Location: Agroecosystems Management Research2018 Annual Report
1a. Objectives (from AD-416):
Objective 1: Design, place, and assess conservation practices for improved water quality and environmental benefits. Sub-objectives: 1.1: Develop and evaluate practices for reducing surface water contaminants in artificially drained landscapes; 1.2: Evaluate perennial systems to reduce runoff, sediment, and phosphorus (P) losses; and 1.3: Increase the efficacy of the Agricultural Conservation Planning Framework (ACPF) toolbox as an approach to conservation planning for improved water quality within Midwest watersheds. Objective 2: As part of the Long-Term Agroecosystem Research (LTAR) network, and in concert with similar long-term, land-based research infrastructure in the Upper Mississippi River Basin Region, use the Upper Mississippi River Basin Experimental Watersheds LTAR site to improve the observational capabilities and data accessibility of the LTAR network and support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the region. Research and data collection are planned and implemented based on the LTAR site application and in accordance with the responsibilities outlined in 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 Greenhouse gas Reduction through Agricultural Carbon Enhancement network (GRACEnet) and/or Livestock GRACEnet projects. Objective 3: Quantify the effects of landscape attributes and management practices on the fate, transformation, and transport of antibiotics, antibiotic-resistant bacteria and other emerging contaminants in surface runoff, drainage water, and streams in agricultural watersheds.
1b. Approach (from AD-416):
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 saturated buffers, bioreactors, fall planted cover crops, and protected surface inlets to subsurface drainage. Bioreactor denitrification capacities will be assessed with microbiological assessments, and modeling studies will be conducted to investigate management practices that may reduce N loss to subsurface drainage in the context of historical climate data. Research will be conducted to improve agricultural conservation planning across the Midwest. Conservation needs also exist in perennial agricultural systems and investigations into the water use, runoff, erosion, and P losses will be carried out. Under the second objective, field and watershed studies will be conducted as part of the Long-Term Agroecosystem Research (LTAR) network that will support research to sustain or enhance agricultural production and environmental quality in the Upper Mississippi River Basin region. The third objective will employ a mix of laboratory, field, and modeling studies to evaluate environmental transport of pathogens and veterinary pharmaceuticals under different landscape attributes and management practices. 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.
3. Progress Report:
Objective 1.1. Twelve saturated buffers have been installed in Iowa and are being continuously monitored for flow, water table position, and nitrate removal. Two more saturated buffers are being planned for installation and will be instrumented for full monitoring. Results from these saturated buffers substantially contributed to the development of the Natural Resources Conservation Service (NRCS) Conservation Practice Standard #604 "Saturated Buffers." A pilot scale denitrifying bioreactor is being investigated for the seventh year. Nitrate removal is being monitored by measuring nitrate loads entering and leaving the bioreactor. Nitrous oxide emissions are monitored both dissolved in the tile water and emitted as gas from the bioreactor. A new treatment plan with fertilizer applied at different times is in its third year for the corn-soybean rotations with and without a fall planted rye cover crop. The treatment plan includes pre-plant fertilizer application and post-plant side-dress according to late spring soil nitrate testing. Crop biomass yields and nitrate, phosphorus, and potassium losses in tile drainage are being measured. Monthly weather under climate change for central Iowa have been developed for the Root Zone Water Quality Model (RZWQM). The RZWQM output with projected climate change is being organized to investigate climate change impacts on nitrogen (N) loss to drainage and crop yield in corn-soybean rotations with winter rye cover crop. Objective 1.2. For perennial systems, overhead pictures of two fields have been taken to determine fraction ground cover, which is related to potential erosion. Leaf area index and evapotranspiration (ET) were determined for several agricultural systems (organic forage, organic rotation, and conventional corn-soybean). The organic forage had green vegetation from early spring to late fall and had significantly more ET in May, June, and October. The four-year organic rotation had good crop growth in spring for the second year alfalfa and starting growth in the oat plots; however, the corn and soybean did not have crops in May or October, and only small crops in June. So the four-year organic rotation had significantly less ET than the forage, but more than the conventional corn-soybean rotation in May, June, and October. The manuscript on leaf area index is in journal review, and the manuscript on ET is in internal review. Patterns of water table depth and ET suggest subsurface lateral transfer of water occurred between the organic plots, and upward movement of water occurred from plots with shallow water tables. Objective 1.3. A multi-watershed analysis has been completed on a set of randomly selected watersheds. Application of the Agricultural Conservation Planning Framework (ACPF) toolbox to watershed data provides a menu of options for placement of conservation practices. Once analyzed, results will show whether/how the ACPF may contribute to regional planning efforts. Under Goal 1.3.2, we have continued to develop and extend the ACPF databases and toolbox. In collaboration with a university, land use and soils databases were made available for download and use in developing watershed conservation plans, for more than 8,700 small (Hydrologic Unit Code or HUC12) watersheds; users have downloaded data for more than 2,200 of these