bluuebunny/crossref_metadata_2025 huggingface dataset:
Establishment of Vegetation on By‐Product Gypsum Materials
Authors: Shahandeh H. , Sumner M.E.
Published: July 2010

The production of by‐product gypsum materials is likely to increase greatly in the future and will require storage in large stacks. Therefore, technology to cover these materials with vegetation will be required. The nutrient requirements for successful plant growth were investigated on three materials [phosphogypsum (PG) from Florida, and two flue gas desulfurization gypsums (FGDG) from Florida and Illinois] using weeping lovegrass (Eragrostic curvula) and lespedeza (Sericia lespedeza) as indicator plants. In the first greenhouse experiment, the requirements for all the essential nutrients were studied in a subtractive design using PG. Significant growth reductions were obtained with the singular elimination of all nutrients except B. Growth on the two FGDG materials was poor due to the presence of high levels of soluble salts. These materials were leached before being studied in the second experiment in which only N, P, and K were varied at constant basal rates of the other essential elements. The 100N‐50P‐150K (mg kg−1) treatment proved to be the best for total plant growth on all three gypsum materials. The results indicate that providing the proper nutrient balance is important in obtaining good growth on by‐product gypsum materials.
Unstable Wetting Fronts in Water‐Repellent Field Soils
Authors: Hendrickx J. M. H. , Dekker L. W. , Boersma O. H.
Published: July 2010

Study objectives are to (i) investigate the effects of a water‐repellent top layer on water flow and solute transport and (ii) examine whether unstable wetting front theories can be used to predict the occurrence of preferential flow in water‐repellent field soils. The study took place on two adjacent plots with grasscover near Ouddorp (The Netherlands)—one plot with a water‐repellent top layer, the other plot with a wettable top layer. The soil at the experimental site is a sand soil of marine origin—mesic Typic Psammaquent. We conducted three different tests to obtain experimental evidence for our hypothesis that flow through a water‐repellent soil would be unstable. An I− coloring technique showed an unstable wetting front with preferential flow paths in the water‐repellent soil; flow through the wettable soil resulted in a homogeneous, stable wetting front. The variability of the soil water contents in the water‐repellent soil was larger than in the wettable soil, indicating that flow through the water‐repellent soil was less stable. A Br− tracer experiment, under conditions of natural precipitation, revealed that solutes in the water‐repellent soil travelled faster to the groundwater than in the wettable soil. After 5 wk with 120 mm precipitation, the Br− amounts in the groundwater under the water‐repellent top layer were 6 to 13 times higher than those under the wettable top layer. These experimental results demonstrate that unstable wetting front theories can be used to predict the occurrence of preferential flow in water‐repellent field soils.
Logistic and Economic Principles in Gas Chromatography—Mass Spectrometry Use for Plant Uptake Investigations
Authors: Eiceman G.A. , Urquhart N.S. , O'Connor G.A.
Published: July 2010

The time and costs for gas chromatography‐mass spectrometry (GCMS) analysis of plant matter and sludge‐amended soil for organic compound residues have been organized using criteria for individual stages of analysis. The majority of time needed for analysis was found in sample pretreatment, regardless of operating conditions for the GC‐MS. Major costs for analysis resided in routine maintenance, depreciation of GC‐MS instrumentation, and labor costs. Whereas total variance is dependent upon concentration of the pollutant, precision is governed mainly by the number of field samples measured. Anticipated precision of more than 1 mg kg−1 can be achieved at an initial concentration of 15 mg kg−1 only after analysis of more than 60 field samples. Total analysis times and costs for a representative plant uptake study suggests GC‐MS can be an expensive and labor‐intensive approach to residue analysis. Findings offered in this analysis may be useful in the design of future experiments and in tempering expectations of advanced analytical instrumentation, in view of variance associated with sludge‐amended soil.
Volatilization of Fonofos, Chlorpyrifos, and Atrazine from Conventional and No‐Till Surface Soils in the Field
Authors: Whang J. M. , Schomburg C. J. , Glotfelty D. E. , Taylor A. W.
Published: July 2010

We measured the effect of no‐till on pesticide volatilization in a side‐by‐side comparison of volatilization rates from no‐till (NT) and conventionally tilled (CT) fields. Volatilization rates were determined using the theoretical profile shape method for 10 of the 26 d following application. Soil and mulch residues were also measured. Volatilization losses of fonofos (O‐ethyl S‐phenyl ethylphosphonodithioate) and chlorpyrifos [O,O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridyl) phosphorothioate] from the NT field were two to four times volatilization losses from the CT field. As much as one‐half of the application volatilized during 26 d. Volatilization of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐ 1,3,5‐triazine‐2,4‐diamine] was also greater from NT, but only 1 to 2% of the application volatilized. Maximum volatilization rates were usually measured at midday, indicating that volatilization was not limited by soil dryness. Over the 26 d of the experiment, volatilization decreased faster than pesticide residue was depleted, suggesting residues were becoming more strongly sorbed to soil and/or mulch, or were becoming less accessible to the surface.
Sorption and Movement of Alachlor in Soil Modified by Carbon‐Rich Wastes
Authors: Guo Lei , Bicki Thomas J. , Felsot Allan S. , Hinesly Thomas D.
Published: July 2010

