bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonia Impacts on Atrazine Leaching through Undisturbed Soil Columns
Authors: Liu Zhuojing , Clay S. A. , Clay D. E. , Harper S. S.
Published: July 2010

Ammonia‐based fertilizers, such as anhydrous ammonia, aqua ammonia, and urea, initially increase soil pH, reducing atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) sorption and increasing atrazine desorption. Increased amounts of atrazine in soil solution may increase atrazine's leaching potential. This laboratory study investigated atrazine leaching behavior when ammonia and atrazine applications overlap. Nondisturbed 15‐cm diam. by 15‐cm depth soil columns were excavated from a Brandt silty clay loam (fine silty, Pachic Udic Haploboroll) and a Ves clay loam (fine silty, mixed mesic Typic Hapludalf). Concentrated NH4OH was applied to the soil surface at 0 or 220 kg N ha−1. Immediately after fertilizer application, 1.9 kg atrazine (spiked with ring‐labeled 14C‐atrazine) ha−1 was applied. One day after chemical application, soil columns were leached with 5.4 L of water. The ammonia application increased leachate and surface soil pH by about 2.5 and 3.5 pH units, respectively. The amount of 14C collected in leachate from ammonia‐treated columns was 60 and 30% greater for the Brandt and Ves soils, respectively, compared with untreated columns. Less 14C remained in the surface of the ammonia‐treated columns than in the surface of the untreated columns. These data indicate that the interaction between ammonia‐based fertilizers and atrazine must be considered when evaluating atrazine movement through soil. Applications of atrazine and ammonia‐based fertilizers that increase pH should be physically separated to limit the leaching potential of atrazine.
Chemical Movement in Relation to Tillage System and Simulated Rainfall Intensity
Authors: Myers J. L. , Wagger M. G. , Leidy R. B.
Published: July 2010

The Piedmont region in the southeastern USA is characterized by sloping, crust‐prone soils conducive to runoff losses of agricultural chemicals. Three tillage‐residue management systems were compared for their effect on concentrations of atrazine [2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine], metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide], and bromide in surface runoff and in the soil profile of a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludults). These systems included conventional tillage (CT), no‐tillage grain production with corn (Zea mays L.) residue (NTG), and no‐tillage silage production without residue (NTS). The first simulated rainfall event consisted of a low (1.27 cm h−1) or high (5.08 cm h−1) rainfall rate applied for 30 min following herbicide and bromide application. One week later, the high rate was simulated on all plots. The CT treatment generally produced less surface runoff, and accompanying lower chemical concentrations, compared with both no‐tillage treatments on the first date. Runoff differences due to tillage system were less on the second date because of surface sealing processes under CT. Averaged over 2 yr, the percentage of applied atrazine lost on the first runoff event was 6.2% for NTG, 4.4% for NTS, and 1.5% for CT. Losses of atrazine in runoff on the second date were 1.5, 1.4, and 1.0% of that applied for NTG, NTS, and CT, respectively. The surface 7.5 cm of soil contained the highest concentrations of chemicals for all treatments, with treatment differences occurring primarily in the surface 0 to 15 cm of soil. Lower runoff values under CT generally resulted in higher soil chemical concentrations.
Soil Depth and Temperature Effects on Microbial Degradation of 2,4‐D
Authors: Veeh R. H. , Inskeep W. P. , Camper A. K.
Published: July 2010

Numerous soil factors and climatic conditions affect the degradation rate of pesticides in soils. A major soil factor influencing herbicide degradation is the composition and abundance of the microbiota, which has been shown to vary considerably with soil depth. Another important variable affecting microbial growth and degradation kinetics is temperature. Soil samples from 0‐ to 30‐, 30‐ to 60‐, and 60‐ to 120‐cm depths of two Montana soils were placed in reaction flasks and treated with 14C‐labeled 2,4‐D at representative field use rates at temperatures of 10, 17, and 24°C. A carrier gas was used to continuously evacuate evolved 14CO2 into NaOH traps as a measure of 2,4‐D degradation. Comparisons of the effects of soil depth and temperature were made by fitting experimental data to both first‐order and logistic kinetic models. Degradation rates of 2,4‐D decreased significantly with increasing soil depth and were positively correlated with bacterial plate counts. Effects of temperature on degradation rate constants were adequately described using the Arrhenius equation. Degradation rates of 2,4‐D and bacterial enumerations were positively correlated with changes in soil organic C as a function of soil depth. These results support the idea that changes in organic C with soil depth could be used as a parameter for estimating changes in degradation rate as a function of soil depth. Efforts to model the transport of 2,4‐D in soils should account for variation in degradation rate as a function of soil depth and temperature.
Calibration and Evaluation of Subsurface Drainage Component of RZWQM V.2.5
Authors: Singh P. , Kanwar R. S. , Johnsen K. E. , Ahuja L. R.
Published: July 2010

