Roughly 46 percent of United States acreage is made up of grassland-pasture, rangeland, and cropland that produce an abundant supply of food and food-based products. Agriculture is vital to the economic and social well-being of all Americans. If not properly managed, however, agricultural activities can degrade the quality of nearby bodies of water.
The National Water Quality Assessment provides information reported every 2 years by the states to the EPA about the conditions in their surface waters. The most recent 2016 report shows that agricultural nonpoint source pollution is the leading source of water quality impacts on surveyed rivers and streams, the third-largest source for lakes, the second-largest source of impairments to wetlands, and a major contributor to contamination of surveyed estuaries and groundwater. Agricultural activities, such as overirrigation, inappropriate fertilizer and pesticide application, overgrazing, removal of riparian vegetation, and improper livestock manure and wastewater management, all generate nonpoint source pollutants that can enter the water supply by seeping into groundwater or running off into surface waters.
The primary agricultural nonpoint source pollutants are nutrients, sediment, animal wastes, salts, and pesticides. Sedimentation is the most common source of agricultural water pollution.
Using agricultural BMPs can help to prevent or minimize the effects of nonpoint source pollution. Most agricultural BMPs help to control sediment carried off of agricultural lands, encourage sound pest and nutrient management techniques, and prevent or minimize potential runoff to ensure economic, environmental, and agronomic sustainability. Adopting agricultural BMPs can ultimately increase efficiency and profits, increase property values, improve water quality, and benefit the local community.
Agricultural BMPs can be structural or nonstructural. Structural practices, such as fences and buffer strips, often involve some sort of construction, installation, and maintenance. Structures can be vegetative (buffers) or nonvegetative (fencing). Nonstructural practices, on the other hand, are activities or behaviors that reflect better planning and management and increased education and awareness. For more information on agricultural BMPs for controlling nonpoint source pollution, visit the Natural Resources Conservation Services website at www.nrcs.usda.gov.
Best Management Practices
Nutrient management includes reducing the amount of fertilizer used by applying only the amount a crop needs. It involves managing the amount, form, methods, and timing of nutrient application (either animal waste, commercial fertilizers, or other forms of nutrients).
Nutrient management is cost-effective because it limits the amounts of nutrients lost. Furthermore, it is one of the best ways to reduce nonpoint source nutrient pollution. Vegetation in riparian buffers and healthy pasture systems help to filter out nutrients before runoff reaches surface waters. Poultry management practices, such as dry stacks and composting, also may minimize nutrient loss.
Integrated pest management (IPM) is an ecologically based strategy of control tactics designed to prevent damage of pest populations from causing negative economic impacts. IPM is not a single pest-control method but rather a series of pest-management evaluations, decisions, and controls aimed at reducing the amount of pesticide used and the amount that moves into the environment. If pests must be controlled, there may be several options:
- biological control (such as releasing natural insect enemies)
- mechanical control (plowing, cultivating)
- cultural control (planting insect-resistant varieties, crop rotation, destroying pest refuge sites)
- chemical control
When pesticides must be used, the objective is to select the least toxic product possible and strictly follow all application guidelines on the product label. For more information on IPM, visit the Alabama Cooperative Extension System website at www.aces.edu.
Irrigation water management promotes the efficient use of irrigation water to produce profitable yields, conserve water, and minimize the leaching of nutrients into groundwater. The timing and amount of irrigation water applied to agricultural lands are critical decisions for each operator, because they affect profits and crop yields.
Applying too much water increases pumping costs, reduces water efficiency, and increases the potential for nitrates (NO3) and pesticides to leach into groundwater. On the other hand, delaying irrigation until plants are water-stressed can reduce yield and make fertilizers and pesticides less effective. An irrigation water management plan should use soil-moisture monitoring techniques to determine when irrigation is necessary. Irrigating only when a crop needs it is an effective BMP for reducing nonpoint source pollutants.
Vegetative and Tillage Practices
Conservation tillage is a way to reduce the amounts of sediment and nutrients that move into water from agricultural lands. Two types of conservation tillage are minimum tillage and no-tillage. Minimum till leaves at least 30 percent of the soil surface covered with plant residue after the tillage or planting operation. No-tillage is the practice of leaving the soil undisturbed from harvest to planting, except for nutrient injection. Crop seeds are planted by a device that opens a trench or slot through the sod or pervious crop residue. Conservation tillage can reduce soil loss by 50 percent or more as compared to conventional tillage.
Contour farming is the alignment of all farm tillage, planting, and harvesting practices with the contour of the land. The goal is to reduce erosion and surface runoff and thus the transport of nutrients and pesticides from the field. Contoured rows retain rainwater, which increases infiltration and reduces runoff.
Cover and green manure crops are crops of close-growing grasses, legumes, or small grains grown primarily for temporary, seasonal soil protection and improvement, except where there is permanent cover as in orchards or vineyards. Green manure crops are plowed under and incorporated into the soil to control erosion, add organic matter and nutrients, suppress weeds, and reduce the need for nitrogen fertilizers.
Vegetative buffer strips or filter strips are strips of grasses or other vegetation placed along streams or drainage areas to slow down runoff water, trap sediment, filter nutrients and other pollutants, and promote the infiltration of water into the soil. The width of a filter strip depends on the slope and amount of land area delivering water to the strip and the type of vegetation used.
Water and sediment-control basins are erosion-control structures commonly installed across the bottoms of drainage ways to prevent bank and gully erosion on farmland and to minimize sedimentation of nearby waterbodies. Basins help to improve water quality downstream by trapping sediment, controlling water flow within a drainage area, and storing runoff water to allow it to slowly infiltrate into the soil profile.
Terraces are level soil embankments that are usually constructed on the contour of the land. They help to control runoff and soil erosion. Because they tend to promote water infiltration into the soil, these structures also are effective in reducing both nutrient and pesticide losses.
Grassed waterways are natural drainages that are planted with sod-forming grasses to help control runoff water from agricultural lands. Covering the drainage way with grass prevents gullies from forming in the fields, traps sediment, absorbs chemicals and nutrients in runoff water, and provides cover for small birds and mammals.
Streambank and shoreline protection involves the use of vegetation, structures, bioengineering, or management techniques to stabilize and protect streambanks, riparian areas, and shorelines. The goal is to reduce the sediment and nutrients entering water from eroding streambanks and shorelines. Healthy riparian and shoreline areas can provide abundant wildlife habitat and cover. Mature, woody vegetation along stream-banks can lower stream temperature and improve fish habitat.
There are many government programs to help farmers and ranchers design and pay for agricultural BMPs to control nonpoint source pollution. For example, the NRCS, EPA, and many state agencies offer cost-share programs, technical assistance, and economic incentives. Many individuals use their own resources to adopt technologies and management practices that protect and improve water quality.