bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen Loss from Coffee Agroecosystems in Costa Rica: Leaching and Denitrification in the Presence and Absence of Shade Trees
Authors: Babbar Liana I. , Zak Donald R. 
Published: July 2010

AbstractCoffee (Coffea arabica L.) management in Costa Rica is changing from traditional agroecosystems, where coffee is grown beneath a tree overstory, to management systems where shade trees are removed and N fertilizer is applied at high rates (ca. 300 kg N ha−1 yr−1). Although fertilization increases coffee bean production, it also increases the potential for substantial loss of N to groundwater and the atmosphere. We investigated NO−3 leaching and the factors controlling denitrification in shaded and unshaded coffee plantations in the Central Valley of Costa Rica; both plantation types were fertilized with 300 kg N ha−1 yr−1. Nitrate leaching was quantified using porous ceramic cup lysimeters placed 60 cm below the soil surface. Losses were estimated by multiplying the soil water NO−3 concentration by the monthly soil water excess, determined as the difference between precipitation and actual evapotranspiration. In addition, a laboratory experiment was conducted to investigate the influence of NO−3, C, and O2 availability on N2O production and total denitrification (N2O‐N + N2‐N). Annual leaching losses of NO−3 were almost three times greater in unshaded plantations (24 kg NO−3‐N ha−1 yr−1) than those in shaded plantations (9 kg ha−1 yr−1). In contrast, mean total denitrification rates in control soil samples from shaded plantations were 60% higher (732 µg N2O‐N kg−1 d−1) than in unshaded plantations (455 µg N2O‐N kg−1 d−1). Carbon additions elicited the largest increase in denitrification, generating nearly a threefold increase (+ C = 8396 µg N2O‐N kg−1 d−1; −C = 2985 µg N2O‐N kg−1 d−1) in both plantation types. Anaerobic conditions also significantly increased denitriflcation (+ O2 = 4331 µg N2O‐N kg−1 d−1; µO2 = 6656 µg N2O‐N kg−1 d−1). In both plantation types, the potential for N loss via NO−3 leaching was small compared with that for gaseous N loss.
Atrazine and Metolachlor Loss in Surface and Subsurface Runoff from Three Tillage Treatments in Corn
Authors: Gaynor J. D. , MacTavish D. C. , Findlay W. I. 
Published: July 2010

AbstractConservation tillage with residue management has been proposed as the most effective means to reduce soil deterioration in southwestern Ontario. Two conservation tillage treatments, ridge (RT) and zero (ZT) tillage, were compared with conventional moldboard plow (CT) tillage from 1987 to 1990 for atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methyethyl)‐1,3,5‐triazine‐2,4‐diamine], deethylatrazine [6‐chloro‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], and metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] loss in surface runoff and tile discharge. Twenty‐five to 44% of the annual rainfall resulted in total field runoff (surface runoff or tile discharge). Conservation tillage increased surface runoff 42% and decreased tile discharge 15% compared with conventional tillage, but total field runoff was the same from all treatments. Runoff events shortly after herbicide application produced the greatest herbicide concentrations and losses in both surface runoff and subsurface drainage. Averaged over years, herbicide concentration in surface runoff and tile discharge was, respectively, 1.3 and 1.8 times greater from conservation than conventional tillage. Conservation tillage altered the source of herbicide loss compared with conventional tillage, but environmental factors after herbicide application were more important in determining total herbicide loss than tillage. Deethylatrazine was found in both surface runoff and tile drainage and accounted for 10 to 27% of combined atrazine and drethylatrazine loss.
Radium in Phosphogypsum Leachates
Authors: Rutherford P. M. , Dudas M. J. , Arocena J. M. 
Published: July 2010

