United States Office of Water EPA 916-F-01-028
Environmental Protection (4606) July 2001
Agency
4>EPA Source Water Protection
Practices Bulletin
Managing Agricultural
Fertilizer Application to Prevent
Contamination of Drinking Water
If improperly managed, elements of fertilizer can move into surface water through field runoff
or leach into ground water. The two main components of fertilizer that are of greatest concern
to source water quality (ground water and surface water used as public drinking water supplies)
are nitrogen (N) and phosphorus (P). This fact sheet focuses on the management of agricultural
fertilizer applications; see the fact sheets on managing agricultural pesticide use, animal waste,
and storm water runoff for other prevention measures that relate to agriculture.
FERTILIZER USE IN AGRICULTURE
Fertilizer application is required to replace crop land nutrients that have been consumed by
previous plant growth. It is essential for economic yields. However, excess fertilizer use and
poor application methods can cause
fertilizer movement into ground and surface
waters. While fertilizer efficiency has
increased, Colorado State University
estimated that about 25 percent of all
preplant nitrogen applied to corn is lost
through leaching (entering ground water as
nitrate) or denitrification (entering the
atmosphere as nitrogen gas).
Fertilizer spreading
WHY IS IT IMPORTANT TO MANAGE FERTILIZER USE NEAR THE SOURCES OF
YOUR DRINKING WATER?
Improper or excessive use of fertilizer can lead to nitrate pollution of ground or surface water.
Nitrogen fertilizer, whether organic or inorganic, is biologically transformed to nitrate that is
highly soluble in water. In this soluble form, nitrate can readily be absorbed and used by plants.
On the other hand, soluble nitrate is highly mobile and can move with percolating water out of
the soil, thus making it unavailable for plant uptakes. Crop producers, therefore, need to match
nitrogen applications to crop uptake to minimize nitrate leaching and maximize efficiency.
Use of nitrogen-containing fertilizers can contribute to nitrates in drinking water. Consumption
of nitrates can cause methemoglobinemia (blue baby syndrome) in infants, which reduces the
ability of the blood to carry oxygen. If left untreated, methemoglobinemia can be fatal for
affected infants. Due to this health risk, EPA set a drinking water maximum contaminant level
(MCL) of 10 milligrams per liter (mg/1) or parts per million (ppm) for nitrate measured as
nitrogen.
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Another major component of fertilizer is phosphorus. Under certain conditions phosphorus can
be readily transported with the soil. In fact, 60 to 90 percent of phosphorus moves with the soil.
Phosphorus is the major source of water quality impairments in lakes nationwide. Even though
regulations that affect the taste and odor of
water are not Federally enforceable under the
Safe Drinking Water Act, municipalities
often must treat their drinking water supplies
for these aesthetic reasons.
The use of organic nutrient sources, such as
manure, can supply all or part of the
nitrogen, phosphorus, and potassium needs
for crop production. However, organic
fertilizers can also cause excessive nutrient
loads if improperly applied. Organic fertilizer application
AVAILABLE PREVENTION MEASURES TO ADDRESS AGRICULTURAL
APPLICATIONS OF FERTILIZER
This section discusses some of the most often used prevention measures, but is not an
exhaustive list of all known measures. For information on additional prevention measures, see
the documents referenced in the last section of this fact sheet. Please keep in mind that
individual prevention measures may or may not be adequate to prevent contamination of source
waters. Most likely, individual measures should be combined in an overall prevention approach
that considers the nature of the potential source of contamination, the purpose, cost,
operational, and maintenance requirements of the measures, the vulnerability of the source
water, the public's acceptance of the measures, and the community's desired degree of risk
reduction.
The goal of these prevention measures is to minimize nutrient losses from agricultural lands
occurring by edge-of-field runoff and by leaching from the root zone. Effective nutrient
management abates nutrient movement by minimizing the quantity of nutrients available for
loss. This is achieved by developing a comprehensive nutrient management plan and using only
the types and amounts of nutrients necessary to produce the crop, applying nutrients at the
proper times and with proper methods, implementing additional farming practices to reduce
nutrient losses, and following proper procedures for fertilizer storage and handling.
Application Rates and Fertilizer Types
One component of a comprehensive nutrient
management plan is to determine proper
fertilizer application rates. The goal is to limit
fertilizer to an amount necessary to achieve a
realistic yield goal for the crop. Soil sampling
and crediting other sources are also parts of the
concept.
Yearly soil sampling is necessary for
determining plant nutrient needs and to make
accurate fertilizer recommendations. Many
factors must be considered when determining
sampling methods and frequency.
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Fertilizer spreader Calculating the optimal rate of application also
includes crediting other sources that contribute nitrogen and phosphorous to the soil. Previous
legume crops, irrigation water, manure, and organic matter all contribute nitrogen to the soil,
while organic matter and manure contribute phosphorus.
