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Preventing Water Quality Pollution for Agriculture

The water cycle
Pollutants in surface waters
How to prevent pollution: good management practices
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The water cycle

A watershed is an area of land that drains to a specific stream, river, or lake. The limits of a watershed vary with scale: smaller watersheds are nested within larger watersheds. The Delaware River Basin includes parts of New York, Pennsylvania, New Jersey, and Delaware, but within this large watershed are many smaller watersheds draining to more local streams, rivers, and creeks.

A diagram of a simplified water cycle.

Water that is delivered to the watershed as irrigation or precipitation can follow different paths as it makes its way to a local stream. Some irrigation and precipitation water will infiltrate into the soil, where it might make its way to shallow groundwater and then move laterally slowly in the soil to maintain the base flow of a local stream. If precipitation or irrigation falls too quickly to infiltrate into the soil, water can move overland as surface runoff. Surface runoff moves quickly to local rivers through ditches and storm drains, exacerbating downstream flooding. Surface runoff is also a concern because it can pick up sediment, fertilizer, and other potential pollutants and deliver them to streams and lakes. Depending on the weather and land use in the watershed, a significant portion of rain or irrigation applied to the land in a watershed may be returned to the atmosphere through transpiration by plants and evaporation from soil and other surfaces.

Pollutants in surface water

Many natural and human activities have the potential for polluting rivers, lakes, and groundwaters. Point sources of pollution are those where there is an identifiable single point of pollution, such as a factory with a smoke stack of a wastewater treatment plant with a discharge pipe. In contrast, non-point sources of pollution are those which are more dispersed over the landscape, including agriculture, rural or suburban residential development, wildlife, domestic animals, and soil erosion.

A variety of pollutants can be contributed by agricultural activities, including nutrients (fertilizers), pesticides, sediment from eroded soils, and bacteria. Each of these has the potential for negative impacts on surface water or groundwater for a variety of desirable water uses including drinking, recreation, and wildlife habitat. While these pollutants can travel with surface runoff, certain pollutants can also move readily with infiltrating water to groundwater. Notably, these pollutants include nitrogen in the form of nitrate and certain herbicides.

How to prevent pollution: good management practices

Irrigation management

Proper irrigation management is critical for the health of crops, and also helps minimize the potential for pollution from agricultural lands. Excessive watering tends to leach nutrients and other agricultural chemicals out of the root zone toward groundwater, as well as wasting water and money. Irrigation systems with a poor uniformity of delivery necessitate overwatering or underwatering some crops. Crops which are overwatered or underwatered may have lower yields or increased incidence of disease.

Use an irrigation system which delivers water uniformly. Inspect water delivery during irrigation to be sure nozzles aren't clogged, and measure the uniformity of water distribution of your system by setting out catch cans. Use filtration where necessary, maintain filters, and flush lines as needed. For solid set systems, ensure all sprinklers are identical and use pressure regulators for long pipe runs and slopes.
Irrigate according to plant needs. Follow recommendations specific to your crops. Use measurements of soil moisture content or local evapotranspiration data to guide the frequency and amount of irrigation. Know the texture of your soils and the rooting depth of your plants so you can determine how much water your soil can hold.
Avoid irrigating areas without crops, including roads and areas where crops have been harvested.

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Nutrient management

Proper nutrient management is critical for the health of your crops and also helps to minimize the potential for pollution from agricultural lands. The two nutrients of most concern for water pollution are nitrogen and phosphorus. Nitrogen may be applied in a variety of forms (ammonium, nitrate, urea, or organic sources), but natural cycles in the soil, under common conditions in a field, will convert much of this nitrogen to the nitrate form. Nitrate is easily dissolved in water and can move with either surface runoff or infiltrating water. Nitrate is a concern as a pollutant in drinking water and in estuarine environments. Phosphorus has the tendency to stick to soil particles, so preventing eroding sediments from leaving your property is important in preventing phosphorus pollution of surface water. Phosphorus is a concern particularly in fresh water bodies, where in excess amounts it causes blooms of algae.

Excessive algae in a pond or lake are an indicator that the water body has been impacted by pollution with nutrients, usually phosphorus. Such impacts can deplete oxygen in the water, killing fish, and make water bodies less enjoyable for swimming and boating.