watersheds. The ACPF is also being trialed in the western Lake Erie basin, with a pilot project including seven watersheds in Indiana and Ohio. An ACPF training session is planned for August 2018, and being arranged by local USDA-NRCS officials. We have used online resources to develop watershed "storymaps," which provide a new way to present ACPF results to stakeholders. We have trialed this approach with a producer workshop in the South Fork of the Iowa River watershed; participants were able to "zoom in" to individual fields and identify/evaluate conservation options for their fields. Feedback was positive and several producers indicated they would consider implementing new practices displayed for their fields, which they had not had the opportunity to consider before. Version 3 of the ACPF will be released during the second half of 2018. Improvements will allow users to merge water bodies and streams for riparian analysis, enabling lakeshore conservation planning as a new application of the results. Objective 2. We acquired data on stream flow, meteorological data, and water quality measurements in three experimental watersheds. Data from these watersheds are deposited in the Sustaining the Earth's Watersheds—Agricultural Research Data System (STEWARDS) database to support the Conservation Effects Assessment Project (CEAP) and Long-term Agroecosystem Research (LTAR) network. An experiment evaluating different conventional and sustainable farming systems was established. This includes the LTAR common experiment, which compares conventional and alternative (aspirational) cropping systems. Data from this site were organized in preparation for final entry into a searchable database to support LTAR. Objective 3. The concentrations of antibiotics and antibiotic resistance genes in the South Fork of the Iowa River (SFIR) were measured. The resistance genes that confer resistance to macrolide antibiotics (erm genes) were present throughout the watershed and subsurface (tile) drainage water had greater concentrations than stream water, providing evidence that movement through the soil is occurring. About 35% of the SFIR receives swine manure each year. Additionally, the macrolide antibiotic tylosin was detected in low concentrations in both stream water and subsurface drainage water in SFIR. We explored the diversity of erm genes by metagenomics sequencing of manure and soil and matched those DNA sequences against qPCR primers commonly used to measure these genes. The qPCR primers were not fully effective in matching the full diversity of erm genes, suggesting that our qPCR assays are underestimating the abundance of these genes in soil and water.
1. Antibiotic resistance genes (ARGs) and antibiotics can move off agricultural fields in subsurface drainage water. Antibiotic resistance is an increasing medical problem and the effects agricultural use of antibiotics has on resistance in human pathogens is not clear. Previous reports have indicated elevated levels of ARGs in surface water and groundwater around confined animal feeding operations which administer antimicrobials, but little information is known how their transport from tile drained fields receiving swine manure application impacts downstream environments. ARS scientists in Ames, Iowa, and Iowa State University collaborators found higher levels of two genes that confer resistance to macrolide antibiotics in tile drainage and river water in spring and fall following swine manure application. Approximately 840,000 swine are raised within the watershed. A companion study also documented the presence of two veterinary antibiotics. The study provides new information establishing that these resistance genes and antibiotics are moving off farmed fields in drainage water. These findings provide new science-based information to improve understanding of this problem.
2. Reported nitrogen (N) accumulations in Mississippi River basin soils by an analysis of USDA-Natural Resources Conservation Service (NRCS) soils database may be incorrect. Accumulations of N in soil would have long-term, negative implications for efforts to improve water quality in the Mississippi River basin. A recent analysis of the USDA National Cooperative Soil Survey Soil Characterization Database (NSCD) showed soil N storage has increased across the Mississippi basin since 1985. Unfortunately, changes in soil analytical methods, not described by downloaded NSCD data, were not considered in that report. ARS scientists in Ames, Iowa, in collaboration with an NRCS scientist at the Kellogg Soil Survey Laboratory in Lincoln, Nebraska, used NSCD archives to correct for the change in methods and determined trends for N and soil organic carbon in farmed soils typical of the U.S. Corn Belt. The correction between methods and the geographic focus on farmed land, nullified the reported trend of accumulating soil N. Rather, decreasing trends in soil N with time were found, with trends in carbon-to-N ratios that suggested susceptibility of soil N to leaching has decreased among farmed soils in the Corn Belt. However, this apparent improvement has been slow, and substantial amounts of mobile soil N remain. Moreover, there is an important caveat: the NSCD was not designed to answer questions about soil change. These results are of interest to those in the agricultural and environmental communities interested in understanding how soils may be changing as cropping and nutrient management systems evolve, and if/how publicly available soils data can be used to document soil change.
3. Soil nutrient variability and groundwater nitrate-nitrogen (N) in agricultural fields. The amount of nutrients in soil and groundwater varies across the landscape as a result of management practices. ARS scientists in Ames, Iowa, showed that a field with highly variable soil nutrients due to management did not show variation due to landscape position. Another field had large variation in landscape positions which did influence the pattern of nutrients in the soil. Ground water nitrate levels in this field remained high over time, perhaps due to long-term manure additions. This information is important to scientists as well as those developing best management practices.
