Central Iowa Research Articles

Evaluation of Wood Chip-Based Biofilters to Reduce Odor, Hydrogen Sulfide, and Ammonia from Swine Barn Ventilation Air

A pilot-scale biofilter was developed in which two types of wood chips (western cedar [WC] and 2-in. hardwood [HW]) were examined to treat odor emissions from a deep-pit swine finishing facility in central Iowa. The biofilters were operated continuously for 13 weeks at different airflow rates resulting in variable empty bed residence times (EBRTs) from 1.6 to 7.3 sec. The effects of three media moisture levels were also evaluated. A dynamic forced-choice olfactometer was used to evaluate odor concentrations from both the control (inlet) plenum and biofilter treatments (outlet). Hydrogen sulfide (H2S) and ammonia (NH3) concentrations were also measured from these olfactometry samples. Solid-phase microextraction (SPME) polydimethylsiloxane (PDMS)/divinylbenzene (DVB) 65-µm fibers were used to extract volatile organic compounds from both the control plenum and biofilter treatments. Analyses of separated odors were carried out using a gas chromatography-mass spectrometry-olfactometry (GC-MS-O) system. Static sample results indicated that both types of chips achieved significant reductions in odor (average 70.1 and 82.3% for HW and WC, respectively), H2S (average 81.8 and 88.6% for HW and WC, respectively) and NH3 (average 43.4 and 74% for HW and WC, respectively) concentrations. GC-MS-O aromagram results showed both treatments reached high odor reduction efficiency (average 99.4 and 99.8% for HW and WC, respectively). The results also showed that maintaining proper moisture content and a minimum EBRT are critical to the success of wood chip-based biofilters.

Concentrations of Bioaerosols, Odors, and Hydrogen Sulfide Inside and Downwind from Two Types of Swine Livestock Operations

Few data on in-barn and downwind concentrations of endotoxin, bioaerosols, and odors from livestock facilities are available, and no studies have compared conventional confinement operations with the more animal-friendly hoop operations. Hoops are open to the environment and use a composted bedding system rather than housing pigs on slatted floors over pits holding manure slurry as in conventional confinements. We assessed airborne toxicants upwind, in barns, and downwind and evaluated determinants of exposure. Inhalable particulate matter, endotoxin, odor threshold, hydrogen sulfide, culturable mesophilic bacteria, culturable fungi, and total airborne microbes, along with wind speed, temperature, and humidity were measured at separate midsized livestock facilities (one hoop, one confinement) in Central Iowa on 10 occasions over 2 years. Significant differences in contaminants were observed between hoops and confinement buildings and across seasons for endotoxin, odors, airborne microorganisms, and hydrogen sulfide. For hoops and confinements, respectively, geometric mean in-barn concentrations were 3250 and 3100 EU/m3 for endotoxin; 1400 and 1910 μg/m3 for particulates; 19.6 and 146 ppb for hydrogen sulfide; 137 and 428 dilutions for odor threshold; and 3.0 × 106 and 1.5 × 106 organisms/m3 for total microbes. Endotoxin, odor, and culturable microorganisms exceeded recommended exposure limits. Reduced analysis of variance models for these contaminants demonstrated differences by barn type, season, number of pigs, and, in some cases, temperature and humidity. Both types of swine operations produced high airborne concentrations of endotoxin, odor, hydrogen sulfide, bacteria, and fungi. Endotoxin and odors were found downwind at concentrations previously associated with adverse health effects.

