Iowa Soybean Association

Iowa Falls, IA, United States

Iowa Soybean Association

Iowa Falls, IA, United States

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Schilling K.E.,Iowa Geological and Water Survey | Jones C.S.,Iowa Soybean Association | Seeman A.,Iowa Soybean Association | Bader E.,The Nature Conservancy | Filipiak J.,The Nature Conservancy
Ecological Engineering | Year: 2012

Many extensive subsurface tile drainage networks in the Corn Belt region of the United States are organized into quasi-governmental drainage districts. Approximately 3000 of these engineered watersheds exist in the state of Iowa. Tile discharge is the source of many headwater streams and contributes to loss of nitrate-nitrogen (NO 3-N) from cultivated fields. Downstream water use by municipal suppliers is impaired by stream concentrations>10mg/l, and load reductions>30% may be necessary to mitigate Gulf of Mexico hypoxia. The objectives of this study were to evaluate NO 3-N concentrations and loads discharged from three typical drainage districts in north-central Iowa and explore the relation of drainage district NO 3-N concentrations to the downstream drainage network. NO 3-N concentrations averaged approximately 13mg/l over a two-year period and exceeded 10mg/l (the standard for safe drinking water in the U.S.) nearly 90% of the time. NO 3-N yields from the studied drainage districts ranged from 33 to 77kg/ha per year. NO 3-N concentrations and episodes>10mg/l were observed to decrease downstream in a linear manner with log drainage area. A load reduction of 55% would be needed at the tile discharge to meet downstream water quality objectives. In-stream NO 3-N processing was observed immediately downstream of the tile outlet, but would appear to offer little potential for meaningful downstream reductions because the time period for NO 3-N processing was poorly timed with seasonal loading patterns. Study results suggest that focusing on NO 3-N reductions at the drainage district scale using best management practices, such as in-field nitrogen management or edge of field treatment, with constructed wetlands, would achieve significant downstream reductions. © 2012 Elsevier B.V.

Jones C.S.,Iowa Soybean Association | Schilling K.E.,Iowa Geological and Water Survey
Journal of Environmental Quality | Year: 2011

Fluvial sediment is a ubiquitous pollutant that negatively aff ects surface water quality and municipal water supply treatment. As part of its routine water supply monitoring, the Des Moines Water Works (DMWW) has been measuring turbidity daily in the Raccoon River since 1916. For this study, we calibrated daily turbidity readings to modern total suspended solid (TSS) concentrations to develop an estimation of daily sediment concentrations in the river from 1916 to 2009. Our objectives were to evaluate longterm TSS patterns and trends, and relate these to changes in climate, land use, and agricultural practices that occurred during the 93-yr monitoring period. Results showed that while TSS concentrations and estimated sediment loads varied greatly from year to year, TSS concentrations were much greater in the early 20th century despite drier conditions and less discharge, and declined throughout the century. Against a backdrop of increasing discharge in the Raccoon River and widespread agricultural adaptations by farmers, sediment loads increased and peaked in the early 1970s, and then have slowly declined or remained steady throughout the 1980s to present. With annual sediment load concentrated during extreme events in the spring and early summer, continued sediment reductions in the Raccoon River watershed should be focused on conservation practices to reduce rainfall impacts and sediment mobilization. Overall, results from this study suggest that eff orts to reduce sediment load from the watershed appear to be working. © 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Jones C.S.,Iowa Soybean Association | Schilling K.E.,Iowa Geological and Water Survey
Journal of Environmental Quality | Year: 2013

Farmed landscapes are engineered for productivity, and research suggests they contribute a disproportionate share of inorganic C to the Mississippi River and Gulf of Mexico. Here we use alkalinity and total organic C (TOC) measurements collected from the Raccoon River of Iowa to (i) evaluate inorganic and organic C concentrations and export patterns, (ii) compare current trends to historical conditions, and (iii) link C transport processes to current land use management. Export of inorganic C averaged 106,000 Mg per year and contributes 90% of the C flux from the basin. Alkalinity concentrations are unchanged from 1931 to 1944 levels (̃53 mg L-1 C), but inorganic C loads have doubled due to increasing discharge. Carbonate-rich glacial deposits and agricultural lime provide a large source of inorganic C, and results confirm that alkalinity export in the Raccoon Basin is transport limited. Although fertilization and tillage practices have possibly helped increase C fluxes over the last 70+ yr, the overriding factor on inorganic C export is discharge. Discharge control over C export provides an opportunity for agriculture in terms of quantifying C sequestration for potential C trading. Controlling water flux through soils can limit inorganic C export similar to practices such as reduced tillage and managed rotations. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Schilling K.E.,Iowa Geological Survey | Jacobson P.J.,Grinnell College | Streeter M.T.,Iowa Geological Survey | Jones C.S.,Iowa Soybean Association
Wetlands | Year: 2016

