bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractMathematical 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

AbstractThe 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

AbstractSlope 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

AbstractSelecting 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

AbstractRapid 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

AbstractThe 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

AbstractFew 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

AbstractMicrobial 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

AbstractSoil 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

AbstractAn 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

AbstractInsufficient 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

AbstractCharacteristics 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

AbstractPrecipitates 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

AbstractEvaluation 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.