AbstractPhosphogypsum (PG) is an acidic by‐product of the phosphate fertilizer industry, and is produced in large quantities by the wet phosphoric acid process. Most PG is sluiced out to repositories, forming large stockpiles. Phosphogypsum is composed mainly of gypsum (Ca‐SO4·2H2O), but contains impurities of environmental concern such as F−, acids, trace elements, and naturally occurring radionuclides, which originate from the phosphate rock used in processing. Possible movement of these impurities into groundwater is an issue. 226Radium is the major source of radioactivity in PG produced from sedimentary phosphate rock. Few studies have addressed the leachability of 226Ra because solid solutions of Ra, Ba, and Sr are very insoluble. The objective of this study was to investigate the concentrations of 226Ra, Ba, and Sr in leachate generated from PG produced from Togo phosphate rock. Phosphogypsum was extracted 30 times with deionized distilled (d.d.) H2O over 30 d. Extractable 226Ra was maximal (0.55 Bq L−1) for Day 1 but remained relatively constant between Day 2 and Day 30. Minimum extractable 226Ra (0.23 Bq L−1) occurred on the Day 30 extraction but still exceeded the current U.S. drinking water standard. Solid phase 226Ra increased between Day 0 (850 Bq kg−1) and Day 30 (1120 Bq kg−1). The 226Ra/Ba ratios in the solid phase and in the extractable liquid phase were nearly equal over the last half of the extraction period. If this relationship holds for other PGs, then solution 226Ra activities can be estimated if solid‐phase 226Ra/Ba ratios are known and Ba solution concentrations are known or estimated.
Fingerlike Wetting Patterns in Two Water‐Repellent Loam Soils
Authors: Dekker Louis W. , Ritsema Coen J. 
Published: July 2010

AbstractIn soils with fingered flow, surface‐applied solutes can reach the groundwater more rapidly than in the case of homogeneous wetting. So far, fingered flow has been thought to be restricted to fine over coarse‐textured soils and homogeneous sandy soils. The present study was undertaken to demonstrate the occurrence of fingerlike wetting patterns in a silt loam and in a silty clay loam soil, and to investigate the influence of dry bulk density and water repellency on the observed soil moisture patterns. Fingerlike patterns were photographed and soil water contents determined by intensive soil core sampling. In both soils, dry bulk density was not a main factor in inducing wet fingerlike patterns and high water content variability. The degree and persistence of potential water repellency were measured on soil samples using the alcohol percentage test and the water drop penetration time (WDPT) test. Spatial variability of degree and persistence of potential water repellency and, accordingly, of soil water contents were high. The actual water repellency was measured on field‐moist samples to obtain critical soil water content values. The soil is wettable above and water‐repellent below these values.
Plant Uptake and Determination of Arsenic Species in Soil Solution under Flooded Conditions
Authors: Onken B. M. , Hossner L. R. 
Published: July 2010

AbstractPrevious studies have not identified the different As species present in soil systems and determined if effective differences exist between As species with respect to plant parameters such as growth rate and As uptake. This study determined the species and concentrations of As present in soil solution of flooded soils and correlated them to As concentration, P concentration, and growth rate of plants grown in treated soils. Rice (Oryza sativa L.) was grown in two soils treated with 0, 5, 15, 25, 35, and 45 mg As kg−1 soil added as either Na‐arsenate or Na‐arsenite. Soil solution samples and plant samples were collected over a period of 60 d. The As concentration of rice plants best correlated to the mean soil solution arsenate concentration in a Beaumont clay (fine, montmorillonitic, thermic Entic Pelludert) and to the mean soil solution arsenite concentration in a Midland silt loam (fine, montmorillonitic, thermic Typic Ochraqualf). In both soils, plant P concentration was best correlated to the amount of As added to the soil rather than any soil solution As concentration. Plant weight was best correlated to the mean soil solution arsenate concentration in both soils. The rate of As uptake by plants increased as the rate of plant growth increased. Plants grown in soils treated with As had higher rates of As uptake for similar rates of growth when compared with plants in untreated soils. However, growth per unit of As uptake was higher for plants in untreated soils than plants in As treated soils.
Water Contamination by Ammonium Nitrogen Following the Spreading of Hog Manure and Mineral Fertilizers
Authors: Gangbazo G. , Pesant A. R. , Barnett G. M. , Charuest J. P. , Cluis D. 
Published: July 2010

