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PubMed2004

Arsenic and lead leaching from the waste derived fertilizer ironite.

The toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP) were performed on commercially purchased samples of the waste-derived soil amendment marketed as Ironite. Ten samples of the 1-0-0 grade (the most widely available in Florida) were tested. Two samples of the 12-10-10 grade and three samples of the 6-2-1 grade (a liquid version) were tested as well. TCLP leachate concentrations from the 1-0-0 grade samples ranged from 5.0 to 8.0 mg L(-1) for lead and 2.2 to 4.8 mg L(-1) for arsenic. SPLP concentrations from the 1-0-0 samples ranged from 0.62 to 3.1 mg L(-1) for lead and 1.9 to 8.2 mg L(-1) for arsenic. All of the 1-0-0 grade samples exceeded the U.S. hazardous waste toxicity characteristic (TC) limit for lead (5 mg L(-1)), while five of the 10 SPLP samples exceeded the TC limit for arsenic (5 mg L(-1)). The greater arsenic leachability in the SPLP relative to the TCLP was determined to be a result of lower pH conditions in the SPLP. A composite sample of the 1-0-0 grade was found to leach much greater concentrations of both arsenic and lead using California's waste extraction test (WET). Lead leachate concentrations were much lower in the two 12-10-10 samples (0.03 mg L(-1) or less); arsenic concentrations in these leachates (both TCLP and SPLP) exceeded 5 mg L(-1). None of the 6-2-1 samples contained lead or arsenic above TC limits. An experiment performed on the 1-0-0 grade which examined leachability as a function of pH found that at pH values in the range of what is encountered in the human digestive system (pH 4.0 to 1.5) lead leached 2-36% of its initial content, and arsenic leached 1-6% of its initial content. A simple gastric acid leaching experiment found 83 and 37% of the lead and arsenic present to leach, respectively.

Arizona↗
PubMed2003

Mobility and degradation of the herbicide imazosulfuron in lysimeters under field conditions.

The mobility and degradation of imazosulfuron, labeled with carbon-14 at the imidazole ([imi-(14)C]imazo) or pyrimidine ring ([pyr-(14)C]imazo), in lysimeters with 1 m(2) surface and 110 cm depth were investigated for three years. One lysimeter was treated with [imi-(14)C]imazo in two successive years at the rate of 50 g of active ingredient (ai)/ha each. The other two lysimeters were treated once with [pyr-(14)C]imazo and a mixture (1:1, w/w) of the two labeled imazosulfurons, respectively (50 g of ai/ha). In the first and second years of monitoring, the yearly mean concentration of (14)C in the leachate water was <0.10 microg/L in each lysimeter. Although in the third year the concentration of (14)C in the leachate water was 0.17 microg/L for the lysimeter treated twice with [imi-(14)C]imazo, the concentration of imazosulfuron and its degradation products in the leachate water ranged from 0.01 to 0.06 microg/L. At the study termination, the main portion of (14)C recovered was found in the upper 30 cm soil layer in each lysimeter, and no (14)C was detected below a depth of 50 cm. These findings indicated that imazosulfuron and its degradation products in soils translocated into groundwater only slightly.

Carbon Radioisotopes↗
PubMed2006

Lysimeter experiment to investigate the potential influence of diffusion-limited sorption on pesticide availability for leaching.

Pesticide leaching from soil has been shown to decrease with increasing time from application to irrigation. It is hypothesized that the availability of compounds for leaching decreases due to diffusion and sorption inside soil aggregates. Previous work showed that pesticide sorption inside soil aggregates increases significantly during the first days after application. The study presented here tested if diffusion into aggregates could explain the leaching of four aged pesticides from manually irrigated soil cores. Azoxystrobin, chlorotoluron, cyanazine, and bentazone were applied to 30 undisturbed cores (25 cm long, 23.7 cm diameter) from a clay loam soil. The soil cores were irrigated 1, 3, 7, 14, and 28 days after application. Leachate was collected and analyzed. The amount of pesticide found in leachate decreased rapidly with time from application. Pesticide losses in leachate declined 2.5-27 times faster than total residues in soil. The decline was 4-5 times faster for the more strongly sorbed pesticides (azoxystrobin, chlorotoluron, and cyanazine) than for bentazone. In previous work, we derived a model to describe sorption and diffusion of the pesticides in small aggregates from the same soil. The diffusion model was used here to describe sorption inside the large aggregates in the soil cores and extended to describe pesticide leaching by interaggregate flow. The model showed a significant decline in leaching with time from application, which supports the theory that diffusion-limited sorption in aggregates influences the availability for pesticide leaching, although it does not exclude alternative explanations for this decline. The model well described the decline in leaching for three out of four pesticides. The interaggregate transport model could, however, not account for the amount of preferential flow in the cores and underestimated the leaching of bentazone.

