. A few samples of clay loam soil with water contents >0.29 m3 m−3 showed excessively high values of dielectric constant. Care should be taken in data interpretation at high water content for these media. Time‐domain reflectometry proved effective in measuring water content with the tested transmission line for values >0.07 m3 m−3. Thus, a tool is provided for in situ measurement of spatial variability or at a spatial scale compatible with many problems ranging from the water uptake of clustered roots to seed germination in the field.
Monitoring Solute Transport in a Multi‐Layered Sandy Lysimeter using Time Domain Reflectometry
Authors: Vanclooster M. , Mallants D. , Vanderborght J. , Diels J. , Van Orshoven J. , Feyen J.
Published: July 2010

The lack of detailed and high‐quality experimental data on the fate of solutes in soil puts a severe constraint on the development and testing of transport models. This study illustrates how detailed measured solute concentration data, collected by means of time domain reflectometry (TDR), are used to identify the governing transport processes in a vertical heterogeneous soil. A lysimeter was constructed, consisting of an undisturbed three‐layered soil monolith placed on an artificial sandy soil column. Tensiometer cups and solution samplers, together with TDR probes, were inserted horizontally at regular depth intervals to monitor pressure head, solution concentrations, soil water content, and bulk electrical conductivity. In the lysimeter, quasi‐steady‐state unsaturated water flow conditions were established and TDR‐estimated transport of solute was monitored during leaching. Solute fluxes at different depths were calculated, resulting in probability density functions of solute travel time to different depths. The first moment of the solute travel time revealed that approximately all soil water was used to transport solute in the top of the lysimeter. The boundary between the top soil and the sandy substratum probably induced instabilities, and hence, preferential flow. The dispersivity increased with depth in the topsoil but approached almost a constant value deeper in the lysimeter.
Quaternary Ammonium Surfactant Effects on Sorption of Trace Metals onto Quartz and Aluminosilicates
Authors: Hayes Kim F. , Chen Chia‐chen , McAvoy Drew C.
Published: July 2010

This study was conducted to investigate the potential impact of quaternary ammonium compounds (QACs) on trace metal ion desorption from soil constituents. Three soil constituents (quartz, kaolinite, and montmorillonite), two trace metal cations [Co(II) and Sr(II)], and three alkyltrimethylammoniumchloride surfactants (C8TMAC, C12TMAC, and C16TMAC) were chosen for this investigation. For the quartz system, Co(II) showed no desorption while Sr(II) showed a slight pH‐dependent desorption. For kaolinite or montmorillonite systems, desorption of Co(II) and Sr(II) by QACs occurred only for the fraction of the trace metal cations sorbed on permanent‐charge sites. In the case of montmorillonite, Sr(II) was significantly desorbed at all pH values. This was thought to be a result of the nearly exclusive sorption of Sr(II) to the permanent‐charge sites in this system. In all other clay systems studied [Sr(II), Co(II) on kaolinite; Co(II) on montmorillonite], desorption only occurred at lower pH from permanent‐charge sites. No desorption occurred at higher pH values where sorption to surface hydroxyl sites was indicated. In general, QAC‐induced desorption of trace metal cations was found to be significant only when QAC sorption equaled or exceeded the cation‐exchange capacity. Surfactant chain length was found to have little effect on the overall pH‐dependent desorption trends. As expected, higher surfactant concentration was required to cause trace metal ion desorption as the surfactant chain length decreased.
Parameters of Surface Heterogeneity from Laboratory Experiments on Soil Degradation
Authors: Pachepsky Ya. A. , Polubesova T. A. , Hajnos M. , Jozefaciuk G. , Sokolowska Z.
Published: July 2010