AbstractInappropriate fertilization practices in regions where livestock manure exceeds crop requirements may cause pollution by NH+4‐N) during snowmelt. Annual and seasonal NH+4‐N losses were evaluated for three consecutive years from 45 m2 corn (Zea mays L.) and timothy (Phleum pratense L.) and red and white clover (Trifolium repens L.) erosion plots that had annually received the recommended chemical fertilizer rates of 180 and 55 kg N ha−1, respectively, plus hog manure at twice those rates. Total N applications for corn and forage were 540 and 165 kg ha−1 except for a check plot receiving only fertilizer. The hog manure was surface‐applied in three different ways: all in the fall, all in the spring, and in a split application with about one‐half in each season. Corn plots receiving fall‐applied manure were immediately rototilled while plots receiving spring‐applied manure were ratotilled prior to planting. Each plot was equipped to collect runoff and drainage water separately throughout the whole year. Total NH+4‐N losses in both runoff and drainage water from autumn application were greater than for the two other application methods for corn and the forages. Plots receiving chemical fertilizer plus hog manure had a significant increase in NH+4‐N losses as compared with the plots receiving fertilizer only. Due to the fall manure effect, NH+4‐N loads increased by three‐fold after the first year (1.11–3.43 kg ha−1), by 1.46 times between the first and the second year, and by 1.14 times between the second and the third year for corn when compared with the fertilizer only treatment and exceeded the standard of 0.5 mg L−1 for raw water. Similar trends were measured for the forages. Most NH+4‐N was lost during the autumn and winter periods for corn. For both crops, there was an increase in loss from fall to winter and a decrease both from winter to spring and from spring to summer.
Pesticides in Eastern North Carolina Rural Supply Wells: Land Use Factors and Persistence
Authors: Maas R. P. , Kucken D. J. , Patch S. C. , Peek B. T. , Van Engelen D. L. 
Published: July 2010

AbstractWater samples were collected from 171 rural domestic well supplies in eastern North Carolina and analyzed for eight pesticides. Information on borehole depth, well‐easing depth, distance to nearest pesticide mixing area, types of pesticides used, and distance to nearest field application was obtained for each site. Four herbicides [alachlor, 2‐chloro‐2′‐6′diethyl‐N‐(methoxymethyl)‐acetanilide; atrazine, 2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine; metolachlor, 2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide; trifluralin, α,α,α‐trifluoro‐2,6‐dinitro‐N,N‐dipropyl‐p‐toluidine] were detected in the samples, with detection frequencies of 8.8, 8.2, 3.6, and 1.8%, respectively. About 15% of the samples contained at least one of these herbicides, with resampling indicating persistence throughout the year. Only alachlor concentrations were in excess of maximum contaminant levels (MCLs; 2.0 μg L−1) or Health Advisory Levels (HALs; 0.4 μg L−1) established by the U.S. Environmental Protection Agency (USEPA). Neither atrazine nor alachlor detection exhibited statistical correlation with well depth, although both were rarely detected in wells >100 feet deep. Atrazine concentrations and detection frequencies did not correlate with distance to nearest application site, while alachlor had a significantly greater detection frequency for wells further from the nearest application site. For nearly one‐half of the wells with detectable atrazine and alachlor, there was no reported usage of either herbicide on the same farm during the previous three years, possibly indicating herbicide transport in groundwater or long times before degrading. No statistically significant relationships were observed between the presence of alachior or atrazine, and distance from the well to the nearest pesticide handling and storage area. Although inconclusive by itself, this indicates that at least some contamination originated from other than point‐source spills. Nitrate‐N concentrations in well water were poor predictors for atrazine and alachlor presence in this study.
A Natural Gradient Transport Study of Selected Herbicides
Authors: Widmer S. K. , Spalding R. F. 
Published: July 2010