Benzothiadiazines↗
PubMed2003

Isolation and structural characterization of a water-soluble germination inhibitor from Scotch thistle (Onopordum acanthium) cypselas.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.

Biological Assay↗
PubMedDate not supplied

Ring-testing and field-validation of a terrestrial model ecosystem (TME)--an instrument for testing potentially harmful substances: effects of carbendazim on nutrient cycling.

The effect of the fungicide carbendazim (applied in the formulation Derosal) on nutrient cycling in soil was determined in Terrestrial Model Ecosystem (TME) tests and corresponding field-validation studies, which were performed in four different countries (United Kingdom, Germany, Portugal, and The Netherlands). The tests used different soil types, and lasted for 16 weeks. On three of the four sites, grassland soils were used while the fourth site had an arable soil. TMEs consisted of intact soil columns (diameter 17.5 cm; length 40 cm) and were taken from the site where the field study was performed. In the first series of TME tests, carbendazim applied at dosages unto 77.8 kg a.i./ha did not affect sulfate and phosphate concentrations in the top 15 cm soil layers. These nutrients were therefore no longer included in the second series of TME tests and the field-validation studies. Ammonium concentrations in the top soil layers of TMEs and field plots, and in the leachates of the TME columns did not show any effect of carbendazim treatment. Nitrate concentrations in soils and leachates did show some reduction at the highest treatment levels (77.8 kg a.i./ha in the first TME tests, 87.5 kg a.i/ha in the second TME tests and the field-validation studies). Since nitrate concentrations in both soils and leachates were correlated with soil moisture content, these effects could however, mainly be attributed to variations in soil moisture contents, and in some cases also indirectly to effects on earthworm activity. It is concluded that carbendazim, even at dosages as high as 87.5 kg a.i./ha, does not have a significant impact on soil nutrient cycling processes. Nutrient levels in TME tests and the field-validation studies generally showed similar patterns, thus confirming the predictive value of the TME test system.

Benzimidazoles↗
PubMed2005

Determination and evaluation of hexavalent chromium in power plant coal combustion by-products and cost-effective environmental remediation solutions using acid mine drainage.

The chromium species leaching from a coal combustion fly ash landfill has been characterized as well as a novel approach to treat leachates rich in hexavalent chromium, Cr(VI), by using another natural waste by-product, acid mine drainage (AMD), has been investigated during this study. It is observed that as much as 8% (approximately 10 microg g(-1) in fly ash) of total chromium is converted to the Cr(VI) species during oxidative combustion of coal and remains in the resulting ash as a stable species, however, it is significantly mobile in water based leaching. Approximately 1.23 +/- 0.01 microg g(-1) of Cr(VI) was found in the landfill leachate from permanent deposits of aged fly ash. This study also confirmed the use of AMD, which often is in close proximity to coal combustion by-product landfills, is an extremely effective and economical remediation option for the elimination of hexavalent chromium in fly ash generated leachate. Speciated isotope dilution mass spectrometry (SIDMS), as described in EPA Method 6800, was used to analytically evaluate and validate the field application of the ferrous iron and chromate chemistry in the remediation of Cr(VI) runoff.

Acids↗
PubMed2006

Pyrolysis-field ionization mass spectrometry of rhizodeposits - a new approach to identify potential effects of genetically modified plants on soil organisms.

