bluuebunny/crossref_metadata_2025 huggingface dataset:
Field Corn Response to Acid Rain‐Drought Stress Interaction
Authors: Banwart W. L. , Ziegler E. L. , Porter P. M.
Published: July 2010

Two studies were conducted in 1988 to examine the effects of simulated acid rain in combination with various levels of drought stress on the grain yield of field grown corn (Zea mays L., ‘B73 × Mo17’ and ‘FS854’). In both studies corn was treated with twice weekly applications of simulated rainfall of pH 5.6 or 3.0 at amounts that totaled 100% (30 cm), 50% (15 cm), and 25% (7.5 cm) of the seasonal average for Champaign‐Urbana, IL. In addition to those treatments, in one of the studies the plants were subjected to daily wetting with the appropriate simulated rain from tassel emergence through pollination and fertilization. In both studies, reduced moisture levels resulted in significant reduction in grain yield but simulated rain of pH 3.0 had no effect on yield at any of the moisture levels studied. For both cultivars in both studies, reducing rainfall application from seasonal average to one‐half of the normal decreased yields by approximately 30%. When only one‐fourth of the seasonal rainfall amount was applied, yields were decreased between 40 and 55% compared to the yield for plants receiving the seasonal average rainfall. Results from these studies suggest that application of simulated acid rain of pH 3.0 has little or no negative effect on grain yield of the corn cultivars evaluated, even when relatively severe moisture stress was present, and when plants were subjected to daily wetting from tassel emergence through fertilization.
Beryllium in Selected Southeastern Soils
Authors: Anderson Michael A. , Bertsch Paul M. , Miller William P.
Published: July 2010

Data regarding the distribution and lability of beryllium (Be) in soils is limited. An interest in the dynamics of Be in soil and aquatic systems prompted this evaluation of the distribution of Be within selected soils of the Piedmont and Coastal Plain physiographic regions of the southeastern USA. Water‐soluble soil Be was below detection limits (<0.2 µg L−1) for all series and depths. Exchangeable Be ranged from <0.1 to 2.2 µmolckg−1, was consistently higher in the Piedmont relative to the Coastal Plain soils, and comprised only 0.0003 to 0.0083% of CEC. Total Be ranged from 0.3 to 30.5 mg kg−1 and, as with exchangeable Be, was consistently higher in the Piedmont soils. No significant correlation between exchangeable and total Be was found (r = 0.28). Exchangeable Be was weakly negatively correlated with depth, however (r = −0.36, significant at 0.10), while total Be tended to increase with depth (r = 0.44, significant at 0.05). Exchangeable Be was also weakly associated with CEC (r = 0.45, significant at 0.05) and exchangeable Ca and Mg (r = 0.39 and 0.38, respectively, both significant at 0.10). Though Al has been previously suggested as a model for Be in soils, no significant association between exchangeable Be and Al was found (r = 0.21). Given the weak association with exchangeable Ca and Mg and the lack of correlation with Al, neither Al nor Ca or Mg appears to serve as an adequate model for Be in southeastern soils.
Cadmium Speciation in Soil Solutions
Authors: Hirsch D. , Banin A.
Published: July 2010

Total Cd concentration was measured in the saturation extract of three unpolluted arid‐zone forest soils to which Cd was added as Cd(NO3)2 solution (0.1 mg Cd kg−1 soil). The ratio of free to total Cd (Cd2+/Cdt) in the extracted soil solution was measured using a Cd selective electrode by an addition method. A chemical equilibrium model including the major complexation reactions of Cd with anionic llgands was used to estimate Cd speciation in solution and was validated by the agreement between the calculated and measured Cd2+/Cdt ratios. Free Cd2+ and CdHCO+3 were each estimated to constitute 35% to 45%, respectively, of total soluble Cd in the calcareous soil solutions studied, which had pH values between 7.5 and 8.5. Agreement between measured and calculated Cd2+/Cdt ratios improved slightly after destruction of organic matter by UV irradiation of the extracted solutions. Organo‐Cd complexes were shown to be present in relatively minor amounts in these soils.
Kinetics of Mercuric Chloride Retention by Soils
Authors: Amacher M. C. , Selim H. M. , Iskandar I. K.
Published: July 2010

A nonlinear multireaction model was used to describe kinetic data for HgCl2 retention by five soils. A three‐parameter version of the model consisting of a reversible nonlinear (nth order, n < 1) reaction and an irreversible first‐order reaction was capable of describing HgCl2 retention data for Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) and Windsor (mixed, mesic Typic Udipsamment) soils at all initial solution Hg concentrations, and data for Norwood, [fine‐silty, mixed (calcareous), thermic, Typic Udifluvent], Olivier (fine‐silty, mixed, thermic Aquic Fragiudalt), and Sharkey (very‐fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) soils at initial solution Hg concentrations below 5 mg/L. A five‐parameter version of the model, with an added reversible nonlinear reaction, provided a more accurate description of the retention data for the Norwood, Olivier, and Sharkey soils at initial solution Hg concentrations above 5 mg/L. The second reaction needed to describe the data at higher Hg concentrations suggests the presence of a second type of sorption sites, or a precipitation or coprecipitation reaction not encountered at lower Hg concentrations. Release of Hg from the soils was induced by serial dilution of the soil solution, but not all the soil Hg was reversibly retained. This was also indicated by the model. Release of soil Hg depended on the concentration of retained Hg with significant Hg release occurring only at high concentrations of retained Hg. A multireaction model is needed to describe Hg retention in soils because of the many solid phases that can remove Hg from solution.
Nutrient Export in Stormflow following Forest Harvesting and Site‐Preparation in East Texas
Authors: Blackburn W. H. , Wood J. C.
Published: July 2010

