Location: Agroecosystems Management Research2016 Annual Report
Objective 1: Assess conservation practices and develop conservation planning tools that can improve agricultural water quality in the Midwest. Sub-objectives: 1) Develop and evaluate practices for reducing surface water contaminants in artificially drained landscapes; 2) Evaluate practices to reduce runoff and sediment losses from urban sites; and 3) Develop and evaluate tools to optimize placement of conservation practices within Midwest watersheds for improved environmental benefits. Objective 2: Determine the effects of climate, land use, and conservation practices on hydrology and water quality in agricultural watersheds. Sub-objectives: 1) Quantify hydrologic and water quality dynamics and their responses to changes in land use, conservation, and climatic conditions in Iowa watersheds; 2) Determine effects of landscape hydrology on soils and water quality in naturally and artificially drained landscapes; and 3) Map stream channel and bank movement in context with riparian land use and geomorphic setting to identify opportunities for restoring riparian ecosystems. Objective 3: Determine the fate and transport of pathogens and trace emergent compounds in agricultural soils and streams. Sub-objectives: 1) Determine transport pathways and environmental residence times of zoonotic pathogens associated with animal agriculture and the effects of management practices on those processes; 2) Determine transport pathways and environmental residence times of veterinary pharmaceuticals and the effects of management practices on those processes; 3) Determine if exposure to trace antibiotic residues in soil or stream sediment affects the persistence of antibiotic resistant bacteria and resistance genes; and 4) As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in Upper Mississippi River Basin region, use the UMRB LTAR to improve the observational capabilities and data accessibility of the LTAR network, to support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the Upper Mississippi River Basin, as per the LTAR site responsibilities and other information outlined in the 2012 USDA Long- LTAR Network Request for Information (RFI) to which the location successfully responded, and the LTAR Shared Research Strategy, a living document that serves as a roadmap for LTAR implementation. Participation in the LTAR network includes research and data management in support of the ARS GRACEnet and/or Livestock GRACEnet projects.
This project will conduct research to investigate the effects of agricultural management practices at field and watershed scales, the dynamics of watershed hydrology, and fundamental processes relevant to contaminant behavior in watersheds. Under the first objective, field studies will evaluate practices that can reduce loss of nitrate-nitrogen from cropped fields. These practices include resaturated buffers and bioreactors, practices that intercept tile drainage, and two practices that can reduce N loss to tiles, namely side-dressing of anhydrous ammonia and fall-planted cover crops. Bioreactor denitrification capacities will be assessed with microbiological assessments, and modeling studies will be conducted to extend experimental results on conservation practices to other areas of the Midwest. Research will be conducted to develop and evaluate watershed analyses to place conservation practices for improved water quality outcomes and determine how those strategies can be regionalized across the Midwest. Conservation needs also exist in urban environments and an experiment to determine how compost amendments can reduce urban runoff will be carried out. The second objective will be conducted in three Iowa watersheds, where stream monitoring will provide databases for watershed modeling studies, and for testing hypotheses about impacts of changes in climate and land use on water quality and hydrology. This research will be supported by efforts to identify field-scale patterns of hydrology and water quality, and better understand how new mapping techniques using Light Detection and Ranging (LiDAR) data can assist in understanding field hydrology, river corridor management, and targeting of conservation practices. The third objective will employ a mix of laboratory and field studies to evaluate environmental transport and residence times of pathogens and veterinary pharmaceuticals in soils and streams, and determine if exposure to trace antibiotic residues in soil or stream sediment affect the persistence of antibiotic resistant bacteria and antibiotic resistance genes. A breadth of watershed monitoring, controlled experiments in field and laboratory, and modeling techniques will be employed in the research. Publications, tools for conservation planning, and databases available to other scientists will be produced. Results are intended to enable agriculture to better manage water resources for multiple needs, particularly in the Upper Mississippi River basin.