AbstractThe behavior of trace quantities of commonly detected herbicides and herbicide degradates was investigated in a shallow sand and gravel aquifer. In 1991, a solute pulse containing approximately 15 mg L−1 bromide, 3 μg L−1 atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine), 2 μg L−1 alachlor (2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl)‐acetanilide), 10 μg L−1 cyanazine (2‐[[4‐chloro‐6‐(ethylamino)‐S‐triazin‐2‐yl]amino]‐2‐methylpropionitrile), and 10 μg L−1 metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide) was injected into a shallow aquifer near Fremont, NE. The plume was monitored for 2 mo following injection using an array of multilevel samplers. A second injection in 1992 included approximately 10 mg L−1 bromide, 1 μg L−1 butachlor (2‐chloro‐2′,6′‐diethyl‐N‐(butoxy methyl) acetanilide), and 3 μg L−1 atrazine, deethylatrazine (DEA) (2‐amino‐4‐chloro‐6‐isopropylamino‐1,3,5 triazine) and deisopropylatrazine (DIA) (2‐amino‐4‐chloro‐6‐ethylamino‐1,3,5 triazine). This plume was monitored for 3 mo. Retardation factors (Rs) were determined for each herbicide by comparing concentration profiles to those of the conservative tracer; Rs were calculated as the ratio of first central moments. Results indicated only slight retention of all injected compounds. Retardation factors for atrazine, DEA, DIA, cyanazine, alachlor, and metolachlor were less than 1.3, with butachlor being slightly more retained (R = 1.65). Persistence of the injected compounds was estimated by the decrease with time in area under the breakthrough curves. Atrazine, DEA, DIA, cyanazine, and metolachlor showed no detectable loss. Losses of alachlor and butachlor were approximately 40 and 70%, respectively, in a 2‐mo period.
Feasibility of Cyclic Reuse of Saline Drainage in a Tomato‐Cotton Rotation
Authors: Shennan C. , Grattan S. R. , May D. M. , Hillhouse C. J. , Schachtman D. P. , Wander M. , Roberts B. , Tafoya S. , Burau R. G. , McNeish C. , Zelinski L. 
Published: July 2010

AbstractUse of saline drainage water for crop irrigation has been proposed as a strategy to reduce drainage volume and conserve good quality water. Over a 6‐yr period, two cyclic drainage‐water reuse practices were tested in a 3‐yr rotation of processing tomato (Lycopersicon esculentum L.) and cotton (Gossypium hirsutum L.). In both practices, drainage water (ECi = 7.4 dS m−1 and 0.74 mmol L−1 B) was applied to processing tomato after first bloom to take advantage of salt‐induced enhancement of fruit quality and increased crop salt tolerance at later developmental stages. In one practice, drainage water was also applied to the following cotton crop after thinning. Nonsaline water was used for irrigation at all other times and throughout for the control. When saline water was applied once every 3 yr, yields of both crops were unaffected. Tomato yields were generally lowest when saline water was applied 2 out of 3 yr, but saline water improved tomato fruit quality by increasing °Brix in most years. Changes in soil chemical and physical quality may limit long‐term reuse. Both B and salts accumulated in the soil over time, particularly at depth (60–140 cm), whereas Se was more readily leached and showed greater fluctuations in the rootzone with irrigation treatment. Calculations using reclamation formulae estimated that for low B drainage water, the amount of drainage wager used exceeded that of nonsaline water needed to return soil ECe to control levels, resulting in significant water savings. For high B drainage water, more than twice the amount of nonsaline water was needed to fully reclaim the profile than was saved by reuse. However, moderately B‐tolerant crops could be successfully grown during the reclamation period, making cyclic reuse for at least 6 yr an attractive option for growers facing limited supplies of nonsaline water supplies, or as a means to reduce effluent volumes.
Soil Characteristics of Oak Stands along an Urban‐Rural Land‐Use Gradient
Authors: Pouyat Richard V. , McDonnell Mark J. , Pickett S. T. A. 
Published: July 2010

AbstractUrban‐rural land‐use gradients are environmental gradients determined by human‐built structures and human activity. Although gradients of land use are readily measurable, little is known about the effects of urbanization on forest soil properties. In this research, soil properties were quantified in oak stands (Quercus sp.) along an urban‐rural transect in the New York City metropolitan area. A suite of 25 soil chemical properties were subjected to a Principal Component Analysis to ordinate stands. The first principal component (PC1) accounted for 42.3% of the variation. Positive loadings of PC1 corresponded to high concentrations of Pb, Cu, Ni, Ca, Mg, and K; high total soluble salt concentrations; high organic matter; high total N; and slightly more soil acidity. Stands located closer to the urban core had positive loadings on PC1; sites located beyond 30 km of the urban core had negative loadings. The variation accounted for by PC1 was significantly explained (P < 0.005) by measures of urban development quantified along the transect, including percent urban cover (r2 = 0.735), population density (r2 = 0.700), traffic volume (r2 = 0.778), and road density (r2 = 0.700). Of the heavy metals measured, Cu and Pb showed a 2.5‐ to fourfold increase in concentration from the rural to the urban land use types, with maximum concentrations for Cu reaching 49.3 mg kg−1 and Pb 181.4 mg kg−1 in the urban sites, repectively. More transects must be established in this and other metropolitan areas to build a data base to develop predictive models of ecosystem change, given the amount and type of urban development in a landscape.
Evaluation of Nitrogen Availability in Irradiated Sewage Sludge, Sludge Compost and Manure Compost
Authors: Wen Guang , Bates Thomas E. , Voroney R. Paul 
Published: July 2010