In this study, we examined the applicability of the theory of gas adsorption on heterogeneous surfaces to assess changes in soil particle surfaces in degrading soils. Soil degradation was simulated by laboratory treatments of gray forest soil (Udic Argiboroll), chernozem soil (Typic Haploboroll), and chestnut soil (Ustolic Orthid) samples. Water vapor adsorption data were used to estimate the frequency distribution of surface adsorption energy and to assess the strength of the surface attractive field. A modified Brunauer‐Emmett‐Teller equation provided a good fit of the water vapor adsorption isotherms on soil minerals for relative vapor pressures in the range of 0.05 to 0.85. This equation was used as a local isotherm equation. The piecewise distribution technique was applied to estimate the surface adsorption energy distribution. After a H2O2 treatment, the monolayer capacity and average adsorption energy decreased in the samples of all three soils. After cyclic wetting‐drying, the adsorption energy range decreased. After silica acid treatments, the monolayer capacity decreased, and the energy distribution became much narrower. All treatments resulted in a loss of the low‐energy adsorption sites and an increase in the number of layers retained by the surface at saturation vapor pressure. The exchangeable Ca content changed after the treatments in the same way as the monolayer capacity did. The exchangeable Mg content increased after organic matter oxidation and slightly decreased after the silica treatments. The exchangeable K content increased after both organic matter oxidation and the wetting‐drying treatments.
Erosion from Alfalfa Established with Oat under Conservation Tillage
Authors: Wollenhaupt N. C. , Bosworth A. H. , Doll J. D. , Undersander D. J.
Published: July 2010

Conservation tillage (CT) methods reduce soil erosion, but effects on establishing alfalfa (Medicago sativa L.) are not well known. Oat (Avena sativa L.) is often planted with alfalfa to reduce erosion during establishment, but results are not well documented. We hypothesized that the inclusion of oat during establishment would not be as effective as CT at reducing soil erosion. Moldboard plowing (MB) was compared with two CT practices of disking (DK) and no‐till (NT), with alfalfa planted alone (SOLO) or with a companion oat crop (COMP). The study was conducted in 1992 and 1993 on Rozetta silt loam soils (fine‐silty, mixed, mesic Typic Hapludalfs) following corn (Zea mays L.) each year. Simulated rainfall, 72 mm h−1 for 1 h, was applied twice per growing season, at planting (1 wk) and during oat canopy development (4 wk). Runoff was reduced from 28 mm in MB plots to 13 mm in CT plots at planting in 1992. Four weeks after planting in 1993, runoff was reduced from 47 mm in SOLO to 44 mm in COMP. Averaged across all simulations, sediment concentration was 23.3 g L−1 for MB and 3.2 g L−1 for CT. The 2‐yr mean soil loss dropped from 644 g m−2 in MB to 94 g m−2 in CT at planting. Mean treatment erosion was reduced 85% by canopy in 1992, a dry year. The wet 1993 growing season had several severe crusting rainstorms that induced large MB soil loss (2173 g m−2) 4 wk after planting. Companion cropping reduced MB soil loss 46% (from 2827 to 1520 g m−2) in 1993 and DK and NT further reduced soil loss to 235 and 123 g m−2. Forage biomass was unaffected by treatment in 1992.
Analysis of Water and Solute Transport Away from a Surface Point Source
Authors: Ward A. L. , Kachanoski R. G. , Elrick D. E.
Published: July 2010

Mathematical theories describing the movement of water and solute away from sources of limited spatial extent mostly assume some form of three‐dimensional flow domain, but few have been rigorously tested, mainly because of the lack of experimental data. The objectives of this study were to obtain water flow and solute transport measurements during three‐dimensional, axially symmetric water flow, using time domain reflectometry (TDR), and to test some of the existing theories of three‐dimensional flow and transport using the measured data. A sandy soil was packed into a Plexiglas box fitted with curved TDR probes at different radial distances from one corner. A constant flux of water was applied at the corner of the box, and a pulse of KCl added as a tracer. Measurements of volumetric water content, θ, and resident solute concentration, CR, as a function of time and radial distance were made along four flowlines. The utility of a quasilinear solution was evaluated by comparing measured and predicted profiles of θ at steady state, and the distribution of solute travel times along various transects. Along the various streamlines, nonlinear least‐squares analysis of measured solute travel times (t*) produced estimates of the slope (α) of the exponential hydraulic conductivity function that were comparable to independently determined values. Estimation of α from t* along a single flowline, using a quasilinear solution, offers potential for field application. This technique could be used as a first step in the investigation of contaminant migration from point sources, or used in trickle‐irrigation design.
Detrimental Sulfate Effects on Formation of Al‐13 Tridecameric Polycation in Synthetic Soil Solutions
Authors: Kerven G. L. , Larsen P. L. , Blamey F. P. C.
Published: July 2010