In December 1979 nine small (2.57 to 2.79 ha) watersheds in East Texas were instrumented to determine the effects on stormflow water quality of: (1) clearcutting, shearing, windrowing and burning; (2) clearcutting, roller chopping, and burning; and (3) undisturbed control. Nutrient losses and concentrations, pH, electrical conductivity, and turbidity were not significantly different for all pre‐treated watersheds. The first year following harvesting and site preparation, most nutrient losses and concentrations were greater from the sheared and chopped watersheds than from the undisturbed watersheds. Most nutrient losses and concentrations during the second and third post‐treatment years were not significantly different from the chopped and undisturbed watersheds, but continued to be significantly greater from the sheared watersheds than from chopped or undisturbed watersheds. During the fifth post‐treatment year all nutrient levels except for K+ losses were not significantly different for all treatments. Although nutrient losses from all treatments were small, shearing and windrowing had the greatest impact on nutrient export. Roller chopping as applied in this study had a minimal impact on stormflow nutrient losses and should not degrade water quality.
Influence of Water Chemistry on Suspended Solids in Coal‐Mine Sedimentation Ponds
Authors: Evangelou V. P.
Published: July 2010

In Kentucky, water quality in coal‐mine sedimentation ponds is lowered by high concentrations of suspended solids. Spoil samples from surface mine sites in eastern and western Kentucky were equilibrated with distilled water to evaluate their effects on suspended solids. The results demonstrate that small changes in salt concentration have large effects on suspended solid concentration. Furthermore, it was determined that for the ranges of water chemistry encountered in such environments, there is a linear relationship between the repulsive index [RI = (0.014 EC)−1/2] and suspended solids. Increasing the electrical conductivity (EC) reduces RI and increases the rate of settling.
Internal and External Proton Load to Forest Soils in Northern Germany
Authors: Bredemeier M. , Matzner E. , Ulrich B.
Published: July 2010

Both external and internal proton sources contribute to total H+ load of the soil in terrestrial ecosystems. The most important internal net proton production (INP) processes are (a) accumulation of a surplus of inorganic cations over anions in organic matter, (b) net production and protolysis of organic acids, (c) dissociation of carbonic acid from root and decomposer respiration, (d) net nitrification of organic N, (e) uptake of a surplus of deposited NH+4 over deposited NO−3 or nitrification of deposited NH+4, (f) buffering of deposited H+ in the canopy and recharging of foliar buffer systems with subsequent H+‐release to the soil. Processes (a) through (d) are proton production processes due to ecosystem state and site conditions; (e) and (f) are due to atmospheric deposition and must be regarded as part of acid deposition. The sum of the rates of all processes plus free acidity (H+) flux in throughfall constitute total proton load (TPL) to a soil. Rates of INP and TPL were evaluated for six experimental forests in northwestern West Germany, which had been monitored in long‐term studies. Internal sources are relevant contributors to total proton load. At five of the six sites, however, H+ load due to atmospheric deposition exceeds 70% of TPL. Total acidity budgets show that soils in the aluminum‐buffer‐range become acid exchangers (3H+ → Al3+), i.e., they almost quantitatively transfer the incoming amount of acid (TPL) to deeper layers of the seepage conductor and eventually the hydrosphere. A comparison of the evaluated TPL rates with maximum rates of buffering by silicate weathering reported in the literature indicates that all carbonate‐free soils will further acidify and reach the Al buffer range.
Evaluating Time‐Dependent Tree Ring and Climate Relationships
Authors: Van Deusen P. C.
Published: July 2010

Techniques for estimating dynamic tree ring and climate relationships with the Kalman filter have been recently introduced to the field of dendroecology. These methods have been used to evaluate effects of long‐term climate change or pollution impacts on tree growth, thereby enhancing the value of tree rings as a historical data source. The verification of time‐varying trends, however, should be based on replication of results, historical knowledge of the forest, and statistical testing to the extent possible. This article introduces several useful statistical tests for model verification and parameter time‐dependency based on prediction errors and maximum likelihood information criteria.
Copper Fertilization to Prevent Molybdenosis on Retorted Oil Shale Disposal Piles
Authors: Stark John M. , Redente Edward F.
Published: July 2010

Plants growing on retorted oil shale disposal piles often have Mo concentrations high enough (>8 mg kg−1) and Cu/Mo ratios low enough (<2.0) to cause molybdenosis in grazing ruminants. High Mo concentrations are present in some plant species in spite of 90 cm of topsoil cover. Copper sulfate was broadcast at rates of 0, 8, 16, and 32 kg Cu ha−1 on plots with 30 and 90 cm of topsoil over Paraho retorted oil shale to determine if Cu fertilization can increase Cu/Mo ratios in plants so that molybdenosis is no longer a hazard. Of the plant species studied winterfat [Eurotia lanata (Pursh) Moquin], northern sweetvetch (Hedysarum boreale Nutt.), alfalfa (Medicago sativa L.), native grasses [Agropyron smithii Rydb., A. inerme (Scribn. and Smith) Rydb., A. dasystachium, (Hook.) Scribn. and Poa ampla Merr.], and introduced grasses [A. desertorum (Fisch.) Schult., A. intermedlum (Host Beauv.), and Bromus biebersteinii Roem. & Schult.], all except alfalfa showed increased tissue Cu concentrations during the first growing season. Because of high Mo concentrations, however, only winterfat under high fertilization rates developed Cu/Mo ratios sufficient to prevent molybdenosis (i.e., >2.0). By the end of the second growing season, increases in Cu concentrations due to fertilization had declined approximately 30%. These results indicate that although Cu fertilization can be used for short‐term improvements in Cu/Mo ratios, it should not be relied upon as the sole technique for preventing molybdenosis on retorted shale disposal piles. Instead, maximum feasible topsoil thicknesses should be used and plant species known to concentrate Mo should be eliminated from seeding mixtures.
Sorption Behavior of s‐Triazine and Thiocarbamate Herbicides on Soils
Authors: Singh G. , Spencer W. F. , Cliath M. M. , van Genuchten M. Th.
Published: July 2010