This study was designed to calibrate and evaluate the subsurface drain flow component of the Root Zone Water Quality Model (RZWQM; Version 2.5) for four tillage‐systems: chisel plow (CP), moldboard plow (MB), no‐tillage (NT), and ridge‐tillage (RT). Measured subsurface drain flow data for 1990 was used for model calibration. Main parameters calibrated were lateral saturated hydraulic conductivity, and effective porosity. Subsurface drain flow predictions were made using calibrated parameters and compared with measured subsurface drain flows for 1991 and 1992. Measured subsurface drain flow data for all 3 yrs was obtained from the Nashua Water Quality Site in Iowa. The model, in general, showed a good agreement between measured and predicted subsurface drain flow values, although discrepancies existed for several days of a given year. Coefficients of determination calculated for predicted vs. measured daily subsurface drain flows ranged from 0.51 to 0.68 for 1990, 0.70 to 0.78 for 1991, and 0.54 to 0.69 for 1992. Simulated tillage effect on subsurface drain flows for 1991 and 1992 were consistent with those for calibrated year 1990 (maximum subsurface drain flow was observed under NT and minimum under MB). However, observed tillage effects varied from year to year, indicating a change in soil hydraulic properties, e.g., macroporosity. Other factors that could have caused the discrepancies between measured and simulated subsurface drain flows were: groundwater flux due to natural gradient, deep seepage, inaccuracies involved in the estimation of breakpoint rainfall data, and spatial variability in soil properties.
Responses of Phytoplankton Photosynthesis and Phosphorus Kinetics to Resuspended Sediments in Copper Sulfate‐Treated Ponds
Authors: Nalewajko C. , Prepas E. E.
Published: July 2010

Six farm ponds (dugouts) and one lake that differ in the history of copper sulfate (CuSO4) treatment were selected for studies of effects of sediments resuspension on phytoplankton. All sites are located within 50 km of Peace River, Alberta, and are shallow, hardwater, and eutrophic. Effects of sediment resuspension on phytoplankton photosynthesis were assessed by changes in the photosynthesis‐irradiance (P‐I) curve parameters, Pmax and a, after addition of sediment at 2% v/v to lakewater samples; the effects on phytoplankton P‐state were assessed by changes in 32P‐PO4 turnover time. Copper concentrations in sediments of Gour no. 4, the dugout that had received the largest dosage of CuSO4, were 60‐times greater than untreated sites but were only 1.5 to 3‐times greater at the other treated sites. Changes of Pmax and a were not correlated with Cu concentrations in the sediments. Instead, the prevailing P‐state in lakewater could better explain the observed trends in Pmax after sediment addition. Pmax values decreased at sites where phytoplankton were P‐limited (32P‐PO4 turnover time <63 min) and increased at more P‐sufficient sites (32P‐PO4 turnover time >63 min). Stimulation of Pmax and increase in 32P‐PO4 turnover time were positively correlated. With the exception of Gour no. 4, values of a increased in all treatments. Similar changes in Pmax and a in response to sediment addition occurred in laboratory experiments with P‐sufficient cultures of Anabaena flos‐aquae. We suggest that, with the exception of grossly Cu‐polluted sediments, resuspension of sediments in waters previously treated with CuSO4 will enhance phytoplankton photosynthesis by increasing P availability, and possibly by supplying Cu at trace metal levels.
Renal Cadmium Concentrations in Mice and Shrews Collected from Forest Lands Treated with Biosolids
Authors: Nickelson Sally A. , West Stephen D.
Published: July 2010

This study examined the long‐term effects of biosolids (mixed domestic‐industrial anaerobically digested sewage sludge) application to forested lands on kidney Cd concentration in omnivorous mice (Peromyscus sp.) and insectivorous shrews (Sorex sp.). Animals from eight biosolids‐treated sites, located in two different areas in western Washington, were examined and compared with those captured on seven control sites. Varying amounts of biosolids had been applied either 4, 11, or 15 yr previously. Kidney Cd was significantly greater in Sorex than in Peromyscus on all treatment sites. Though Cd levels in Peromyscus from some treatment sites were significantly increased over corresponding controls, levels from the highest dose treatment sites were comparable to controls found at other sites, so it is doubtful that biosolids had a significant long‐term effect on the omnivores. Cadmium levels in Sorex from all treatment sites except those receiving the lowest dose of biosolids were significantly greater than controls. Kidney Cd concentrations in shrews trapped from the 11‐yr postapplication sites were approximately equivalent to those in shrews trapped 2 yr after application on those same sites. However, the elevated levels of Cd found in Sorex, while highly significant statistically, did not appear to be biologically significant.
Evaluation of a Prototype Decision Support System for Selecting Trench Cap Designs
Authors: Paige G. B. , Stone J. J. , Lane L. J. , Yakowitz D. S. , Hakonson T. E.
Published: July 2010

A computer‐based prototype decision support system (PDSS) to assist the risk manager in selecting an appropriate trench cap design for waste disposal sites is evaluated. The selection of the “best” design among feasible alternatives requires consideration of multiple and often conflicting objectives. The methodology used in the selection process consists of: selecting and parameterizing decision variables, using data, simulation models, or expert opinion; selecting feasible trench cap design alternatives; ordering the decision variables and ranking the design alternatives. The simulation models incorporated in the PDSS are the Hydrologic Evaluation of Landfill Performance (HELP) model which is used to simulate the trench cap water balance and the Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) erosion component that is used to simulate trench cap erosion. The decision model is based on multi‐objective decision theory and uses a unique approach to order the decision variables and rank the design alternatives. The PDSS is evaluated using the Hill Air Force Base landfill cover demonstration project. The water balance and surface erosion of four alternative landfill cover designs were monitored for a 4‐yr period. Two of the cover designs were used to calibrate and test the simulation models. The results of the PDSS, using both data from all four designs and long‐term simulations from two of the designs, illustrate the relative advantages of each of the cover designs and which cover is the “best” alternative for a given set of criteria and a particular importance order of those decision criteria.
Carbofuran Degradation and Metabolite Incorporation during Solid State Fermentation
Authors: Willems Hans P. L. , Berry Duane F. , Mullins Donald E.
Published: July 2010

