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Groundwater resources in semiarid lands of central Argentina are currently threatened by contamination from agricultural pesticides. This chapter addresses the vulnerability and risk assessment of the quaternary aquifer system as regards pesticide pollution. We used pesticide DRASTIC Index and PIRI GIS-based models to assess the groundwater vulnerability and leaching potential of commonly used herbicides. DRASTIC and PIRI are two indices that provide complementary information. Incorporating them into a decision support system would help policy makers to identify areas most vulnerable to groundwater pollution and develop herbicide usage guidelines that protect groundwater resources.

In a 2‐yr field study, we evaluated the emergence and early growth of Chenopodium album L. (common lambsquarters) seedlings as affected by the landscape position in which the seeds (i) developed, (ii) overwintered, and (iii) were planted. Results indicated that a higher proportion of seeds originating from lower slope positions emerged compared with seeds originating from the backslope or upper slope. The timing of emergence was the same for all seed source locations. There was no influence of overwintering location on weed emergence. Regardless of the seed source, we observed faster emergence and growth of C. album planted in the lower slope, where soil conditions were more conducive to growth. These experiments will support the development of new strategies and decision aids to improve weed management.

BACKGROUND Biochar, a carbon-rich product of biomass pyrolysis, could limit glyphosate transport in soil and remediate contaminated water. The present study investigates the sorption/desorption behavior of glyphosate on biochars prepared from different hardwoods at temperatures ranging from 350 to 900 °C to elucidate fundamental mechanisms. RESULTS Glyphosate (1 mg L−1) sorption on biochars increased with pyrolysis temperature and was highest on 900 °C biochars; however, total sorption was low on a mass basis (

Leaching of nitrate (NO3-N) from manure-applied cropping systems can represent a substantial N-loss to the environment for dairy farms, particularly in fields with artificial subsurface drainage. In this on-farm study, we used a Before/After analysis to assess the effectiveness of summer fertigation with reduced manure rates (years 2010 – 2015) versus fall injection (2007 – 2009) of dairy slurry in terms of subsequent corn silage yield, corn N removal, soil NO3-N distribution, and NO3-N losses in subsurface tile drainage from a 65-ha field in Minnesota, USA. Yield was similar between periods (average of 18.8 Mg ha-1), but crop %N, N removal, and manurial N-use efficiency were 15, 12, and 126% greater during the fertigation than injection period. Fertigation reduced spring soil NO3-N concentrations to 60-cm depth by an average of 53% relative to injection, except in the 15 to 30 cm increment, where no difference was found. Similarly, fall soil NO3-N concentrations from 30 to 90 cm were 48% lower, on average, under fertigation than injection. Weekly flow-weighted mean NO3-N concentration in tile drainage was lower during fertigation (47.7 mg L-1) than injection (56.8 mg L-1), although mean weekly drainage depth was greater during fertigation (2.3 versus 1.1 mm). This resulted in similar weekly loads between periods (mean of 0.96 kg NO3-N ha-1). For non-snowmelt flow, relationships between drainage and NO3-N load showed log–log slopes of near 1.0 for injection and 0.97 for fertigation, indicating dilution of concentrations with increased flow during fertigation, but not during injection. Differing intercepts indicated a treatment effect of fertigation independent of flow effects, and corresponded to loads of 5.9 kg NO3-N ha-1 for injection and 4.7 kg NO3-N ha-1 for fertigation, a reduction of 20% at a 10 mm weekly flow depth. The magnitude of the reduction in load increased to 22% at a 25 mm weekly flow depth. Results suggest that summer fertigation with attendant reduction in application rate is a viable method for reducing drainage NO3-N losses without impacting yield of irrigated silage corn in the U.S. Midwest.

The use of neonicotinoid insecticides in the United States has grown by about a factor of four since the mid-2000s. Seed treatments account for a significant fraction of overall insecticide application to crops, and a large proportion of major U.S. crops are now planted using seed treated with neonicotinoids. Neonicotinoid insecticidal seed treatments are primarily intended to protect crops against sporadic or minor early-season pests. A better understanding of factors that influence the risk of economic infestations and extent of crop damage by sporadic pests is needed to target neonicotinoid insecticidal seed treatments use based on expected pest pressure. In a series of papers, we review the distribution, ecology, and historical management of seed and seedling pests targeted by neonicotinoid seed treatments in U.S. corn (Zea mays), soybean (Glycine max), wheat (Triticum aestivum), and cotton (Gossypium hirsutum L.). This information is key to region-specific management practices that reduce the risks and increase the benefits of neonicotinoid seed treatments.

The use of insecticides at planting has been a common crop management practice in cotton for several decades. Historically, U.S. cotton growers relied on in-furrow applications of insecticides, such as aldicarb, to control early-season insect pests. In-furrow applications have largely been replaced with insecticide-treated seed. Since 2012, more than 60% of the U.S. cotton crop is planted with seed treated with insecticide, primarily the neonicotinoids imidacloprid or thiamethoxam. Several insects or insect groups are included on the labels of these neonicotinoids for use as seed treatments. An increased understanding of the risks associated with economically injurious populations of insect pests is needed to optimize use of early-season insecticides and reduce over-reliance on them in cotton, especially when initial decisions for insect control before planting have subsequent influence on future pest abundance. Existing literature pertaining to these early-season cotton insect pests was examined to identify factors favoring their distribution and abundance and the importance of insect control tactics used at planting. The relative importance of some of these pests is dependent on the cotton-growing region and impacted by local production practices. Thrips (predominantly Frankliniella spp.) (Thysanoptera: Thripidae) are the most prevalent early-season insect group in cotton across the United States and the primary target of initial insect control. Other targeted insects include the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), aphids (predominantly Aphis gossypii Glover) (Hemiptera: Aphididae), plant bugs (Hemiptera: Miridae), and wireworms (Coleoptera: Elateridae).