The soil‐water partitioning coefficient (Kd) is an important parameter for predicting the transport of herbicides in soils. We studied the sorption behavior of two s‐triazines [atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5 triazine) and prometon (2,4‐bis(isopropylamino)‐6‐methoxy‐s‐triazine)] and two thiocarbamates [EPTC (s‐ethyl dipropylthiocarbamate) and triallate (s‐(2,3,3‐trichloroallyl)diisopropyl‐thiocarbamate)] on two soils [Hanford sandy loam (HSL) (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthents) and Tujunga loamy sand (TLS) (mixed, thermic Typic Xeropsamments)] with varying organic matter content and soil texture. The Kd‐values were determined with a mass balance equilibrium batch technique in which the solution as well as the sorbed phase concentration was directly measured. Two grams of soil were equilibrated with 20 mL of aqueous herbicide solution for 24 h at 25 ± 1 °C. Four concentrations of each herbicide at one‐half, one‐fourth, and one‐sixth, and one‐eighth of their respective aqueous solubilities were selected for the experiments. Sorption constants were calculated with both linear and nonlinear Freundlich isotherms. The exponents 1/n of the Freundlich isotherm varied between 0.767 and 0.984, thus indicating considerable nonlinearity in some of the isotherms. The K∞‐values (soil‐water partitioning constants based on the organic C fraction of a soil) were calculated as the ratio of the measured Kd‐values and the soil organic fraction of the HSL and TLS soils. Using the mass balance equilibrium method, the average K∞‐values of atrazine, EPTC, prometon, and triallate for the two soils were found to be 54, 196, 76, and 2838 m3/Mg, or 0.42, 0.50, 0.21, and 0.88 times those estimated from measured soil solution concentrations only. Since the latter values are much closer to reported literature values (most of which were determined from measured solution concentrations only), we believe that the variability and ambiguity of current literature K∞‐values may be due largely to inaccurate determination of Kd‐values. We also estimated the K∞‐values from basic soil physical and chemical properties by using previously reported predictive equations.
Sorption of Napropamide on Clay and Soil in the Presence of Dissolved Organic Matter
Authors: Lee Dar‐Yuan , Farmer Walter J. , Aochi Y.
Published: July 2010

Dissolved organic matter (DOM) can affect the distribution of solutes between solution and sorbed phases and the availability and environmental fate of the solutes. Batch sorption isotherm techniques were used to evaluate solute‐solute and solute‐sorbent interactions that control the effects of DOM on the sorption of a nonionic, moderately polar organic solute by solid sorbents. The sorption of napropamide (2‐(α‐naphthoxy‐N,N‐diethyl propionamide) by Na+‐, Cu2+‐, and Al3+‐montmorillonite decreased when dissolved humic acid derived from peat (peat‐DHA) was present in the slurry. For Na‐montmorillonite, the effect of DOM on sorption was reduced when a dialysis membrane prevented contact between the DOM and the clay. This suggests that competition for sorption sites on the clay between DOM and the pesticide contributed to decreased napropamide sorption. The extent of the DOM effect was also dependent on the concentration and the source of DOM added. In contrast to the montmorillonite system, the effect of DOM on napropamide sorption by soil was observed only when the dialysis membrane was present or when the dissolution of native organic matter from the sorbate surface itself was enhanced by increasing the pH of the slurry system. These results demonstrate that the effect of DOM on the sorption of nonionic pesticides by soils and sediments can be a function of the association of DOM with pesticides in the solution phase, interactive forces of both DOM and the pesticide with the sorbent surface and the nature of the sorbent surface.
Application of a Hollow‐Fiber, Tangential‐Flow Device for Sampling Suspended Bacteria and Particles from Natural Waters
Authors: Kuwabara James S. , Harvey Ronald W.
Published: July 2010

The design and application of a hollow‐fiber tangential‐flow filtration device has been used to concentrate bacteria and suspended particles from large volume surface water and groundwater samples (i.e., hundreds of liters). Filtrate flux rates (4–8 L min−1) are equal to or faster than those of other devices that are based on continuous flow centrifugation and plate and frame filtration. Particle recovery efficiencies for inorganic particles (approximately 90%) were similar to other dewatering devices, but microbial cell recoveries (30–90%) were greatly improved by this technique relative to other currently available methods. Although requirements for operation and maintenance of the device are minimal, its size, as with other dewatering devices, limits its applicability at remote sample sites. Nevertheless, it has proven useful for sample collection in studies involving microbial transport and analysis of particle‐associated trace inorganic solutes.
Elevated Nitrate Levels in Soils of the Eastern Mojave Desert
Authors: Marrett D. J. , Khattak R. A. , Elseewi A. A. , Page A. L.
Published: July 2010