We investigated the suitability of solid state fermentation (SSF) as a means to dispose of carbofuran (2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl methylcarbamate). The fate of [U‐ring‐14C] labeled carbofuran was determined in incubation chambers containing either sphagnum peat moss (limestone‐amended) or a peanut hulls/peat moss/steam‐exploded wood (1:1:1) mixture (PPW). Ethyl acetate‐extractable, and alkali soluble and insoluble fractions were evaluated for radioactivity following either a 4‐ or 8‐wk incubation period at 35°C. The majority of the radioactivity (80–98% of applied activity) was associated with the matrix materials at the end of the incubation period for both matrix materials with no significant mineralization observed. For peat, the majority of radioactivity was associated with the alkali insoluble fraction (63.5%), with only 8% of the applied activity found in the ethyl acetate extract after 8 wk. For the PPW mix, 71% of the applied radioactivity was recovered in the ethyl acetate extract, whereas 11% of the applied activity was found in the alkali insoluble fraction after 8 wk. The metabolite carbofuran‐7‐phenol, detected in the ethyl acetate extracts of the peat and PPW mix following 4 and 8 wk of incubation, was susceptible to oxidative coupling in the presence of horseradish peroxidase (HRP) and H2O2, suggesting that this metabolite had become covalently bound to organic matter during humic substance formation. These results may provide the basis for the development of an effective and economical method for detoxification or containment of waste pesticide residue.
Atmospheric Deposition to a Low‐Elevation Spruce‐Fir Forest, Maine, USA
Authors: McLaughlin James W. , Fernandez Ivan J. , Richards Karen J.
Published: July 2010

A spruce‐fir forest in central‐Maine, USA, has been the site of dry and wet atmospheric deposition measurements since 1988. Precipitation flux of hydrogen ions (H+) and sulfate (SO2−4) decreased by 24 and 42%, respectively, during the study period, but no temporal trends occurred for precipitation H+ or SO2−4 concentrations. Decreased precipitation fluxes were likely due to a 33% decrease in precipitation amounts during the latter years of the study. Both H+ and SO2−4 concentrations and fluxes in throughfall decreased, corresponding to decreases in dry deposition of those constituents. No nitrate (NO−3) concentration or flux trends occurred in precipitation, throughfall, or dry deposition. Hydrogen, NO−3, and NH+4 had a negative net canopy exchange (NCE) attributable to N deficiency at this site and acid neutralization in the canopy. Sulfate and magnesium (Mg2+) were conservative and had no NCE. Calcium (Ca2+) and potassium (K+) had a positive NCE due to canopy leaching. A comparison of bulk and wet‐only precipitation collectors showed that SO2−4, Ca2+, and K+ concentrations were greater in solutions from a bulk collector compared with a wet‐only collector. The differences were partially attributable to dry deposition. Throughfall H+, Ca2+, and dissolved organic carbon (DOC) concentrations were higher in weekly wet‐only collections composited monthly, compared with weekly bulk collections composited either weekly or monthly. Nitrate concentration, however, was lowest in the wet‐only throughfall collections. Differences likely resulted from spatial variability. Ongoing research is attempting to further define trends apparent to date, and to determine the mechanisms controlling these characteristics.
Fate of Dissolved Toluene during Steady Infiltration through Unsaturated Soil: I. Method Emphasizing Chloroform as a Volatile, Sorptive, and Recalcitrant Tracer
Authors: Allen‐King Richelle M. , Gillham Robert W. , Barker James F.
Published: July 2010

Chloroform can be used as a volatile, sorptive, and recalcitrant tracer compound relative to volatile and transformable organic compounds, such as toluene, in aerobic unsaturated soil column experiments. Chloroform concentrations <4 mg/L did not affect the rate of toluene oxidation and chloroform itself was not transformed aerobically. In the current experiments, chloroform was applied at lower concentrations than the degradable compound. Chloroform was used to estimate the column mass balance without degradation so that mass loss for the degradable compound in the column could be confidently attributed to transformation. Consistent numbers of viable heterotrophic microorganisms in soil samples from column experiments with and without chloroform added suggest that the added chloroform did not have a negative effect on the soil microorganism population.
Fate of Dissolved Toluene during Steady Infiltration through Unsaturated Soil: II. Biotransformation under Nutrient‐Limited Conditions
Authors: Allen‐King Richelle M. , Gillham Robert W. , Barker James F. , Sudicky Edward A.
Published: July 2010

Biotransformation rates for dissolved toluene in unsaturated sandy soil were determined in dynamic column infiltration experiments. Transformation rates under N‐limited conditions and in the presence of sufficient oxygen were 8 to 35 mg (kg d)−1 and appeared to follow zero order kinetics. Toluene‐degrading microoganisms were demonstrated to increase significantly in both activity and numbers with exposure to toluene. Relatively low CO2 production to oxygen consumption ratios were observed during these experiments suggesting incomplete toluene mineralization. Over the ranges tested, water flux (20–80 cm d−1) and toluene concentration (4–46 mg L−1) appeared to have a secondary control on rate relative to nutrient and/or oxygen limitations. Under conditions where the oxygen concentration was near zero due to removal by toluene degradation in the soil columns, the transformation rate was sufficiently low to be insignificant relative to column residence time.
Biodegradation of 3‐Chlorobenzoate as Affected by Rhizodeposition and Selected Carbon Substrates
Authors: Haby Paul A. , Crowley David E.
Published: July 2010