The objectives of the present study were (1) to investigate the qualitative composition of rhizodeposits leached from soils cropped with non-transgenic and genetically modified (GM) potatoes, and disclose if there were GM-specific modifications in potato rhizodeposition, and (2) to compare these results with conventional bulk parameters of microbial activity in soil. We have raised potatoes from a non-transgenic line (Solanum tuberosum L. cv. Désirée) and three GM lines, which expressed a gene for the resistance to kanamycin (DLH 9000) and a gene for T4 lysozyme (DL10 and DL12). A sandy soil placed in 340 cm3-"CombiSart" containers was used, from which the rhizodeposit was leached after a six-week growth period. The freeze-dried leachates were analyzed by pyrolysis-field ionization mass spectrometry (Py-FIMS). The Py-FI mass spectra gave detailed molecular-chemical information about the composition of leachates, indicating that the potato growth generally altered the composition of the soil solution. Moreover, a principal component analysis of the mass spectra showed differences between the leachates from the non-transgenic parent line and the GM potatoes as well as among the latter group. However, these differences in molecular composition could not be assigned to the release of T4-lysozyme into soil. Dehydrogenase activity and substrate-induced soil respiration as more common bulk parameters of soil microbial activity failed to disclose any significant effects of the various potatoes grown. The limitations of the described rhizodeposit leaching and analysis for risk assessment of GM potato cropping under field conditions are discussed critically. However, it could be concluded that the Py-FI mass spectrometric "fingerprint" can be developed as a fast, comprehensive, highly sensitive and reproducible analytical approach to discern any effects GM-crops may exert on soil ecological parameters.

Animals↗
PubMed2006

Leaching potential of some phenylureas and their main metabolites through laboratory studies.

BACKGROUND, AIMS AND SCOPE: Laboratory studies were conducted with the aim of defining the leaching potential of some phenylureas and their metabolites. A first study was performed for calculating their leaching index (as GUS) on the base of intrinsic properties: persistence (as DT50) and mobility (as Koc) in soil. Another study consisted of aged column leaching experiments whose meaning was to semi-quantify the occurrence of the tested compounds in the leachates, so simulating in field conditions. METHODS: The tested compounds were: diuron, linuron and monolinuron (parents); 3,4-dichloroaniline (DCA), 4-chloroaniline (CLA), 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), 1-(4-chlorophenyl)urea (CPU) and monuron, this latter considered both as a metabolite and parent compound. The Koc values of the examined substances were determined by the HPLC screening methods, according to the OECD TG 121. DT50 determinations and aged column leaching experiments were carried out according to SETAC procedures. RESULTS AND DISCUSSION: The examined compounds showed a rather wide range of persistence in soil, with DT50 values less than 2 days for DCA and CLA, close to 8 days for DCPU and CPU and from 16 (diuron) up to 24.8 (DCPMU) days for the others. Their mobility was generally high, based on their Koc values, which ranged from 33 (CPU) to 406 (linuron). The GUS indices indicated that monuron has a clear potential to contaminate groundwater (> 2.8); DCPMU, monolinuron, CPU and diuron are intermediate contaminants (1.8-2.8). Linuron, DCPU, CLA and DCA exhibited a non-leaching behaviour (< 1.8). The aged leaching column experiments showed that parents were found in the leachates at very high percentages respect to the doses applied. The metabolites reached much less percentages, the highest values were observed for monuron from diuron (5.7), CPU (7.2) and DCPMU (8.2%). CONCLUSION: Diuron, Monuron, CPU and DCPMU on the basis of their intrinsic properties, formation from their parents and occurrence in leachates from aged column leaching studies, seem to possess the characteristics of groundwater contaminants. The methodological approach of this study is relatively easy and rapid, hence it can represent a tool for a first screening of compounds such as pesticide metabolites (generally available only in small quantities and for which a field study is not conceivable) or other compounds for which not adequate environmental data are available.

Herbicides↗
PubMed1997

Comparison of gas chromatography and immunoassay methods for the detection of atrazine in water and soil.

Leachate and soil samples collected from different tillage systems were analyzed for atrazine using gas chromatography (GC) and an enzyme-linked immunosorbent assay (ELISA) based on magnetic particle technology. Solid-phase extraction (SPE) was used to concentrate atrazine residues in leachate samples and soil extracts before GC analysis. Atrazine concentrations determined by GC ranged from 0.1 to 600 micrograms L-1 for water samples and from 1.0 to 700 micrograms kg-1 for soil samples. Atrazine concentrations in 92 leachate samples as determined by ELISA were well-correlated (R = 0.97) with GC levels over the entire concentration range. Soil samples (215) were prepared and analyzed by three combinations of extraction/detection methods: 1) conventional extraction for GC/detection by GC analysis; 2)conventional extraction for GC/detection by ELISA analysis; 3)extraction for ELISA using a commercially available field kit/detection by ELISA analysis. Methanol (MeOH) in water was the common extractant. Although the initial comparison of soil extracts between the two different systems (Method 1 versus Method 3) was favorable (R = 0.97), two-thirds of the samples contained levels below the lower threshold for atrazine detection by both methods and some extracts were perceived to provide unfavorable substrate conditions (> 10% MeOH). Elimination of these data points reduced the correlation value (R = 0.77). To determine possible sources of variability, the extraction and detection methods were examined separately. In a comparison of extraction methods (Method 2 versus Method 3), ELISA analysis of kit extracts underestimated (R = 0.71) atrazine levels compared to those conventionally extracted, suggesting that differences in extraction time between methods may have accounted for reduced kit efficiency. Where detection methods (Method 1 versus Method 2) were compared on specific extracts (< 10% MeOH), good agreement (R = 0.99) was achieved between ELISA and GC values, illustrating that control of extractant concentration is critical in using this assay for atrazine detection in soil.