Laboratory studies were conducted to determine the effects of waste‐activated carbon (WAC), digested municipal sewage sludge (DMS), and animal manure (AM) on the sorption and leaching of alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl)acetanilide] in a Plainfield sandy soil (Typic Udipsamment). A total of 7500 mL of simulated rain water was applied to soil columns under three flow regimes with or without the waste amendments. The WAC most effectively reduced the mobility of alachlor, DMS was superior to AM. Amounts of alachlor recovered in the leachates, which ranged from <0.1% (2.1 t C ha−1 of WAC amended soil) to 74% (unamended soil) of that applied, depended upon the C loading rate of the wastes and upon the source of C‐containing species. The dissipation of alachlor from soil was greater when soil was amended with DMS and AM than when amended with WAC. Sorption of alachlor, which was determined by batch equilibration, was generally inversely related to its leaching in the amended soil, this observation suggested that sorption by soil organic matter controlled the mobility of alachlor. Application of C‐rich wastes to sandy coarse‐textured soils may be useful for reducing pesticide leaching to groundwater.
Reclamation of Heavy Metal—Contaminated Soils: Field Studies and Germination Experiments
Authors: Geiger Gabriella , Federer P. , Sticher H.
Published: July 2010

Field studies and germination experiments have been performed to assess the fertility restoration by different reclamation procedures on heavy metal‐polluted soils. In a contaminated area in Switzerland we have investigated the metal accumulation of lettuce (Lactuca sativa L., ‘Apollo’) on four different experimental plots: F1 was untouched, F2 was plowed, on F3 the highly contaminated litter was removed, and on F4 the surface layer was removed and replaced with uncontaminated soil. The metal content in plant tissue decreased from F1 over F2 and F3 to F4. The lettuce grown on F4 had normal metal tissue concentrations (Cd, 0.92 mg/kg; Cu, 28 mg/kg; Zn, 87 mg/kg) whereas tissue concentrations on the untilled plot F1 were strongly elevated (Cd, 6.1 mg/kg; Cu, 57 mg/kg; Zn, 864 mg/kg). Growth chamber experiments served to test the suitability of different soil substrata for plant development. We have studied the germination and growth of cress (Lepidium sativum L.) and lettuce on different heavy metal‐polluted media and observed that the structure of the litter is the main reason for poor development of the seedlings. We conclude that from the reclamation procedures considered, only the replacement of the highly contaminated topsoil will lead to good germination, normal plant development, and heavy metal contents essentially below all toxicity limits.
Bioavailability of Zinc, Cadmium, and Lead in a Metal‐Contaminated Alluvial Soil
Authors: Pierzynski Gary M. , Schwab A. Paul
Published: July 2010

Metal mining activities can cause a variety of soil contamination problems including the deposition of sediments having high concentrations of heavy metals on alluvial soils. This study was conducted to investigate the effects of various soil amendments or combinations of amendments on Zn, Cd, and Pb bioavailability in a metal‐contaminated alluvial soil as indicated by a chemical fractionation procedure and soybean [Glycine max (L.) Merr.] growth and heavy metal composition. Total soil concentrations were 1165 mg/kg for Zn, 11 mg/kg for Cd, and 110 mg/kg for Pb, and evidence suggested that Zn phytoxicity was limiting soybean growth. In one greenhouse experiment, the addition of limestone, N‐Viro soil, and K2HPO4 significantly increased soybean yields; and the addition of limestone, limestone suspension, cattle manure, poultry litter, N‐Viro, and K2HPO4 significantly decreased soybean tissue Zn concentrations as compared to the control. The limestone, limestone suspension, cattle manure, N‐Viro, and K2HPO4 amendments also significantly reduced KNO3‐extractable Zn as compared to the control. In a second greenhouse experiment, the combination of limestone at 1.12 or 2.24 Mg/ha and 10 Mg/ha of cattle manure produced significantly higher soybean yields as compared to either amendment alone for the first cutting. For the same cutting, a significant limestone by manure rate interaction was found for concentrations of Zn, Cd, and Pb in soybean tissue and for Zn, Cd, and Pb uptake. Generally, the effects of increasing limestone rate were diminished as the manure rate increased. Root dry weights significantly increased and root tissue Zn concentrations significantly decreased with both rates of limestone application compared to 0 Mg limestone/ha for samples taken at the completion of experiment two. Root tissue Cd or Pb concentrations were not significantly influenced by limestone or manure rates. Significant increases in NaOH‐extractable Zn and Pb were found with increasing limestone rates whereas NaOH‐extractable Cd significantly decreased. Correlations between soybean tissue Zn concentrations and various Zn fractions and diethylenetriaminepentaacetic acid (DTPA)‐extractable Zn indicated significant relationships for KNO3‐Zn (r = 0.92), NaOH−Zn (r = 0.62), KNO3 + H2O−Zn (r = 0.82), KNO3 + NaOH−Zn (r = 0.88), KNO3 + H2O + NaOH−Zn (r = 0.54), and DTPA extractable Zn (r = 0.70).
Physiographic and Land Use Characteristics Associated with Nitrate‐Nitrogen in Montana Groundwater
Authors: Bauder J. W. , Sinclair K. N. , Lund R. E.
Published: July 2010