Deep cores taken on an uncultivated desert alluvial fan revealed two large volumes of coarse soil with high NO3 levels (20–208 mg L−1 NO3‐N in water saturation extracts). Nitrate levels were unpredictable both laterally and vertically and unrelated to alluvial strata. The large soil volumes with elevated NO3 levels were found 2.7 to 7.3 m deep in four cores at one 3 by 3 m site, and 8.8 to 21 m deep in two cores at another site. Isolated samples with elevated NO3 were found in three other cores and six cores contained no elevated NO3. Overall, nitrate was best correlated with EC, Na, SO4, and Cl (r = 0.68, 0.66, 0.67, and 0.73, respectively; P ≤ 0.05). Stronger correlations were found within the four individual sites and 15 cores, but the ions best correlated with NO3 varied, even between cores from the same site. Saturation extract NO3 was not correlated with bulk soil total organic C or total N. The NO3 distribution patterns found appear related to inorganic processes (salinization and leaching), but specific processes of N redistribution and primary N sources remain unclear. Elevated NO3 in deep soils appears to be a natural phenomena that reflects Pleistocene site conditions and possible geologic NO3 sources. Local volcanic rocks contain up to 73 mg NO3‐N kg−1 rock (water‐extractable). Naturally elevated NO3 levels in rocks and coarse alluvial fan soils are poorly understood and easily overlooked potential sources of groundwater NO3.
Denitrification in Porous Media during Rapid, Continuous Leaching of Synthetic Wastewater at Saturated Water Flow
Authors: Yamaguchi T. , Moldrup P. , Teranishi S. , Rolston D. E.
Published: July 2010

Increasing interest is given to land treatment and especially rapid infiltration (RI) systems as a method to remove N in wastewater by denitrification. The purpose of this article is to investigate denitrification in porous media at conditions corresponding to RI land treatment systems. Denitrification in six porous media columns (98% decomposed granite or sand and 2% field soil) during saturated leaching at constant flow rates of synthetic wastewater was investigated. Concentrations of NO3‐N and methanol between 20 and 60 mg L−1 were applied and vertical concentration profiles of NO3‐N, NO2‐N, and NH4‐N were measured for 45 d at 30 °C (three columns) and 10 °C (three columns). A time lag in denitrification of 10 d was found at 10 °C. Complete N removal was obtained after 3 d at 30 °C but was not obtained at high N‐loading at 10 °C. A NO2‐N leaching was observed between Day 1 and 3 at 30 °C. Assuming first‐order denitrification at steady state, the corresponding first‐order reaction rate coefficients (k1) for NO3 reduction in the columns were estimated to be between 1.4 and 5.0 h−1 at 30 °C and between 0.017 and 0.14 h−1 at 10 °C. The NO3‐N concentration in the influent found to be the most optimal for denitrification at steady state was 20 mg N L−1 at 10 °C and 40 mg N L−1 at 30 °C. No significant differences in k1 values in columns containing decomposed granite and sand, respectively, were found. Steady‐state NO3 profiles were obtained between 1.5 to 4.5 wk after the experiments were started.
Volatilization, Off‐Site Deposition, and Dissipation of DCPA in the Field
Authors: Ross L.J. , Nicosia S. , McChesney M.M. , Hefner K.L. , Gonzalez D.A. , Seiber J.N.
Published: July 2010

Residues of dimethyl, 2,3,5,6‐tetrachloroterephthalate (DCPA) have been found repeatedly in recent years on a variety of produce grown in California to which this herbicide had not been applied. In response to this problem, drift, volatilization, and dissipation of DCPA were investigated in a circular plot seeded with bunch onions [Allium cepa (L.) var. White Lisbon], and off‐site deposition was measured in a surrounding area seeded with parsley [Petroselinum crispum (Mill.) Mansf. var. Green Modified Curl Leaf]. Contamination by residual soil residues remaining on field after harvest was also examined by reseeding the circular plot with parsley. Atmospheric residues detected downwind on resin and filters indicated DCPA moved off‐target as a vapor as well as on particles both daring and up to 21 d after application. Volatilization flux, measured using the aerodynamic method, reached a maximum rate of 5.6 g ha−1h−1. An estimated 10% of the DCPA applied was lost to the atmosphere within 21 d of application. Deposition of DCPA outside the circular plot was evidenced by residues found on potted parsley plants and soil set out up to 23 m from the treated area. Parsley, seeded around the circular plot at the time of application and sampled 63 d later, contained residues ranging from 51 to 250 µg kg−1 indicating DCPA continued to move off‐target in air up to 60 d after application. The mass of DCPA in soil exhibited a log‐linear decline from which a 50 d dissipation half‐life was calculated. Parsley planted in the circular plot after the onion harvest did not contain DCPA residues when sampled 217 and 336 d after the original application. Results indicated that drift during, and volatilization and subsequent atmospheric transport after, application are potentially important sources of DCPA contamination occurring on nontarget crops in California.
Sorption of Nonionic Organic Compounds by Corn Residues from a No‐Tillage Field
Authors: Boyd Stephen A. , Xiangcan Jin , Lee Jiunn‐Fwu
Published: July 2010