Atrazine↗
PubMed1998

Adsorption and leaching of trifluralin, metolachlor, and metribuzin in a commerce soil.

Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], metolachlor [2-chloro-N-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) aceta mide], and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4,-triazin-5(4H) -one] were selected to study adsorption and leaching potentials related to pollution on Commerce silty clay loam soil near Baton Rouge, Louisiana. At a I:10 soil/water ratio, the Koc values for trifluralin, metolachlor and metribuzin were 875, 135, and 96, respectively. Leaching of these herbicides was evaluated in soil columns (5.4 cm i.d. x 26 cm long). Total recoveries of the herbicides applied to the soil column were 73.1% +/- 4.1%. When the soil columns were leached with three pore volumes of water, the distributions of trifluralin in soil and leachate were 99.993% and 0.007% of the total recoveries, respectively. The distributions of metolachlor was 65.27% in soil and 34.7% in leachate. The distributions of metribuzin was 11.42% in soil and 88.58% in leachate. The results showed that metolachlor and metribuzin were readily leached, while trifluralin was strongly adsorbed to soil. Leaching of three herbicides in the soil column followed the leaching trends of their calculated leaching indices 1.41 x 10(4), 4.18 x 10(6), and 3.38 x 10(8) for trifluralin, metolachlor, and metribuzin, respectively. The results of the study demonstrated the potential of pollution for metolachlor and metribuzin to be leached into the ground water in soils with shallow aquifer.

Acetamides↗
PubMed1999

Anaerobic treatment of poultry mortalities in a modified LB-UASB system.

The efficiency of a modified LB-UASB system in treating poultry mortalities was tested. The anaerobic digestion system consisted of an upflow anaerobic sludge blanket (UASB) and three leachbeds (LB). The LBs were batch-loaded with mortality to be treated. The LBs were sequentially connected to the UASB, one at a time. Leachate from a connected LB was fed to the UASB while effluent from the UASB overflowed to the LB to form a closed loop. When the concentrations of leachate from the first LB became so low that it could no longer support accelerated methanogenesis in the UASB, it was replaced by a second LB containing a new batch of mortality. Concentrated leachate from the second LB allowed the UASB to continue operation at higher loading rates (LR), thus, alleviating the problems of lengthy LR build-up and idling time. Meanwhile, the off-lined LB continued to mature independently. The UASB was connected to a third LB when the second LB entered accelerated methanogenesis phase. Operation of the first LB was stopped when CH4 production rate from it became marginal. The remaining solids material was replaced by a new batch of mortality to start the second cycle. The first cycle was completed when fermentation in the third LB was ended. The modified LB-UASB system performed significantly better than the original system. It took an average of only 86 days to treat one batch of mortality, yet, the methane yield was about 40% higher. The average methane yield was 0.28 m3 (kg wet weight)-1. Strategies to optimize system performances are discussed.

Anaerobiosis↗
PubMed2003

A novel electrobiotechnology for the recovery of precious metals from spent automotive catalysts.

Platinum group metals are routinely used in automotive catalysts but recycle technology lags behind demand. There is no available 'dean technology' and leach solutions (e.g. aqua regia) to solubilise the metals from scrap are highly aggressive. A microwave-assisted leaching method was developed which gave 80% metals recovery, with the leach time reduced from 2 h to 15 min using 50% (aq.) diluted aqua regia to give potentially a more biocompatible leachate. Desulfovibrio desulfuricans reduces soluble platinum group metals to cell-bound insoluble base metals (e.g. Pd(II) --> Pd(0)). For use, biofilm was immobilised on a Pd-23% Ag solid alloy membrane which delivered H. to the cells via an electrochemical chamber at the back-side. The biomass-coated Pd-Ag alloy electrode was used in a flow-through reactor for recovery of Pd, Pt and Rh from aqua regia leachates (pH 2.5) of spent automotive catalysts with up to 90% efficiency at a flow residence time of 15 minutes. Free cells did not reduce platinum group metals from the leachates but the electrobioreactor did so using biofilm-cells pre-loaded with Pd(0). Reactors lacking biomass or reactors with heat-killed biofilm removed less platinum group metals, via electrochemically-synthesised H. reductant alone. The use of an active biofilm layer in a flow-through electrobioreactor provides a simple, dean and rapid potential recycle technology.