Occurrence of NO−3‐N in drinking water at concentrations > 10 mg L−1 is being reported in the literature with increasing frequency. Some occurrences of high NO−3‐N concentrations have been attributed to irrigation and fertilization practices. A private well water testing program in Montana, involving nearly 3400 well owners, found NO−3‐N concentrations > 10 mg L−1 in nearly 6% of all tested wells. Most of the agricultural land in Montana is nonirrigated and is not subject to high rates of N fertilization. Dryland crop/fallow cereal grain rotations are the main practices. Well water test results were combined with MAPS, a geographic information system (GIS), to identify correlations between county average NO−3‐N concentration in groundwater, well water sample probability of exceeding 10 mg L−1 NO−3‐N, geographic, climatic, and geologic conditions, and land‐use practices. From a list of 67 independent variables, county average well water NO−3‐N concentration and percentage of tested wells in each county with NO−3‐N concentration >10 mg L−1 were correlated (P < 0.10) with 16 independent variables, most of which were associated with precipitation, soil properties, and land‐use practices. The closest correlations were with March 1 through June 30 precipitation, distribution of dryland crop production and summer fallow, soil water‐holding capacity, and mapping units of the general soil map of Montana. Two‐, three‐, and four‐variable, linear, multiple regression models indicated that 53 to 61% of the variability in county average well sample NO−3‐N concentration could be accounted for by these independent variables. Results of these analyses support the hypothesis that summer fallow practices and associated mineralization of organic matter may be contributing to regionalized NO−3‐N contamination of shallow groundwater in Montana.
Degradation of the Pesticides Mecoprop and Atrazine in Unpolluted Sandy Aquifers
Authors: Klint Mikala , Arvin Erik , Jensen Bjørn K.
Published: July 2010

The potential for biodegradation of the pesticides mecoprop [(+/−)‐2‐(4‐chloro‐2‐methyl‐phenoxy)propionic acid] and atrazine [2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine] in an aerobic aquifer was investigated in laboratory batch experiments. The experiments were performed with groundwater and suspensions of groundwater and aquifer sediment collected from a pristine sandy aquifer. Following a lag period of 35 to 40 d, mecoprop in a concentration of 100 µg/L was degraded in 30 d in groundwater at 10°C. New additions of 100 to 140 µg mecoprop/L were degraded within a week. In suspensions of groundwater and aquifer sediment, mecoprop in the concentration range 75 to 300 µg/L was degraded in 15 d, following a lag period of less than 7 d. Experiments performed with sediments taken from different depths indicate that there was a considerable variation in the degradation potential within the aquifer. Atrazine was not degraded during an incubation period of 539 d in groundwater and 174 d in suspensions of groundwater and aquifer sediment. The addition of nutrients, primary substrates (acetate and naphthalene), and a pH or temperature increase had not effect on the recalcitrance of atrazine.
Groundwater Nitrate Dynamics in Grass and Poplar Vegetated Riparian Buffer Strips during the Winter
Authors: Haycock N.E. , Pinay G.
Published: July 2010

Nitate retention in riparian buffer strips is well documented in summer periods, but the potential of winter retention within these zones is poorly documented. Two sites, grass (Lolium perenne L.), and poplar (Populus italica)‐vegetated riparian strips, were investigated in southern England (River Leach). Groundwater flow was via subsurface pathways within the sites, NO−3 concentration gradients and loading rates were calculated over the winter period. Nitrate retention was found to be linearly dependent on load rate. Nitrate retention occurred at the edge of the riparian zone. This was most obvious in the poplar site where all hillslope‐derived NO−3 was absorbed within the first 5 m of flow within the riparian strip. When loading rates into the sites increased, NO−3 absorption migrated upslope from the riparian site. The poplar‐vegetated riparian zone was found to be more resilient (99% retention of NO−3) than the grass‐vegetated riparian zone (84% retention of NO−3) in the winter months. It is postulated that although vegetation has no active role in retaining NO−3 in the winter, above‐ground vegetative biomass does contribute C to the soil microbacterial biomass that is engaged in NO−3 reduction in the winter months, this accounted for the greater efficiency of the poplar vegetated site.
Cadmium, Lead, Zinc, Copper, and Nickel in Agricultural Soils of the United States of America
Authors: Holmgren G.G.S. , Meyer M.W. , Chaney R.L. , Daniels R.B.
Published: July 2010

Three thousand forty‐five surface soil samples from 307 different soil series were analyzed for Pb, Cd, Zn, Cu, Ni, cation exchange capacity (CEC), organic C, and pH in the course of a study of trace element uptake by major agricultural crops. The soil data from this study are summarized here statistically and in map form to show their interactions and generalized geographic distribution patterns. Amounts of all five metal elements are generally low in the Southeast. A regional high of about 15 mg/kg Pb covers the Mississipi, Ohio, and Missouri River valleys. Higher values for other elements are generally concentrated in the West and in the lower Mississippi River Valley. Maximum Cd levels were found in soils of the coast ranges of central and southern California. Copper levels are noticeably higher in organic soil areas of Florida, Oregon, and the Great Lakes. Nickel and Cu concentrations are high in serpentine soil areas of California. Nickel levels are also somewhat higher in the glaciated areas of the northern great plains and in northern Maine. For the entire dataset, the values of the minimum‐maximum, 5th, 50th, and 95th percentiles are as follows: (mg/kg dry soil) Cd, <0.005 to 2.0, 0.036, 0.20, 0.78; Pb, 0.5 to 135, 4.0, 11, 23; Zn, 1.5 to 264, 8.0, 53, 126; Cu, 0.3 to 495, 3.8, 18.5, 95; Ni, 0.7 to 269, 4.1, 18.2, 57; pH (pH units) 3.9–8.9, 4.7, 6.1, 8.1; CEC (cmol/kg) 0.6 to 204, 2.4, 14.0, 135; and organic C % 0.09 to 63, 0.36, 1.05, 33.3. Metal levels generally increased with increasing clay concentration.
Oxidation and Acidification of Anaerobic Sediment‐Water Systems by Autoclaving
Authors: Tratnyek Paul G. , Wolfe N. Lee
Published: July 2010