Soybean faces potential economic damage from a wide variety of early-season invertebrate pests. The objective of this article was to determine the extent and intensity of nine early-season soybean insect pests targeted for control by insecticidal seed treatments in the United States and to identify various management options for them: bean leaf beetle (Cerotoma trifurcate Förster, Coleoptera: Chrysomelidae); grape colaspis, Colaspis brunnea (F.) (Coleoptera: Chrysomelidae); leafhoppers (Hemiptera: Ciccadellidae); seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae); soybean aphid (Aphis glycines Matsumura, Hemiptera: Aphididae); threecornered alfalfa hopper, Spsistilus festinus (Say) (Hemiptera: Membracidae); thrips (Thysanoptera: Thripidae); white grubs (Coleoptera: Scarabaeidae); and wireworms (Coleoptera: Elateridae). Seedcorn maggot, white grubs, and wireworms have been limited to a relatively small proportion of soybean fields with readily defined factors regarding their risk. However, questions about the pest status of the other six pests were identified. Bean leaf beetle, which vectors Bean pod mottle virus to soybean, has been present across major soybean-production regions, but frequency and proportion of soybean fields that economically impacted is not adequately documented. The impact of threecornered alfalfa hopper and thrips on soybean productivity varied within regions, but specific reasons for the variation were unclear. Early-season management of grape colaspis and leafhoppers has been infrequent, but factors that promoted economic injury and the need for management in specific fields were undetermined. Although early-season management of soybean aphid has not proven feasible for individual fields, questions remain regarding its management in fields near overwintering stands and the possibility for areawide suppression.

A preventative insecticide treatment is a tactic compatible with an integrated pest management (IPM) strategy for a particular pest only when a rescue treatment is not a realistic option, and if there is a reasonable expectation of economic damage by that pest. Most corn, Zea mays L., planted in the United States is protected from several sporadic early-season insect pests by neonicotinoid seed treatments, usually without the knowledge of the threat posed in a given field. We undertook an extensive literature review of these sporadic pests to clarify the prevalence of economic infestations in different regions of the United States, and the agronomic, biotic, and abiotic factors that affect the likelihood of attack. The summaries of the prevalence and risk factors presented here should help farmers and consultants better assess the value of preventative protection of seedling corn under local conditions, and provide others with a better understanding of the complexities farmers face in assessing risks posed by potential pests. The profiles suggest that, in general, pressure from most sporadic pests on seedling corn is rare or local, seldom high enough to decrease yield. However, this is not true in all regions for all sporadic pests. An important issue exposed by the profiles is that the value of preventative insecticide protection of seedling corn depends on understanding the likely combined pressure from multiple species. While such risk may often still be negligible, there is a great need for robust methodology to assess the risk posed by multiple pests. This represents a significant challenge for future research.

The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae); cereal aphids (Hemiptera: Aphididae); and wireworms (Coleoptera: Elateridae) are three common and important insect pests of seedling wheat, Triticum aestivum L., in the United States. Though less common as pests, false wireworms (Coleoptera: Tenebrionidae) may also be problematic in situations that favor wireworms. In addition, cereal aphids vector viruses that cause barley yellow dwarf, a serious and widespread wheat disease. Scientific journal publications, review articles, and management guidebooks on wheat insect pests were consulted to determine the extent and intensity that these pests impose on wheat production in the United States. Widespread outbreaks occur infrequently, but local outbreaks happen nearly every year for the three major pests and cause several millions of dollars in crop losses annually. Hessian fly perennially threatens wheat in the southeastern United States, and wireworms are persistent pests in northwestern wheat-production systems. Otherwise, the particular location and severity of outbreaks vary yearly and are largely unpredictable. However, particular agronomic practices can greatly reduce risk of infestation such as elimination of volunteer wheat and weedy hosts and planting wheat during periods of reduced pest abundance. In addition, resistant cultivars can limit Hessian fly and Russian wheat aphid (Diuraphis noxia [Kurdjumov]) damage in some areas, but virulent biotypes of each pest complicate their management. Although several preemptive tactics reliably suppress infestations and barley yellow dwarf severity, they are not compatible in all agricultural systems. Consequently, insecticides are necessary in certain areas and within particular production systems to manage major early-season insect pests of wheat.

As pollinator decline continues, the need to provide high value forage for insects increases. Finding agricultural crops to diversify the landscape and provide forage is one way to improve pollinator health. Three winter industrial oilseed crops (pennycress, winter camelina, and winter canola) were grown in Morris, Minnesota, and Brookings, South Dakota, during the winters of 2012–2013 and 2013–2014. Each of the three crops has pollinator-friendly flowers and value as winter cover crops and cash seed crops. The crops were evaluated for pollinator use, nectar production, green cover, and yield. Pennycress, camelina, and canola flowers had high insect activity with maximum visitation rates of 67 ± 11.5, 22 ± 3.1, and 61 ± 6.8 insects min−1. Cumulative nectar produced by pennycress, camelina, and canola was 13, 100, and 82 kg of sugar ha−1 during the 2014 anthesis period, providing an important food resource to pollinators during early spring when there is little else on the agricultural landscape that is blooming. Green cover in early spring ranged from 0 to 60% amongst the three crops, with camelina providing >25% green cover across all four site-years. Maximum seed yields were 1.1 ± 0.04, 1.4 ± 0.05, and 1.2 ± 0.19 Mg ha−1 for pennycress, camelina, and canola, respectively, which are economically viable harvests. Of the three crops, winter camelina provided the highest combined agroecosystem value through pollinator resources, green cover, and seed yields.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Biochar is a solid material obtained when biomass is thermochemically converted in an oxygen-limited environment. In most previous studies, the impacts of biochar on soil properties and organic carbon (C) were investigated under controlled conditions, mainly laboratory incubation or greenhouse studies. This 2-year field study was conducted to evaluate the influence of biochar on selected soil physical and chemical properties and carbon and nitrogen fractions for two selected soil types (clay loam and a sandy loam soil) under a corn (Zea mays L.)-soybean (Glycine max L.) rotation. The three plant based biochar materials used for this study were corn stover (CS), ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue (PW), and switchgrass (Panicum virgatum L.) (SG). Data showed that CS and SG significantly increased the pH of acidic soil at the eroded landscape position but produced no significant change in soil pH at the depositional landscape position. The effects of biochar treatments on cold water extractable C (WSC) and nitrogen (WSN) fractions for the 0–7.5 cm depth were depended on biochar and soil type. Results suggested that alkaline biochars applied at 10 Mg ha−1 can increase the pH and WSC fraction of acidic sandy loam soil, but the 10 Mg ha−1 rate might be low to substantially improve physical properties and hot water extractable C and N fractions of soil. Application of higher rates of biochar and long-term monitoring is needed to quantify the benefits of biochar under field conditions on soils in different environmental conditions.