The chemistry of Al in soil solutions and in surface waters is complex and has included evidence of the tridecameric polycation, known as Al13, in an acid forest soil. The Al13 polycation is the dominant species formed when Al solutions are partially neutralized under controlled laboratory conditions, and solution culture studies have shown Al13 to be highly toxic to root growth. Doubt has been raised, however, as to the occurrence of the Al13 polycation in natural systems. The objective of this study was to examine the effects of solution composition, comparable with soil solutions extracted from acid soils, on the formation of the Al13 polycation using both 27Al nuclear magnetic resonance (NMR) and spectrophotometric methods. The presence of Ca, Mg, K, Cl, and NO3 during partial neutralization had no effect on the formation of the Al13 polycation. However, SO4 at ≥50 µM during partial neutralization to a OH/Al ratio of R = 2.0 precipitated the major proportion of Al and interfered with the formation of the Al13 polycation. The addition of similar concentrations of SO4 after neutralization had no effect on the measured Al13 concentration. The presence of ≥250 µM SO4 resulted in no detectable Al13 polycation present after the solution had been neutralized to R = 2.5. We suggest that in view of the ubiquitous nature of the SO4 anion in soil solutions and surface waters, the Al13 polycation is unlikely to be formed in measurable quantities.
Empirical Analysis of Slope and Runoff For Sediment Delivery from Interrill Areas
Authors: Huang Chi‐hua
Published: July 2010

Slope steepness (S) and runoff discharge (qw) are two major factors in determining sediment delivery rates (qs) from interrill areas. Under the current interrill erosion model concept, these two factors are assumed to have independent effects on qs; thus, each factor can be quantified individually if the other factor is kept constant. This study was conducted to show the effects of S and qw on qs and their interdependency. Sediment discharge rates, measured under different rainfall intensities and slope gradients, for eight soils from two laboratory studies were analyzed empirically with curve‐fitting procedures. Results showed that there was a pair of empirical equations for each soil: qs = A1 q2w + A2 qw + A3 and qs = B1 S2 + B2 S + B3, where A1, A2, and A3 are functions of S and B1, B2, and B3 are functions of qw. In other words, effects of slope steepness and runoff on sediment delivery are dependent on each other. When S and qw were combined together as stream power, Ω, and plotted against sediment concentration, qs/qw, a unique nonlinear relationship existed for each soil: qs/qq = D1Ω2 + D2Ω + D3, where D1, D2, and D3 are soil‐dependent coefficients. The stream power, which encompasses both slope and runoff effects, may provide improved estimates for interrill erosion. Although not based on theory, this result may be useful in process‐based erosion models.
Comparing Potassium Soil Tests with a Flexible Function and a Modifier Variable
Authors: Avellaneda Manuel O. , Jauregui Mario A.
Published: July 2010