The plant rhizosphere has been hypothesized to generally increase the population numbers and activity of soil microorganisms that degrade various xenobiotic contaminants. However, the relative importance of increased C availability in the rhizosphere to microorganisms that directly metabolize xenobiotics as a C source for growth or that degrade xenobiotics through growth‐linked metabolism and cometabolism is not well understood. We hypothesized that when a xenobiotic can be used directly as a growth substrate, the rhizosphere would have relatively little influence on the catabolizer population since the substrate provides an independent nutritional niche. However, increased C levels in the rhizosphere might enhance the numbers of microorganisms that degrade the xenobiotic through cometabolism or metabolism that is linked to growth on other substrates. To further examine this hypothesis, experiments were conducted with soil containing indigneous microorganisms capable of degrading the model compound 3‐chlorobenzoate (3‐CB). The results showed degradation of 3‐CB in 1:1 soil/water slurries from ryegrass rhizosphere soil that had not been previously exposed to 3‐CB had a faster initial rate of 3‐CB degradation than nonrhizosphere soil. This rhizosphere effect could be simulated in nonrhizosphere soil using glucose, mannitol, or benzoate. A long‐term experiment further showed that the population size of microorganisms that degraded 3‐CB in the absence of supplemental C (catabolizers), and those that degraded 3‐CB in the presence of supplemental C, for example, via growth‐linked metabolism or cometabolism, were enriched by 40‐ and 250‐fold, respectively, in rhizosphere soil. In contrast, planted and nonplanted microcosms that were repeatedly exposed to 3‐CB over 24 wk were similarly enriched for 3‐CB degraders, which had a MPN of 4 × 108 g−1 soil. Our results suggest that under conditions where there is not constant exposure of the microbial population to 3‐CB as a C source, C provided by rhizodeposition may primarily enhance the population numbers of microorganisms that degrade 3‐CB by cometabolic or growth‐linked metabolism, and thereby promote rapid depletion of 3‐CB from soil during short term or low level exposure to the xenobiotic.
Use of XAS to Determine the Chemical Speciation of Bioaccumulated Manganese in Potamogeton pectinatus
Authors: Lytle C. M. , Lytle F. W. , Smith B. N.
Published: July 2010

Manganese (Mn) accumulation was measured in Potamogeton pectinatus L. (sago pondweed) over a growing season. Leaf tissue Mn content increased from 120 mg kg−1 in June to 4990 mg kg−1 by October. Our objective was to chemically speciate bioaccumulated Mn in P. pectinatus with x‐ray absorption spectroscopy (XAS). Differences were found in Mn valence in leaf tissue between June, October, and January when compared to model inorganic Mn compounds. Manganese in June leaf tissue was most like [Mn2+ (H2O)6]. By October, average valence of Mn in leaf and root tissues was similar to Mn3O4. However, there was little agreement in the chemical structure of Mn in these tissues and Mn3O4. Senescent leaf tissue in January differed from October because the valence had shifted back toward Mn2+. The Mn3+ fraction had leached from leaf tissue between October and January. This coincided with a decrease in total Mn concentration during this same period. Manganese bioaccumulation in this aquatic species occurs in two phases: (i) Mn2+ is bound in finite sites and coordinated by water, (ii) once filled, Mn2+ is oxidized and stored as a Mn3+ oxide within the plant that can be leached upon senescence.
A Site‐Specific Farm‐Scale GIS Approach for Reducing Groundwater Contamination by Pesticides
Authors: Mulla D. J. , Perillo C. A. , Cogger C. G.
Published: July 2010

It has been proposed to vary pesticide applications by patterns in surface organic C to reduce the potential for contamination of groundwater. To evaluate the feasibility of this “precision farming” approach, data for carbofuran concentrations from 57 locations sampled to a depth of 180 cm were fit to the convective‐dispersive equation. Fitted values for pore water velocity (v) ranged from 0.17 to 1.92 cm d−1, with a mean of 0.68 cm d−1. Values for dispersion (D) ranged from 0.29 to 13.35 cm2 d−1, with a mean of 3.49 cm2 d−1. Values for the retardation factor (R) ranged from 1.28 to 6.83, with a mean of 2.57. With this data, risks of pesticide leaching were estimated at each location using the attenuation factor (AF) model, and dispersion based leached factor (LF) model. Using the AF model gave two locations with a very high pesticide leaching risk, 32 with a high pesticide leaching risk, 15 with a medium risk, 6 with a low risk, and 2 with no risk. Using the LF model, 6 had a high risk, 13 had a medium risk, 18 had a low risk, and 20 had no risk. Pesticide leaching risks were not correlated with any measured surface soil properties. Much of the variability in leaching risk was because of velocity variations, so it would be incorrect to assume that surface organic C content controls the leaching risk.
Scale‐Dependency of Solute Transport Modeling/GIS Applications
Authors: Wagenet R. J. , Hutson J. L.
Published: July 2010