Use current nutrient management guidelines for your specific crops. Time applications and determine amounts according to plant needs.
Use soil tests to guide lime and phosphorus applications.
Use plant tissue analysis to guide fertilizer applications if recommendations are available for your crops.
In nutrient planning, account for nitrogen and phosphorus that will be plant-available in irrigation water, soil, manure, and compost.
Where appropriate, incorporate solid fertilizer, manure, and composts into the soil.
Calibrate fertilizer spreaders, sprayers, or injectors.
Practice appropriate irrigation management for your crops.
Store fertilizers in an appropriate structure. Mix and load fertilizers over an impermeable surface, such as a concrete floor, where spills can be swept-up. Prepare for onsite spills and clean up spills immediately. Protect fertilizers from rain and wind.

Pest management

Following an integrated pest management (IPM) program is a cost-effective and environmentally-responsible way to control crop pests. A variety of pesticides can cause ecological harm if they are transported to surface water or groundwater. Pesticides differ according to their toxicity to different organisms. For example, pyrethroid pesticides have lower toxicity to mammals than do some other insecticides, but are toxic enough to fish and a variety of invertebrate animals to be of ecological concern.

The potential for water contamination with a pesticide will depend on various properties of the pesticide as well as properties of the site. Pesticides vary in their tendency to stick to solids like soil particles and organic matter. Pesticides which do adhere to particles will move with those particles in runoff water. Other pesticides that are more water soluble have the potential to leach to groundwater. The leaching of pesticides will be more likely on sandy or gravelly soils, sites with a high water table, and soils with little clay or organic matter. Pesticides also differ by their residual. Compounds with a longer residual continue acting as pesticides longer in the field, but also retain their toxicity longer if they are moved offsite with leaching or runoff water.

Use an integrated pest management (IPM) program. The program should include a formal plan for pest scouting; pest identification; the use of economic thresholds to determine the course of action; and record keeping for pest locations, number, and damage. Consider using the services of agricultural pest control consultants.
Use current recommendations specific for your crops, specific pests, and pesticide products.
Rotate classes of pesticides according to current recommendations.
Use cultural controls and sanitation to minimize the incidence and damage of pest outbreaks. Remove diseased plants. Pay attention to weeds and plant debris. Consider preserving habitat for natural enemies of pests.
Calibrate sprayers. Measure pesticide product accurately. Follow label directions. Use best application methods such as spraying only infected areas of crops or applying at the lowest effective label rate. Use adjuvants—stickers or spreaders—where appropriate.
Use pesticides with a lower environmental risk. Avoid applying materials when wind or rain potential is high. Use narrow-spectrum pesticides that target your specific pests.
Store pesticides indoors, and perform all mixing and loading over an impermeable service such as a concrete floor. Have a plan for spills, and clean up all spills immediately.
Where possible, capture tailwater in a basin or pond. Use vegetated buffers, berms, or sediment traps to decrease runoff or prevent sediment form moving offsite.

A detention impoundment at a commercial nursery. The impoundment captures runoff from irrigation and rain events. The water is treated and reused onsite for irrigation.

Erosion, runoff, property, and landscaping

Many potential pollutants can move from agricultural areas with runoff water. These pollutants can be either dissolved in the water itself or associated with sediments or organic matter. Because some pollutants tend stay associated with particular matter, it is desirable to keep eroded soil sediments onsite by filtering runoff water with vegetated buffers, gravel, or mulch, or capturing sediment in sediment traps, ponds, or basins. These technologies also slow runoff, allowing it to infiltrate slowly into the soil. While some pollutants can move with percolating water, vegetation and microbes in the soil tend to reduce pollutants. It is therefore usually better to allow water to infiltrate onsite rather than leave the property as runoff. Pollutants can leave an agricultural site also as drift from wind. It is important to keep fertilizers and pesticides protected from drift losses during storage, mixing, loading, and application. Runoff from roofs and roads also can contain pollutants, including metals from roofs and motor oil from roads or vehicle storage.

Use vegetated buffers, gravel, or mulch on bare soil to reduce erosion and increase infiltration. Depending on your crop, these methods can applied at row ends, between rows, or on the path the water flows before leaving the property. Use ponds, basins, or wetlands to detain runoff before it exits the property or reaches a pond or stream.
Pay special attention to sloped and hilly areas. Employ terracing, berms, and vegetation to prevent erosion.
Improve soil permeability by incorporating organic amendments into sandy or clayey soils. Use unincorporated mulch and cover crops also to improve soil permeability.
Use windbreaks in windy areas. Use water to keep dust down on dirt roads.
Apply similar concerns to non-cropped areas. Use water bars to minimize erosion on roads. Direct runoff from roofs to pervious areas or to dry wells. Prevent fluids from vehicles from leaving the property with runoff.

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