The effect of autoclaving on the acid/base and redox properties of anaerobic sediment slurries was determined to facilitate the interpretation of autoclaved controls in studies of environmental reduction reactions. Autoclaving decreased electrode measurements of pH by 0.26 to 0.68 units and increased electrode measurements of Eh by 34 to 94 mV. To corroborate this effect, we added redox indicators to the slurries and observed that autoclaving caused a shift in color consistent with the change in electrode measurements. Further investigation demonstrated that the observed effects are a common characteristic of autoclaving anaerobic sediment and are not limited to very restricted sediment types and are not artifacts of the way the experiments were performed.
Biological Effects of Agriculturally Derived Surface Water Pollutants on Aquatic Systems—A Review
Authors: Cooper C. M.
Published: July 2010

Environmental manipulations and other human activities are major causes of stress on natural ecosystems. Of the many sources of surface water pollutants, agricultural activities have been identified as major contributors to environmental stress, which affects all ecosystem components. In water, agricultural contaminants are most noticeable when they produce immediate, dramatic toxic effects on aquatic life although more subtle, sublethal chronic effects may be just as damaging over long periods. Aquatic systems have the ability to recover from contaminant damage if not seriously overloaded with irreversible pollutants. Thus, contaminant loading level is as important as type of pollutant. Although suspended sediment represents the largest volume of aquatic contaminant, pesticides, nutrients, and organic enrichment are also major stressors of aquatic life. Stream corridor habitat traps and processes contaminants. Loss of buffering habitat, including riparian zones, accelerates effects of pollutants and should be considered when assessing damage to aquatic life. Protection of habitat is the single most effective means of conserving biological diversity. Current available management practices and promising new technology are providing solutions to many contaminant‐related problems in aquatic systems.
Spatial Variability of Microbial Processes in Soil—A Review
Authors: Parkin T. B.
Published: July 2010

Microbial transformations of fertilizers and pesticides in the surface soil have a direct impact on the mass of the agrochemical that is susceptible to leaching losses. Thus, our greatest potential for controlling leaching losses of agrochemicals is through the management of these compounds in the surface soil. A variety of strategies have been employed to maximize the residence time of applied chemical in the surface soil, including: timing of application, formulation (e.g., slow‐release fertilizers and encapsulated pesticides), and the use of compounds that modify microbial activity in soil (e.g., nitrification inhibitors). Although these strategies have met with some success, more precise quantification of the microbial transformations of agrochemicals is required to aid the development of improved management strategies. The high spatial variability exhibited by many microbial processes, in many cases, precludes precise quantification. A greater understanding of the factors contributing to the variability of microbial processes allows for improved estimation, as well as for the assessment of key driving variables controlling microbial processes in soil. This article reviews several aspects of spatial variability associated with microbial populations and processes. The discussion focuses on the scale at which variability is expressed, and the soil and environmental variables that serve to control variability at each scale. Implications for the development of new management strategies are also discussed, and finally, some statistical considerations for characterizing variability are presented.
Agricultural Chemical Discharge in Surface Water Runoff
Authors: Smith S. J. , Sharpley A. N. , Ahuja L. R.
Published: July 2010

The discharge of agricultural chemicals (i.e., soil‐fertilizer nutrients and pesticides) in runoff waters is important from both agronomic and environmental standpoints. Presented here is an overview of our current concepts and approaches employed for describing this discharge, based on studies we have conducted over the past decade. Most of our field testing and validation of concepts regarding chemical discharge has focused on approximately 24 grassland and cropland watersheds across the Southern Plains. Chemicals considered include N, P, K, S, atrazine [2‐chloro‐4(ethylamino)‐6‐(isopropylamino)‐s‐triazine], alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl) acetanilide], and cyanazine [2‐[[4‐chloro‐6‐(ethylamino)‐s‐triazine‐2‐yl]amino]‐2‐methylpropionitrile]. Soluble chemical discharge has been described by kinetic desorption and uniform or nonuniform mixing approaches, incorporating parameters reflecting watershed management and the nature of the surface soil × precipitation interaction. Particulate chemical discharge has been described by the relationship between the discharge enrichment ratio (chemical content of eroded sediment/source soil) and soil loss. Special situations considered include type of tillage, computed water and sediment runoff, severe storms, bioavailability of P, cover crops, and manure applications. For the most part, predicted chemical discharge values compared favorably with their measured counterparts, r2 values often being >0.9. Further research needs include refinement and development of the prediction equations, data bases, runoff indices, and multidisciplinary systems.
A Pragmatic Field‐Scale Approach for Modeling Pesticides
Authors: Hutson J. L. , Wagenet R. J.
Published: July 2010