In an energy-limited world, biomass may be converted to energy products through pyrolysis. A byproduct of this process is biochar. A better understanding is needed of the sorption characteristics of biochars, which can influence the availability of plant essential nutrients and potential water contaminants such as phosphorus (P) in soil. Knowledge of P retention and release mechanisms when applying carbon-rich amendments such as biochar to soil is needed. The objectives of this study were to quantify the P sorption and availability from biochars produced from the fast pyrolysis of corn stover (Zea mays L.), Ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue, and switchgrass (Panicum virgatum L.). We determined the impact of biochar application to soils with different chemical characteristics on P sorption and availability. Sorption of P by biochars and soil–biochar mixtures was studied by fitting the equilibrium solution and sorbed concentrations of P using Freundlich and Langmuir isotherms. Biochar produced from Ponderosa pine wood residue had very different chemical characteristics than corn stover and switchgrass. Corn stover biochar had the highest P sorption (in average 79% of the initial solution P concentration) followed by switchgrass biochar (in average 76%) and Ponderosa pine wood residue biochar (in average 31%). Ponderosa pine wood residue biochar had higher bicarbonate extractable (available) P (in average 43%) followed by switchgrass biochar (33% of sorbed P) and corn stover biochar (25% of sorbed P). The incorporation of biochars to acidic soil at 40 g/kg (4%) increased the equilibrium solution P concentration (reduced the sorption) and increased available sorbed P. In calcareous soil, application of alkaline biochars (corn stover and switchgrass biochars) significantly increased the sorption of P and decreased the availability of sorbed P. Biochar effects on soil P was aligned with their chemical composition and surface characteristics.

Biochar, a carbon-rich product of biomass pyrolysis, could limit glyphosate transport in soil and remediate contaminated water. The present study investigates the sorption/desorption behavior of glyphosate on biochars prepared from different hardwoods at temperatures ranging from 350 to 900 °C to elucidate fundamental mechanisms.Glyphosate (1 mg LResults from this study suggest a combined impact of surface chemistry and physical constraints on glyphosate sorption/desorption on biochar. Based on the observed phosphate-induced desorption of glyphosate, the addition of P-fertilizer to biochar-amended soils can remobilize the herbicide and damage non-target plants; therefore, improved understanding of this risk is necessary. © 2017 Society of Chemical Industry.

Biochar, a by-product of pyrolysis made from a wide array of plant biomass when producing biofuels, is a proposed soil amendment to improve soil health. This study measured herbicide sorption and efficacy when soils were treated with low (1% w/w) or high (10% w/w) amounts of biochar manufactured from different feedstocks [maize (Zea mays) stover, switchgrass (Panicum vigatum), and ponderosa pine (Pinus ponderosa)], and treated with different post-processing techniques. Twenty-four hour batch equilibration measured sorption of (14)C-labelled atrazine or 2,4-D to two soil types with and without biochar amendments. Herbicide efficacy was measured with and without biochar using speed of seed germination tests of sensitive species. Biochar amended soils sorbed more herbicide than untreated soils, with major differences due to biochar application rate but minor differences due to biochar type or post-process handling technique. Biochar presence increased the speed of seed germination compared with herbicide alone addition. These data indicate that biochar addition to soil can increase herbicide sorption and reduce efficacy. Evaluation for site-specific biochar applications may be warranted to obtain maximal benefits without compromising other agronomic practices.

Calendula is an alternative oilseed crop whose seed oil is valued as a substitute for tung oil and a replacement for petroleum-based volatile organic compounds in paints and other coatings. Calendula tolerances to most POST-applied herbicides are unknown. Two POST-applied herbicides were tested for tolerance by calendula. Imazamethabenz at 0.44 kg ai ha−1 plus surfactant and desmedipham plus phenmedipham at 0.36 + 0.36 kg ai ha−1 were tolerated by calendula, but the latter herbicide must be applied after the four–leaf-pair stage of growth to avoid severe injury. Neither herbicide adversely affected calendula seed yield if applied at the four–leaf-pair stage. Because these herbicides can control several weed species, calendula tolerance to them may encourage more growers and crop advisors to test this new oilseed crop on commercial farms. Nomenclature: Desmedipham; imazamethabenz; phenmedipham; calendula, Calendula officinalis L.

BACKGROUND: Sorption and dissipation of aged metolachlor were characterized in rehabilitated and eroded prairie soils using sequential batch slurry (conventional) and accelerated solvent extraction (ASE). RESULTS: In spite of an almost twofold difference in soil organic carbon (OC) content, S-metolachlor sorption coefficients (Kd) and dissipation rates (DT50) were the same in soils from different landscape positions within an eroded landform. Soil was moved within the landform to increase productivity. In areas receiving topsoil addition, S-metolachlor Kd was higher and DT50 was longer than in eroded areas. The efficiency of extraction was higher for ASE than for conventional extractions. No consistent aging effect on Kd was observed. Mineralization in 8 weeks accounted for < 10% of the applied metolachlor. CONCLUSION: The results of this laboratory study support a field dissipation study. Both showed that S-metolachlor has the same retention and dissipation rate throughout an eroded landform, which was not expected owing to the large variability in soil properties, including OC concentrations. Altering soil properties by adding topsoil increased metolachlor sorption and persistence. The method of extraction (conventional versus ASE) affected calculated sorption coefficients and dissipation rates. In all cases, groundwater ubiquity scores (GUSs) categorized metolachlor as having intermediate mobility. Published 2012 by John Wiley & Sons, Ltd.