Selecting the appropriate functional form and using modifier variables are key issues in soil test calibration. Flexible functions capture all the information conveyed by the data, except for stochastic aberrations of local maxima, minima, and inflexion points. The objective of this study was to show that a flexible function can be used for comparing soil tests including the sediment volume (SV) as a modifier variable. Data used in this test were collected from 30 irrigated Torrifluvents in which K availability had been evaluated with the Neubauer method. The dependent variable was total K uptake by ryegrass (Lolium perenne L.). Independent soil K variables corresponded to seven soil test methods: NH4OAc‐exchangeable K; HNO3‐extractable K; H2CO3‐extractable K; soluble K; resin‐extractable K; K potential; and K adsorption ratio. The modifier variable, SV, is a quick, inexpensive, and fairly accurate attribute widely used in western Argentina to appraise soil texture. Data were evaluated using the generalized Cobb‐Douglas (GCD) function. Explanation of variability in K uptake using the GCD model, with exchangeable K and SV as independent variables, was highly satisfactory (R2 = 0.88). The other six methods of soil testing gave R2 values from 0.55 to 0.76. Contribution of SV as a modifier for the interpretation of K availability was significant (α < 0.01) for all soil K indices. The GCD function captured a positive interaction between the independent variables. This indicates that the higher K buffering capacity of the finer textured soils was an overriding factor that favored K absorption by plants.
Macropore Transport of a Surface‐Applied Bromide Tracer: Model Evaluation and Refinement
Authors: Ahuja L. R. , Johnsen K. E. , Heathman G. C.
Published: July 2010

Rapid transport of surface‐applied agrichemicals to groundwater through macropores is a major problem that requires a better understanding and quantification. A simple model of macropore flow and transport of a surface‐applied Br− tracer under rainfall was evaluated and refined by testing against soil‐column data reported earlier. The experiments consisted of eight treatment combinations, each in duplicate, of the following conditions: soil initially air dry vs. soil initially wetted by rainfall; a 10‐mm layer of dry aggregates on the surface vs. no aggregates; and a 3‐mm artificial macropore made along the column's vertical axis vs. no macropore. A solution of SrBr2 was atomized over the surface, followed by application of simulated rainfall. Evaluation of the model indicated that: (i) once the Green‐Ampt infiltration parameters were calibrated on control columns, water flow into other columns was simulated correctly; however, in order to match the macropore bottom outflow, the lateral absorption of water from macropore to soil matrix had to be adjusted for compaction of the macropore wall and variable water pressure around the pore circumference under small macropore flow rates; (ii) for chemical mass in macropore outflow, better results were obtained if, in the wetted portion of the soil profile, the water flow down the macropore mixed with ≈0.5 mm of soil around the walls and its soil solution; (iii) microporosity of surface aggregates determined from control columns resulted in fairly good simulations of the increase of the chemical in macropore flow caused by aggregates.
Cation‐Exchange Hysteresis and Dynamics of Formation and Breakdown of Montmorillonite Quasi‐Crystals
Authors: Verburg Kirsten , Baveye Philippe , McBride Murray B.
Published: July 2010

The phenomenon of cation‐exchange hysteresis seems to suggest that a number of cation‐exchange reactions are characterized by an extremely slow kinetic. This, however, is in direct conflict with the fast equilibration times that have been reported in the literature in recent years. These seemingly contradictory observations have been reconciled recently in a conceptual model in which the exchanger is assumed to first undergo a fast reaction, followed by a much slower, second kinetic stage. This conceptual model links cation‐exchange hysteresis to hysteresis in the formation and breakdown of quasicrystals during the forward and backward exchange reactions. Because the results in the literature on the kinetics of these processes are contradictory, the objective of this study was to assess their dynamics and long‐term kinetics. Initial rates of quasi‐crystal formation and breakdown were found to be fast, but the processes proceeded thereafter for at least 5 mo at a slower rate. The results also suggest that the slow kinetics of quasi‐crystal formation and breakdown is related to the presence of activation energy barriers for intercrystalline swelling and can cause quasi‐crystals to be inherited from the preparation procedure.
Nutrient Accumulation during Primary Succession in a Montane Tropical Forest, Puerto Rico
Authors: Zarin Daniel J. , Johnson Arthur H.
Published: July 2010