The movement of water through the soil profile and the consequent displacement and transformation of chemicals dissolved in the water is a key concern in preventing water quality degradation, with its eventual impact on living systems, both human and otherwise. Predictions of the effect of a particular water and chemical management system at the soil surface will lead to more enlightened control of chemicals introduced into the environment as pesticides, fertilizers, or waste products. The use of geographic information systems (GIS) in concert with simulation modeling of soil leaching processes is becoming more widespread as a procedure applied to environmental chemical fate issues. The use of GIS has brought to the forefront the spatial scale of such databases as soil survey, elevation, climate and land use, and their use in the modeling process. An accompanying concern is the spatial scale at which any simulation model is assumed to be accurate, and the spatial scale at which both model input and field‐verification data should be generated. Such modeling presently consists of a number of approaches, some useful at several spatial scales, and others more limited by the assumptions inherent in their development. This paper discusses these issues, and presents two case studies as examples.
Estimating Recharge Rates for a Groundwater Model Using a GIS
Authors: Fayer M. J. , Gee G. W. , Rockhold M. L. , Freshley M. D. , Walters T. B.
Published: July 2010

Some of the defense wastes at the Hanford Site in southeastern Washington State are stored in the vadose zone. It is possible that natural recharge could mobilize and transport the contaminants in these wastes to the groundwater, as well as influence groundwater velocities and directions. The objective of this study was to estimate the areal distribution of natural recharge for use as a boundary condition for a groundwater flow and transport model. A geographic information system (GIS) was used to identify all possible combinations of soil type and vegetation and assign to each an appropriate estimate of recharge. The strategy was to assign estimates based on field data and supplement with simulation results only when necessary. The estimated rates varied from 0.7 to 127.1 mm/yr. The order of preference for assigning estimates was lysimetry > water content measurements > tracers > modeling, based on qualitative estimates of the relative error of each method as applied. The GIS software was used to estimate the annual recharge volume attributable to specific soil‐vegetation combinations. The total annual recharge volume was 8.47 × 109 L for the 765 km2 portion of the site containing the major waste storage areas. This volume is from 2 to 10 times higher than estimates of runoff and groundwater flow from adjacent higher elevations and is equivalent to facility discharges in 1992. The recharge map showed the impact of a 1984 fire on increasing recharge; it also illustrated the higher recharge rates associated with disturbed soils in the waste storage areas.
Using GIS in Simulation of Nitrate Leaching from Heterogeneous Unsaturated Soils
Authors: Wu Q. Joan , Ward Andrew D. , Workman Stephen R.
Published: July 2010

Solute transport within and through unsaturated soils are important processes that can affect agricultural systems and groundwater supply and contamination. Nitrate (NO−3) leaching from three 10‐ha experimental plots under different agricultural practices was studied. A Geographic Information System (GIS) model, ARC/INFO was used to help decompose the three hydrologic environments into 34 subenvironments. Each subenvironment was discretized vertically as three modeling units. Within each modeling unit, soil physical and chemical properties were described by a random multivariate normal (MVN) vector with conditional probability. A one‐dimensional, field‐scale, continuous flow model, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS), was then stochastically applied to each subenvironment by using generated MVN realizations for every modeling unit. Observed NO−3 leaching below 1‐m depth was estimated with a mass balance approach based on suction lysimeter data. The observed NO−3 loads were then compared to predictions from the stochastic simulation. Statistical analysis of the effects of agricultural practice and soil type on NO−3 leaching was conducted based on modeling results. Observed and predicted results showed (i) no significant difference between mean values of observed and predicted mean NO−3 leaching below the 1‐m depth; (ii) agricultural practice and soil type as well as their interaction had an effect on NO−3 leaching; and (iii) a large amount of spatial variability with respect to NO−3 leaching. The results are important for better understanding solute leaching from heterogeneous agricultural fields and useful in decision making.
Atrazine Loss in Runoff from No‐Tillage and Chisel‐Tillage Systems on a Houston Black Clay Soil
Authors: Pantone D. J. , Potter K. N. , Torbert H. A. , Morrison J. E.
Published: July 2010

Herbicide concentration and mass load of runoff depends, to a large extent, on soil management. This study was conducted to determine how tillage impacts herbicide losses in runoff from a vertisol soil on the Blackland Prairie of Texas. Atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] was applied at a rate of 2 kg a.i. ha−1 to a Houston Black clay soil (fine, montmorillonitic, thermic Udic Pellustert) in 1993 at the Blackland Research Center in Temple, TX. For 4 yr, the test area was under continuous management using a wide‐bed system with a wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum [Sorghum bicolor (L.) Moench] rotation. Tillage treatments consisted of no‐tillage or chisel‐tillage. All experiments were repeated four times. A rainfall simulator with an intensity of 12.5 cm h−1 was used to apply rainfall 24 h after the atrazine application. Sediment and runoff samples were collected during five time periods (from runoff initiation to 5, 5 to 10, 10 to 20, 20 to 30, and 30 to 40 min). No differences in atrazine concentrations were found among treatments in either the runoff water or sediment from any of the five time periods; however, crop residues prevented surface seal development and erosion resulting in reduced runoff and sediment losses. No‐tillage treatments significantly reduced runoff and sediment yield, rather than the atrazine concentration of the runoff, resulting in a 42% decrease of the atrazine load in the runoff and a 77% decrease in atrazine associated with the sediment. As a percentage of the total amount applied, runoff accounted for <2% of the atrazine. Sediment‐transported atrazine was much less important and represented <0.03% of the total amount applied.
A Comparison of Distribution Tests and Relevant Point and Interval Estimators
Authors: Haarstad Ketil
Published: July 2010