The sorptive uptake of three representative nonionic organic compounds (NOCs) from water by corn (Zea mays L.) residues and surface soil from a no‐tillage field was evaluated. Sorption isotherms of benzene, ethylbenzene, and 1,2,3‐trichlorobenzene by the corn residues and soils were linear, and the degree of uptake was inversely related to the water solubility of the NOC. Sorption coefficients of the corn residues were from 35 to 60 times greater than for the surface soil (1.9% organic matter), demonstrating the high sorptive capabilities of these residues. The sorptive characteristics of isolated plant cuticle were also evaluated. The linear isotherms, lack of competitive effects in binary solute systems and similarity of cuticle Kom values to the corresponding Kow values provided strong mechanistic evidence for the role of cuticle as a partition phase in the sorption of NOCs by corn residues. The sorptive capabilities of corn residues and soil organic matter for NOCs were nearly identical as indicated by the similarity of the corresponding Kom values. This suggests it may be unnecessary to distinguish crop residue C and soil humus C when predicting NOC sorption coefficients from the organic C content of soil.
The Residual Effect of Sewage Sludge on Heavy Metal Content of Tobacco and Peanut
Authors: King Larry D. , Hajjar Lisa M.
Published: July 2010

Sewage sludge normally would not be applied on land where peanut (Arachis hypogaea L.) or tobacco (Nicotiana tabacum L.) are being grown because of possible contamination of peanut with pathogens and increased Cd concentration in tobacco. These crops, however, might be grown in rotation with other crops to which sludge had been applied. The residual effect of sewage sludge on metal concentrations in tobacco and peanut was evaluated in a greenhouse pot experiment with a Typic Hapludult soil from a field that received aerobically digested municipal sewage sludge at 0, 9, 18, and 27 Mg ha−yr−1 for 3 yr. Cumulative amount of metals applied at the 27‐Mg rate were (kg ha−1) 1.8 Cd, 39 Cu, 48 Cr, 9 Ni, 30 Pb, and 84 Zn. Sulfuric acid or Ca(OH)2 was used to effect three soil pH regimes: 5.2, 5.8, and 6.4 (median value within each regime). Tobacco (‘Speight G‐28’) was grown to flowering and peanut (NC 7) was grown to maturity. At the termination of the experiment, soils were extracted with diethylenetriaminepentaacetic acid (DTPA) and Mehlich 3 extractant (M3) for metal analysis. Tobacco dry weight (averaged over pH) increased from 66 g pot−1 with no sludge to 94 g pot−1 at the highest sludge rate. Peanut kernel yield (averaged over pH) was depressed at the highest rate (35 g pot−1) as compared to the lower rates (mean of 48 g pot−1). At low pH peanut top growth was depressed by sludge (probably a result of Zn toxicity) and no kernels were formed at the medium and high rates. Sludge rates and soil pH had little effect on concentration of Cr and Pb in tobacco or peanut. Concentration of Cd, Ni, and Zn in tobacco and in peanut top growth decreased as soil pH increased to 5.8 to 6.0 but no decrease was noted at higher pH. Sludge rate effect was significant at low pH but diminished as pH increased. Concentration of Cd, Ni, and Zn declined but Cu concentration increased with increasing height of leaf on the tobacco stalk. Results of stepwise multiple regression using linear and quadratic forms of cumulative sludge rate, soil pH, and DTPA‐extractable metals and pH × rate and pH × DTPA‐extractable metals interactions as independent variables and metal concentration in the lower tobacco leaves or in peanut tops as dependent variables suggested DTPA would predict tissue metal concentrations better than would M3.
Accumulation of Selenium in Plants Grown on Selenium‐Treated Soil
Authors: Banuelos G. S. , Meek D. W.
Published: July 2010

High concentrations of Se found in the environment may be detrimental to sustainable agriculture in parts of the western USA. Greenhouse pot experiments were conducted to study Se concentrations in different plant species grown in soil with added Se. Astragalus incanus L. (no common name), creeping saltbush (Atriplex semibaccata R. Br. L.), Old Man saltbush (Atriplex nummularia Lindl L.), wild brown mustard (Brassica juncea Czern L.), and tall fescue grass (Festuca arundinacea Schreb L.) were grown in potting soil to which 3.5 mg Se6+ or Se4+ kg−1 was added either as Na2SeO4 or Na2SeO3, respectively. During the growing season, plants from both Se‐treated soils were clipped either once, twice, or three times. After 50 to 55 d in Se‐treated soil, plants were harvested, separated into shoots and roots, and analyzed for total tissue Se. Soils from each species were analyzed for total residual Se. Each species grown in Se6+‐treated soils, accumulated significantly (P < 0.001) more Se than plants grown in Se4+‐treated soil. For both Se6+ and Se4+ treatments, wild brown mustard and A. incanus had the highest and lowest tissue Se concentrations, respectively. Clipping of plants significantly (P < 0.05) increased the accumulation of Se in the total harvested shoot tissue for wild brown mustard and slightly for the other species tested (except Old Man saltbush). Reduction in soil Se was observed for each species, with the greatest reduction occurring when plants of wild brown mustard were grown and clipped. Within any given treatment, wild brown mustard accumulated the highest concentrations of Se. In the remaining species, Se accumulated in the following order: Old Man saltbush > creeping saltbush > tall fescue > A. incanus. Selenium removal from soil by each species generally followed the same order as the accumulation of Se in the plant.
Cumulative Effects of Land Management on Soil and Water Resources: An Overview
Authors: Sidle Roy C. , Sharpley Andrew N.
Published: July 2010