Effects of a livestock manure windrow composting site with a fly ash pad surface and vegetative filter strip buffers on sediment, nitrate, and phosphorus losses with runoff

This study quantified the effects of a livestock manure-based windrow compost- ing practice with a fly ash composting pad surface and vegetative filter strip (VFS) buffers on losses of runoff, runoff percent of rainfall, total solids, nitrate-nitrogen, ortho-phosphorus (PO 4 -P), and total-phosphorus during natural rainfall events. Runoff data from six events were collected during June and July (early season) and August and September (late season) 60-day duration composting periods from 2002 through 2004 at an Iowa State University research farm near Ames, central Iowa, USA. The research site was selected on uneven terrain with average slopes of 5% and 2% on the VFS buffer and composting pad plot areas, respec- tively. Runoff treatments were comprised of three compost windrows:VFS buffer area ratios that included 1:1, 1:0.5, and 1:0 (no buffer) control. The 1:1 and 1:0.5 area ratios represented a 6.0-m (20-ft) wide × 23-m (75-ft) long fly ash composting pad area compared to VFS buffer areas of equal and one-half size, respectively. All treatments had three replications for a total of nine runoff plots in a randomized complete block design. Results from the study indicate significantly higher levels (p < 0.05) of runoff, runoff percent of rainfall, total solids, nitrate- nitrogen, PO 4 -P, and total-phosphorus from the 1:0 control plots compared to the 1:1 and 1:0.5 VFS buffer plots. Results also show the 1:1 and 1:0.5 VFS buffer treatments were not significantly different (p < 0.05) and that average runoff loss reductions from the 1:1 and 1:0.5 VFS buffer plots were 98% and 93%, respectively, compared to the 1:0 control plots. These results reflect the effectiveness of VFS buffers for reducing runoff and contaminant losses from a windrow composting site. Compost nutrient mass balance analysis results indicate 41% and 26% of PO 4 -P were lost from the compost windrows during the 2004 early season and late season composting periods, respectively. However, only 0.1% to 0.4% of PO 4 -P was lost to runoff from the 1:0 control plots during the respective 2004 early season and late season com- posting periods. We hypothesize the relatively lower PO 4 -P losses in runoff may be attributed to potential chemical and physical effects of the fly ash composting pad material.

Notes on A Collection Of Caddisflies (Trichoptera) from Carroll County, Iowa, U.S.A.

Abstract Six families, 18 genera, and 34 species of Trichoptera are reported from Carroll County in western Iowa of which 18 are new state records. Hydropyschidae, Hydroptilidae, and Leptoceridae made up over 80% of the caddisfly fauna. The caddisfly assemblage corresponded to streams that were highly altered by agricultural activity with heavy sedimentation and reduced canopy cover. Supplemental collections from central and eastern Iowa were also made. Assemblages in Carroll County were markedly different than those in the Paleozoic Plateau/Coulee Section in northeastern Iowa. We located an additional 14 species records in the literature and have an additional 13 new state records, primarily from central and eastern Iowa collections, for a total of 63 caddisfly species now reported for the state.

Model-Based Synthesis of Household Travel Survey Data in Small and Midsize Metropolitan Areas

Household travel data synthesis–simulation has become a promising alternative or supplement to survey data from both small urban areas and large metropolitan regions in which data are expensive to collect or the data required to support the planning process have become outdated. This paper proposes and applies model-based approaches [i.e., small area estimation (SAE) methods] to synthesize household travel characteristics. The proposed methods address the sampling-bias concerns in the existing methods. Specifically, three SAE methods–-the generalized regression estimators method, the empirical best linear unbiased predictor (EBLUP) method, and the synthetic method (an EBLUP without random area effects)–-are applied to synthesize household travel characteristics at both census tract and individual levels. The SAE framework of synthesizing household travel characteristics is demonstrated with the National Household Travel Survey data and the Census Transportation Planning Package data in the Des Moines metropolitan area in central Iowa. Results indicate that SAE methods are promising approaches to synthesize unbiased aggregate and disaggregate household travel characteristics by incorporating population auxiliary information and local, small-household travel survey data. The proposed data synthesis methods and analysis findings will provide a useful tool for practitioners, planners, and policy makers in transportation analyses. The paper also points out that by linking population synthesis with the travel data simulation framework described here, this method could be of broad application in transportation planning.