4. Harvesting fertilized rye cover crop. Food and biofuel production along with global nitrogen (N) use are expected to increase over the next few decades, which complicates the goal of reducing N loss to the environment. Studies suggest harvesting rye as a biofuel feedstock is a promising method to provide producer income and increase biofuel production without decreasing food production, however, the impact on N loss to drainage is unknown. ARS scientists in Ames, Iowa; Fort Collins, Colorado; and St. Paul, Minnesota, along with university collaborators from Penn State, Iowa State, and China used the Root Zone Water Quality Model (RZWQM) to determine that adding an additional spring fertilizer application prior to winter rye harvest reduced drainage N loss substantially compared with no cover crop, and estimates of producer revenue and net energy were also positive with fertilized and harvested rye biomass. These results suggest double-cropping fertilized winter rye is a promising strategy to provide revenue and reduce N loss to drainage. Producers may be interested in the additional revenue potential of harvested rye winter cover crop, and policy makers may be interested in the increased biomass production and reduced N loss to the environment without decreased food production.
5. Streambank erosion measured at watershed scale. Stream bank erosion can damage riparian and aquatic ecosystems and impact water use downstream and may be increased during extreme flood events. Bank erosion along the South Fork Iowa River (SFIR) watershed caused by 2008 flooding was measured by ARS scientists in Ames, Iowa, using high-resolution topographic data and aerial imagery. Along upper (smaller) streams, channels were widened by up to 3.5 feet, amounting to an average 1.1 tons lost per yard of stream length and at least 21 acres of land lost along 65 miles of channel. Below a major confluence, impacts increased and the larger stream was widened by 14.5 ft along a length of 6.1 miles, with about 8.1 tons of sediment lost per yard of stream length. The 2008 floods substantially altered these channels, but riparian areas along the upper channels in permanent vegetation showed less bank erosion, indicating riparian buffers may help maintain stream corridors even under extreme flooding. This information is of interest to the conservation community and those interested in reducing impacts of extreme flood events on surface waters and aquatic ecosystems.
6. Electrical stimulation of woodchip bioreactors for nitrate removal. Woodchip bioreactors are a promising technology for removing nitrate from subsurface drainage water in the Midwest and other regions. However, there is a tradeoff between bioreactor size and cost and nitrate removal. ARS researchers in Ames, Iowa, and Iowa State University collaborators conducted a series of experiments to explore the possibility of electrical stimulation of microbial denitrification in woodchip bioreactors. The experiments identified the most promising materials for the electrodes, electrode positioning, and documented nitrate removal under a range of currents. While electrical stimulation could remove an additional 37-72% of annual nitrate loads, this additional removal was more costly than nitrate removal by woodchip bioreactors without electrical stimulation. The project received stakeholder support and the results inform researchers that may further investigate this process.
7. N (nitrogen) loss to drain flow and N2O emissions from a corn-soybean rotation with winter rye. The U.S. National Academy of Engineering listed “Manage the Nitrogen Cycle” as one of the grand challenges for the 21st century. Only limited studies, however, are available that simultaneously investigate nitrous oxide-N emissions and nitrate-N losses to subsurface drain flow. ARS scientists in Ames, Iowa; Fort Collins, Colorado; and St. Paul, Minnesota, along with collaborators from China and Germany, used the Root Zone Water Quality Model (RZWQM) to evaluate nitrate losses to drain flow and nitrous oxide emissions in a corn-soybean system with a winter rye cover crop (CC) in central Iowa over a nine-year period. The model accurately simulated N loss to drainage and N2O emissions over the period of study 2002-2010, and the simulations agree with field data that winter rye cover crop substantially reduces N loss to drainage. In contrast to previous research, both observed and model simulated monthly nitrous oxide flux was generally greatest when N loss to leaching was greatest during corn years, mostly because relatively high rainfall occurred during the months fertilizer was applied. The results suggest that RZWQM is a promising tool to estimate nitrous oxide emissions from subsurface drained corn-soybean rotations in central Iowa and to estimate the relative effects of a winter cover crop over a nine year period on nitrate loss to drain flow. This research will help model developers, model users, and agricultural scientists more clearly understand N2O emissions and nitrate transport under subsurface drained conditions that include a winter rye cover crop, which will help in the design of more effective management to reduce N export to air and water.
8. Digging to the top (soil). Human-transported fill material is common in urban areas and is often of poor quality for plant growth. Understanding the characteristics of these sites could help improve urban soil quality. ARS researchers in Ames, Iowa, showed up to 3 feet of fill material in an urban area. The material had only a thin topsoil layer over light-colored subsoil, and much of the material was full of lime. The buried topsoil was much deeper than the new topsoil layer. Carbon was stored in the limey material as well as the buried subsoil. This information is important for urban planners who desire to improve the site after construction.
9. Nutrient leaching when soil is part of plant growth media. Nutrients can leach through engineered plant growth media despite this material often containing sand, organic matter, and other materials (purchased or waste products) to help reduce phosphorus leaching. ARS researchers in Ames, Iowa, showed that adding soil to the mixture was good enough to prevent phosphorus loss without using non-soil materials. This information is useful for urban planners and greenhouse managers who use artificial plant growth mixes.
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