The concept of cumulative effects encompasses a broader spectrum of resources and land uses than has typically been evaluated in research. As management pressures in large drainage basins intensify, pristine areas may be subjected to multiple human activities. These activities are distributed through time and space, and their effects can occur at the location of a particular land use or away from the location. Even though individual land uses may not significantly degrade environmental components such as soil productivity, water quality, or aquatic habitat, the combined effects of several activities may be unacceptable. Theoretically, cumulative effects of land management may also provide benefits to portions of ecosystems, such as increased stream productivity generated by nutrient inputs. Cumulative effects of land management must also be evaluated within the context of natural processes and events, such as large storms, wildfire, geochemical weathering, and vegetation succession. This overview provides examples of cumulative effects of land management and introduces the papers in this issue that were presented at a special symposium held during the American Society of Agronomy meetings in 1989.
A Case for Agricultural Systems Research
Authors: Oberle S. L. , Keeney D. R.
Published: July 2010

Agricultural science is a complex and multidisciplinary field that represents the vital link between human (socioeconomic) systems and the natural environment. Development of effective strategies for efficient farm resource allocation and management requires a general understanding of the fundamental components of farming systems and their interactions, and properly begins with the analysis of farm manager goals and limitations. This article defines important systems concepts and discusses the role of systems theory in agricultural research and problem solving. In addition, several agricultural systems examples are described and a systems method is used to identify and discuss the components and general goals of agricultural systems. We believe to the extent that it is utilized, systems theory provides a powerful tool to assist those involved in agricultural research, education, and production in understanding complex interactions among system components and component technologies, and in identifying and prioritizing information or research needs.
Landfill Leachate Recirculation: Effects on Vegetation Vigor and Clay Surface Cover Infiltration
Authors: Cureton P. M. , Groenevelt P. H. , McBride R. A.
Published: July 2010

Continuous recirculation of two municipal solid waste (MSW) landfill leachates from Ontario, Canada, through a vegetated clay surface cover was field tested in 39 bottom‐draining lysimeters over two field seasons. The more concentrated of the two leachates had an osmotic potential of about −1 kJ kg−1, an electrical conductivity of 0.8 to 1.0 S m−1, a chemical oxygen demand of 9.9 to 18.7 g kg−1, and a pH of 6.5 to 7.0. Vegetation tested included reed canarygrass (Phalaris arundinacea L.), meadow foxtail (Alopecurus pratensis L.), weeping willow (Salix babylonica L.), and hybrid poplar (Populus sp. nigra × maximowiczii). Leachate recirculation stimulated height growth by 36 to 141% in the four species tested relative to the growth observed in the water‐irrigated control plants. Chlorosis of early season foliage and widespread necrosis and leaf desiccation were visible in leachate‐irrigated hybrid poplar and weeping willow saplings after a total leachate application over two seasons of 740 ram. Leaf senescence in the hybrid poplar saplings preceded the normal senescence date by 5 to 6 wk. By the second field season, stomatal conductance was reduced by 73%, photosynthesis rate by 63%, and transpiration rate by 68% in leachate‐irrigated hybrid poplar sapling leaves relative to the water‐irrigated controls. Vegetative stress was most likely a result of osmoregulation disruption arising from a depressed soil solution osmotic potential. In the reed canarygrass swards, total actual evapotranspiration over the second field season was increased by 50%, height growth by 87%, and foliar biomass production by 160% through recirculation with the more concentrated MSW leachate in comparison to the water‐irrigated reed canarygrass. No phytotoxic symptoms or excessive trace metal accumulations were observed in reed canarygrass leaf tissue. Reed canarygrass shows good potential as a cover vegetation species for leachate recirculation sites under northern temperate climatic conditions. The field‐saturated hydraulic conductivity of the silty clay surface covers irrigated with landfill leachate, measured to be in the order of 10−5 m s−1, was significantly higher than that measured on the water‐irrigated surface covers after a cumulative total irrigant application of 2.9 pore volume equivalents. No evidence existed of soil pore clogging with particulates. Volumetric shrinkage of the clay‐rich soil cover due to physicochemical incompatibility with applied leachates containing organic solvents and salts was thought to be the principal contributing factor.
Downstream Effects of Timber Harvesting on Channel Morphology in Elk River Basin, Oregon
Authors: Ryan Sandra E. , Grant Gordon E.
Published: July 2010

Downstream effects, a type of cumulative watershed effect, were identified using changes in the width and distribution of open riparian canopies measured from aerial photography taken between 1956 and 1979 in Elk River basin, southwest Oregon. Open canopies appear on aerial photographs of densely forested basins as unvegetated areas bordering stream channels. Opening occurs when large disturbances, such as landslides, debris flows, large floods, and excessive sedimentation, disrupt the vegetation in the riparian corridor. Downstream changes in channel morphology, inferred by the changing pattern of open reaches were linked to upslope forestry activities; a causal link was assumed where: (i) open reaches extended continuously downstream from clearcuts and roads or (ii) the timing and pattern of opening downstream varied in direct relation to the intensity of upslope forestry activities. Open riparian canopies were observed in first‐ through fifth‐order channels, though only 11% of open reaches in low‐order channels were spatially connected to open reaches in higher order channels. Open reaches on low‐order tributaries were attributed to landslides and surface erosion generated from clearcuts and roads; the total length of open reaches in low‐order channels increased 30‐fold during the study period. Open reaches occurred on higher‐order channels throughout the study period but did not increase in size or change location in relation to upslope harvest activities. Instead, open canopies were restricted mainly to wide and low gradient channel reaches, which comprised approximately one‐third of the length of higher‐order channels. Limited downstream change in riparian canopies associated with upslope forestry activity during the study period, which included a 100‐yr storm, was attributed to three physical factors: (i) lack of debris flows in most parts of the basin; (ii) channels constrained by competent hillslopes limiting the potential for opening; and (iii) low harvest levels over much of the basin at the time of the 100‐yr storm. While air photo interpretation proved useful in deciphering the gross disturbance history of the basin and in distinguishing the general processes which generate downstream effects, sedimentation processes that do not disturb the riparian canopy may also be active in Elk River basin but were not detected due to the coarseness of the techniques used.
A Hydride Generation Atomic Absorption Technique for Arsenic Speciation
Authors: Masscheleyn P. H. , Delaune R. D. , Patrick W. H.
Published: July 2010