The impact of agriculture on regional air quality creates significant challenges to sustainability of food supplies and to the quality of national resources. Agricultural emissions to the atmosphere can lead to many nuisances, such as smog, haze, or offensive odors. They can also create more serious effects on human or environmental health, such as those posed by pesticides and other toxic industrial pollutants. It is recognized that deterioration of the atmosphere is undesirable, but the short- and long-term impacts of specific agricultural activities on air quality are not well known or understood. These concerns led to the organization of the 2009 American Chemical Society Symposium titled . An outcome of this symposium is this special collection of 14 research papers focusing on various issues associated with production agriculture and its effect on air quality. Topics included emissions from animal feeding operations, odors, volatile organic compounds, pesticides, mitigation, modeling, and risk assessment. These papers provide new research insights, identify gaps in current knowledge, and recommend important future research directions. As the scientific community gains a better understanding of the relationships between anthropogenic activities and their effects on environmental systems, technological advances should enable a reduction in adverse consequences on the environment.

The aim of this study was to assess the effects of soil fumigation with methyl bromide (MeBr; CH(3)Br) and methyl iodide (MeI, iodomethane; CH(3)I) on the microbial community structure and diversity in two soils and determine the effects of microbial diversity on the survival of Escherichia coli O157:H7 from contaminated irrigation water. Polymerase chain reaction (PCR) was used to amplify 16S rRNA from total bacterial community composition and the products were subjected to denaturing gradient gel electrophoresis (DGGE). The Shannon-Weaver index of diversity (H') was used to determine the effects of both fumigants on soil microbial diversity. The effect was more severe in sandy soil than in clay soil at the normal application rate of MeBr and MeI. Our results showed that MeBr and MeI have about the same effects on soil microbial diversity. The two fumigants had greater impact on microbial diversity in sandy soil than in clay soil and this resulted in higher survival of E. coli O157:H7 in sandy soil than in clay soil during the 50 days that the study was conducted. MeBr has been used as soil fumigant for >40 years with no serious detrimental effects on agricultural production and our research also suggests that the use of MeI may also produce no long-term detrimental effects on agricultural production since both fumigants had about the same effects on soil microbial communities. Therefore, soil systems with reduced microbial diversity may offer greater opportunities for the survival of pathogenic bacteria such as E. coli O157:H7.

Rhizosphere and phyllosphere microbial communities were evaluated on roots and leaves of growth chamber-grown lettuce (Lactuca sativa (L.) cv. Green Forest) plants by culture-dependent and -independent methods after soil fumigation. Denaturing gradient gel electrophoresis (DGGE) with 16S rRNA primers followed by cloning and sequencing was used to identify major rRNA bands from the rhizosphere and phyllosphere. Three weeks after fumigation, there were no differences (P = 0.16) in rhizosphere microbial communities between the fumigated treatments and the control. The same effect was observed during week seven after fumigation (P=0.49). Also, no significant differences (P=0.49) were found in the phyllosphere microbial communities between the fumigated treatments and the control during the growth period of the plant. A majority of the bands in the rhizosphere were related to known bacterial sequences with a 96 to 100 % sequence similarity. Some of the derived sequences were related to Pseudomonas syringae pv. tomato DC300 and Bradyrhizobium japonicum USDA 110. A total of 23 isolates were identified from leaf surface by both culture-dependent and independent methods, and only Photorhabdus luminescens was found on leaf surface using both techniques. All the Biolog isolates from phyllosphere were from the Proteobacteria phylum compared to the culture-independent bands from the leaves that were from different bacterial phyla. Based on our data, methyl bromide (MeBr) and methyl iodide (MeI) did not have any significant negative effects on rhizosphere and phyllosphere microbial communities throughout the growing period of lettuce.

Aims: The major objective of this study was to determine the effects of low levels of Escherichia coli O157:H7 contamination on plant by monitoring the survival of the pathogen on the rhizosphere and leaf surfaces of lettuce during the growth process. Methods and Results: Real-time PCR and plate counts were used to quantify the survival of E. coli O157:H7 in the rhizosphere and leaf surfaces after planting. Real-time PCR assays were designed to amplify the stx1, stx2 and the eae genes of E. coli O157:H7. The detection limit for E. coli O157:H7 quantification by real-time PCR was 2·4 × 103 CFU g−1 of starting DNA in rhizosphere and phyllosphere samples and about 102 CFU g−1 by plate count. The time for pathogens to reach detection limits on the leaf surface by plate counts was 7 days after planting in comparison with 21 days in the rhizosphere. However, real-time PCR continued to detect stx1, stx2 and the eae genes throughout the experimental period. Conclusion: Escherichia coli O157:H7 survived throughout the growth period as was determined by real-time PCR and by subsequent enrichment and immunomagnetic separation of edible part of plants. Significance and impact of the Study: The potential presence of human pathogens in vegetables grown in soils contaminated with E. coli O157:H7 is a serious problem to our national food supply as the pathogen may survive on the leaf surface as they come in contact with contaminated soil during germination.

The impact of varying soil, landscape, and climate conditions on the off-site transport of pesticides must be determined to develop improved pesticide management practices. This study quantified the rate of S-metolachlor dissipation after fall and spring application in eroded and rehabilitated landforms in which topsoil was moved from the lower slope to the upper slope. Fall-applied metolachlor provided no control of annual grasses because approximately 80% was removed from the root zone during the winter and early spring, presumably by leaching and runoff. S-Metolachlor dissipated in the spring with a DT(50) of 24-29 days. These results suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination. Although landscape position and bulk soil movement within the landform had a large impact on soil properties, no significant differences in metolachlor dissipation between different landscape positions and between eroded and rehabilitated landforms were observed.

