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Protecting Agricultural Watersheds

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ARS promotes stewardship of water resources to support agricultural production while protecting environmental, human, and animal health. Agricultural watersheds cover more than 70 percent of the continental United States. Operating a national network of experimental watersheds and long-term agroecosystem research sites, ARS is uniquely situated to develop integrated watershed management strategies for agriculture across broad regions of the continental United States. The following accomplishments highlight ARS advances in watershed protection research in FY 2019. Hyperlinked accomplishment titles point to active parent research projects.

New bank stability assessment technology protects rivers and streams. The erosion resistance of streambank soils can vary significantly in space and time. Current bank erosion prediction technology does not account for this variability, which makes it difficult to select appropriate soil erosion-resistance values when assessing bank erosion. ARS researchers in Oxford, Mississippi, used stochastic analysis to develop a new way of estimating expected bank erosion by incorporating parameters such as soil erodibility and shear strength into ARS’s widely used Bank Stability and Toe Erosion Model (BSTEM). The new BSTEM version is able to determine the probability that bank retreat magnitudes may be exceeded. This is crucial information when critical infrastructure is located near rivers and streams. As part of the $1.6 billion American River Common Features project, the new technology is currently being used by the Sacramento District of the U.S. Army Corps of Engineers to prioritize bank protection measures to prevent levee failure around the City of Sacramento, California.

Oilseed cover crops reduce unwanted soil nitrogen loss. Contamination of water from the leaching and runoff of labile soil nitrogen and phosphorus from corn-soybean cropping systems in the Upper Midwest is a major concern. This loss occurs mostly during fall and spring when the soil is left bare between summer crops. Winter annual cover crops can use leftover nitrogen and phosphorus from the previous crop and keep these nutrients from contaminating water. ARS researchers from Morris, Minnesota, in collaboration with University of Minnesota scientists, demonstrated that winter camelina and pennycress grown as cover crops are as effective as winter rye at using excess nitrogen and preventing its escape from agricultural systems into waterways. Scientists compared results of cultivating camelina and pennycress winter oilseeds with results from a typical no-till and conventional till system lacking a cover crop and found the oilseed cover crops reduced soil water nitrate nitrogen losses of 84 percent and 91 percent, respectively. Camelina and pennycress also can be harvested as oilseed cash crops, adding yet more value to the system. This information will benefit growers interested in cover cropping, agricultural scientists, extension educators, and consultants, and is being used in developing new sustainable cropping systems.

Cover crops reduce nitrate leaching. Nitrogen left in the soil after crop harvest is susceptible to leaching loss, which can reduce groundwater and surface water quality. ARS scientists in Beltsville, Maryland, performed a global meta-analysis of the available literature to understand how well cover crops reduce nitrate leaching from agroecosystems. Compared to no cover crop controls, cover crops reduced nitrate leaching by 56 percent. Soil type, planting and termination dates, shoot biomass, and climate each influenced the extent to which cover crops reduced nitrate leaching. These findings indicate that cover crops are an effective way to reduce nitrate leaching and should be integrated into existing cropping systems for water quality benefits. This work will help farmers to make cover crop management decisions and inform policymakers to minimize agriculture’s impact on water quality.

Mulch and gypsum reduce nutrient export into rivers. Runoff containing excess nitrogen and phosphorus fertilizer from agricultural fields can be transported into water bodies and cause algal blooms and dead zones that affect fisheries and tourism. Denitrification is a natural process that transforms nitrogen, like that from fertilizer, into an unreactive gas. ARS researchers in Oxford, Mississippi, examined the ability of additions such as hardwood mulch and mulch mixed with gypsum to enhance denitrification in sediment cores taken from edge-of-field systems. Mulch and mulch-gypsum amendments were able to remove 65 to 69 percent of the nitrogen load in the system. When gypsum was included with the mulch, release of phosphorus from the system significantly decreased. Adding organic carbon sources to the sediment cores significantly increased denitrification rates. By adding inexpensive organic sources such as hardwood mulch to edge-of-field systems such as ditches, farmers can reduce the impact of nitrogen pollution while maintaining agricultural production

Design and demonstration of the construction of a phosphorus removal structure. Phosphorus removal structures are intended to reduce phosphorus pollution that causes eutrophication of surface water bodies such as Lake Erie. Reducing eutrophication to surface waters is important to the economy, ecosystem, drinking water treatment, and recreational use. Phosphorus removal structures help filter dissolved phosphorus before it reaches a body of water. This new conservation practice needs to be disseminated to farmers, nonprofit organizations, and State agencies, and potential service providers need training. ARS scientists in West Lafayette, Indiana, designed a large, underground tile drain phosphorus filter using 60 tons of slag on a large swine farm near Holland, Michigan. This was the largest tile drain filter ever constructed using tanks. An American Society of Agronomy journalist filmed and documented the process for future use in training modules. At least 20 people came to see the construction of the unit, representing nonprofit organizations such as Friends of Lake Macketawa, the Outdoor Discovery Center, American Society of Agronomy, and American Society of Agricultural and Biological Engineers, as well as NRCS engineers and conservationists. Some participants released photographs to social media, which prompted several groups to contact ARS for more information, including Drainage Contractor magazine. This effort trained people who were interested in how to construct phosphorus removal structures and resulted in the dissemination of the technology to an unknown number of people. Increased adoption of this practice and training of people for providing the service will eventually reduce dissolved phosphorus loading to surface water bodies and improve water quality.

Conservation practices for the eastern Corn Belt. Nutrient loss, particularly phosphorus, from crop production has been linked to harmful and nuisance algal blooms in Lake Erie and other Ohio freshwater systems. The binational agreement between the United States and Canada calls for a 40 percent reduction in phosphorus delivery. Using a paired edge-of-field approach, ARS researchers in Columbus, Ohio, in collaboration with Lake Erie stakeholders and partners, quantified the surface and subsurface (tile) water quality contributions of various crop production and conservation management practices. The combination of legacy phosphorus and discharge significantly contribute to agricultural losses and highlight the need for regionally based conservation management. Promotion and adoption of “4R” practices (right source, rate, time, and place) and drainage water management could potentially reduce agriculture’s environmental footprint in the Midwestern United States. Cover crops have a significant impact on nitrogen losses but do not have an equal impact on phosphorus. These findings have been shared and delivered to Lake Erie stakeholders and partners (e.g., NRCS, The Nature Conservancy, Lake Erie Foundation) and are being promoted to producers to help address eutrophication of Lake Erie. Adoption of these practices would reduce agriculture’s environmental footprint and make progress toward the 40 percent phosphorus reduction goals set for the Western Lake Erie Basin.