Based on an investigation of hydride generation responses in solutions of various acidities containing nanogram quantities of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) a sensitive analytical method for the accurate determination of inorganic and organic As species in aqueous solutions was developed. After a pH‐selective reduction, the arsenic species were condensed in a U‐tube filled with a gas chromatographic packing immersed in liquid N2. The species were then separated by slow warming of the trap and measured with an atomic absorption spectrophotometer. The arsines from inorganic As (III) were selectively generated from a solution buffered at a pH of 6.0. The solution of then further acidified to a pH corresponding to 2 M HCl and analyzed for As(V). A second sample aliquot, buffered at pH 1.5 with oxalic acid, was used for the quantitative determination of [As(III) + As(V)], MMAA and DMAA.
Influence of Fertilizer, Irrigation, and Non‐Growing Season Precipitation on Soil Nitrate‐Nitrogen under Corn
Authors: Liang B.C. , Remillard M. , MacKenzie A.F.
Published: July 2010

Corn (Zea mays L.) production requires large amounts of N fertilizer, which may be lost due to leaching or denitrification. Prediction of the amount lost would be helpful in minimizing these losses. A field experiment was conducted to investigate the effects of fertilization, irrigation, and non‐growing season precipitation on soil NO3‐N under corn in southwestern Quebec from 1984 to 1987. The high rate of fertilization (400 kg N ha−1, 300 kg P25 ha−1, 400 kg K2O ha−1) over the normal rate (170 kg N ha−1, 100 kg P25 ha−1, 170 kg K2O ha−1) significantly increased soil NO3‐N during the growing season, and a residual effect of fertilizer rate on soil NO3‐N levels was noted in 2 of 3 yr during the non‐growing season. The high rate of fertilization, however, did not increase NO3‐N accumulation in the soil profile over the normal rate of fertilization in successive years. Irrigation significantly decreased soil NO3‐N during the growing season. At the normal rate of fertilization, gains of soil NO3‐N over winter were found with lower winter precipitation. At the high rate of fertilization, however, losses of soil NO3‐N over winter occurred in 2 of the 3 yr. The changes in NO3‐N in the rooting zone over winter depended upon the precipitation received during the preceding winter and the amount of NO3‐N in the soil the previous fall.
Accumulation and Interactions of Arsenic, Selenium, Molybdenum and Phosphorus in Alfalfa
Authors: Khattak Riaz A. , Page A. L. , Parker D. R. , Bakhtar Dariush
Published: July 2010

Arsenic (As), selenium (Se), and molybdenum (Mo) have become increasingly important in the terrestrial and agrobiological environment in some parts of the western USA. A four factorial [3 As × 3 Se × 2 Mo × 2 P concentrations] completely randomized glasshouse study was conducted to evaluate the competitive interactions between As(V), Se(VI), Mo(VI) and P using nutrient solution concentrations representative of soil solutions and agricultural drainage waters. Alfalfa [Medicago sativa L., Germain WL 512] was grown in sand culture and irrigated five times per day with half‐strength Hoagland's solution containing 0 (background), 0.05 and 0.10 mg L−1 As as Na2HAsO4; 0, 0.05, and 0.10 mg L−1 Se as Na2SeO4; and 0.01 (background) and 1.0 mg L−1 Mo as Na2MoO4. Instead of 16 mg L−1 P and 16 mg L−1 S commonly used in the half‐strength Hoagland solution, 1.0 or 4.0 mg L−1 P added as KH2PO4 and one somewhat lower level (8.0 mg L−1) S added as MgSO4 were used. The results indicated no adverse effect of As and Se on shoot yield. Selenium and P strongly depressed shoot As concentrations, and their combined effects were multiplicative rather than additive (significant Se × P interaction). Uptake of Se was decreased by increasing P, but was stimulated by increasing As, and the combined effects of P and As were approximately additive (non‐significant As × P interaction). Tissue concentrations of Mo and P were less dramatically influenced by solution concentrations of the other elements.
Sorptive Reversibility of Atrazine and Metolachlor Residues in Field Soil Samples
Authors: Pignatello Joseph J. , Huang Lee Q.
Published: July 2010