Comparing Energy Use and Efficiency in Central Iowa Agroecosystems

Comparing Energy Use and Efficiency in Central Iowa Agroecosystems

Temporal variations of Escherichia coli concentrations in a large Midwestern river

Summary The Raccoon River used by the Des Moines Water Works to serve more than 400,000 people in central Iowa is threatened by contamination from Escherichia coli bacteria from point and nonpoint sources. The 9389 km 2 watershed is highly agricultural, with 73% of the land in row crop production and widespread animal production. Results from 2155 grab samples from 1997 to 2005 for E. coli analysis were examined for temporal variations. E. coli concentrations were found to vary across years, seasons, and flow conditions, with a 9-year mean value of 1156 most probable number (MPN)/100 ml. Monthly concentrations exhibited clear seasonality with highest values in May through July. Although E. coli concentrations were higher during periods of greater discharge, the relation of log E. coli to log discharge was not particularly strong ( r 2 = 0.35). The variogram of E. coli concentrations showed temporal correlation within a span of 4 days suggesting that concentrations measured on 1 day may be related in time to concentrations measured up to 3 days later and beyond 4 days the concentrations vary randomly. The spectral analysis of the time series of E. coli was also carried out and was fitted well with the spectrum of an exponential covariance function. Deciphering temporal patterns and correlation of E. coli bacteria in streams may be useful for developing future monitoring strategies to track concentration patterns and loads.

Simulated Effects of Nitrogen Management and Soil Microbes on Soil Nitrogen Balance and Crop Production

Searching for environmentally friendly N management practices in the midwestern United States is an ongoing task in the agricultural community. Many practices have shown promise in reducing N in tile drainage that may contribute to hypoxia in the Gulf of Mexico. In this study, an agricultural system in central Iowa, managed using a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation from 1996 to 2005 was evaluated with the Root Zone Water Quality Model (RZWQM) for crop yield, grain N, annual N loss in tile drainage flow, and residual soil NO3–N under high (H, 199 kg N ha −1), medium (M, 138 kg N ha−1), and low (L, 69 kg N ha−1) N application rates shortly after planting, and a split (S, 69 kg N ha−1 shortly after planting and again at midseason) N treatment. The model adequately simulated the responses of yield and N loss to N application rates. Simulated N losses to drainage flow from 1996 to 2005 were 348, 277, and 228 kg N ha−1 for the H, M, and L treatments, respectively, compared with corresponding measured values of 369, 265, and 201 kg N ha−1 The S treatment had simulated and measured total N losses in drainage flow of 194 and 172 kg N ha−1, respectively, from 1999 to 2005. The study also demonstrated that RZWQM without soil microbial growth produced very similar simulation results for crop production and soil N and water balances as RZWQM with dynamic soil microbial growth.

Comparison of DAYCENT‐Simulated and Measured Nitrous Oxide Emissions from a Corn Field

Accurate assessment of N(2)O emission from soil requires continuous year-round and spatially extensive monitoring or the use of simulation that accurately and precisely predict N(2)O fluxes based on climatic, soil, and agricultural system input data. DAYCENT is an ecosystem model that simulates, among other processes, N(2)O emissions from soils. The purpose of the study was to compare N(2)O fluxes predicted by the DAYCENT model to measured N(2)O fluxes from an experimental corn field in central Iowa. Soil water content temperature and inorganic N, simulated by DAYCENT were compared to measured values of these variables. Field N(2)O emissions were measured using four replicated automated chambers at 6-h intervals, from day of year (DOY) 42 through DOY 254 of 2006. We observed that DAYCENT generally accurately predicted soil temperature, with the exception of winter when predicted temperatures tended to be lower than measured values. Volumetric water contents predicted by DAYCENT were generally lower than measured values during most of the experimental period. Daily N(2)O emissions simulated by DAYCENT were significantly correlated to field measured fluxes; however, time series analyses indicate that the simulated fluxes were out of phase with the measured fluxes. Cumulative N(2)O emission calculated from the simulations (3.29 kg N(2)O-N ha(-1)) was in range of the measured cumulative N(2)O emission (4.26 +/- 1.09 kg N(2)O-N ha(-1)).