Objective 1. We have installed nine saturated buffers across Iowa and are monitoring water flow and nitrate removal at each. Some saturated buffers are removing virtually all nitrates while others are not as effective. We are investigating the reasons for this difference. A pilot-scale saturated buffer continues to be monitored, and a paper describing our attempts to model the performance has been published. We also continued to monitor the performance of in-field denitrification walls, which are still performing as well 16 years after installation as the first year. The side-dressing of corn using anhydrous ammonia was completed after a four-year study in a corn-soybean rotation field and a manuscript published showing the benefit of side-dressing over fall application for both crop yield and water quality. Research to determine cover crop impacts on water quality and crop yield is continuing to show decreased nitrate concentrations, by 30% to 60% depending if they are oat (30%) or rye (60%). The Root Zone Water Quality Model (RZWQM) was used in ongoing work to simulate growth and N uptake of rye cover crops and a new effort to develop a greenhouse gas component of RZWQM representing tile drainage conditions in Iowa. In addition, urban/turfgrass conservation practices utilizing compost were assessed using a rainfall similator to measure infiltration, runoff, and nutrient loss in runoff. Although treatment differences were not significant, the compost-treated lawn soils had lower soil bulk densities near the surface, and periodic soil water content measurements are showing compost-treated lawns frequently have significantly higher soil water content (about one-fourth of the time). Visual evaluation of soil structure showed significant improvement following compost and aeration treatment to the lawns. A draft manuscript is being prepared. Our effort to develop a new, precision-conservation based approach to watershed planning was substantially progressed with the release of the GIS-based Agricultural Conservation Planning Framework (ACPF) software toolbox at the beginning of FY2016. A website to host this software and accompanying database was developed by the North Central Region Water Network, which is coordinated through the University of Wisconsin Extension Service. This website includes links to published journal papers and to a three-state database. The toolbox is being expanded to enable users to identify locations where saturated riparian buffers and denitrifying bioreactors can be installed in tile drained watersheds; this new version will be released in October 2016. The database is also being expanded to include eastern Kansas, enabling ACPF users to access watershed-scale information on field-specific crop rotations on nearly 5000 HUC12 watersheds, including for each of the 428,464 cropped fields being farmed in Iowa. ACPF training sessions were held in Ames, Iowa, and Madison, Wisconsin, during FY2016. Objective 2. Stream monitoring at the South Fork Iowa River (SFIR) and two Walnut Creek watersheds were continued; we passed 20 years of stream flow and water quality data for the SFIR watershed during the year. Hydrologic and water quality data from these watersheds were deposited in the Sustaining the Earth's Watersheds Agricultural Research Data System (STEWARDS) database. A manuscript comparing the hydrology and nutrient loads of SFIR and the Little Cobb River in southern Minnesota was published through a collaboration with U.S. Geological Survey (USGS) scientists. A plot-scale version of the Long-term Agroecosystem Research (LTAR) Common Experiment was established near Ames, Iowa. The experiment compares the business as usual (BAU) cropping system consisting of corn-soybean in rotation with tillage and fall-applied anhydrous N fertilizer to an aspirational (ASP) system consisting of corn-camelina-soybean rotation with corn N applied in the spring based on the Late-Season-Nitrate Test. Soybeans are inter-seeded into the live camelina crop and the oil-seed camelina is harvested in June. A third treatment is the corn-soybean rotation with a cereal rye winter cover crop. The plots at this site have individual tile drains which allow the measurement of nitrate loss in drainage, which is an important issue in the Midwest. A LTAR Observatory was also established in the South Fork Iowa River watershed. Measurements of water and CO2 fluxes will be measured on both the corn and soybean phases of the rotation along with periodic measurements of net primary productivity and soil properties. A manuscript describing results from 11 years of edge-of-field monitoring was published. This monitoring effort is being repositioned to support new (outside-funded) biomass/bioenergy research. Evaluations of the changes in climate and precipitation patterns on the hydrology have been evaluated for the Midwest and reveal that shifts in spring precipitation will increase the potential for runoff and erosion. The largest land use practice affecting the water balance is the maintenance of crop residue on the surface to increase the infiltration rates and the diversification of cropping systems to increase the water use rates in the early spring. Objective 3. Transport of antibiotics and antibiotic resistance genes was evaluated at field and watershed scales. At Nashua, Iowa, plot-scale studies compare antibiotic persistence and transport after spring and fall manure applications. Both antibiotics and antibiotic resistance gene transport were measured in soil and in tile drainage water in field plots with and without swine manure. Preliminary data indicates that antibiotic resistance genes may be more persistent after spring application. Laboratory studies measured the adsorption and degradation of tylosin and sulfamethazine in preparation for modeling their behavior in soil. In the South Fork Iowa River, data from a multi-year study on macrolide resistance genes were analyzed. The frequency of detection ranged from 52% to 97% at five sites where water samples were collected. Greater concentrations of resistance genes were found in tile drainage water than in stream water. In contrast, the concentrations of the rRNA gene (a proxy for total bacteria) were greater in surface water than tile drainage water. Concentrations of the macrolide antibiotic tylosin were also detected in these waters, but at trace concentrations. Finally, we reported on marker genes indicating presence of pathogenic E coli, Salmonella, and swine hepatitis E virus. Detection was more frequent in the SFIR watershed than in Walnut Creek watershed, corresponding to the very different populations of swine in these watersheds.