Few studies document both above‐ and belowground changes in ecosystem nutrient capital with successional time. This study was conducted to assess the resiliency of soil and biomass nutrient capital in a montane tropical forest following catastrophic disturbance. We report measurements of soil and biomass C, N, P, K, Ca, and Mg pools in a chronosequence of landslide scars ranging from 1 to >55 yr (n = 12) in the Luquillo Experimental Forest, Puerto Rico. Pool sizes are also reported for plots located in the two late‐succession vegetation associations, which represent both potential mature forest stages for aggrading landslide scars and the dominant predisturbance forest types at that elevation: the palm brake forest (n = 3), dominated by sierra palm [Prestoea montana (R. Grah.) Nichols], and the palo colorado forest (n = 5), dominated by palo colorado [Cyrilla racemiflora L.] and other dicots. The soils of new landslide scars contain much less exchangeable nutrient cation capital than that present in biomass + soil exchange pools in either of the mature forest types or in the >55‐yr landslide scars. Nonetheless, recovery of N, P, K, and Mg to levels present in both mature forest associations occurs during the brief course of this primary succession chronosequence, suggesting that forest recovery is not limited by the availability of those nutrients. Recovery of C and Ca pools is apparently slower.
Nutritional Management of Microbial Polysaccharide Production and Aggregation in an Agricultural Soil
Authors: Roberson Emily B. , Shennan Carol , Firestone Mary K. , Sarig Shlomo
Published: July 2010

Microbial extracellular polysaccharides (EPS) contribute to the stability of soil aggregates. Nitrogen supply affects microbial growth and metabolism. The effects of fertilizer and cover crop N supply on EPS production and soil aggregation were examined in an irrigated annual cropping system. Two winter cover crops, wooly pod vetch (Vicia dasycarpa L.), a N2 fixer, and oat (Avena sativa L.), and three N fertilizer regimes [0, 168, or 280 kg ha−1 (NH4)2SO4‐N] were used to vary soil N supply in a California tomato (Lycopersicon esculentum Mill.) field. Carbohydrate in the soil heavy fraction (HF, density >1.74 g mL−1) was found to have a monosaccharide composition consistent with microbial EPS and was used as an indicator of EPS. The HF carbohydrate content, aggregate slaking resistance, and saturated hydraulic conductivity (Ksat) were greatest in the vetch and 168 kg N ha−1 treatments and lower in the 0 and 280 kg N ha−1 treatments. The HF carbohydrate content was significantly correlated with Ksat and aggregate stability. Organic C and N, microbial biomass, and light‐fraction carbohydrate (density <1.74 g ml−1) were not correlated with either aggregate stability or Ksat. These results demonstrate that EPS can be important factors affecting soil structure in cultivated soils and that EPS production can be managed by N supply. The HF carbohydrate content may be a useful indication of the effects of soil nutrient and organic matter management on microbial EPS production.
Organic Carbon Content and Rates of Sequestration in Soils of Albania
Authors: Zdruli Pandi , Eswaran Hari , Kimble John
Published: July 2010

Soil organic carbon (SOC) was measured in 17 pedons, representing major agricultural soils in Albania. The soils studied were Inceptisols, Vertisols, Mollisols, and Alfisols. Within each order, the wet members (aquic suborders) had 10 times or more SOC than their well‐drained counterparts. Radiocarbon dates were determined on wood fragments found in a few of the soils. The steady‐state rates of accumulation range from 20 to 60 g m−1 m−2 yr−1 in the wet soils. Only one well‐drained soil was available for comparison and this had an accumulation rate of SOC of <1 g m−1 m−2 yr−1. Drainage of the wet soils results in a marked decrease in SOC. The rate of decrease is much smaller (26 g m−1 m−2 yr−1 during a 38‐yr period) than the accumulation rate, which was about 210 g m−1 m−2 yr−1 (during 2000 yr) in the one pedon studied. In the same climatic environment, the well‐drained soils accumulate SOC at significantly lower rates than their poorly drained counterparts, making the former inefficient sinks of SOC. Thus, from the point of view of sinks of atmospheric CO2, emphasis must be given to the wetland soils.
Influence of Salinity and Sodicity on Soil Structural and Hydraulic Characteristics
Authors: Crescimanno Giuseppina , Iovino Massimo , Provenzano Giuseppe
Published: July 2010