There are few experimental data available on how herbicide sorption coefficients change across small increments within soil profiles. Soil profiles were obtained from three landform elements in a strongly-eroded agricultural field and segmented into 2-cm intervals to 0.6 m depth in the knoll (eroded-upper slope), to 1.0 m depth in the toeslope (deposition zone) and to 1.6 m depth in the trough (eroded water-way). Soil samples were analyzed for soil organic carbon content (SOC) (n = 154), soil pH (n = 155), soil carbonate content (n = 126), CEC (n = 126), soil texture (n = 32), bulk density (n = 160), 2,4-D [2,4-(dichlorophenoxy) acetic acid] or glyphosate [N-phosphonomethylglycine] sorption by soil (Kd) (n = 90), and 2,4-D or glyphosate sorption per unit soil organic carbon (Koc) (n = 90). Considering all soil profiles, 2,4-D Kd values ranged from 0.12 to 2.61 L kg− 1 and were most strongly influenced by variations in SOC. In contrast, glyphosate Kd values ranged from 19 to 547 L kg− 1 and were predominantly controlled by variations in soil pH and clay content. Two hundred and fifty-two PRZM (pesticide root zone model) version 3.12.2 simulations were also performed. PRZM predicted that glyphosate would be immobile in soils even under an extreme rainfall scenario of 384 mm at one day after herbicide application. In contrast, for 2,4-D, PRZM predicted that up to 6% of the applied herbicide would move to a 15 cm depth under an actual rainfall scenario. PRZM output was particularly sensitive to input values of Kd, relative to input values of soil properties. The greatest change to PRZM outputs occurred when Kd values of toeslope profiles, ranging from 0.16 to 1.77 L kg− 1, were replaced by those measured in knoll profiles, ranging from 0.12 to 0.50 L kg− 1, when the amount of 2,4-D leached to a 15 cm depth increased by 29,081% (from 0.09 to 26.17 g ha− 1) under an actual rainfall scenario. We conclude that, when pesticide fate models such as PRZM are being used in policy analyses at larger-scales, data on Kd values in different landform elements and at the soil horizon level could be important for strengthening pesticide leaching predictions.

In hilly landforms subject to long-term cultivation, erosion has denuded upper slope positions of topsoil and accumulated topsoil in lower slope positions. One approach to remediate these eroded landforms is moving soil from areas of topsoil accumulation to areas of topsoil depletion, termed here soil-landscape rehabilitation. These experiments were conducted in an eroded undulating landform typical of the prairie pothole region. The summit, shoulder, upper and lower backslope were depleted in soil nutrients and organic carbon and had enriched inorganic carbon contents through the incorporation of calcareous subsoil material into the tilled layer. Surface soil organic carbon contents in lower slope positions were at least twice that in the most eroded positions. Six replicate plots were established that extended from the summit to the toeslope of the test area. Soil-landscape rehabilitation was performed on three plots by moving 15–20 cm of soil from the lower slope (footslope and toeslope) to the upper slope (summit, shoulder, and upper backslope) positions. The three remaining plots were undisturbed. In lower slope positions, soil properties were shifted upwards with respect to the soil surface by 15–20 cm in rehabilitated plots (where soil was removed). In upper slope positions, soil properties were shifted downwards by 15–20 cm in rehabilitated plots (where soil was applied, original soil was buried). After rehabilitation, the top 15 cm of soil in rehabilitated plots had characteristics similar to the footslope and toeslope, from which the soil was taken. Thus, soil properties were much more uniform from summit to toeslope in rehabilitated plots compared to undisturbed plots. Productivity was measured in two cropping years characterized by summer drought conditions. In rehabilitated plots, yields were relatively consistent across landscape positions, whereas in undisturbed plots, yields were depressed in eroded landscape positions. Grain yields in rehabilitated plots were increased by 30% in areas of soil addition. These yield increases were accompanied by yield decreases of 50% (year 1) and 20% (year 2) in areas of soil removal. Results indicate that movement of accumulated topsoil from lower slope positions to eroded upper slope positions can result in large yield increases in upper slope positions and more consistency in crop yields across the landscape, but additional research is needed to provide a more complete analysis of the soil productivity impacts of this approach.

Tillage is a driving force of soil movement in cultivated fields. Soil constituents, together with the mass of soil, are redistributed across landscapes by tillage. The pattern of tillage-induced soil constituent redistribution is determined by the pattern of tillage erosion (tillage-induced soil mass loss or gain) and the dispersivity of translocation. In this study, we used a convoluting procedure and developed a Tillage Translocation Model (TillTM) to simulate the tillage translocation process and to demonstrate tillage-induced soil mass and soil organic carbon (OC) (as an example of soil constituents) redistributions across four hypothetical landscapes subjected to different tillage patterns (directions) and over different lengths of tillage period. We determined that the local tillage-erosion rate is mainly dependent on topography and that the effects of tillage pattern and the length of tillage period are relatively minor. The redistribution of OC content in the till layer is mainly determined by the number, location, and size of soil loss positions in the landscape, as well as the soil loss rates at these positions. Net loss of OC content occurs in the till layer and this loss increases with time. In contrast, an increase of OC content in the sublayer occurs at soil accumulation positions. The model was validated against field data collected at a site near Cyrus, MN. The patterns of OC and inorganic C redistribution can be adequately estimated by TillTM. There are discrepancies, however, between the model-estimated values and the field measurements due to the limitations and uncertainties associated with the model. The results clearly showed that tillage translocation causes the vertical redistribution of soil constituents across the landscape, which implies that tillage translocation is one of the driving forces behind the spatial variability of soil properties and properties that impact biophysical processes.

Negative impacts on methane (CH4) oxidation capacity have already been observed for a variety of agronomic practices, but the effect of soil fumigation on CH4 oxidation has not been investigated. Fumigation is a common practice in agricultural crop and nursery seedling protection. Soils from various agricultural experiment stations, forest nurseries, and a landfill were evaluated for effects of 1,3-dichloropropene (1,3-D), methyl isothiocyanate (MITC), and chloropicrin (CP) on CH4 oxidation capacities. All three fumigants significantly reduced CH4 oxidation rates in historically non-fumigated soils (>50%). 1,3-D enhanced CH4 oxidation in 3 out of 5 previously fumigated soils and MITC increased CH4 oxidation rates in all historically MITC-fumigated soils compared to controls. CP universally decreased oxidation capacity regardless of fumigation history. These results support the conclusion that CH4 oxidation effects are fumigant specific and that prior fumigation history plays a vital role in determining the impact on CH4 oxidizer community functionality, which may have implications on the global CH4 cycle.

Two-year field dissipation studies were conducted in three soil types in Minnesota to examine the processes affecting the dissipation of the herbicide isoxaflutole and its phytotoxic diketonitrile metabolite (DKN) under relatively cool, wet soil conditions. Plots of cuphea were treated with isoxaflutole and potassium bromide, a nonsorbed, nondegraded tracer. Replicate soil cores were collected six times during the growing season to a depth of 1 m, and the bromide or herbicide concentration was measured in each of five depth increments. The dissipation half-life (DT50) of isoxaflutole + DKN was 8-18 days in each soil. Bromide and herbicide concentrations were low at depths >40 cm throughout the study, and herbicide concentrations in soil 100 days after application were usually undetectable. Simulation modeling using Hydrus-1D for the loam soil suggested that plant uptake was an important mechanism of dissipation.