Predictions of the fate and transport of organic compounds in soils depend on sound sorption models. The impacts of slowly reversible (nonequilibrium) sorption on compound fate are not well quantified. Soil samples containing residues of the herbicides atrazine (2‐chloro‐4‐ethylamino‐6‐isopropyl‐1,3,5‐triazine) and metolachlor (2‐chloro‐N‐[2‐ethyl‐5‐methylphenyl]‐N‐[2‐methoxy‐1‐methylethyl]‐acetamide) were collected from fields 2 to 15 mo after their last application to assess the sorptive reversibility of these residues. The apparent sorption constant of the native herbicide, Kapp, was determined from the sorbed and solution concentrations after suspension of the sample in water for 24 h. The “equilibrium” sorption constant, Kd, was determined in the same samples from 24 h sorption isotherms of freshly added herbicide, taking into account the fraction of labile native herbicide (fL). The ratio Kapp/Kd varied from 2.3 to 42 and was directly related to the “age” of the residue (i.e., time between sampling and last application). The value of fL ranged from 0.056 to 0.60 and was inversely related to the age of the residue. The results indicate that contaminated samples collected from the field can contain a large fraction of contaminant in a slowly reversible sorbed state, and that this fraction increases with time.
Long‐Term Ionic Increases from a Central Appalachian Forested Watershed
Authors: Edwards Pamela J. , Helvey J. David
Published: July 2010

The electrical conductivity of stream water draining from an unmanaged and undisturbed control watershed has been increasing rather steadily, about 0.03 mS m−1 yr−1, since 1971. During this period, NO−3 and Ca2+ concentrations increased and were shown to mathematically account for the ionic contribution to conductivity; therefore, they are believed to be primarily responsible for the increase. However, the percentage of conductivity explained by the two ions was different over time. The percentage of conductivity attributable to NO−3 increased in a pattern very similar to concentration. In contrast, the percentage of conductivity attributable to Ca2+ decreased slightly over time. The Ca2+ is believed to be pairing with the NO−3 as the NO−3 ions leach through the soil. While nitrification in mature stands can be strongly inhibited, limited nitrification, especially in forest gaps, and high anthropogenic inputs of NO−3 probably were primary sources of the leached NO−3. Preferential adsorption of SO2−4, rather than NO−3, on soil colloids is given as an explanation for the lack of retention of NO−3 in the soil system and subsequent leaching to the stream.
Pesticide and Nutrient Movement into Subsurface Tile Drains on a Silt Loam Soil in Indiana
Authors: Kladivko E. J. , Van Scoyoc G. E. , Monke E. J. , Oates K. M. , Pask W.
Published: July 2010

The objectives of this study were to determine field‐scale pesticide and nutrient losses to subsurface tile drains over a 3‐yr period on a low organic matter and poorly structured silt loam soil under typical agricultural management practices. A subsurface drain spacing study was instrumented to measure drain discharge rates and to collect drainflow samples continuously on a flow‐proportional basis. Two replicates of three drain spacings (5, 10, and 20 m) were included in the study. Water samples were analyzed for all applied pesticides (atrazine, cyanazine, alachlor, carbofuran, terbufos, and chlorpyrifos)1 as well as major nutrients (N, P, K) and sediment. Small amounts of carbofuran, atrazine, cyanazine, and alachlor were detected in subsurface drainflow within 3 wk of pesticide application and after less than 2 cm net subsurface drainflow from the soil. This early arrival of pesticides at the drain is consistent with preferential flow concepts. Annual carbofuran losses in subsurface drainflow ranged from 0.8 to 14.1 g ha−1, or 0.05 to 0.94% of the amount applied to the soil. Losses of all other pesticides were ≤0.06% of the amount applied. The rank‐order of pesticide mass losses corresponded with the rank‐order of sorption coefficients of the pesticides. Total mass of pesticides, nutrients, sediment, and water removed by subsurface drains on a per‐area basis was greatest for the 5 m spacing and least for the 20‐m spacing. Annual nitrate‐N losses to subsurface drainflow ranged from 18 to 70 kg ha−1 and averaged 41.7 kg ha−1. Annual average ammonium‐N, soluble P, and K losses were 0.5, 0.04, and 2.6 kg ha−1, respectively.
Transport and Food Chain Modeling and Its Role in Assessing Human Exposure to Organic Chemicals
Authors: Jones K. C. , Keating T. , Diage P. , Chang A. C.
Published: July 2010

This paper reviews the underlying assumptions behind environmental transport and food chain modeling of organic chemicals, and highlights the uncertainties affecting model applicability to exposure assessment. Limitations in: (i) our knowledge of fundamental transport and transfer mechanisms, (ii) parameter quantification, and (iii) model validation currently restrict most assessment applications of models to screening calculations. Simple multimedia partitioning and screening models identify major pathways of exposure or principal environmental sinks. Their use, however, is currently limited by a lack of accurate physicochemical data for the test chemicals.

Exposure assessments for specific sources (e.g., landfill sites, incinerators, factory discharges) must evaluate the fluxes of emissions from the source to the receptor population via air, soil, surface and groundwaters, and the food chain. Current organic chemical transport models introduce many uncertainties to the exposure evaluation. This may be because the models are inherently unsatisfactory, inadequately describing the fundamental transport mechanisms likely operating in the field. Further limitations arise because some of the parameters are difficult to quantify accurately, because the environmental behavior of the test chemical is poorly understood, or because of temporal and spatial variabilities in field conditions. Until these processes are more fully understood, the usefulness of detailed simulation models for human exposure evaluations will be limited. Some media‐specific models, notably of air and surface water transport, are mechanistically sound and considerably more sophisticated than the available input data. Emphasis should therefore be placed on field calibration and validation. Even a validated model, however, can not be routinely applied to other chemicals and/or at other locations.