The prairie pothole region covers 700,000 km2 of North America and once contained millions of pothole wetlands but agricultural drainage was used to convert many these wetlands to agriculture. Termed “drained wetlands” in this study, groundwater hydrology and quality beneath these pothole depressions is poorly understood. In this study we characterized water table levels and nutrient concentrations at eight drained wetland sites in Iowa. During the 2011 to 2014 study period that ranged from drought to above-normal rainfall, water table levels exhibited a clear seasonal pattern, rapidly increasing in the spring with rainfall and decreasing in the late summer due to evapotranspiration (ET) and lateral flow to subsurface drainage tiles. The average water table depth ranged from approximately 90 to 130 cm near the typical tile depth in Iowa (120 cm). Results suggest that ponding observed at the farmed pothole depressions is rarely due to groundwater rise. High concentrations of NO3-N and PO4-P were present in shallow groundwater beneath the drained wetlands, averaging 16.7 and 0.4 mg l−1, respectively. Overall, both groundwater hydrology and quality of drained wetlands appear to be dominated by the agricultural land use. © 2016 Society of Wetland Scientists

Schilling K.E.,Owa Geological and Water Survey | Jones C.S.,Iowa Soybean Association | Seeman A.,Iowa Soybean Association
Journal of Environmental Quality | Year: 2013

Quantifying the effectiveness of perceived best management practices (BMPs) at the field and landscape-scale is difficult, so paired watershed studies are used to detect water quality improvements. We evaluated concentrations of NO3-N discharged from three tiled Iowa watersheds during a 4-yr period to assess their suitability for a paired watershed approach. Our objectives were to evaluate similarities in physical characteristics, concentration patterns, and correlation among the three paired sites and perform a minimum detectable change (MDC) analysis on paired site configurations. The study results demonstrate that concentration variability within and between sample sites affected correlation among the paired basins, even though the physical characteristics of the basins are quite similar. Restricting comparisons to the active tile drainage period (March-July) improved correlations. The lack of a suitable correlation will impair the ability to detect changes expected to result from BMP implementation. The MDC for NO3-N concentration change detection varied from 6.9 to 12.9% and averaged 8% for the best control-treatment pair. To ensure that conservation resources are being used effectively, implemented BMPs should focus on practices capable of achieving at least this magnitude of change. These practices may include reduced fertilizer applications, adoption of cover crops, and land use change. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Stott D.E.,U.S. Department of Agriculture | Cambardella C.A.,Ames Laboratory | Tomer M.D.,Ames Laboratory | Karlen D.L.,Ames Laboratory | Wolf R.,Iowa Soybean Association
Soil Science Society of America Journal | Year: 2011

Soil quality assessment is a proactive process for understanding the long-term effects of crop and soil management practices within agricultural watersheds. Fields with both well-developed and poor (N-deficient) corn (Zea mays L.) canopy growth were identifi ed within the Iowa River's South Fork Watershed. Our objectives were to quantify several soil quality indicators, including the near-surface soil organic carbon (SOC) content, and determine if the Soil Management Assessment Framework (SMAF) could distinguish between the well-developed and poor corn canopy areas. Four sites, three representing the major soil series in the well-developed canopy areas and one in the poor area, were identifi ed and sampled (0-10 cm) within 50 fi elds. Th ere were no significant diff erences between performance zones when analyzed collectively. Using SMAF indicator scores, SOC, bulk density (D b), water-fi lled pore space (WFPS), electrical conductivity (EC), and microbial biomass carbon (MBC) were significantly lower in the poor canopy areas; however, no single indicator scored significantly less across all 50 fi elds. When separated by landscape position (hilltop, sideslope, toeslope, or depression), only SOC was significantly diff erent between performance zones across each position. Other indicators that diff ered in at least one slope position included D b, WFPS, MBC, EC, P, Fe, Cu, Zn, or potentially mineralizable C. A majority of fi elds had multiple indicators with SMAF ratings at least 0.10 lower in the poor areas than in the corresponding well-developed canopy areas. Soil quality assessment on a fi eld-by-fi eld basis thus provides an approach for identifying potential specific soil-based causes for the poor canopy development. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.

Jones C.S.,University of Iowa | Kult K.J.,Iowa Soybean Association
Journal of Environmental Quality | Year: 2016

In recent years, the agricultural community has reduced flow of nitrogen from farmed landscapes to stream networks through the use of woodchip denitrification bioreactors. Although deployment of this practice is becoming more common to treat high-nitrate water from agricultural drainage pipes, information about bioreactor management strategies is sparse. This study focuses on the use of water monitoring, and especially the use of alkalinity monitoring, in five Iowa woodchip bioreactors to provide insights into and to help manage bioreactor chemistry in ways that will produce desirable outcomes. Results reported here for the five bioreactors show average annual nitrate load reductions between 50 and 80%, which is acceptable according to established practice standards. Alkalinity data, however, imply that nitrous oxide formation may have regularly occurred in at least three of the bioreactors that are considered to be closed systems. Nitrous oxide measurements of influent and effluent water provide evidence that alkalinity may be an important indicator of bioreactor performance. Bioreactor chemistry can be managed by manipulation of water throughput in ways that produce adequate nitrate removal while preventing undesirable side effects. We conclude that (i) water should be retained for longer periods of time in bioreactors where nitrous oxide formation is indicated, (ii) measuring only nitrate and sulfate concentrations is insufficient for proper bioreactor operation, and (iii) alkalinity monitoring should be implemented into protocols for bioreactor management. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA.