Environmental assessments of the fate of pesticides and other agricultural chemicals usually require estimation of chemical concentrations, with some indication of their accuracy. These estimations are usually based on a few measurements combined with existing data bases and predictive tools that include regression equations, empirical relationships, and simulation models. Comprehensive simulation models are attractive from a scientific standpoint, since they consider leaching of the chemical by water as well as the various chemical, biological, and physical processes that affect the chemical's fate during its transport. A number of simulation modeling approaches have been developed to describe soil‐water‐chemical systems, but a fundamental question remains regarding the degree of model complexity required to simulate agrochemical movement to groundwater. Most model complexity in soil‐water‐chemical simulation models arises from the manner in which water flow and chemical transport are considered. It is therefore logical, especially for management purposes, to consider alternative, pragmatic, and yet sufficiently accurate approaches to the description of water flow and chemical transport. Such approaches would require less characterization of soil hydraulic and physical/chemical properties and would reduce computation time. A method for such simplification and use is described, starting with LEACHP, a model based on the Richards and convection‐dispersion equations. The resulting model is shown to be sufficiently accurate for many management decisions.
Environmental Research Careers in Industry
Authors: Lehmann Robert G.
Published: July 2010

The educational needs for environmental scientists in industry are discussed. Questions about honesty in industry, publishing opportunities, job security, and the pace of work are answered. The article is intended for students curious about research careers in industry.
A Field Study to Evaluate Leaching of Aldicarb, Metolachlor, and Bromide in a Sandy Loam Soil
Authors: Smith Charles N. , Parrish Rudolph S.
Published: July 2010

Transport and transformation of pesticides used in agricultural situations are subject to variability from several sources that are impossible to simulate in laboratory settings. This study was conducted to characterize pesticide leaching behavior under conventional cropping conditions and to determine the impacts of related sources of variability. An agricultural field site (Ardilla fine sandy loam, Clarendon loamy sand, Tifton loamy sand, and Lucy loamy sand) located within the Dougherty Plain region of southwest Georgia was used to study pesticide movement in unsaturated and saturated soil zones from 1984 through 1988. A granular formulation of aldicarb [2‐methyl‐2‐(methylthio) propionaldehyde O‐(methylcarbamoyl) oxime], an emulsifiable concentrate of metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide], and a bromide (Br−) tracer were applied on peanut (Arachis hypogea L.) crops under modified conventional tillage practices. Postapplication vertical movement was monitored for periods of up to 111 d for pesticides and 1307 d for Br−. Application distributions for aldicarb showed measured coefficients of variation ranging from 42 to 72, and for metolachlor from 23 to 44. Spatial variability analyses indicated the existence of small‐scale correlation for both pesticides upon initial application, and some large‐scale trending was observed for metolachlor. Field‐based transformation rates of aldicarb were up to three times higher than laboratory‐based values. There was no evidence of migration of any of the pesticides into the saturated zone during the study, although Br− was observed at less than 1 mg kg−1 in well‐water samples. Aldicarb degraded almost completely within 90 d each year, and it was not observed below 1.2 m. Metolachlor profiles always showed concentrations decreasing with increasing depth, and there was no significant movement below 0.3 m. Bromide was observed in soil samples as deep as 3 m only on the 1307th d, and the profiles showed peak concentrations no lower than 1.5 m with relative vertical dispersion increasing continuously.
Relationship between Soluble and Extractable Phosphorus in Some Calcareous Soils of Iran
Authors: Sichani Seifollah Amin , Parsa Shahrokh Zand , Nelson D.W.
Published: July 2010

The relationship between water‐extractable P (soluble P) and NaHCO3‐extractable P was determined in different water/soil ratios. The values of 0, 45, 90, and 180 mg kg−1 soil as KH2PO4 were added to seven calcareous soil series from southern Iran (for two soil series additional P rates of 360, 720, and 1080 mg P kg−1 soil as KH2PO4 also was employed). Soluble P in water/soil ratios of 10:1, 25:1, 100:1, and 500:1 was measured by Murphy and Riley method (1962) after 2 h shaking. Sodium bicarbonate—extractable P also was determined in all soils. The results indicate that there was a linear relationship between the logarithm of soluble and NaHCO3‐extractable P when NaHCO3‐extractable P was less than 150 mg P kg−1 soil. There also was a linear relationship between soluble P and the water/soil ratio up to 100:1 for these soils. The amount of P released per unit soil weight at water/soil ratios greater than 100:1 was approximately constant.
Atrazine and Alachlor Losses from Subsurface Tile Drainage of a Clay Loam Soil
Authors: Buhler D. D. , Randall G. W. , Koskinen W. C. , Wyse D. L.
Published: July 2010

Herbicide losses in subsurface drainage from agricultural land is not well understood. Research was conducted to assess atrazine [6‐chloro‐N′‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl) acetamide] losses in subsurface tile drainage during and after long‐term use on a Webster clay loam soil (Typic Haplaquoll) at Waseca, MN, under typical agricultural management conditions. Individual subsurface drainage systems were installed in 1975 to plots cropped continuously to corn (Zea mays L.) under moldboard plow and no‐tillage systems. Annual alachlor and atrazine use was initiated in 1974 and 1975, respectively. Alachlor use was continued through 1991 while atrazine use was terminated after the 1988 application. Tile drainage water was collected and analyzed for atrazine and alachlor beginning in October 1985. Alachlor was detected in only 2% of the samples from 1985 through 1991. Atrazine was detected in 97% of the samples from 1985 through 1990. Atrazine detection frequency declined to 78% in 1991. Atrazine concentration in October 1985 was 0.56 µg L−1. Average atrazine concentration in tile drainage water in 1986 was 1.0 µg L−1 and estimated loss by leaching was 4.1 g ha−1. Average atrazine concentrations in 1987 and 1988 were 1.24 and 0.84 µg L−1, respectively, but due to limited tile flow, atrazine losses were less than 1 g ha−1 each year. Twelve to 18 mo after the last atrazine application, average atrazine concentration in tile water did not decline. However, from 24 to 30 mo after the final atrazine application, average concentration dropped to 0.42 µg L−1 and during the following growing season average concentration declined to 0.29 µg L−1. There was little fluctuation in atrazine concentration during any year. Tillage systems had minimal impacts on atrazine concentration or loss in tile drainage water. This research indicates that low concentrations of atrazine may contaminate tile drainage water during and after long‐term use and may persist for several years after use is stopped. Contamination of drainage from similar use of alachlor appears minimal.
Hydrologic and Land‐Use Factors Associated with Herbicides and Nitrate in Near‐Surface Aquifers
Authors: Burkart Michael R. , Kolpin Dana W.
Published: July 2010