Automated determination of management units for precision conservation

The use of models to target conservation efforts, or conservation, has become a research interest due to its ability to evaluate different conservation practices in multiple areas and determine where conservation expenditures will provide the best return. To determine if automation of the data collection process is possible, the intersection of USDA common land unit maps, which define the boundaries of agricultural lands, with vegetative cover maps, represented by the USDA cropland data layer, was analyzed for accuracy on approximately 80 central Iowa fields over two years.The resulting dataset successfully determined mean field centroid within 3 pixels, area with an r 2 of 0.99, crop cover with 95% accuracy, and when compiled over a period of years, crop rotations.The value of the resulting map can also be extended with the use of other technologies to determine field average of properties such as residue cover, tillage, yield, and biomass production. The dataset can also serve as an input for numerous precision conservation models and enable the ability to create maps of other field level processes or properties, such as residue cover, tillage, or fertilization, by defining the boundaries over which management uniformly occurs.

Evaluation of Management Strategies for Bean Leaf Beetles (Coleoptera: Chrysomelidae) and Bean Pod Mottle Virus (Comoviridae) in Soybean

Cerotoma trifurcata Förster (Coleoptera: Chrysomelidae) and Bean pod mottle virus (Comoviridae) (BPMV) both can reduce yield and seed quality of soybean, Glycine max (L.) Merr. Field experiments were conducted to evaluate the effects of systemic, seed-applied, and foliar-applied insecticides for the management of this pest complex at three locations in central, northeastern, and northwestern Iowa during 2002-2004. Seed-applied insecticide was evaluated according to a currently recommended management program for Iowa (i.e., insecticide applications that target emerging overwintered beetles, F0, and the first seasonal generation, F1 ). The experimental treatments included seed-applied (thiamethoxam, 0.3-0.5 g [AI] kg(-1)] or clothianidin, 47.32 ml [AI] kg(-1)) and foliar-applied (A-cyhalothrin, 16.83-28.05 g [AI] ha(-1)) or esfenvalerate (43.74-54.69 g [AI] ha(-1)) insecticides. Applications of the foliar insecticides were timed to target F0, F1 or both F0 and F1 populations of C. trifurcata. Our results confirm that insecticides timed at F0 and F1 populations of C. trifurcata can reduce vector populations throughout the growing season, provide limited reduction in virus incidence, and improve both yield and seed coat color. Furthermore, seed-applied insecticides may be the more reliable option for an F0-targeted insecticide if used within this management strategy. An F0-targeted insecticide by itself only gave a yield improvement in one out of eight location-years. However, by adding an F1-targeted insecticide, there was a yield gain of 1.42-1.67 quintal ha(-1), based on contrast comparisons at three location-years.

Woody Encroachment Removal from Midwestern Oak Savannas Alters Understory Diversity across Space and Time

Recovering biodiversity is a common goal during restoration; however, for many ecosystems, it is not well understood how restoration influences species diversity across space and time. I examined understory species diversity and composition after woody encroachment removal in a large-scale savanna restoration experiment in central Iowa, United States. Over a 4-year time series, restoration had profound effects across space and time, increasing richness at local and site-level scales. Restoration sites had increased α (within sample) Simpson’s diversity and α and γ (site level) species richness relative to control sites, although γ and β (among sample) Simpson’s diversity, β richness, and α species evenness were not affected. Changes in richness were driven by graminoids at the α and γ scales and woody species (and some evidence for forbs) at the α scale. Interestingly, indicator species analysis revealed that at least some species from all functional groups were promoted by restoration, although no species were significant indicators of pre-treatment or control sites. Both savanna and nonsavanna species were indicators of restored sites. Restoration promoted exotic species at both scales, although species with spring phenologies were unaffected. Woody encroachment removal may be a means to promote species establishment in savannas; however, in this study, it resulted in establishment and proliferation of native and exotic and savanna and nonsavanna species. Future work might consider reintroduction of key savanna species to supplement those that have established. Work like this demonstrates the utility of restoration experiments for conducting research on large- and multiscale processes, such as species diversity.

