Farming for Cleaner Water in the Chesapeake Bay Watershed

Based on a U.S. Geological Survey fact sheet for farmers, "Your land, your water."

Farmland is a key part of the Chesapeake Bay watershed's economy and heritage, and a focus of conservation. The streams and rivers around farms supply drinking water and recreation, but too many nutrients and too much sediment can spoil them. In many Chesapeake Bay streams, agricultural land is the largest source of nutrients and sediment, more than the atmosphere, wastewater, or urban and suburban land. Farmers are voluntary conservation partners with a big role in cleaning the water.

Common conservation practices expected to reduce nutrient and sediment loads in the Chesapeake Bay watershed. USGS figure.

What has changed since 1985

• Less farmland, more intensive farming. Agriculture covered about a quarter of the watershed in 1985 and has shrunk since. But crop and animal production has intensified in many places, especially Virginia and West Virginia's Shenandoah Valley, southeastern Pennsylvania and the Delmarva Peninsula.
• More manure. Growing poultry numbers mean more manure produced and spread.
• Fertilizer use was generally lower in 2020 than in 1985, though it varied by year and place.
• Far more conservation. Land under conservation practices was nearly five times larger in 2020 than in 1985, which is expected to cut nutrient and sediment loads by millions of pounds.

General changes in agricultural land, manure and fertilizer applications from 1985 through 2020 (Chesapeake Bay Program, 2020). USGS figure.

Do the practices work?

On fields and farms, yes:

• Cover crops can reduce soil erosion and the movement of nitrogen into groundwater.
• Buffers can reduce sediment carried to streams in runoff and nutrients reaching streams through groundwater.
• Combined systems of conservation tillage, nutrient management and other cropland practices can reduce nutrient loads.

But the reductions expected from field and plot studies often don't show up in water quality measured in larger watersheds, and expected reductions vary widely. Farmers and scientists are working together to learn why.

What gets in the way

• More nutrients applied. Increases in manure and fertilizer use can overshadow expected reductions. Surplus applications, beyond what crops need, have risen in recent years, and stream loads may not fall until those surpluses do.
• Legacy nutrients. Nitrogen in groundwater and phosphorus in soils from past farming can take years to reach streams, so improvements may be slow.
• Changing weather. Recent years have generally been warmer and wetter, with droughts in some months and floods in others. Wetter years deliver more nutrients and sediment to streams, and warmer, wetter years can change how much is stored in soils, taken up by plants or needed by crops, altering how well some practices work.

What makes practices effective

• Match nutrients to crop needs: adjust the source, method, rate and timing of applications. Soil tests show how much crops need, and avoiding overapplication saves fertilizer costs as well as protecting water.
• Fit the local site and adapt over time: manage manure in animal areas, avoid excess fertilizer on cropland, reduce streambank erosion (a major sediment source in small streams), keep clean water away from polluted areas, and control what reaches streams during high flows.
• Use systems of practices that address several sources and pathways, which may do more than single practices.
• Target high-loading areas, which can be cost-effective.
• Try precision agriculture and other new technology to better match nutrients to crop needs.
• Monitor water quality, which gives an accurate local picture to guide and assess practices; more long-term monitoring is needed in small, heavily managed farm watersheds.

Example: Smith Creek, Virginia

In the Smith Creek watershed in the Shenandoah Valley, an area of focused conservation and monitoring, manure is a major nutrient source, so practices addressing how, how much and when manure is applied may help; streambanks are a major sediment source, so reducing streambank erosion may help; and continued monitoring can track the results.

Getting help

The USGS summarizes scientific findings on water-quality responses at https://usgs.gov/SIMPLE, and works with federal, state and local technical specialists who help farmers plan and carry out conservation practices.

Sources

• U.S. Geological Survey, "Your land, your water—Using research to guide conservation practices on local farms in the Chesapeake Bay watershed," Fact Sheet. https://pubs.usgs.gov/publication/fs20233050
• The fact sheet cites Webber and others (2021), Gellis and Gorman Sanisaca (2018), U.S. Environmental Protection Agency (2018) and Clune and others (2021).
• Figures recovered from the fact sheet PDF; its photographs, used there with permission, are not reproduced.