AbstractA field experiment was conducted during 2 yr to determine plant availability of organic N from organic wastes, and effects of gamma irradiation on organic N availability in sewage sludge. The wastes investigated were: digested, dewatered sewage sludge (DSS), irradiated sewage sludge (DISS), irradiated, composted sewage sludge (DICSS), and composted livestock manure (CLM). The annual application rates were: 10, 20, 30, and 40 Mg solids ha−1. Fertilizer N was added to the control, to which no waste was applied, as well as to the waste applications to ensure approximately equal amounts of available N (110 kg N ha−1) for all treatments. Lettuce (Lactuca indica L.), petunias (Petunia × hybrida Vilm.), and beans (Phaseolus vulgaris L.) were grown in 1990 and two cuts of lettuce were harvested in 1991. Crop yields and plant N concentrations were measured. Assuming that crop N harvested/available N applied would be approximately equal for the control and the waste treatments, the N from organic fraction of the wastes, which is as available as that in fertilizer, was estimated. With petunia in 1990 and the combination of first and second cut of lettuce in 1991, the percentage ranged from 11.2 to 29.7 in nonirradiated sludge, 10.1 to 14.0 in irradiated sludge, 10.5 to 32.1 in sludge compost and 10.0 to 19.7 in manure compost. Most often, the highest values were obtained with the lowest application rates. Yields of petunia and N concentrations in second cut lettuce in 1991 were lower with irradiated sludge than with nonirradiated sludge suggest that the availability of organic N in digested sludge may have been reduced after irradiation. Irradiation of sludge appears to have released NH+4‐N. The availability of organic N, however, appears to have been reduced by irradiation by greater amount than the increase in NH+4‐N.
Potential Microencapsulation of Pyrite by Artificial Inducement of Ferric Phosphate Coatings
Authors: Evangelou V. P. 
Published: July 2010

AbstractPyrite in mining waste is initially oxidized by the atmospheric O2, releasing acidity and Fe2+. At a pH below 3.5, Fe2+ is rapidly reoxidixed by Thiobacillus ferrooxidans to Fe3+, which oxidizes pyrite at a much faster rate than O2. Commonly, the approach used in preventing pyrite oxidation in the field involves the use of limestone. This approach, however, has a short span of effectiveness because the surfaces of pyrite particles in mining waste are still exposed to the atmospheric O2 after treatment. The objective of this study was to examine the feasibility in controlling pyrite oxidation by creating an FePO4 coating on pyrite surfaces to block access of the atmospheric O2 to pyritic surfaces. The coating methodology involved leaching pyrite using a chromatographic column with a 1 cm i.d. and a flow rate of 0.5 mL min−1 at 40°C with a PO4 solution containing hydrogen peroxide (H2O2); when this solution reached pyrite surfaces, H2O2 oxidized the surface portion of pyrite and released Fe3+ so that Fe phosphate precipitated and formed a passive coating on pyritic surfaces. This laboratory‐scale study demonstrated that Fe phosphate coatings on pyritic surfaces could be established with a solution containing as low as 10−4 tool L−1 phosphate and 0.03 mol L−1 H2O2 and that the FePO4 phosphate coating could effectively protect pyrite from oxidizing further.
Swine Manure Nitrogen Conservation in Storage using Sphagnum Moss
Authors: Barrington S. F. , Moreno R. Garcia 
Published: July 2010

AbstractSphagnum peat moss, floating on swine manure in storage, was tested during three summers as an N conservation method in experimental tanks which measured 0.75 m in diameter and 3.0 m deep. Three depths of floating peat moss (0, 10, and 20 cm) were tested. The swine manure was analyzed prior to the tests and after 14 wk of storage, from June to mid‐September. An average of 54, 60, and 76% total N conservation was observed for the respective treatments. Twenty centimeters of peat moss significantly reduced manure N losses and manure evaporation during storage.