This study was undertaken to determine sorption coefficients of eight herbicides (alachlor, amitrole, atrazine, simazine, dicamba, imazamox, imazethapyr, and pendimethalin) to seven agricultural soils from sites throughout Lithuania. The measured sorption coefficients were used to predict the susceptibility of these herbicides to leach to groundwater. Soil-water partitioning coefficients were measured in batch equilibrium studies using radiolabeled herbicides. In most soils, sorption followed the general trend pendimethalinalachloratrazine approximately amitrole approximately simazineimazethapyrimazamoxdicamba, consistent with the trends in hydrophobicity (log K(ow)) except in the case of amitrole. For several herbicides, sorption coefficients and calculated retardation factors were lowest (predicted to be most susceptible to leaching) in a soil of intermediate organic carbon content and sand content. Calculated herbicide retardation factors were high for soils with high organic carbon contents. Estimated leaching times under saturated conditions, assuming no herbicide degradation and no preferential water flow, were more strongly affected by soil textural effects on predicted water flow than by herbicide sorption effects. All herbicides were predicted to be slowest to leach in soils with high clay and low sand contents, and fastest to leach in soils with high sand content and low organic matter content. Herbicide management is important to the continued increase in agricultural production and profitability in the Baltic region, and these results will be useful in identifying critical areas requiring improved management practices to reduce water contamination by pesticides.

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha−1 year−1 were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing ∼19 g kg−1 of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha−1 year−1 exhibited thick sola with low inorganic carbon content (mean 3 g kg−1) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.

Metam sodium is the most widely used soil fumigant in the United States. The primary breakdown product of metam sodium in soil is methyl isothiocyanate (MITC), an active pesticidal agent with a high toxicity and a great potential for volatilization. Reducing atmospheric emissions of MITC is therefore critical to maintain air quality. The objective of this study was to examine the rate and efficiency of conversion of metam sodium to MITC in soil and to investigate the potential of using surface water sealing to reduce MITC emissions. The conversion of metam sodium to MITC was a rapid abiotic decomposition process. At typical field application rates, the conversion efficiency depended on the initial content of metam sodium in soil, but was independent of soil moisture, soil type, and soil atmospheric conditions. A soil column system was used to measure the emission and distribution of MITC after subsurface and surface application of metam sodium. Volatilization flux and cumulative emission loss of MITC was substantially reduced with surface water sealing compared to uncovered soil columns after subsurface application of metam sodium. When metam sodium was surface applied in simulated chemigation, surface water sealing was ineffective, suggesting the need for additional emissions reduction practices when metam sodium is broadcast. Overall, the results of the column experiment indicate that surface water sealing with subsurface application of metam sodium may be an effective and economical strategy to reduce MITC emissions while maintaining pest control efficacy.

The chlorinated fumigants chloropicrin (trichloronitromethane) and 1,3-dichloropropene (1,3-D) are extensively used in agricultural production for the control of soilborne pests. The reaction of these two fumigants with hydrogen sulfide species (H2S and HS - ) was examined in well-defined anoxic aqueous solutions. Chloropicrin underwent an extremely rapid redox reaction in the hydrogen sulfide solution. Transformation products indicated reductive dechlorination of chloropicrin by hydrogen sulfide species to produce dichloro- and chloronitromethane. The transformation of chloropicrin in hydrogen sulfide solution significantly increased with increasing pH, indicating that H2S is less reactive toward chloropicrin than HS - is. For both 1,3-D isomers, kinetics and transformation products analysis revealed that the reaction between 1,3-D and hydrogen sulfide species is an SN2 nucleophilic substitution process, in which the chlorine at C3 of 1,3-D is substituted by the sulfur nucleophile to form corresponding mercaptans. The 50% disappearance time (DT50) of 1,3-D decreased with increasing hydrogen sulfide species concentration at a constant pH. Transformation of 1,3-D was more rapid at high pH, suggesting that the reactivity of hydrogen sulfide species in the experimental system stems primarily from HS - . Because of the relatively low smell threshold values and potential environmental persistence of organic sulfur products yielded by the reaction of 1,3-D and HS - , the effects of reduced sulfide species should be considered in the development of alternative fumigation practices, especially in the integrated application of sulfur-containing fertilizers.

Soybean is an important crop worldwide. Soybean cultivars differ in their sensitivity to soil salinity and herbicide damage. In these experiments, we examined the impact of salinization an...

Propachlor and other chloroacetanilide herbicides are frequently detected contaminants of groundwater and surface water in agricultural regions. The purpose of this work was to develop a new approach to remove propachlor residues from the environment via chemical remediation by the nitrification inhibitor thiourea. The transformation processes of propachlor and thiourea mixed in aqueous solution, sand, and soil were elucidated. Analysis of transformation products and reaction kinetics indicated that an SN2 nucleophilic substitution reaction occurred, in which the chlorine of propachlor was replaced by thiourea, detoxifying the herbicide. It appears that propachlor undergoes a catalytic reaction in sand or soil amended with thiourea, which results in a significantly accelerated transformation rate as compared to the reaction in aqueous solution. The second-order reaction process was examined at different temperatures to investigate the role of the activation energy. The enthalpy of activation (ΔH) for the ...

Methyl iodide (MeI) is a promising alternative to methyl bromide in soil fumigation. The pest-control efficacy and ground water contamination risks of MeI as a fumigant are highly related to its gas-phase distribution and leaching after soil application. In this study, the distribution and leaching of MeI in soil following shank injection and subsurface drip application were investigated. Methyl iodide (200 kg ha(-1)) was directly injected or drip-applied at a 20-cm depth into Arlington sandy loam (coarse-loamy, mixed, thermic Haplic Durixeralfs) columns (12-cm i.d., 70-cm height) tarped with virtually impermeable film. Concentration profiles of MeI in the soil air were monitored for 7 d. Methyl iodide diffused rapidly after soil application, and reached a 70-cm depth within 2 h. Relative to shank injection, drip application inhibited diffusion, resulting in significantly lower concentration profiles in the soil air. Seven days after MeI application, fumigated soil was uncapped, aerated for 7 d, and leached with water. Leaching of MeI was significant from the soil columns under both application methods, with concentrations of >10 mug L(-1) in the early leachate. The leaching was greater following shank injection than drip application, with an overall potential of 33 g ha(-1) for shank injection and 19 g ha(-1) for drip application. Persistent residues of MeI remaining in soils after leaching were 50 to 240 ng kg(-1), and the contents were slightly higher following shank injection than drip application. The results suggest that fumigation with MeI may pose a risk of ground water contamination in vulnerable areas.

