Location: Agroecosystems Management Research2012 Annual Report
1a. Objectives (from AD-416):
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; and 3) Determine if exposure to trace antibiotic residues in soil or stream sediment affects the persistence of antibiotic resistant bacteria and resistance genes.
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 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.
3. Progress Report:
Objective 1. The potential water quality impact of fall-planted cover crops across the U.S. Midwest was quantified using the Root Zone Water Quality Model (RZWQM). The analysis suggests that winter cover crops can reduce Nitrogen (N) loss in tile flow 42.5% or about 195 million kg/year. Site selection for two experiments has been completed, including sites for agricultural and urban conservation practices. Objective 2. Model development to simulate pesticide transport to subsurface drains in Nashua, Iowa, was progressed in a collaboration between ARS and the United States Geological Survey (USGS) scientists. Preliminary results suggest the Root Zone Water Quality Model (RZWQM) can accurately simulate pesticide transport to subsurface tile drains via preferential flow under varying tillage and soil conditions. Conservation practice targeting requires data sets that integrate landscape features, water flow, cropping sequences, and soils at the field scale. We are using Geographic Information Systems to develop these data sets. These databases are being used to characterize conservation planning opportunities at watershed scale and movement of streambanks in the South Fork of the Iowa River. Objective 3. The second year of a field study was conducted to determine the transport of tylosin and tylosin-resistant bacteria in drainage water after swine manure application. Elevated levels of the erm genes, which confer resistance to tylosin, were observed in soil after manure application, and these populations persisted into the following spring, but after two years the erm genes in manured soil were similar to background levels. Concentrations of erm genes in tile drainage from plots receiving swine manure did not differ from that in non-manured plots.
1. Potential water quality impact of fall-planted cover crops in the Midwest. A fall-planted cover crop is a management practice with multiple benefits including reducing nitrate losses from artificially-drained fields. While the practice is widely used in the southern and eastern states of the U.S., little is known about the efficacy of the practice under Midwest U.S. conditions where artificial subsurface drainage is widely used and winters are longer and colder. ARS scientists in Ames, Iowa, used the Root Zone Water Quality Model (RZWQM) to predict the impact of a cereal rye cover crop on reducing nitrate losses from drained fields across five states in the Midwest. Winter cover crop planted at main crop maturity in a corn–soybean rotation reduced Nitrogen (N) loss in tile flow 42.5% across the region. If winter cover crops were implemented on the area of the five states draining to the Mississippi River, the potential reduction in nitrate-N losses from drained fields would be 166 million kg yr-1, or about 20% of the total nitrate-N load in the Mississippi River. The cost of nitrate-N removed by cover crops would be from U.S. $2.08 to $4.13 per kg, a cost quite competitive with other management practices that can reduce nitrate loss to surface water. These results are of interest to a broad spectrum of stakeholders seeking viable ways to reduce Gulf of Mexico Hypoxia.
2. Antibiotic resistance genes in tile drainage. There is controversy over the contribution of antibiotic use in animal agriculture to the global problem of increasing antibiotic resistance. ARS scientists in Ames, Iowa, and Iowa State University, conducted a two-year field study to determine the transport of tylosin and tylosin-resistant bacteria in drainage water after swine manure application. Tylosin was fed to swine producing manure for the experiment. Elevated levels of genes which confer resistance to tylosin (erm genes) were observed in soil after manure application, and these elevated gene concentrations persisted into the following spring. However, after two years the erm genes in manured soil were similar to background levels. Concentrations of erm genes in tile drainage from plots receiving swine manure did not differ from that in non-manured plots. Similar results were obtained for Enterococcus and tylosin-resistant Enterococcus in soil and drainage waters. The study shows that use of tylosin in swine production does result in increased antibiotic-resistance genes in manure, but manure application to soil does not increase sub-surface movement of antibiotic-resistant microorganisms. The results are of interest to a variety of stakeholders seeking to understand and mitigate impacts of antibiotic use in livestock production.
3. Temporal variability of surface soil density and water content across different landscape positions. The density of soil changes over time due to tillage, compaction, wet-dry, and freeze-thaw action. An ARS scientist in Ames, Iowa, showed that bulk density was related to landscape properties on wet sampling dates but rarely on dry sampling dates. Dense soil results in poor root growth, inadequate aeration, reduced water infiltration, and increased runoff, erosion, and nutrient loss. These results will help scientists devise landscape scale assessments of management impacts and help farmers be aware of how compaction risks can vary across fields.