This is a study of samples from natural, terrestrial environments, with coefficients of variation ranging from 4 to 211%. To select estimators, physical and chemical sample distributions are separated into three categories: normal (N), lognormal (LN), and nonparametric (NP) distributions. The type of distribution is given by (i) the Lilliefors procedure of the Kolmogorov‐Smirnov test (KST), (ii) the Shapiro‐Wilk test (SWT), or (iii) the Skewness test (ST). For 46 samples, 14 (30%) were NP, 14 (30%) were LN, and 18 (39%) were N, based on test (i). Test (ii) gave 14 (30%) NP, 19 (41%) LN, and 13 (28%) N. Only 29 of the 46 samples could be tested by Method (iii) due to the limit on minimum sample size of 25:11 (38%) were NP, 9 (31%) LN, and 9 N. The KST and SWT disagreed in 35% of the samples, whereas KST and ST disagreed in 24% of the samples. The SWT disagreed with ST results in 10% of the samples, when categorizing the distributions at a significance level of 5%. The ratio between the selected point estimator and the mean varied from 13 to 249%, with mean values of 73% for NP and 112% for LN. The ratio between the selected interval estimator and the range varied from 2 to 71%. It is not possible to characterize one of the distribution tests as superior to the others based on the results from this study.
A Versatile Sun‐lit Controlled‐Environment Facility for Studying Plant and Soil Processes
Authors: Tingey David T. , McVeety Bruce D. , Waschmann Ron , Johnson Mark G. , Phillips Donald L. , Rygiewicz Paul T. , Olszyk David M.
Published: July 2010

A new environmental‐tracking, sun‐lit controlled‐environment facility (terracosm) that can control and manipulate climatic and edaphic factors while maintaining natural environmental variability was developed to study the effects of environmental stresses on a model ecosystem (i.e., plant and soil processes). An analysis of terracosm performance data indicates that the terracosms simulated natural seasonal and diurnal changes in atmospheric CO2, air and soil temperatures, vapor pressure deficit (VPD), and soil moisture. The terracosm performance data indicate that between 92 and 100% of the hourly CO2 concentrations are within ±50 µmol mol−1 of the target concentrations for both ambient and elevated treatments (1 Nov. 1993 through 30 Nov. 1994). Air temperatures are within 2°C of the target temperature between 85 and 100% of the hours for both ambient and elevated temperature treatments. The VPD was approximately the same (0.09 kPa difference between treatments) in the ambient and elevated temperature treatments. Distributed process control was implemented to minimize downtime. Terracosm downtime, periods when terracosm environmental conditions could not be reliably controlled, varied between 2.4 and 2.8% of all hours, and was equally distributed between biological sampling and equipment problems.
Observed and Simulated Solute Transport Under Varying Water Regimes: I. Bromide and Pentafluorobenzoic Acid
Authors: Pearson R. J. , Inskeep W. P. , Wraith J. M. , Comfort S. D. , Gaber H. M.
Published: July 2010

Comparison of observed and predicted solute transport under field conditions is a necessary component for validating various modeling approaches. The objectives of this study were to compare transport of Br− and pentafluorobenzoic acid (PFBA) under cropped and fallow conditions for a range of soil water contents and evapotranspirative demands, and to evaluate the predictive capability of a computer simulation model (LEACHM) using independent estimates of model input parameters. A field study was conducted (1991) using in situ columns (0.2 m diam., 1.22 m depth) on a Brocko silt loam (mixed, mesic Borollic Calciorthid) in Gallatin Co., MT. The transport of two tracers (Br− and PFBA) was measured at three depths (0.36, 0.66, and 0.96 m) for three water regimes under cropped (barley, Hordeum vulgare L.) and fallow conditions for 60 d following chemical application. Observed breakthrough curves (BTCs) demonstrated increased travel times with increasing depth and decreasing water application. Solute transport in cropped columns was significantly slower than fallow as a result of higher evapotranspiration. Comparison of Br− and PFBA BTCs under cropped conditions suggested significantly greater plant uptake of Br− compared to PFBA. Predicted volumetric water contents, evaporation (under fallow conditions), and solute BTCs using LEACHM agreed favorably with observed results. Under cropped conditions, agreement between predicted and observed soil water contents was less favorable, most likely a result of inaccurate assumptions concerning depth‐dependent root water uptake. LEACHM‐predicted mean travel times (d) agreed within 22% of observed PFBA values for fallow conditions and within 9% of observed PFBA values for cropped conditions. Results indicated that adequate predictions of the transport of PFBA were obtained using LEACHM when coupled with independent estimates of model input parameters.
Nitrate and Water Present in and Flowing from Root‐Zone Soil
Authors: Weed D. A. J. , Kanwar R. S.
Published: July 2010