HABITAT AND LANDSCAPE CHARACTERISTICS UNDERLYING ANURAN COMMUNITY STRUCTURE ALONG AN URBAN–RURAL GRADIENT

Urbanization has been cited as an important factor in worldwide amphibian declines, and although recent work has illustrated the important influence of broad-scale ecological patterns and processes on amphibian populations, little is known about the factors structuring amphibian communities in urban landscapes. We therefore examined amphibian community responses to wetland habitat availability and landscape characteristics along an urban-rural gradient in central Iowa, USA, a region experiencing rapid suburban growth. We conducted call surveys at 61 wetlands to estimate anuran calling activity, and quantified wetland habitat structure and landscape context. We used canonical correspondence analysis (CCA) to examine patterns in anuran community structure and identify the most important variables associated with those patterns. Urban density at the landscape scale had a significant negative influence on overall anuran abundance and diversity. While every species exhibited a decrease in abundance with increasing urban density, this pattern was especially pronounced for species requiring post-breeding upland habitats. Anurans most affected by urbanization were those associated with short hydroperiods, early breeding activity, and substantial upland habitat use. We suggest that broad-scale landscape fragmentation is an important factor underlying anuran community structure in this region, possibly due to limitations on the accessibility of otherwise suitable habitat in fragmented urban landscapes. This study underscores the importance of a regional approach to amphibian conservation in urban and urbanizing areas; in fragmented landscapes, a network of interconnected wetland and upland habitats may be more likely to support a successful, diverse anuran community than will isolated sites.

Seasonal patterns in depth of water uptake under contrasting annual and perennial systems in the Corn Belt Region of the Midwestern U.S.

In agricultural landscapes, variation and ecological plasticity in depth of water uptake by annual and perennial plants is an important means by which vegetation controls hydrological balance. However, little is known about how annual and perennial plants growing in agriculturally dominated landscapes in temperate humid regions vary in their water uptake dynamics. The primary objective of this study was to quantify the depth of water uptake by dominant plant species and functional groups growing in contrasting annual and perennial systems in an agricultural landscape in Central Iowa. We used stable oxygen isotope techniques to determine isotopic signatures of soil water and plant tissue to infer depth of water uptake at five sampling times over the course of an entire growing season. Our results suggest that herbaceous species (Zea mays L., Glycine max L. Merr., Carex sp., Andropogon gerardii Vitman.) utilized water predominantly from the upper 20 cm of the soil profile and exhibited a relatively low range of ecological plasticity for depth of water uptake. In contrast, the woody shrub (Symphoricarpos orbiculatus Moench.) and tree (Quercus alba L.) progressively increased their depth of water uptake during the growing season as water became less available, and showed a high degree of responsiveness of water uptake depth to changes in precipitation patterns. Co-existing shrubs and trees in the woodland and savanna sites extracted water from different depths in the soil profile, indicating complementarity in water uptake patterns. We suggest that deep water uptake by perennial plants growing in landscapes dominated by rowcrop agriculture can enhance hydrologic functioning. However, because the high degree of ecological plasticity allows some deep-rooted species to extract water from surface horizons when it is available, positive effects of deep water uptake may vary depending on species’ growth patterns and water uptake dynamics. Knowledge about individual species’ and plant communities’ depth of water uptake patterns in relation to local climate conditions and landscape positions can provide valuable information for strategically incorporating perennial plants into agricultural landscapes to enhance hydrologic regulation.