Selected herbicides, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) metabolites, and NO−3 were examined in near‐surface unconsolidated and bedrock aquifers in the midcontinental USA to study the hydrogeologic, spatial, and seasonal distribution of these contaminants. Groundwater samples were collected from 303 wells during the spring and late summer of 1991. At least one herbicide or atrazine metabolite was detected in 24% of the samples collected for herbicide analysis (reporting limit 0.05 µg/L). No herbicide concentration exceeded the USEPA's maximum contaminant level (MCL) or health advisory level. The most frequently detected compound was the at razine metabolite deethylatrazine [2‐amino‐4‐chloro‐6‐(isopropylamino)‐s‐triazine] followed by atrazine, deisopropylatrazine [2‐amino‐4‐chloro‐6‐(ethylamino)‐s‐triazine], prometon (2,4‐bis(isopropylamino)‐6‐methyoxy‐s‐triazine), metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1methylethyl)acetamide], alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide], metribuzin [4‐amino‐6‐(tert‐butyl)‐3‐methylthio‐as‐triazine‐5(4H)‐one], simazine [2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine], and cyanazine [2‐[[4‐chloro‐6‐(ethylamino)‐1,3,5‐triazin‐2‐yl]amino]‐2‐methylpropionitrile]. Nitrite plus nitrate, as nitrogen (N), exceeding 3.0 mg/L (excess NO−3), was found in 29% of the samples, and 6% had −3 exceeding the MCL of 10 mg/L. Ammonium as N was detected in excess of 0.01 mg/L in 78% of the samples. A nonlinear increase in the frequency of atrazine detection occurred with decreases in reporting limit. The frequency of atrazine residue detection (atrazine + deethylatrazine + deisopropylatrazine) was 25% greater than for atrazine alone. Herbicide detections and excess NO−3 were notably lacking in the eastern part of the study region where it was estimated that herbicide and fertilizer use were among the largest in the region. Prometon, the second most frequently detected herbicide, was associated with non‐agricultural land use. Herbicide and excess NO−3 were more frequent in unconsolidated aquifers than in bedrock aquifers. Aquifer depth, as direct measurement of proximity to recharge sources, was inversely related to frequency of herbicide detection and excess NO−3.
Soil Loss as Affected by Different Combinations of Surface Litter and Rock
Authors: Benkobi Lakhdar , Trlica M. J. , Smith James L.
Published: July 2010

The effects of various surface cover types, their combinations, and bare ground on soil loss from a clay loam topsoil were studied on small plots in the laboratory using a rotating boom rainfall simulator. A total of 105 plots with various types and amounts of surface cover were exposed to simulated rainfall at 100 mm/h for 30 min. Cover treatments included herbaceous litter of sedges (Carex spp.) and bluegrass (Poa spp.), shrub litter of willows (Salix spp.), small rocks, and mixtures of these cover types at several levels of cover (0, 25, 50, 75, 100%) and bare ground (control). Experimental data for high intensity storm were used to develop an equation to quantify soil loss and surface cover relationships for a clay loam soil. Regression analysis indicated high correlation (R2 = 0.86) between soil loss and types and amounts of surface cover. Soil loss from bare plots was about 13 000 kg/ha. A surface cover proportion of about 0.60 for vegetation litter, and 0.85 for rock, would reduce soil loss to about 5000 kg/ha. Rocks were not as effective as vegetation litter in our experiment in protecting the soil from erosion. However, surface coverage of 100% with combinations of vegetation litter and rocks offered the best protection of the soil against erosion. This combination was better than either 100% vegetation litter cover or 100% rock cover alone. Rock in combination with vegetation litter may have increased roughness and allowed deposition of sediment.
Reducing Soil Erosion and Agricultural Chemical Losses with Conservation Tillage
Authors: Seta A. K. , Blevins R. L. , Frye W. W. , Barfield B. J.
Published: July 2010

As nonpoint source pollution of water becomes more evident, more concern is being focused on the effects of agricultural practices on water quality. This study evaluated the effects of conventional tillage (CT), chisel‐plow tillage (CP), and no tillage (NT) on the quality of runoff water from a Maury silt loam soil (fine, mixed, mesic Typic Paleudalf) near Lexington, KY. The mean runoff rate, total runoff volume, mean sediment concentration, and total soil losses were significantly less for NT than for CP and CT. Concentration of NO−3, NH+3, and PO3−4 in the runoff water from NT were greater than from CP or CT. Concentration of atrazine [6‐chloro‐N‐ethyl‐N′‐(I‐methylethyl)‐1,3, 5‐triazine‐2,4‐diamine] in the runoff water tended to be higher from CP than from NT or CT. Total losses of NO−3, NH+4, PO3−4, and atrazine in runoff water were generally in the order CT > CP > NT. The sum of all chemicals lost was less than 3% of the total amount of each applied.
Thermodynamic Modeling of Zinc, Cadmium, and Copper Solubilities in a Manured, Acidic Loamy‐Sand Topsoil
Authors: Hesterberg Dean , Bril Jan , del Castilho P.
Published: July 2010