An exchangeable sodium percentage (ESP) >15 is traditionally considered to affect soil structural and hydraulic characteristics. Recent investigations show that both this critical value and the concept of critical threshold need reconsideration, because soil degradation often takes place even at lower ESP in dilute solutions, and soil behavior at increasing ESP appears to be a continuum. This study was carried out to analyze the response of two Sicilian Typic Haploxererts to ESP values up to 15, at a low cationic concentration. The investigation was carried out on aggregate stability, rating of soil shrink‐swell potential, and both saturated and unsaturated hydraulic conductivity. The specific purpose was to verify if a critical ESP threshold exists, or if the hypothesis of a continuum behavior is more appropriate. The high‐energy moisture characteristic technique was used for determining aggregate stability, and Brasher's method for the shrinkage characteristic. The constant‐head method was used for determining saturated hydraulic conductivity, and the parameter estimation method based on one‐step outflow experiments for unsaturated hydraulic conductivity. Almost linear relationships were found between the investigated soil properties and ESP, indicating no critical ESP threshold; furthermore, the results obtained indicate that an effective hazard of soil quality degradation can be forecast even in a 2 to 5 ESP range at a low cationic concentration. This is a basic indication for irrigation management aimed to combat and prevent degradation of soil quality.
Salinity and Sodicity Changes under Irrigated Alfalfa in the Northern Great Plains
Authors: Wienhold Brian J. , Trooien Todd P.
Published: July 2010

Insufficient water is the greatest limitation to crop production and choice of crops grown in the Northern Great Plains. Supplemental irrigation can overcome this limitation. Uncertainties about the drainage capacity of fine‐textured subsoils and the effect of irrigation on soil properties has impeded irrigation development. In this study we quantified salinity changes in soils with fine‐textured subsoils receiving a range of irrigation treatments. Alfalfa (Medicago sativa L.) was planted in 18 nonweighing lysimeters at two sites having fine‐textured subsoils. Irrigation was applied at three levels so that irrigation plus precipitation equaled either one, two, or three times the calculated evapotranspiration rate using two water qualities (electrical conductivity of irrigation water [EC1] 0.1 S m−1, sodium adsorption ratio of irrigation water [SARi] 4; or ECi 0.34 S m−1, SARi 16). Changes in the electrical conductivity of saturated soil extracts (ECe) and the sodium adsorption ratio of saturated soil extracts (SARe) were determined from soil cores collected to a depth of 1.5 m nine times between the years of 1984 and 1993. Averaged across irrigation levels, the profile‐averaged ECe increased from 0.03 to 0.12 S m−1 and the SARe increased from 1 to 6 in lysimeters receiving the 0.1 S m−1 water. In lysimeters receiving the 0.34 S m−1 water, the profile‐averaged ECe increased from 0.03 to 0.23 S m−1 and the SARe increased from 1 to 11. Salinity exhibited seasonal fluctuations. Changes in sodicity were persistent, exhibiting little seasonal variation. Supplemental irrigation of alfalfa is a viable management option in the Northern Great Plains when irrigation water quality is not a problem.
Spectroscopy of Aqueous Extracts of Forest Litter. II: Effects of Management Practices
Authors: Gressel N. , McColl J. G. , McGrath A. E. , Powers R. F.
Published: July 2010