A preliminary watershed scale soil quality assessment in north central Iowa, USA

Soil quality assessment has been recognized as an important step toward understanding the long-term effects of conservation practices within agricultural watersheds. Our objective was to assess soil quality within the South Fork watershed of the Iowa River using various indicators and assessment approaches. Soil samples were collected during 2003 and 2004 from 29 areas of 32 ha (80 acres) each along two transects traversing the watershed. Soil pH, Mehlich III extractable P, K, Ca and Mg, electrical conductivity (EC), total organic carbon (TOC), and total N (TN) were measured. The Soil Management Assessment Framework (SMAF) was used to compute a soil quality index (SQI), while soil loss, the soil tillage intensity rating (STIR), N-leaching potential, and soil conditioning index (SCI) were determined for each sampling area using the 2003 version of the Revised Soil Loss Equation (RUSLE2). Overall, there were no soil fertility limitations within the watershed based on an average pH of 6.96 and extractable P and K levels of 36 and 162 mg kg −1, respectively. Soil loss, STIR, N-leaching, and SCI averaged 1.13 Mg ha −1, 68, 3, and 0.4, respectively. The SMAF analysis indicated soils within the watershed were functioning at 87% of their full potential. The lowest indicator score was associated with TOC (0.60) because the average value was only 28.4 g kg −1. The SCI and SQI indices were positively correlated although since it used measured data, the SMAF appears to provide more information about the effects of management practices within the watershed. Soils in upper landscape positions had lower TOC and C:N ratios indicating an increased risks for both erosion and for nitrate leaching. Management of soils on hilltops may be the most effective way to minimize N and P losses within the watershed.

Performance evaluation of a wood-chip based biofilter using solid-phase microextraction and gas chromatography–mass spectroscopy–olfactometry

A pilot-scale mobile biofilter was developed where two types of wood chips (western cedar and 2in. hardwood) were examined to treat odor emissions from a deep-pit swine finishing facility in central Iowa. The biofilters were operated continuously for 13 weeks at different air flow rates resulting in a variable empty bed residence time (EBRT) from 1.6 to 7.3s. During this test period, solid-phase microextraction (SPME) PDMS/DVB 65μm fibers were used to extract volatile organic compounds (VOCs) from both the control plenum and biofilter treatments. Analyses of VOCs were carried out using a multidimentional gas chromatography–mass spectrometry–olfactometry (MDGC–MS–O) system. Results indicated that both types of chips achieved significant reductions in p-cresol, phenol, indole and skatole which represent some of the most odorous and odor-defining compounds known for swine facilities. The results also showed that maintaining proper moisture content is critical to the success of wood-chip based biofilters and that this factor is more important than media depth and residence time.

The past, present, and future of prairie potholes in the United States

S mall prairie wetlands left in the wake of retreating glaciers are commonly known as potholes. The US prairie pothole region (PPR), the area covered by late Wisconsin Pleistocene glaciation and historically dominated by tall and mixed grasslands, covers north central Iowa and western Minnesota, the area of North and South Dakota east and north of the Missouri River, and northeastern Montana. Potholes formed when ice blocks buried in glacial till melted over a period of hundreds or thousands of years and the till slumped creating a closed depression. Prairie potholes are highly productive ecosystems of unparalleled importance to breeding waterfowl and many other species of wetland wildlife. Moreover, they are important nutrient sinks, store runoff that reduces flooding, sequester carbon, and provide other environmental and socioeconomic values. Prairie potholes are also perceived to reduce agricultural land value and to impede large-scale mechanized farming. Prairie potholes are routinely classified by how long they remain ponded during the growing season, from temporary potholes (ponded for 1 to 3 weeks) to seasonal potholes (ponded for 3 weeks to 90 days) to semipermanent potholes that are usually ponded throughout the growing season and may have surface water present for many consecutive years (Stewart and …