From 1990 through 1992, we studied water and nitrate‐nitrogen (NO3‐N) present in the soil and flowing into a subsurface drainage system. Tillages were chisel plow (CP), moldboard plow (MB), no‐till (NT), and ridge‐till (RT). Crops were continuous corn (Zea mays L.) and a corn‐soybean [Glycine max (L.) Merr.] rotation. Tillage and crop only slightly influenced soil NO3‐N and water. Drainage water flows were highest for treatments that minimized soil disturbance and maximized crop residues produced during the previous year. The 3‐yr total flows by crop were 38 cm water for rotation‐corn plots, 56 for rotation soybean, and 59 for continuous corn. Flows by tillage were 41 cm water for MB plots, 52 for RT, and 55 for both CP and NT. In continuous corn, NT plots had more monthly water drainage than MB plots for most of 1990. Ridge‐till and CP plots had more drainage than MB plots for part of 1991. Crop rotation had the greatest effect on NO3‐N drainage loss. The 3‐yr total NO3‐N losses were 77 kg ha−1 for rotation corn plots, 84 for rotation soybean, and 164 for continuous corn. Tillage losses were 95 kg ha−1 for RT, 102 for MB, 106 for NT, and 131 for CP. No‐till and RT plots always had the lowest NO3‐N concentrations in drainage water; their yearly NO3‐N losses were usually smallest. Leaching can be best minimized by applying fertilizer in amounts to just meet crop N demand and at times closest to peak uptake.
Molybdate‐Reactive Phosphorus Losses in Surface and Drainage Waters from Permanent Grassland
Authors: Hawkins J. M. B. , Scholefield D.
Published: July 2010

Although the loss of P in agricultural runoff can provide freshwater eutrophication, little information is available on losses from permanent grasslands. Thus, 14 lysimeter plots (each of 1 ha), established in 1982 on a clay loam soil under grazed grassland management, were monitored between 1989 and 1991 for release of molybdate‐reactive phosphorus (MRP). The plots enabled the daily measurement of discharge through field drains (to 85 cm) or by surface lateral runoff (to 30 cm). Sward type was either perennial ryegrass (Lolium perenne L.) or a perennial ryegrass‐clover (Trifolium sp.) mixture. The plots were grazed continuously by beef cattle and received either 200 or 400 kg N ha−1 yr−1 in various combinations. Having collected >7500 data points during the 3 yr, it was found that there was no significant difference between the effects of either agronomic or drainage variables (P > 0.05) within years. However, there was a significant difference (P < 0.05) between drainage variables when the data from the 3 yr were combined, as there were larger MRP losses from undrained treatments. There was no relationship between concentration of MRP and drainage volume. The MRP concentrations ranged from 0.01 to 0.7 mg L−1 with an average concentration of 0.02 mg L−1. Losses of MRP as great as 0.4 kg ha−1 yr−1 were measured in surface lateral runoff from undrained plots and 0.2 kg ha−1 yr−1 in water percolating through field drains. The data show this type of grassland system may have the potential to be an important diffuse source of P to fresh waters.
Herbicides in Karst Groundwater in Southeast West Virginia
Authors: Pasquarell G. C. , Boyer D. G.
Published: July 2010

A field study was conducted to determine the karst groundwater impact of herbicide application to feed crops in support of livestock production in southeast West Virginia. Grab samples were taken on a weekly/biweekly schedule at three resurgences for two agriculturally intensive karst watersheds. Two surface water sites were also sampled. The samples were analyzed for the presence of 12 different analytes: atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine), its two metabolites, desethylatrazine (2‐chloro‐4‐ethylamino‐6‐amino‐1,2,5‐triazine) and desisopropylatrazine (2‐chloro‐4‐amino‐6‐isopropylamino‐1,3,5‐triazine), and nine additional triazine herbicides. Little impact was detected at the two surface water sites. In contrast, 6 of the 10 herbicides were detected in at least two of the three resurgences. Three of them, atrazine (ATR), metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide], and simazine [2‐chloro‐4‐6‐(ethylamino)‐s‐triazine], were detected in more than 10% of all samples at all three resurgences. ATR and desethylatrazine (DES) were detected in more than 50% of samples at all three resurgences; median ATR values were 0.060, 0.025, and 0.025 µg/L. DAR*, the ratio of DES to ATR plus DES, was used to differentiate atrazine leaching following storage for long periods in the soil, from transport that bypassed deethylation in the soil through sinkholes and other solutionally developed conduits. DAR* was low (median of <0.5) and highly varied during the periods immediately following ATR application, indicating that significant quantities of ATR were present. In the winter, a release of ATR metabolites from the soil was evidenced by a steadier, and higher DAR* (median of 0.64). The maximum detected ATR concentration was 1.20 µg/L, which is within the USEPA maximum contaminant level of 3 µg/L.
Distribution and Mineralization of Biosolids Nitrogen Applied to Dryland Wheat
Authors: Barbarick K. A. , Ippolito J. A. , Westfall D. G.
Published: July 2010

The greatest challenge in land application of biosolids (sewage sludge) for beneficial use is predicting N‐mineralization rates so that managers can amend the soil with an agronomic rate of material. We used 11 yr of field‐study information from biosolids addition to dryland hard‐red winter wheat (Triticum aestivum L. ‘Vona’ or ‘TAM107’) to determine not only the distribution of applied N but also to estimate net N mineralization rates. This study is unique since it involves multiple biosolids application in a dryland summer fallow agroecosystem. We applied five or six applications of biosolids from the cities of Littleton and Englewood, CO (L/E) to Weld loam (Aridic Paleustoll) or Platner loam (Abruptic Aridic Paleustoll) at four locations. This paper focuses on the O (control) and the 56‐ or 67‐kg N ha−1 fertilizer rate, and the 6.7 and 26.8 dry Mg biosolids ha−1 rates that we added every crop year. The 6.7 dry Mg biosolids ha−1 treatment resulted in the following average N distributions: 54% soil residual, 9% grain removal, and 38% unaccounted. At the larger application rate of 26.8 dry Mg biosolids ha−1 treatment, we found the following average N distributions: 35% soil residual, 2% grain removal, and 63% unaccounted. We estimated a net mineralization of 25 to 57% and a first‐year N net mineralization of 13 to 43% for 6.7 dry Mg ha−1 and a net mineralization of 62 to 78% and a first‐year N net mineralization of 41 to 67% for 26.8 dry Mg ha−1.
Composition and Decomposition of Soybean and Sorghum Tissues Grown under Elevated Atmospheric Carbon Dioxide
Authors: Henning F. P. , Wood C. W. , Rogers H. H. , Runion G. B. , Prior S. A.
Published: July 2010