Bioreactors↗
PubMed2002

[Lead and zinc recovery by adsorption on peat moss during municipal incinerator used lime decontamination].

The objective of this research was to evaluate the efficiency of peat moss for lead and Zn recovery from alkaline leachates (pH 11.5) produced during decontamination of municipal incinerator fly ash. Tests carried out with peat moss columns (density of 0.13 g m l(-1)) gave very high removal yields for lead (98.9 to 100%) and Zn (98.4 to 99.8 %). The initial metal concentrations in the leachates were 126 to 138 mg Pb l(-1) and 14.4 to 23.5 mg Zn l(-1). The columns were fed using two rates (20 and 40 ml min(-1)), which correspond respectively to 17.6 and 8.8 min as contact time on peat moss. Adsorption efficiencies of 16 to 18 mg Pb g(-1) and 1.7 to 3.2 mg Zn g(-1) have been measured during this fly ash leachate treatment study. The adsorbed toxic metals can be desorbed using a chlorhydric acid solution. The peat moss can be regenerated and reused for several adsorption cycles without loss of the lead and Zn adsorption efficiencies.

Adsorption↗
PubMed1998

Stabilization of a chromium-containing solid waste: immobilization of hexavalent chromium

This article describes the stabilization/solidification (S/S) of a steel industry waste, using a common type-F fly ash from a coal power station as the main binder. The waste, which contains hazardous levels of metals, may be stabilized by a conventional S/S to achieve permissible Pb, Cd, and Zn concentrations in the Toxicity Characteristic Leaching Procedure (TCLP) leachates of S/S solids. On the other hand, the stabilization of Cr(VI), also present in the waste, requires a reducing pretreatment stage with ferrous sulfate to attain TCLP leachates within limits. A bibliographic study on the stabilization of Cr(VI)-containing wastes is included in the paper, along with a discussion on the lowest Cr concentration in TCLP and aqueous (DIN) leachates.

Journal Article↗
PubMed2005

Geological characterization and environmental implications of the placement of the Morelia Dump, Michoacán, Central Mexico.

The landfill of Morelia, the capital city of the state of Michoacán in central-western Mexico, is located 12 km west of the city and has operated since 1997 without a structure engineered and designed to control the generation in situ of biogas and leachates. A geological evaluation of the landfill site is presented in this paper. The results indicate that the site lacks ideal impermeable subsurface strata. The subsurface strata consist of highly fractured basaltic lava flows (east-west fault and fracture system trend) and sand-size cineritic material with high permeability and porosity. Geochemical analysis of groundwater from Morelia's municipal aquifer shows a high concentration of heavy metals (Cd, Pb, As) exceeding the Mexican environmental regulations, along with the presence of some organic pollutants (phenols). Analyses of samples of the landfill's permanent leachate ponds show very high concentrations of the same contaminants. Samples were taken from the leachate pond and from nearby water-wells during the rainy season (summer 1997) and the dry season (spring 1997, 1998, and 1999). In all cases, the concentration of contaminants registered exceeded the standards for drinking water of the World Health Organization (American Public Health Association, American Water Works Association, and Water Pollution Control Federation, 2000). Some metal contaminants could be leaching directly from the landfill.

Decision Making↗
PubMed2002

Removal of pollutants from wastewater by coal bottom ash.

Coal bottom ash produced from a thermal power plant was used in a batch experiment to investigate the adsorption characteristic of this bottom ash. The adsorbate solutions were synthetic wastewaters contained copper (Cu2+) or COD and a sanitary landfill leachate. The influences of various factors, such as contact time, pH, initial adsorbate concentration and temperature on the sorption have been studied. Experimental results show that coal bottom ash had a good adsorption capacity for copper and COD and could reduce the concentrations of various pollutants in the leachate. The adsorption capacities of each gram of coal bottom ash were 0.48 mg Cu (at pH 4 and temperature 25 degrees C) and 7.5 mg COD (at pH 5 and temperature 25 degrees C); their adsorption behaviors conformed to Freundlich's adsorption model. In treating leachate, the removal efficiencies of COD, NH3--N, total Kjeldah nitrogen, phosphorus, Fe3+, Mn2+ and Zn2+ were 47, 39.4, 31.1, 92.9, 96.5, 94.3 and 82.2%, respectively. Based on these results we can conclude that it is possible to use coal bottom ash for removing pollutants from wastewaters. The adsorption capacities of coal bottom ash for pollutants were also determined.