Liang X.,Nanjing University | Schilling K.,University of Iowa | Zhang Y.-K.,Nanjing University | Zhang Y.-K.,University of Iowa | Jones C.,Iowa Soybean Association
Water Resources Management | Year: 2016

Daily nitrate-nitrogen (NO3-N) loads in the Raccoon River, Iowa, were estimated using Ordinary kriging (OK), Cokriging (CK), and a standard rating curve method (LOADEST) based on a dataset of 3451 measurements of NO3-N concentration collected over 19 years. The CK estimation utilizes the temporal correlation of NO3-N load with daily discharge and honors the measured points to improve estimation relative to regression based models. Loads were estimated using the observed concentrations and three subsets of the measured data that correspond to three frequencies (weekly, biweekly, and monthly). Results indicated that daily NO3-N loads were best estimated by CK using measured loads with daily discharge. Daily load estimates produced by OK using weekly data matched well with measured values, but discrepancies emerged when samples were collected less frequently, e.g., biweekly and monthly. For the entire 19-year dataset, compared to measured loads, the estimated total NO3-N load decreased using OK when samples were collected monthly, but increased using CK. Load estimation using the seven-parameter LOADEST model did not perform well for the Raccoon River because the correlation of NO3-N concentration to river discharge was poor. For the site studied, weekly and biweekly sampling may be sufficient to estimate daily NO3-N loads with CK when daily discharge data is available. © 2016, Springer Science+Business Media Dordrecht.

ZHANG J.,Temple University | BLACKMER A.M.,Iowa State University | KYVERYGA P.M.,Iowa Soybean Association | GLADY M.J.,Winfield Solutions LLC. | BLACKMER T.M.,Iowa Soybean Association
Pedosphere | Year: 2010

To evaluate the temporal patterns of N deficiencies in corn and assess the ability of remote sensing to diagnose N deficiencies during the vegetative growth of corn, three field-scale experiments were conducted with various rates (56, 112, and 168 kg N ha-1), timing (early and late applications) and placement (injected into soil and dribbled on soil surface) of N fertilization in a split-plot design. Relationships between canopy reflectance during the growing season and yield data at the end of growing season were studied for different treatments. Results showed significant variation in both grain yields and canopy reflectance among the three cornfields. The N fertilization made in early June resulted in low canopy reflectance in early July, but the differences disappeared as the season progressed. The effect of N rates on canopy reflectance was not significant in early July but it gradually became detectable in mid-July and thereafter. The fertilizer placement had a significant effect on grain yields only in one field but not on canopy reflectance in all three fields. These observations suggest that the deficiency of N developed under field conditions is a dynamic phenomenon, which adds complexity for accurately defining "N deficiency" and effectively developing management strategies for in-season correction. Remote sensing throughout the season helps collect information about important interactions that have not been given enough attention in the past. © 2010 Soil Science Society of China.

Hua G.,South Dakota State University | Salo M.W.,South Dakota State University | Schmit C.G.,South Dakota State University | Hay C.H.,Iowa Soybean Association
Water Research | Year: 2016

Woodchip bioreactors have been increasingly used as an edge-of-field treatment technology to reduce the nitrate loadings to surface waters from agricultural subsurface drainage. Recent studies have shown that subsurface drainage can also contribute substantially to the loss of phosphate from agricultural soils. The objective of this study was to investigate nitrate and phosphate removal in subsurface drainage using laboratory woodchip bioreactors and recycled steel byproduct filters. The woodchip bioreactor demonstrated average nitrate removal efficiencies of 53.5-100% and removal rates of 10.1-21.6 g N/m3/d for an influent concentration of 20 mg N/L and hydraulic retention times (HRTs) of 6-24 h. When the influent nitrate concentration increased to 50 mg N/L, the bioreactor nitrate removal efficiency and rate averaged 75% and 18.9 g N/m3/d at an HRT of 24 h. Nitrate removal by the woodchips followed zero-order kinetics with rate constants of 1.42-1.80 mg N/L/h when nitrate was non-limiting. The steel byproduct filter effectively removed phosphate in the bioreactor effluent and the total phosphate adsorption capacity was 3.70 mg P/g under continuous flow conditions. Nitrite accumulation occurred in the woodchip bioreactor and the effluent nitrite concentrations increased with decreasing HRTs and increasing influent nitrate concentrations. The steel byproduct filter efficiently reduced the level of nitrite in the bioreactor effluent. Overall, the results of this study suggest that woodchip denitrification followed by steel byproduct filtration is an effective treatment technology for nitrate and phosphate removal in subsurface drainage. © 2016.

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