Soil fumigation is useful for controlling soil-borne pests and diseases in high-cash-value crops. Fumigants are highly volatile, and approaches to reduce atmospheric emissions are required to protect human and environmental health. Application of fumigants through drip irrigation has been proposed as a means to decrease fumigant emissions, improve fumigant distribution in soil, and minimize worker exposure. These experiments were conducted to investigate the effect of the configuration of the drip system on the volatilization and distribution of the fumigants 1,3-dichloropropene (1,3-D), propargyl bromide (PrBr), and methyl isothiocyanate (MITC) in bedded systems. Results indicated that changing the drip emitter spacing and using multiple drip lines in each bed had little effect on the emissions and distribution of any fumigant. Increasing the depth of application from 15 to 30 cm reduced volatilization of MITC by approximately 20 to >90%; emissions were reduced due to a decrease in the flux from the bed top, and deeper injection did not change the amount of fumigant volatilized from the bed side slope and furrow. Increasing the application depth resulted in a slight decrease in the rate of fumigant dissipation in soil, indicating the potential for some improvement in pest-control efficacy with deeper application.

Chloropicrin (CP) and metam sodium are commonly used as fumigants in agricultural soils in order to provide effective control of nematodes, soil-borne pathogens, and weeds in preparation for planting of high-value cash crops. Repeated application of these compounds to agricultural soils for many years may result in the enrichment of microorganisms capable of degrading them. In this study, a microcosm-enrichment approach was used to investigate bacterial populations that may be components of metam-sodium- and CP-degrading microorganisms in compost-amended soils. After 6 months incubation, with repeated application of metam sodium and CP, degradation wasor =70% faster in compost-manure-amended (CM) soil compared toor =50% in the unamended soils. The accelerated fumigant degradation may have been due to the addition of compost or to the development of new microbial populations with enhanced degradation capacity. Denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified regions of 16S rRNA genes were used to identify dominant bacterial populations responsible for the accelerated fumigant degradation. The DGGE results indicated that specific bacterial types had been enriched and these were similar to strains isolated from basal minimal media. Fragments from DGGE bands and colonies were cloned, sequenced, and compared with published 16S rRNA sequences. Cloned sequences were dominated by Pseudomonas, Bacillus, Arthrobacter, Mycobacterium and uncultured bacterial species. The addition of organic amendment to soil during fumigation practices has the potential to increase the diversity of different microbial species, thereby accelerating fumigant degradation and reducing atmospheric emissions.

Combined application of fumigants is a potential strategy to replace methyl bromide in the control of soil-borne pests. Unfortunately, abiotic and biotic interactions among fumigants restrict some combined application approaches. In this study, the kinetics and mechanisms of reaction between metam sodium (sodium methyldithiocarbamate) and the halogenated fumigants chloropicrin (trichloronitromethane) and 1,3-dichloropropene (1,3-D) were investigated in aqueous solution. For chloropicrin, an extremely rapid oxidation-reduction process occurred in the presence of metam sodium. The second-order rate constant for the reaction between chloropicrin and metam sodium was approximately 2 orders of magnitude greater than that for the reaction between 1,3-D isomers and metam sodium. Transformation of 1,3-D by metam sodium was associated with an aliphatic S(N)2 nucleophilic substitution process. The nucleophilic reaction of cis-1,3-D with metam sodium was significantly faster than that of the trans isomer and was correlated with a lower reaction activation energy for the cis isomer in the transition state. Combining Telone C-35 (65% 1,3-D and 35% chloropicrin) and metam sodium in solution might yield some nucleophilic sulfur species, which played an important role in the dissipation of 1,3-D. The incompatibility of chloropicrin and 1,3-D with metam sodium was also examined in soil under different application scenarios. Simultaneous application of metam sodium with chloropicrin or 1,3-D accelerated the transformation of the two halogenated fumigants, reducing their availability in soil. A sequential strategy for multiple fumigants was developed, which could be applied without the loss of active ingredient that occurs due to the reaction between fumigants. The proposed methodology may enhance pest control while maintaining environmental protection.

Hydrolysis is the major pathway for fumigant 1,3-dichloropropene (1,3-D) degradation in water and soil, yet the process is not well understood. Experiments were conducted to investigate the effect of various environmental factors on the rate of 1,3-D hydrolysis. Cis-, trans-1,3-D and their isomeric mixture were spiked into water and Arlington soil (coarse-loamy, mixed, thermic Haplic Durixeralfs) and incubated under different conditions. The rate of 1,3-D hydrolysis in water and soil were evaluated based on its residual amount and Cl- release, respectively. 1,3-D hydrolyzed rapidly in deionized water, with a half-life of 9.8 d at 20 degrees C. The hydrolysis was pH dependent, with low pH inhibiting and high pH favoring the reaction. Other factors such as isomeric differences, photo irradiation, suspended particles, and small amounts of co-solutes had little effect on the reaction. In soil, 1,3-D hydrolyzed following pseudo first-order kinetics. The hydrolysis rate constant increased with soil moisture content and decreased with the initial 1,3-D concentration. At 20 degrees C, > 60% of the 1,3-D applied at < 0.61 g kg(-1) in 10% moisturized soil hydrolyzed within 30 d. The soil particle size and mineralogy had little effect on the reaction rate. Organic matter promoted 1,3-D degradation via direct substitution reactions, and the trans-isomer showed preference over the cis- to react with certain organic molecules. Microbial contributions were initially insignificant, and became important as soil microorganisms adapted to the fumigant. The results suggest that to accelerate 1,3-D degradation, pH, soil moisture, and organic amendment should be considered.