It has been hypothesized that changes in both quantity and quality of plant residue inputs to soils as atmospheric carbon dioxide (CO2) concentration increases may alter carbon (C) and nitrogen (N) turnover rates and pool sizes. We determined the effect of elevated atmospheric CO2 on plant tissue quality, and how modifications in tissue quality affect C and N mineralization. Soybean [C3; Glycine max (L.) Merr. cv. Stonewall] and sorghum [C4; Sorghum bicolor (L.) Moen. cv. Savanna 5] were grown under elevated (704.96 ± 0.33 µmol CO2 mol−1) and ambient (357.44 ± 0.12 µmol CO2 mol−1) atmospheric CO2 in open‐top chambers. Leaf and stem tissues were separated from harvested plants and analyzed for C, N, lignin, and cellulose. Tissues were applied to Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudult) and aerobically incubated for 70‐d to determine C and N mineralization, C turnover, relative N mineralization, and C/N mineralized. Elevated CO2 had no effect on plant residue C concentration, but N concentration of soybean leaves and stems and sorghum stems was reduced; however, CO2 enrichment increased C/N ratio and lignin concentration for only sorghum stems and soybean leaves, respectively. Source of plant residue (i.e., produced under either elevated or ambient CO2) had no impact on soil C turnover, relative N mineralization, cumulative C and N mineralization, and C/N mineralized. These data suggest that increasing atmospheric CO2 will have little effect on composition or decomposition of field crop residues. Thus, since CO2 enrichment results in increased photosynthetic C fixation, the possibility exists for increased soil C storage under field crops in an elevated CO2 world.
Carbon Dioxide and Ozone Effects on Growth of a Legume‐Grass Mixture
Authors: Johnson B. G. , Hale B. A. , Ormrod D. P.
Published: July 2010

Atmospheric carbon dioxide (CO2) and photochemical ozone (O3) have been increasing in the biosphere and will continue to do so with further industrialization and burning of fossil fuels. The purpose of this study was to examine the interaction of CO2 and O3 on plant growth and aboveground competition using a forage mixture of alfalfa (Medicago sativa L.) and timothy (Phleum pratense L.). Mixtures were grown at two CO2 levels (350 and 700 µL/L) in controlled environment chambers and exposed to four weekly O3 episodes of 8‐h duration with peak daily concentrations of 0.03, 0.08, 0.13, or 0.18 µL/L on Days (d) 21, 28, 35, and 42 after seeding. Roots of individual plants were in separate containers. The plants were harvested 2 d after the final O3 exposure. Total dry biomass of alfalfa and timothy was 50 and 40%, respectively, greater at 700 than at 350 µL CO2/L with low O3. Increasing peak O3 concentration decreased alfalfa shoot dry biomass at 700 µL CO2/L but not at 350 µL/L and decreased root dry biomass at both CO2 levels. In timothy, intermediate O3 levels reduced shoot growth but the highest level of O3 resulted in more shoot growth in the mixture at both CO2 levels. Partitioning of dry matter to alfalfa roots was strongly retarded by increasing O3, particularly in the CO2‐enriched environment, while timothy root growth was unaffected by O3. The enhancement of timothy shoot biomass in the mixture by exposure to the highest level of O3 at either CO2 level could not be fully explained by changes in competition between timothy and alfalfa in relation to differential O3 tolerance.
Spreader Performance Evaluation for Forest Land Application of Wood and Fly Ash
Authors: Wilhoit John H. , Ling Qingyue
Published: July 2010

Land application is an important disposal alternative for ash, but materials handling and spreading difficulties are obstacles to increased utilization of this alternative, especially in forest situations. A horizontal spinner‐type spreader mounted on a forwarder, a specialized tractor for hauling logs out of the forest, was used to conduct distribution pattern trials spreading wood ash and fly ash in a pine (Pinus sp.) plantation stand. The materials were spread at two conveyor speeds, and the results were analyzed for application rate and spreading uniformity, as indicated by coefficient of variation (CV), at different simulated swath widths. Spreader uniformity was generally poor in comparison to standards for spreading fertilizer, and the uniformity results were inconsistent from one trial to the next. Both of the materials exhibited similar trends, however, with best uniformities (indicated by minimum CV values) occurring at both narrow (5.5–7.3 m) and wide (10.9–12.8 m) simulated swath widths. At the 19 cm s−1 speed, fairly high application rates were achieved with fly ash, which was dry and uniform in consistency. The wood ash, which was wet and mud‐like in consistency, could only be spread satisfactorily at a lower application rate (7.1 cm s−1 conveyor speed). For the operating conditions used in these tests, estimated costs (for spreading only) at an application rate of 10 Mg ha−1 ranged from $1.31 Mg−1 ($1.35 m−3) to $2.62 Mg−1 ($2.70 m−3), depending on loading and travel time requirements.