1. Side-dressing N fertilizer benefits crop yield and water quality. Surprisingly, little research has examined the corn yield, N use efficiency, and water quality implications of the timing of N fertilizer application. Research by ARS scientists in Ames, Iowa, showed corn yields when N was side-dressed (SD) were at least 24 bushels per acre greater than for the N applied in the fall (F) or pre-plant (PP) in the spring. The nitrogen use efficiency by the corn followed the pattern of SD>PP>F. Nitrate losses in tile drainage water from the treatments were significantly different and followed the pattern F>SD>PP. As expected, there were no significant differences in soybean yield for any N treatment. Considering crop yield, N use efficiency by the crop, and nitrate losses to water, side-dressing N was clearly superior to fall application in a corn–soybean rotation. This study alone will help guide farmers, agricultural retailers, and state action agencies in applying N fertilizer in the most efficient manner to protect yields and regional water quality. (#314186)
2. Nitrate removal by denitrification bioreactors. Woodchip denitrification bioreactors, a relatively new technology for edge-of-field treatment of subsurface agricultural drainage water, have shown potential for nitrate removal. However, few studies have evaluated the performance of these reactors under varied controlled conditions including a range of hydraulic retention times (HRTs) and temperatures similar to the field. ARS scientists in Ames, Iowa, and university collaborators found that the removal of nitrate-N increased from 8 to 55 (% of concentration at inlet) as HRT increased from 1.7 to 21 hours. Nitrate removal on a mass basis did not follow the same trend, with relatively consistent mass removal measured as HRT increased from 1.7 to 21 hours, suggesting that the microbial community had achieved maximal removal rates. The removal data at various combinations of flow, nitrate concentration, and temperature provide a range of expected results informing engineers and field technicians about the importance of HRT in bioreactor design. (#314273)
3. Salmonella in drainage water after poultry manure application. Salmonella is a bacterial pathogen that may be transported off-site after manure applications. USDA-ARS scientists in Ames, Iowa, and university collaborators investigated the transport of the bacterial pathogen Salmonella into subsurface drains beneath cropped fields that received poultry manure prior to corn planting. Salmonella was detected in the poultry manure and drainage water along with the fecal indicator bacteria E coli and Enterococcus. Salmonella transport may be increased in soils with continuous macropores, such as in no-till fields. Concentrations of Enterococcus were more strongly correlated to Salmonella than for E coli, suggesting that Enterococcus might be a better indicator of contamination. This information is of interest to scientists, poultry producers, and water quality specialists in state government. (#318639)
4. Carbon sources for low temperature denitrification bioreactors. Nitrate losses in drainage waters from the Upper Mississippi River Basin are often greatest in the early spring when high flows and cold temperatures are common. Denitrification is a microbial process that converts nitrate to atmospheric N gas and the passage of drainage water through these bioreactors is a promising conservation practice, but there are concerns about performance of these bioreactors under low-temperature conditions. ARS scientists in Ames, Iowa, and Saint Paul, Minnesota, along with university collaborators compared the ability of corn cobs, corn stover, barley straw, and wood chips to support denitrification at 15.5 and 1.5 C temperatures. Wood chips removed the least nitrate which was consistent with lower populations of denitrifying bacteria. While the other materials supported more denitrification, the rate declined over the six months of the study, whereas this trend was not seen with wood. The removal data for different carbon sources and temperatures provide a range of expected results informing engineers and field technicians about the performance of these reactors under cold temperatures. (#318515)
5. Long-term comparison of edge-of-field phosphorus losses. Monitoring runoff at field edges can show how cropping systems and conservation practices affect runoff hydrology and water quality, but the variable, ephemeral nature of rainfall-runoff events mean multi-year studies are needed to quantify these effects. ARS scientists in Ames, Iowa, tracked runoff and phosphorus losses from two Iowa fields that were in the same corn-soybean rotation, but only one field received applications of swine manure. Runoff amounts for the two fields were similar, but the manured field lost 70% more phosphorus. Large storms (>2.4 inches rainfall) only produced 12-16% of the runoff phosphorus losses, while moderate storms (1.2-2.3 inches rainfall) generated 65-70% of the phosphorus losses from both fields. Results highlighted the risk of phosphorus loss that occurs when significant rains occur following manure applications, but also indicated these risks can be managed where conservation practices reduce runoff from moderate sized (<2.4 inch) storms. These results are of interest to farmers, conservation planners, and policy makers, who seek to understand how extreme weather events can impact water quality performance of agricultural systems and mitigation of associated risks. (#316203)