Greenhouse experiments were conducted to determine the effect of salinity, imazethapyr, and chlorimuron on weed growth. Five species, barnyardgrass, common cocklebur, ivyleaf morningglory, common purslane, and yellow nutsedge, were grown in potting soil and irrigated with nonsaline (EC ∼ 2 dS m−1) or sulfate-dominated saline (EC ∼ 7 dS m−1) nutrient solution. Plants were treated after emergence with imazethapyr (Pursuit formulation) at 70 g ae ha−1 or chlorimuron ethyl (Classic formulation) at 8.8 g ai ha−1. Results indicated that irrigation with saline water had no overall effect on the growth or survival of most tested weed species. Growth of yellow nutsedge (maximum height and stem diameter) was reduced for plants irrigated with saline water. Observed growth and survival trends in saline and nonsaline treatments were consistent with information on the herbicide label. Complete control of common purslane was not achieved by either chlorimuron or imazethapyr. Growth and survival of ivyleaf morni...

Halogenated fumigants are some of the most heavily used pesticides worldwide. A number of studies have shown that fumigant transformation in soil is correlated with soil organic matter content. However, relatively little is known about the mechanisms of fumigant interaction with soil organic matter. In this study, we used 14 C-labeled 1,3-dichloropropene (1,3-D) and methyl bromide (MeBr) to characterize their incorporation into soil organic matter and the association of bound radioactivity with the different organic matter components. The 14 C activity of bound residues increased with time and reached 38-49% for 1,3-D and 37-42% for MeBr after 72 d of incubation at 25°C. More bound residues were produced for 1,3-D than for MeBr in the same soils. The distribution of 14 C activity in soil humic substances followed the order of fulvic acids >> humin > humic acids. These observations suggest that incorporation into soil organic matter is the predominant pathway for transformation of halogenated fumigants in soil and that fulvic acids are likely the most significant sink of all soil organic matter fractions. It is further speculated that bound residues formed as a result of alkylation of organic matter by the fumigants through nucleophilic replacement.

The fumigant 1,3-dichloropropene (1,3-D), in combination with chloropicrin, is considered a major replacement to methyl bromide (MeBr). This study was conducted to better understand phase partitioning of 1,3-D and the role of organic matter in its adsorption to soil. Partition of 1,3-D between air and water (K(H)), and between soil and water (K(f)), was determined by quantifying the concentration in both phases upon equilibrium. At 20 degrees C, the K(H) values of (Z)- and (E)-1,3-D were 0.052 and 0.033, respectively. In four California and Florida soils, the K(f) values of 1,3-D isomers ranged from 0.39 to 8.55, and the K(oc) values ranged from 18 to 60. The relatively high K(H) and low K(f) imply that 1,3-D is highly mobile in most soils after subsurface application. Adsorption of 1,3-D in native soils and soils amended with manure compost increased with increasing soil organic matter content. This suggests that organic wastes may be applied to soil to increase 1,3-D adsorption, thus reducing its potential for offsite movement.

Yates, S. R., Gan, J., Papiernik, S. K., Dungan, R., and Wang, D. 2002. Reducing fumigant emissions after soil application. Phytopathology 92:1344-1348. Volatilization and soil transformation are major pathways by which pesticides dissipate from treated agricultural soil. Volatilization is a primary source of unwanted agricultural chemicals in the atmosphere and can significantly affect fumigant efficacy. Volatile pesticides may cause other unique problems; for example, the soil fumigant methyl bromide has been shown to damage stratospheric ozone and will soon be phased out. There is also great concern about the health consequences of inhalation of fumigants by people living in proximity to treated fields. Because replacement fumigants will likely face increased scrutiny in years ahead, there is a great need to understand the mechanisms that control their emission into the atmosphere so these losses can be minimized without loss of efficacy. Recent research has shown that combinations of vapor barriers and soil amendments can be effective in reducing emissions. In this paper, some potential approaches for reducing fumigant emissions to the atmosphere are described.

Soil fumigation in greenhouses or agricultural fields often includes tarping the soil surface with polyethylene (PE) films to contain the fumigant in the soil and reduce emissions to the atmosphere. Previous research has demonstrated that PE films are permeable to methyl bromide and other fumigant compounds. In these experiments, the effect of temperature, fumigant mixtures, condensed water, and field aging on the permeability of high-density polyethylene (HDPE) was determined. Mass transfer coefficients (h, a measure of permeability) of the fumigants methyl bromide, 1,3-dichloropropene, propargyl bromide, and chloropicrin across HDPE films were determined. In these studies, temperature and HDPE film type had the largest impact on the h of fumigant compounds across HDPE films. Other factors investigated, including fumigant mixtures, condensed water on the film, and field aging of UV-stabilized film, did not have a significant impact on h. The results of these experiments suggest that the permeability of an intact piece of an agricultural film will increase with increasing temperature but is relatively constant despite changes in other environmental conditions.

The diversity of microbial communities constitutes a critical component of good soil-management practices. To characterize the effects of different management practices, molecular indicators such as phospholipid fatty acid (PLFA), denaturing gradient gel electrophoresis (DGGE) and composition of ammonia-oxidizing bacteria were used to analyze bacterial community structure and diversity from four eastern Washington State soils. Samples from four sites were collected representing a transect of high-precipitation to low-precipitation areas that covered different agronomic zones with different management and cropping practices. Biomass amounts estimated from extractable PLFA were significantly higher in the no-till (NT) soil than in the conventional-till (CT) soil. Similarities among the different 16S rDNA DGGE band profiles were analyzed quantitatively using correspondence analysis and this confirmed that the CT soil was the most dissimilar soil. DGGE analysis of 16S rDNA ammonia-oxidizing bacteria from the four soils revealed two identical bands, indicating little effect of agronomic practices and precipitation on these species. A second set of primers, specific for amoA (ammonia monooxygenase) genes, was used to examine ammonia oxidizers in the samples. Six banding patterns (clusters) from amplified rDNA restriction analysis of 16S rDNA fragments were observed after restriction analysis with HinfI. Sequencing of these clones revealed the presence of only Nitrosospira-like sequences. Analysis of the sequences showed that ammonia oxidizers from the NT soil were more diverse compared to those from the CT and conservation reserve program soils. Our data showed that management and agronomic practices had more impact on bacterial community structure than annual precipitation.