Deciphering complex soil/site formation in sands

This paper summarizes aspects of the geoarchaeological research at two adjacent multi-component archaeological sites, 13JP86 and 13JP87, along Indian Creek in central Iowa, USA. The sites, both recently salvaged but now destroyed, formed in late Pleistocene sands reworked from glacial sediments that emanated from the wasting Des Moines Lobe glacier some 13,000–14,000 years ago. The soils contained shallowly dispersed and mixed artifacts that span the Paleoindian-to-historic cultural spectrum. In open areas, as at Indian Creek, site formation processes equate to natural soil genetic processes, plus human imprints. Cultural materials, once deposited, become part of the soil and subject to dynamic soil processes. These soils had reasonably well expressed Ap, A, and E horizons that collectively formed thick one-layered biomantles, underlain by well expressed argillic Bt horizons. The biomantles had been well bioturbated, deeply in some pedons, but still exhibited organized A and E horizons. The Bt horizons were also bioturbated, though less so, and consisted of multiple thin to thick sandy clay bands, termed illuvial clay lamellae (icl's). The icl's contained modest to appreciable amounts of illuvial clay as bridges between grains, and as diffuse splotches and blebs separated by less clayey, E horizon-like interlamellar sandy zones. Deeper and less bioturbated E-like sandy zones had accumulated so much clay that they had coalesced with icl's into thick, complexly banded argillic Bt horizons. The process histories of the sandy pedons were obviously extremely complex. The geoarchaeological aspects of the project, which were mainly complex pedologic ones, were largely interpreted by drawing on the genetic principles of dynamic denudation to explain soil/site evolution. Many questions were raised, and most were answered under these principles. New concepts and perspectives were gained in this study, and the resulting interpretive scenarios carry explanatory implications for sandy soils everywhere, whether charged with cultural materials or not.

Crop rotation and nitrogen fertilization effect on soil CO 2 emissions in central Iowa

Depending upon how soil is managed, it can serve as a source or sink for atmospheric carbon dioxide (CO 2). As the atmospheric CO 2 concentration continues to increase, more attention is being focused on the soil as a possible sink for atmospheric CO 2. This study was conducted to examine the short-term effects of crop rotation and N fertilization on soil CO 2 emissions in Central Iowa. Soil CO 2 emissions were measured during the growing seasons of 2003 and 2004 from plots fertilized with three N rates (0, 135, and 270 kg N ha −1) in continuous corn and a corn–soybean rotation in a split-plot design. Soil samples were collected in the spring of 2004 from the 0–15 cm soil depth to determine soil organic C content. Crop residue input was estimated using a harvest index based on the measured crop yield. The results show that increasing N fertilization generally decreased soil CO 2 emissions and the continuous corn cropping system had higher soil CO 2 emissions than the corn–soybean rotation. Soil CO 2 emission rate at the peak time during the growing season and cumulative CO 2 under continuous corn increased by 24 and 18%, respectively compared to that from corn–soybean rotation. During this period, the soil fertilized with 270 kg N ha −1 emitted, on average, 23% less CO 2 than the soil fertilized with the other two N rates. The greatest difference in CO 2 emission rate was observed in 2004; where plots that received 0 N rate had 31% greater CO 2 emission rate than plots fertilized with 270 kg N ha −1. The findings of this research indicate that changes in cropping systems can have immediate impact on both rate and cumulative soil CO 2 emissions, where continuous corn caused greater soil CO 2 emissions than corn soybean rotation.

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci from the European corn borer, Ostrinia nubilalis (Hübner) (Insecta: Lepidoptera: Crambidae)

Few useful microsatellites are available for population studies of the European corn borer, Ostrinia nubilalis (Hübner). An enrichment strategy was used to develop microsatellite markers for O. nubilalis, and over 500 positive clones were isolated. Seventy-five contained unique microsatellites, 10 of which were polymorphic with discernable polymerase chain reaction products. The 10 loci were surveyed for variability in 72 wild individuals from central Iowa. Five loci showed no deviation from Hardy-Weinberg proportions, and all were successfully cross-amplified in the related Asian corn borer, Ostrinia furnacalis. These loci represent a significant addition to microsatellites appropriate for population studies of O. nubilalis.