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Along with soil samples and fertilizer credits from other sources, nitrogen fertilizer
recommendations are based on yield goals established by the crop producers. Yield
expectations are established for each crop and field based on soil properties, available moisture,
yield history, and management level.
Applying the appropriate form of nitrogen fertilizer can reduce leaching. Nitrate forms of
nitrogen fertilizer are readily available to crops, but are subject to leaching losses. Nitrate
fertilizer use should be limited when the leaching potential is moderate to high. In these
situations, ammonium nitrogen fertilizers should be used because they are not subject to
immediate leaching. However, ammonium nitrogen transforms rapidly into nitrate when soils
are warm and moist. More slowly available nitrogen fertilizers should be used in these
conditions. Nitrification inhibitors can also delay the conversion of ammonium to nitrate under
certain conditions.
Phosphorus fertilizer is less subject to leaching, but loss through surface runoff is more
common. To minimize losses of phosphorus fertilizer, applications should only be made when
needed (determined through soil testings) and at recommended rates.
Fertilizer Application Timing
Nitrogen fertilizer applications should be timed to coincide as closely as possible to the period
of maximum crop uptake. Fertilizer applied in the fall has been shown to cause ground water
degradation. Partial application of fertilizer in the spring, followed by small additional
applications as needed, can improve nitrogen uptake and reduce leaching. Reasons to alter
nitrogen amounts include abnormal weather or crop quality.
Fertilizer Application Methods
Fertilizer application equipment should be inspected at least once annually. Application
equipment must also be properly calibrated to insure that the recommended amount of fertilizer
is spread.
Correct fertilizer placement in the root zone can greatly enhance plant nutrient uptake and
minimize losses. Subsurface applied or incorporated fertilizer should be used instead of a
surface broadcast fertilizer. The most efficient application method for many crops, especially in
erosive soils, is to place dry fertilizer into the ground in bands. Band or drilled row fertilizers
are applied closer to the seed and can be recovered by the crop more efficiently. All surface-
applied fertilizers should be mechanically incorporated into the soil to reduce losses through
surface runoff and volatilization. Fertilizer should never be applied to frozen ground, and also
should be limited on slopes and areas with high runoff or overland flow.
Irrigation water should be managed to maximize
efficiency and minimize runoff or leaching. Irrigated
crop production has the greatest potential for source
water contamination because of the large amount of
water applied. Both nitrogen and phosphorus can leach
into ground water or run off into surface water when
excess water is applied to fields. Irrigation systems, such
as sprinklers, low-energy precision applications, surges,
and drips, allow producers to apply water uniformly and
with great efficiency. Efficiency can also be improved
by using delivery systems such as lined ditches and gated
pipe, as well as reuse systems such as field drainage
recovery ponds that efficiently capture sediment and nutrients. Gravity-controlled irrigation or
furrow runs should be shortened to prevent over-watering at the top of the furrow before the
lower end is adequately watered.
Runoff
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Additional Farming Practices
A complete system is needed to reduce fertilizer loss. Components of this system often include
farming practices that are not strictly related to fertilizer, such as conservation tillage and
buffers.
Conservation tillage is another field management
method used to reduce runoff. In conservation tillage,
crops are grown with minimal cultivation of the soil.
When the amount of tillage is reduced, the plant
residues are not completely incorporated and most or
all remain on top of the soil. This practice is critical
to reducing phosphorus losses because the residue
provides cover and thereby reduces nutrient runoff
and erosion by water.
Conservation tillage
Creating buffer strips or filter strips can impede runoff and help filter nitrogen and phosphorus
from runoff. Buffer strips and filter strips are created by planting dense vegetation near surface
water bodies. The root systems of these plants hold soil in place, thereby decreasing the
velocity of runoff and preventing erosion. The vegetation and soils strain and filter sediments
and chemicals. For more information on buffer strips and filter strips see the fact sheet on storm
water runoff.
Crop rotation can often yield crop improvement and
economic benefits by minimizing fertilizer and
pesticide needs. Planting legumes as part of a crop
rotation plan provides nitrogen for subsequent crops.
Deep-rooted crops can be used to scavenge nitrogen
left in the soil by shallow-rooted crops. Cover crops
stop wind and water erosion, and can use residual
nitrogen in the soil.
Wheat-corn-fallow rotation
A high-tech way to level or grade a field is to use
laser-controlled land leveling equipment. Field leveling helps to control water advance and
improve uniformity of soil saturation in gravity-flow irrigation systems. This improves
irrigation efficiency and reduces the potential for nutrient pollution through runoff.
Fertilizer Storage and Handling
Follow label directions for storing and mixing fertilizer and for disposing empty containers.
Lock or secure storage container valves when the container is not in use.
Protect permanent fertilizer storage and mixing sites from spills, leaks, or storm water
infiltration. Storage buildings should have impermeable floors and be securely locked.
Impermeable secondary containment dikes can also be used to contain liquid spills or leaks. Do
not store fertilizer in underground containers or pits.