Soil solution samples collected during a 14‐mo period from manured, loamy‐sand soil profiles in the Netherlands showed variations in dissolved Zn, Cd, and Cu concentrations of up to two orders of magnitude. To try to account for variations in the dissolved metals, a thermodynamic model was developed for the chemical‐equilibrium computer program CHARON. In addition to solution complexation and solid‐phase precipitation of inorganic components, the model accounted for metal complexation with dissolved organic carbon (DOC) ligands and with a solid organic matter (OM) exchanger phase. Both dissolved and solid organic materials were assumed to behave like fulvic acid having a complexing capacity for Zn2+, Cd2+, Cu2+, Ca2+, Mg2+, and Al3+ of 2 tool kg−1 of C. To obtain a single (pH‐dependent) stability constant for each metal‐organic ligand complex, stoichiometries of 1:1:n metal/organic‐ligand/OH− complexes were determined from published linear relationships between pH and average equilibrium quotients normalized for complexing capacity of a polyfunctional complexer. Exchange in the exchanger phase included monovalent cations and anions to maintain phase electroneutrality. Model predictions of dissolved Zn, Cd, and Cu were calculated from relevant soil properties and macrochemical concentrations in each of 44 soil‐solution samples collected from three manured field plots. Model‐predicted Zn and Cd concentrations deviated from measured concentrations on the average 1.4‐ and 2‐fold for measured concentration ranges of 120‐ and 34‐fold (respectively). Copper was typically underpredicted by the model. Model‐predicted speciation between the two principal dissolved metal species, free‐ionic and DOC ligand‐complexed, varied depending on soil solution macrochemistry. Soil solution chemical conditions ranged from pH 4.5 to 6.7, 30 to 260 g DOC m−3, and electrical conductivities (EC) of 15 to 510 mS m−1.
Resin Adsorption for Describing Bromide Transport in Soil under Continuous or Intermittent Unsaturated Water Flow
Authors: Li Z. M. , Skogley E. O. , Ferguson A. H.
Published: July 2010

Accurate information on movement of soil‐applied chemicals toward water tables is necessary for improving agricultural and environmental management. Current methods for studying related processes have major limitations. Objectives of this research were to investigate resin capsule adsorption for measuring Br− transport, to compare results with those from vacuum extraction, and to determine the utility of resin capsule technology for field studies. Laboratory experiments were conducted with a uniformly packed soil column under continuous or intermittent, unsaturated water flow using Br− as a tracer. Field experiments were also conducted with intermittent water flow applied by a line‐source irrigation system. Bromide accumulated by mixedbed ion‐exchange resin capsules inserted into the soil at several depths in the soil column was compared with Br− in solutions collected at the same depths by vacuum extraction through porous ceramic candles. Delayed timing of peak Br− leaching patterns (BLPs) at the uppermost sampling point, and earlier peak BLPs at the lowest sampling depth, when resin capsule data were used, suggest that the accuracy of measuring Br− transport is method‐dependent. Under intermittent water flow, distinct spikes of BLPs measured by resin capsules corresponded to soil water potential changes. Only broad plateaus for BLPs were measured with vacuum extraction, implying greater sensitivity of the resin capsule methodology to soil moisture changes. Field results demonstrated the utility of resin capsules for detecting Br− transport as influenced by irrigation intensity, plant water use, and plant Br− uptake. The resin capsule methodology may provide a simple, accurate alternative to vacuum extraction or repetitive soil sampling for studying solute transport. It provides “in situ solid‐phase extraction” of the target solute simultaneously with other ions in soil solution.
Soil Cadmium Mobility as a Consequence of Sewage Sludge Disposal
Authors: Lamy I. , Bourgeois S. , Bermond A.
Published: July 2010

Anaerobically digested liquid sewage sludge was applied as a single treatment to a loamy hydromorphic drained soil, characteristic of agricultural soils in the North of France, at a rate of 11 Mg of dry solids ha−1. Total Cd concentrations of drainage waters for both amended and unamended plots were monitored at selected times to follow the mobility of Cd after sludge disposal. The drained groundwater of the plot that exhibited the highest discharge of sludge soluble organic matter (SSOM) exhibited about twice the Cd levels of the control plot during the first few weeks following sludge disposal (average of 3 and 1.5 µg L−1, respectively). Laboratory experiments were conducted to provide estimates of the relative binding strength of Cd‐soil interactions as well as Cd‐SSOM interactions. The behavior of Cd in a mixed sludge‐soil system showed that the addition of sludge soluble organic matter to the soil led to a decrease in the sorption of this cation across the pH range between 5 and 7. The laboratory studies highlighted the role of soluble organic matter in soil Cd speciation, and can be used to speculate on the perturbations induced by high levels of sludge soluble organic matter introduced into a soil.
Technique for Measuring Air Flow and Carbon Dioxide Flux in Large, Open‐Top Chambers
Authors: Ham Jay M. , Owensby C. E. , Coyne P. I.
Published: July 2010

