Agricultural Runoff

Overview

Agriculture is essential to all people: farms provide us with food and fiber, natural areas, and aesthetic and environmental benefits. But agriculture is also the single largest source of nutrient and sediment pollution entering the Bay. While conventional tillage, fertilizers and pesticides can be beneficial to crops, their excessive use can pollute rivers and streams, pushing nutrients and sediment into waterways.

Why is agriculture important?

Agriculture is essential to all people: farms provide us with food and fiber, natural areas, and aesthetic and environmental benefits. According to estimates from the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), there are more than 83,000 farm operations here, comprising nearly 30 percent of the 64,000-square-mile region and producing more than 50 commodities, including corn, soybeans, wheat, fruits and vegetables.

How does agriculture affect the Chesapeake Bay?

Unfortunately, some agricultural practices—including over-irrigating farmland, over-tilling soil and over-applying fertilizers and pesticides—can push pollution into the Bay and its local waterways. Agriculture is the single largest source of nitrogen pollution entering the Chesapeake Bay. According to 2022 estimates from the Bay Program, agriculture contributes 48% of the nitrogen load entering the Bay. It’s estimated that 27% of the phosphorus load and 9% of the sediment load are from agriculture, with the greatest source of phosphorus and sediment loads coming from the “natural” sector which includes stream bed & bank and shoreline sediment loads, forests, and wetlands.

But well-managed agricultural lands can offer the Bay watershed a number of benefits and services: sustained crop yields, restored rivers and streams, and valuable insect, bird and animal habitat. When effective agricultural land cover occurs year-round, these systems can store carbon, minimize soil erosion and reduce the watershed’s vulnerability to flooding and the effects of climate change.

Irrigation

Through the use of hoses, sprinklers or other watering methods, irrigation can ensure consistent crop production in a range of weather conditions. But poor irrigation practices, including the over-watering of crops, can promote erosion and push pollution into rivers and streams:

• Excess water that is not absorbed into the soil can wash into local waterways, carrying with it soil and sediment, fertilizers and pesticides, and nutrient-rich animal manure.

• Excess water that soaks into the soil can push nutrients into groundwater supplies, where it can remain for decades.

Tillage

To prepare a field for planting, a number of farmers practice “conventional tillage,” turning the earth over with a plow. While tillage can loosen the soil and promote crop growth, it can also damage soil structure. Heavy machines can compact the soil, making it difficult for rainfall to trickle into groundwater supplies. Loosened surface soil is also prone to erosion.

Manure and poultry litter

Livestock manure and poultry litter are often used as a form of fertilizer, providing the nutrients crops need to grow. But when more manure is applied to the land than a crop can absorb, or when large amounts of manure are improperly stored, the nutrients and bacteria that manure contains can be carried by runoff into rivers and streams or seep into groundwater supplies.

The Environmental Protection Agency report Guidance for Federal Land Management in the Chesapeake Bay Watershed provides estimates from the Chesapeake Bay Program’s suite of modeling tools that show manure accounts for 19% of nitrogen and 26% of phosphorus pollution reaching the Bay. These excess nutrients can fuel the growth of algae blooms that block sunlight from reaching underwater grasses and, during decomposition, rob the water of oxygen that plants and animals need to survive.

Chemical fertilizers

Like manure, chemical fertilizers can provide crops with the nutrients needed to grow. But when more fertilizer is applied to the land than a crop can absorb, these nutrients can be carried by runoff into rivers and streams or seep into groundwater supplies. The Environmental Protection Agency report Guidance for Federal Land Management in the Chesapeake Bay Watershed provides estimates from the Chesapeake Bay Program’s suite of modeling tools that show chemical fertilizers account for 17 percent of the nitrogen and 19 percent of the phosphorous entering the Bay.

Pesticides

Chemical pesticides can protect crops from weeds and insects. Some pesticides target just one or a few species, while others are considered “broad-spectrum” and target a group of similar species. Like livestock manure and chemical fertilizers, when pesticides are applied in excess, they can be carried by runoff into rivers and streams or seep into groundwater supplies.

According to a 2012 report from the EPA, U.S. Geological Survey (USGS) and U.S. Fish and Wildlife Service, pesticides are frequently present in our streams and groundwater. While pesticide concentrations in local waterways are seldom high enough to harm human health, pesticide concentrations in a number of streams can impact aquatic and fish-eating wildlife. Scientific studies have discovered potential links between pesticide exposure and:

• the suppression of behavioral and immune systems in fish,

• the development of intersex conditions in fish, and

• the impaired reproduction of fish-eating birds.

How are farmers working to reduce agricultural pollution?

Bay Program partners are working with farmers across the watershed to curb agricultural runoff. Conservation practices—often called “best management practices” or “BMPs”—can be implemented on area farms, and watershed states are counting on the expanded use of these practices to help them meet the goals set forth in the Chesapeake Bay “pollution diet,” or Total Maximum Daily Load (TMDL).

Farmers can use conservation practices to reduce agricultural runoff into rivers, streams and the Chesapeake Bay. These tools can reduce a farm’s operational costs and improve a farm’s production. Some conservation practices are voluntary or incentive-based, while others—like nutrient management planning for all agricultural operations in Maryland—are mandatory.

Conservation tillage

Conservation tillage leaves one-third or more of a farm field covered with crop residue or vegetation throughout the year. When tillage is reduced and soil is left undisturbed, a field is less prone to erosion. Continuous no-till and minimum-till farming are two forms of conservation tillage.

Cover crops

Grown to provide soil cover and prevent erosion, cover crops can be annual, biennial or perennial plants grown in a single or mixed stand during all or part of the year, including the non-growing season. Common cover crops include legumes (like cowpeas or clover), forage radish and cereal grains (like wheat, rye or barley).

Cover crops are used to fill in bare soil when a main crop has been harvested, when there is a niche in a season’s crop rotation or when there is a need to interplant a cover crop with a cash crop. They provide ground cover, reduce erosion, suppress weeds, reduce insect pests and diseases, absorb excess fertilizer, reduce nutrient leaching and enrich soil with organic matter.

Forest buffers

Grasses, trees and shrubs planted along the edges of farm fields and along rivers and streams can reduce the amount of pollutants flowing from the land into local waterways. These “buffers” can slow and absorb polluted runoff, stabilize stream banks, curb erosion and serve as habitat for wildlife.

Streamside fencing

Using streamside fences to exclude livestock from local waterways can reduce the amount of nutrients and pathogens entering the water, prevent stream bank damage and erosion, and improve animal health. Fences can be woven wire or electric, and permanent or moveable.

Nutrient management planning

A nutrient management plan is a written, site-specific plan that reduces nutrient pollution while maintaining crop production and, in some cases, increasing farm profits. By developing a “nutrient budget” for a farm and applying nutrients at the right time, with the right methods, a farmer can limit the amount of nutrients that run off their land and into local waterways.

Most nutrient management plans contain a field’s crop production potential, the amount of nutrients needed to achieve this level of production and the recommended application amount, form, source, rate, placement and timing of manure or fertilizer.

Manure and poultry litter management

According to 2010 estimates from the EPA, livestock manure and poultry litter account for almost half of the nutrients entering the Bay. Bay Program partners have committed to reducing this nutrient load by working with farmers to properly apply manure to cropland, develop animal waste storage systems, transport excess manure to areas in need, restrict or exclude animals from streams and locate or move livestock facilities away from streams.

How can you help?

To support agriculture in the Bay watershed, consider purchasing products from a local farm. Buying local can reduce the pollution associated with transporting goods over long distances and the packaging needed to transport or store fresh produce.