Characteristics of dissolved organic matter (DOM) in aqueous extracts of litter may provide early indications of alteration of soil organic matter due to disturbances. Aqueous extracts of litter (pine and understory components) were prepared from two young ponderosa pine (Pinus ponderosa Doug. ex Laws.) plantations in California. Treatments were vegetation control (understory removal by herbicides), full nutrient fertilization, and control (untreated). Early changes due to management practices shown by spectroscopic techniques were not revealed by standard chemical analysis of DOM concentrations, pH or C/N ratios. Fourier‐transform infrared spectroscopy (FTIR) showed that DOM from both treatments at the warmer site (Whitmore) had relatively more COOH, phenolics, and aliphatics compared with controls, for both pine and understory components. At the cooler site (Chester) similar trends were observed only for understory DOM. Ultraviolet‐visible spectroscopy (UV‐VIS) showed that the ratio of absorptions at 465 vs. 665 nm (E4/E6 ratio) was higher for vegetation‐control DOM at both sites (6.7), compared with controls (5.9). Fertilization increased E4/E6 ratios at Whitmore only. The E4/E6 ratio was higher at Whitmore (6.7) than at Chester (5.1). The DOM from treated plots had smaller or less condensed chromophores, and relatively higher COOH, phenolics, and aliphatics, compared with the control. These effects were not as pronounced at Chester. At Whitmore warmer temperatures and increased water availability resulting from understory removal, and increased nutrient supply resulting from fertilization, may enhance the activity of decomposers. Total nutrients in litter increased with fertilization and decreased with understory removal. However, at Whitmore, understory removal increased the nutrients stored specifically in pine litter.
Mineralogy of Iron Precipitates in a Constructed Acid Mine Drainage Wetland
Authors: Karathanasis A. D. , Thompson Y. L.
Published: July 2010

Precipitates forming at various stages of acid mine drainage treatment in a high metal load (≈1000 mg L−1 Fe) and low pH (≈3) constructed wetland were characterized by chemical dissolution, x‐ray diffraction, thermal analysis, and scanning electron microscopy. Minerals precipitating in flumes and in entry wetland cells lacking vegetation included poorly crystalline ferrihydrite, lepidocrocite, goethite, possibly an akaganéite‐like mineral, and high Fe/S ratio Fe oxyhydroxysulfates (similar to schwertmannite). Within vegetated wetland cells lined with crushed limestone, well‐crystallized gypsum, lepidocrocite, and Fe‐oxyhydroxysulfate minerals with low Fe/S ratios were accompanied by gradual reductions in ferrihydrite and akaganéite. The Fe/S molar ratios of Fe oxyhydroxysulfates in flume precipitates averaged 5.2 ± 0.3, while those of cell precipitates averaged ≈3.5 ± 0.5. The oxalate‐extractable (Feox) to total (Fet) Fe fraction of the precipitates was considerably higher in wetland cells (1.1 ± 0.3), where organic C was 10‐fold higher than in entry flumes (0.7 ± 0.1). Scanning electron micrographs of flume precipitates showed a fiber‐like morphology of densely aggregated spherical particles, 1.5 to 2.0 mm in diameter, with a closely packed microcrystalline matrix. Precipitates collected from vegetated wetland cells formed aggregates of somewhat smaller diameter spherical particles with grassy surfaces or finger‐like projections entangled with bacterial cells. The overall composition of the precipitates suggested that the Fe chemistry is controlled primarily by the solubility of Fe oxyhydroxides in flumes and by S‐enriched Fe oxyhydroxysulfates inside the wetland cells. Although jarosite and goethite are thermodynamically favored in the wetland cells, their formation appeared to be inhibited by the presence of organics and the precipitation of Fe oxyhydroxysulfates and gypsum.
Nitrogen and Water Interactions in Subsurface Trickle‐Irrigated Leaf Lettuce II. Agronomic, Economic, and Environmental Outcomes
Authors: Thompson Thomas L. , Doerge Thomas A.
Published: July 2010