Open‐Top Chambers (OTCs) are commonly used to evaluate the effect of CO2, O3, and other trace gases on vegetation. A study was conducted to develop and test a new technique for measuring forced air flow and net CO2 flux from OTCs. Experiments were performed with a 4.5‐m diam. OTC that had a sealed floor and a specialized air delivery system. Air flow through the chamber was computed with the Bernoulli equation using measurements of the pressure differential between the air delivery ducts and the chamber interior. An independent measurement of air flow was made simultaneously to calibrate and verify the accuracy of the Bernoulli relationship. The CO2 flux density was calculated as the product of chamber air flow and the difference in CO2 concentration between the air entering and exhausting from the OTC (Cin ‐ Cout). Accuracy of the system was evaluated by releasing CO2 within the OTC at known rates to emulate respiration from the field surface. Data were collected with OTCs at ambient and elevated CO2 (≈700 µmol mol−1). Results showed that the Bernoulli equation, with a flow coefficient of 0.7, accurately measured air flow in the OTC to within ±5% regardless of flow rate and air duct geometry. Experiments in ambient OTCs showed that CO2 flux density (µmol m−2 s−1), computed from 2‐min averages of air flow and Cin ‐ Cout, was typically within ±10% of actual flux, provided that the exit air velocity at the top of the OTC was greater than 0.6 m s−1. Obtaining the same level of accuracy in CO2‐enriched OTCs, however, required a critical exit velocity near 1.2 m s−1 to minimize the incursion of ambient air and prevent contamination of the exit gas sample. When flux data were integrated over time to estimate daily CO2 flux (µmol m−2 d−1), actual and measured values agreed to within ±2% for both ambient and CO2‐enriched chambers, suggesting that accurate measurements of daily net C exchange are possible with this technique.
Estimation of Nitrate Concentrations in Groundwater Using a Whole Farm Nitrogen Budget
Authors: Barry D. A. J. , Goorahoo D. , Goss M. J.
Published: July 2010

Contamination of groundwater under agricultural land by NO3 is influenced by the kind of farming system. One possible method of selecting farming systems that result in less NO3 leaching is to calculate whole farm N budgets, that are simplified by assuming soil‐N remains constant from one cycle of a rotation to the next. This method was applied to two model crop rotations using average crop yield data for two regions of Ontario, and to a cash‐crop farm and a dairy farm using information on purchases, sales, and crop yields, for these farms. The model rotations were corn (Zea mays L.)‐soybean [Glycine max (L.) Merr.]‐wheat (Triticum aestivum L.) and corn‐soybean‐wheat‐hay (mixture of timothy, Phleum pratense L. and alfalfa, Medicago sativa L.)‐hay‐hay. Atmospheric deposition (18.4 kg N ha−1 yr) was obtained by literature review. Symbiotic N2 fixation by legume crops with different yields was estimated from regression equations. A net surplus in the N balance was converted to maximum mean NO3‐N concentration in groundwater by assuming a groundwater recharge rate of 160 mm yr−1, and no denitrification. Predicted NO3‐N concentrations in leachate for the model corn‐soybean‐wheat rotation were greater for southwestern Ontario (22.4 mg L−1) than western Ontario (8.5 mg L−1), probably because more fertilizer was recommended in the southwest. Including hay in the model rotation increased the amount of N leached by a factor of two in western Ontario, but only by 9% in the southwest. Predicted NO3‐N concentration in groundwater for the cash crop farm was 6.7 mg L−1, compared with an average measured value of 9.5 mg L−1 in the tile drainage water. For the dairy farm the predicted value was 58 mg L−1 and a measured value was not available. The simplified N balance method provided useful estimates of potential NO3 leaching losses even though it relied on some major assumptions. A major uncertainty was atmospheric deposition of ammonia volatilized from on‐farm sources. Denitrification could be as much as 62 kg N ha−1 yr−1 under continuous production of grain corn, based on differences between N present after harvest and amount of N leached.
Theoretical Investigation of Multicomponent Volatile Organic Vapor Diffusion: Steady‐State Fluxes
Authors: Amali S. , Rolston D. E.
Published: July 2010

Liquid mixtures of volatile organic chemicals (VOC) contaminating many underground sites give rise to multicomponent mixtures of their vapors. Previous investigation has shown that in an isoharic, isothermal multicomponent vapor system, Fick's law estimates of the diffusive flux for each species should not be used when the effective binary diffusion coefficients used are sufficiently different. Our theoretical investigation of a multicomponent, semihypothetical “gasoline” mixture containing relatively volatile aromatic constituents plus CCl4 as an additional component shows that the multicomponent effect also can be observed when the binary diffusion coefficients are not substantially different, but when the total mole fraction of the diffusing species is sufficiently high. The importance of both diffusion coefficients and total mole fraction when modeling total diffusive fluxes requires that simulations be performed for any given vapor mixture. For our “gasoline” mixture, an approximate total mole fraction of 0.05 was found to lead to underestimation of single species fluxes by Fick's law of up to 5%. Simulations of steady‐state fluxes further indicate that O2 and N2 do not need to be treated differently and can be combined to form one species, “air.” Likewise various VOC species with almost identical diffusion coefficients can be grouped to form one representative class. Our investigation of diffusion in nonuniform, multinary mixtures of gases also included pressure diffusion. Pressure diffusion causes heavier (lighter) molecules to diffuse toward the higher (lower) pressure regions of a closed system. The contribution of pressure diffusion to the total diffusive flow under the natural gravitational pressure gradient was calculated to be significant only when the simulated soil column was more than 100 m long. It does not need to be included in multicomponent diffusion formulations involving shorter transport lengths.