To prevent accidental contamination of water supplies, mix, handle, and store fertilizer away
from wellheads and surface water bodies. Installing anti-backflow devices on equipment can
also prevent spillage. Ideally, mix and load fertilizers at the application spot.
Immediately recover and reuse or properly dispose of spills. Granular absorbent material can be
used at the mixing site to clean up small liquid spills.
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FOR ADDITIONAL INFORMATION
These references have information on agricultural fertilizer use and best management practices.
All of the following documents are available for free on the internet. You should also contact
the U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS),
Conservation District, and Agricultural Extension Service representatives in your area for more
information on nutrient management and cost-share programs, such as the Environmental
Quality Incentives Program (EQIP), the Conservation Reserve Program (CRP), and the
Conservation Reserve Enhancement Program (CREP), to assist in financing source water
protection measures.
Contact local government authorities in your area to see if there are ordinances in place to
manage fertilizer use. Numerous examples of local source water protection-related ordinances
for various potential contaminant sources can be found at:
http://www.epa.gov/r5water/ordcom/
http://www.epa.gov/owow/nps/ordinance/
http://www.epa.gov/owow/nps/ordinance/links.htm
The following documents provide more detailed information on prevention measures for
fertilizer use on the farm.
Colorado State University Cooperative Extension. Best Management Practices for Nitrogen
Fertilization (XCM-172). (1994, August). Retrieved February 9, 2001 from the World Wide
Web: http://www.ext.colostate.edu/PUBS/CROPS/pubcrop.htmMsoil
Colorado State University Cooperative Extension. Best Management Practices for Pesticide
and Fertilizer Storage and Handling (XCM-178). (1994, August). Retrieved February 9, 2001
from the World Wide Web: http://www.ext.colostate.edu/PUBS/CROPS/pubcrop.html#soil
Colorado State University Cooperative Extension. Best Management Practices for Phosphorus
Fertilization (XCM-175). (1994, August). Retrieved February 9, 2001 from the World Wide
Web: http://www.ext.colostate.edu/PUBS/CROPS/pubcrop.htmMsoil
Farm*A*Syst - University of Wiscocsin. Retrieved May 22, 2001 from the World Wide Web:
http://www.uwex.edu/farmasyst/
Kansas State University Cooperative Extension Service. Best Management Practices for
Nitrogen. (1996, March). Retrieved February 9, 2001 from the World Wide Web:
http://www.oznet.ksu.edu/library/ageng2/#WaterQuality
Kansas State University Cooperative Extension Service. Best Management Practices for
Phosphorus. (1998, February). Retrieved February 9, 2001 from the World Wide Web:
http://www.oznet.ksu.edu/library/ageng2/#WaterQuality
North Carolina State University. Sustainable Practices for Vegetable Production in the South -
Conservation Tillage. (1997, July 9). Retrieved March 14, 2001 from the World Wide Web:
http://www.cals.ncsu.edu/sustainable/peet/tillage/c03tilla.html
Purdue University Extension Service. Fertilizer Storage and Handling on the Farm. (1999).
Retrieved February 12, 2001 from the World Wide Web:
http://pasture.ecn.purdue.edu/~epados/farmstead/fert/src/title.htm
Texas Agricultural Extension Service. Reducing the Risk of Ground Water Contamination by
Improving Fertilizer Storage and Handling (B-6026). (n.d.). Retrieved February 9, 2001 from
the World Wide Web: http://agpublications.tamu.edu/catalog/index.html
University of Maryland - Cooperative Extension. Agricultural Nutrient Management.
Retrieved May 22, 2001 from the World Wide Web:
http://www.agnr.umd.edu/users/agron/nutrient/
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University of Saskatchewan, Department of Agriculture. Fertilizer: The Basics, (n.d.).
Retrieved February 16, 2001 from the World Wide Web:
http://www.ag.usask.ca/cofa/departments/hort/hortinfo/misc/fertiliz.html
U.S. Department of Agriculture. Irrigation Systems and Land Treatment Practices. (2001,
February 6). Retrieved March 14, 2001 from the World Wide Web:
http://151.121.66.126/Briefmg/wateruse/Questions/glossary.htm
U.S. Department of Agriculture, Natural Resources Conservation Service. Comprehensive
Nutrient Management Planning - Technical Guidance. (2000, December). Retrieved April 30,
2001 from the World Wide Web:
http://www.nhq.nrcs.usda.gov/PROGRAMS/ahcwpd/ahCNMP.html
U.S. Department of Agriculture, Natural Resources Conservation Service. Conservation
Practices Training Guide. (1999, August). Retrieved April 30, 2001 from the World Wide
Web: http://www.ftw.nrcs.usda.gov/tech_refhtml
Virginia Cooperative Extension. Fertilizer Storage, Handling, and Management (442-906).
(1996, June). Retrieved February 9, 2001 from the World Wide Web:
http://www.ext.vt.edu/pubs/farmasyst/442-906/442-906.html
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