Adsorption↗
PubMed2005

Epoetin-associated pure red cell aplasia in patients with chronic kidney disease: solving the mystery.

A substantial increase in the incidence of pure red cell aplasia (PRCA) associated with recombinant human erythropoietin (epoetin) treatment occurred in 1998. The upsurge of antibody-mediated PRCA was almost exclusively associated with chronic kidney disease patients who received subcutaneous epoetin therapy and the formulation of epoetin-alpha distributed outside the USA (EPREX/ERYPO). A systematic programme of technical, immunological and epidemiological investigations was initiated to identify the possible causes. The potential causes were evaluated on the basis of the following criteria: temporal correlation with the increase in incidence of PRCA, significant difference between EPREX/ERYPO and other epoetin products, sufficient concentration in the product to elicit a weak immune response, evidence of immunogenic activity in animals supportive, and consistent with available clinical data. Organic compounds that were leached from rubber stoppers through the action of polysorbate 80 were detected in pre-filled syringes with uncoated rubber stoppers containing polysorbate 80-formulated EPREX/ERYPO (introduced outside the USA in 1998). The leachates were not present when the stoppers were coated, in the product formulated with human serum albumin or in other epoetin products. The adjuvant activity of the leachates was demonstrated in mice. The incidence of PRCA was significantly higher in patients exposed to the polysorbate 80 formulation of epoetin-alpha delivered from pre-filled syringes with uncoated rubber stoppers, which were recalled in 2003, than in patients exposed to the same formulation from syringes with coated rubber stoppers. In conclusion, these data strongly suggest that leachates were the critical contributory factor in the increased incidence of antibody-mediated PRCA attributed to EPREX/ERYPO.

Anemia↗
PubMed2001

Effect of winter cover crops on soil nitrogen availability, corn yield, and nitrate leaching.

Biculture of nonlegumes and legumes could serve as cover crops for increasing main crop yield, while reducing NO3 leaching. This study, conducted from 1994 to 1999, determined the effect of monocultured cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum), and hairy vetch (Vicia villosa), and bicultured rye/vetch and ryegrass/vetch on N availability in soil, corn (Zea mays L.) yield, and NO3-N leaching in a silt loam soil. The field had been in corn and cover crop rotation since 1987. In addition to the cover crop treatments, there were four N fertilizer rates (0, 67, 134, and 201 kg N ha(-1), referred to as N0, N1, N2, and N3, respectively) applied to corn. The experiment was a randomized split-block design with three replications for each treatment. Lysimeters were installed in 1987 at 0.75 m below the soil surface for leachate collection for the N 0, N 2, and N 3 treatments. The result showed that vetch monoculture had the most influence on soil N availability and corn yield, followed by the bicultures. Rye or ryegrass monoculture had either no effect or an adverse effect on corn yield and soil N availability. Leachate NO3-N concentration was highest where vetch cover crop was planted regardless of N rates, which suggests that N mineralization of vetch N continued well into the fall and winter. Leachate NO3-N concentration increased with increasing N fertilizer rates and exceeded the U.S. Environmental Protection Agency's drinking water standard of 10 mg N l(-1) even at recommended N rate for corn in this region (coastal Pacific Northwest). In comparisons of the average NO3-N concentration during the period of high N leaching, monocultured rye and ryegrass or bicultured rye/vetch and ryegrass/vetch very effectively decreased N leaching in 1998 with dry fall weather. The amount of N available for leaching (determined based on the presidedress nitrate test, the amount of N fertilizer applied, and N uptake) correlated well with average NO3-N during the high N leaching period for vetch cover crop treatment and for the control without the cover crops. The correlation, however, failed for other cover crops largely because of variable effectiveness of the cover crops in reducing NO3 leaching during the 5 years of this study. Further research is needed to determine if relay cover crops planted into standing summer crops is a more appropriate approach than fall seeding in this region to gain sufficient growth of the cover crop by fall. Testing with other main crops that have earlier harvest dates than corn is also needed to further validate the effectiveness of the bicultures to increase soil N availability while protecting the water quality.

Agriculture↗