6. Guidelines for parameterization of hydrologic models. Among the most difficult and important aspects of using agricultural system models is imparting knowledge of the physical processes of a system to the model and determining a set of parameter values that describe a hydrologic or water quality process within a model application (i.e., parameterization). However, there are few studies devoted to developing general parameterization guidelines to assist in hydrologic model application. ARS scientists in Ames, Iowa, Columbia, Missouri, Oxford, Mississippi, and Fort Collins, Colorado, along with several university collaborators, developed the following model parameterization guidelines: 1) use site specific measured or estimated parameter values where possible; 2) focus on the most uncertain and sensitive parameters; 3) minimize the number of optimized parameters; 4) constrain parameter values to within justified ranges; 5) use multiple criteria to help optimize parameter values; 6) use “soft” data to optimize parameters; and 7) use a warm-up period to reduce model dependence on initial condition state variables. Several “case studies” from previously reported research illustrate implementation of the parameterization guidelines. This research will help improve model parameterization resulting in more consistency, better representation of the field or watershed, and reduced range of parameter value sets resulting in acceptable model simulations. (#304399)
7. Determining components of plant growth media to support environmental quality. Engineered plant growth media should support plant growth while reducing environmental impact. Research by an ARS scientist in Ames, Iowa, showed there was substantial nutrient leaching when the media included compost containing manure. Layering the compost over the plant media reduced nutrient leaching compared with mixing the compost with the plant media. Plant growth was improved when soil was included in the growth media. The benefits of including iron filings in plant growth media to sorb phosphorus and reduce leaching was also studied. However, iron filings cemented the plant growth media, but may be useful in filter beds that do not support plant growth, but are not recommended in plant growth media. This information is useful for those who use engineered plant media in urban rain gardens or in greenhouses. (#312847, #311234)
8. Comparing watershed records of stream sediment and field erosion in differing Mississippi tributaries. Changes in sediment loads along a river course can be used to diagnose the role of alluvial plains and other landscape sediment sinks, or may indicate scales at which channel and/or field erosion has a dominant impact. ARS scientists in Ames, Iowa, and collaborators evaluated changes in sediment with watershed size in Iowa (Iowa River) and Mississippi (Yazoo River). Watersheds in the Yazoo basin had steady decreases in sediment yield as basin size increased, but the Iowa River basin showed sediment yields were greatest in intermediate-sized watersheds (i.e., 12 to 200 square miles). Subsurface tile drainage and limits to channel incision decreased the amounts of sediment that could be sourced from Iowa River uplands, leading to channel widening in intermediate basins. Despite these differences, when the sediment-basin size data were plotted against field erosion rates determined from research on conservation and conventional tillage in these basins, it was apparent that historical soil losses that occurred prior to conservation efforts are still impacting sediment loads in both river basins. These results are of interest to conservationists and hydrologists seeking to understand long-term changes in sediment loss as affected by watershed scale, and the apparent disconnect between agricultural conservation efforts and sediment loading in Mississippi tributary rivers. (#312537)
9. Comparative analysis of nutrient losses from two tile drained watersheds. Nitrogen and phosphorus loads from artificially drained agricultural watersheds contribute to Gulf of Mexico hypoxia and affect local aquatic ecosystems; cross-watershed comparisons of these loads may help fine tune remediation strategies. An ARS scientist in Ames, Iowa, and collaborators compared nutrient losses from the Little Cobb River in southern Minnesota and the South Fork Iowa River in northern Iowa during 1996-2007. Nutrient loads peaked during snowmelt in the Little Cobb, but peak loads from the South Fork occurred during late spring and early summer. Annual nutrient loads were substantially greater from the South Fork than the Little Cobb for both nutrients; this was possibly associated with more acreage in continuous corn and a larger number of livestock feeding operations in the South Fork. Strategies aimed to reduce nutrient loads should address vulnerability during seasonal peak flows, which differed between these two watersheds separated only by about 100 miles. These results are of interest to a range of agricultural and conservation stakeholders interested in greater agricultural efficiency and water quality protection. (#322468)
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