Evaluation of trickle‐irrigated crop production systems should address agronomic, economic, and environmental outcomes. The objectives of this research were to: (i) determine plant N uptake, residual soil inorganic N, unutilized fertilizer N, and unaccounted fertilizer N for subsurface trickle irrigated leaf lettuce (Lactuca sativa L. cv. Waldmann's Green), and (ii) use spatial analysis techniques to simultaneously evaluate agronomic, economic, and environmental production criteria for leaf lettuce within one growing season. Field experiments were conducted using buried trickle irrigation during three winter growing seasons in southern Arizona. Deficient to excessive N (35–300 kg ha‐1) and target soil water tension (SWT) treatments (12.0–4.0 kPa) were applied in factorial combinations each year. Fertilizer N recovery was determined by the difference method. Spatial analysis of response surfaces was used to determine overlap of zones with acceptable values for marketable yield, net economic return, and unaccounted fertilizer N for leaf lettuce during 1992–1993. Maximum unutilized fertilizer N was 216 kg ha‐1 for leaf lettuce, and maximum unaccounted fertilizer N was 149 kg ha‐1. Unutilized fertilizer N and unaccounted fertilizer N increased sharply when adequate N and water rates were exceeded. Spatial analysis of response surfaces for 1992–1993 showed a small region bounded by 6.6 to 7.3 kPa SWT and 238 to 252 kg N ha‐1 that would have resulted in >95% of maximum predicted marketable yield and net return while limiting NO3‐N concentrations in drainage water to ≤10 mg L‐1.
Spatial Variability of Soil Actual and Potential Acidity in the Mangrove Agroecosystem of West Africa
Authors: Sylla M. , Stein A. , van Mensvoort M. E. F. , van Breemen N.
Published: July 2010

Spatial variability of soil acidity in coastal lowlands results from a complex interaction of climate, coastal morphology, river hydrology, vegetation, landform, and tidal flooding. This study was conducted to determine whether the causal factors of soil acidification can be related to soil total actual acidity (TAA) and total potential acidity (TPA) in 12 sites selected along four river basins in West Africa. A hierarchical framework was designed corresponding to the scale at which each factor has the greatest influence on acidification. In the dry season of 1991, soil samples to be analyzed for TAA and TPA were taken from three strips within each river basin, perpendicular to the river at different distances from the mouth, following a 40 by 20 m grid, at five soil depths. The contribution of the different causal factors of acidity spatial variability was analyzed with a nested analysis of variance (ANOVA) and related to the hierarchical framework. Geostatistics were used to study spatial variability at the most detailed scale. We defined main ecoregions identified between watersheds at the macroscale, subenvironments identified with distance from the river mouth within watersheds, and zones identified with positions within toposequences. Practical implications for water management in acid sulfate were developed. At the macroscale, a broad subdivision of the study area into two ecoregions was possible, at the mesoscale, site position along rivers significantly predicted a river‐dependent longitudinal variability of soil acidity, whereas at the microscale, kriged maps showed different patterns of soil acidity.
Furrow Irrigation Water‐Quality Effects on Soil Loss and Infiltration
Authors: Lentz R. D. , Sojka R. E. , Carter D. L.
Published: July 2010

Irrigation‐induced erosion is a serious problem in the western USA where irrigation water quality can vary seasonally and geographically. We hypothesized that source‐water electrical conductivity (EC) and sodium adsorption ratio (SAR = Na/[(Ca + Mg)/2]0.5, where concentrations are in millimoles of charge per liter) affect infiltration and sediment losses from irrigated furrows, and warrant specific consideration in irrigation‐induced erosion models. On a fallow Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid), tail‐water sediment loss was measured from trafficked and nontrafficked furrows irrigated with waters of differing quality. Treatments were the four combinations of low or high EC (0.6 and 2 dS m‐1) and low or high SAR (0.7 and 12 [mmolc L‐1]0.5). Slope is 1%. Twelve irrigations were monitored. Each furrow received two irrigations. Main effects for water quality, traffic, and first vs. second irrigations were significant for total soil loss, mean sediment concentration, total outflow, net infiltration, and advance time. Average tail‐water soil losses were 2.5 Mg ha‐1 from low EC/low SAR furrows, 4.5 Mg ha‐1 from low EC/high SAR furrows, 3.0 Mg ha‐1 from high EC/high SAR furrows; and 1.8 Mg ha‐1 from high EC/low SAR furrows. Elevating water EC decreased sediment concentration from 6.2 to 4.6 g L‐1, but increasing SAR increased sediment concentration from 6.2 to 8.7 g L‐1. Net infiltration decreased 14% in high SAR compared with low SAR treatments. Soil loss increased 68% for second irrigations, and net infiltration fell 23% in trafficked furrows, but water‐quality effects were the same. Water quality significantly influenced infiltration and erosion processes in irrigated furrows on Portneuf soils.