Responsible Fertilizer Practices for Lawns
Robert J. Mugaas
2013 Regents of the University of
Minnesota. All rights reserved.
Few soils have enough natural nitrogen (N) to maintain desired
turfgrass quality and recuperative ability throughout the growing
season. Shortages can cause slow growth, yellowing of the plants,
thinning out of the turf, and increased incidence of some diseases.
However, an overabundance of N can lead to excessive shoot and leaf
growth, reduced root growth, low plant carbohydrate (food) reserves,
increased susceptibility to environmental stresses, and some diseases.
A primary consideration in using N fertilizers responsibility is to
match the site conditions and the desired maintenance program with the
proper N fertilizer sources.
Nitrogen fertilizer sources
Nitrogen fertilizer sources are often categorized as inorganic types
or organic types. A brief description of several N sources is given in
Inorganic fertilizers such as ammonium nitrate and ammonium sulfate are
all water-soluble or quick-release N sources. That is, N becomes
available as soon as water is applied to the turf. These fertilizers
respond quickly and results are fairly immediate. However, their burn
potential is quite high and the effects are rather short lived. On sandy
soils, high application rates of these products combined with high
irrigation or rainfall amounts may result in higher N losses due to
leaching. Leaching is the movement of water and possibly nutrients down
into and potentially beyond the turfgrass rootzone.
Once beyond the rootzone, nitrates can continue moving through the soil
and may find their way into groundwater sources.Organic fertilizer
products, natural or synthetic, contain carbon in their chemical
structure. Nitrogen from natural organic sources becomes available only
after the product breaks down through soil microbial action. These are
considered slow-release N sources as N is gradually released to the soil
becoming available for plant use. Soil temperature and moisture are key
factors governing the microbial activity and thereby the N release.
Compared to quick-release sources, slow-release N sources have a lower
leaf-burn potential and can be applied at slightly higher rates without
damaging the turf.
The primary synthetic organic fertilizer product is urea. It is
considered a quick-release N product with a relatively high leaf burn
potential. Urea has been further processed and/or combined with other
materials giving these fertilizer products more or less of a slow-release
characteristic. The N released from these slow-release N products depends
on soil chemical and/or microbial action, has a fairly low-leaf burn
potential, and can be applied at slightly higher rates than quick-release
Nitrogen fertilizer use
The amount of N required by turfgrass depends on the type of grasses
present and the management practices used. High maintenance lawns often
contain the more vigorous, improved Kentucky bluegrass and turf type
perennial ryegrass varieties. These lawns will perform better when
adequate water and fertilizer are regularly provided. Low maintenance
lawns usually consist of common types of bluegrass in combination with a
mixture of fine fescue grasses. These lawns grow and spread more slowly
and usually receive little extra water or N fertilizer. Table 2
describes the annual application of N requirements for these lawn types
and how clippings left on the lawn impact yearly N requirements.
On highly leachable soils--sands and sandy loams-- the recommended N
application rates may result in excessive loss of nitrate-N due to
leaching. Where soluble N sources are used on these soil types, reducing
the N rates to 1/4 to 1/2 lb. N/1,000 ft2
= 1000 square feet
per application may minimize potential nitrate-N leaching. If frequent,
lower N rate applications are not practical, slow-release N sources may
be a better choice for these soils. This practice is adaptable to late
season N fertilization and may be especially true where sandy soils are
in close proximity to surface water or groundwater.
Watering practices that move water beyond the root zone may increase
potential nitrate-N leaching. Daily irrigation during cool, moist periods
increases the potential for leaching. Irrigation practices that take into
consideration the grass plant's needs during any particular climate
condition are more effective. Adding enough water to compensate for that
removed by plant uptake and evaporation minimizes potential N pollution
problems from leaching. Sloped areas may require more frequent but
smaller amounts of water per application. They are more vulnerable to
runoff before water has infiltrated into the soil.
Irrigation of 1/4 to 1/2 inch of water immediately after applying a
quick-release N source helps move the N into the surface soil where it
can be used by the grass plant. Also, the N will be protected from runoff
and possible volatilization back to the atmosphere.
Nitrogen fertilizer product knowledge and being familiar with the site
may minimize or even eliminate potential adverse impacts on water
quality. In addition, always follow manufacturer guidelines or consult
with local extension turf specialists for appropriate application rates.
Phosphorus (P) is an essential nutrient contained in every living grass
plant cell. The amount of P needed by the grass plant is significantly
less than nitrogen or potassium. It has positive effects on turfgrass
establishment, rooting, and root branching. Phosphorus is particularly
important during early grass seedling growth and development stages.
While P is an important nutrient for grasses and other green plants, it
is also an important nutrient for algae and weeds in our lake systems.
Phosphorus is often the least abundant nutrient in freshwater lakes,
which limits growth of algae and weeds. Lake enrichment with P can cause
undesirable algae blooms and vigorous growth of other lake weeds, a
process termed eutrophication. For this reason, much concern has been
raised about the contribution of lawn and garden fertilizers to lake
Off-site movement of phosphorus
Phosphates, P combined with oxygen, are removed from the soil solution
and immobilized in the soil. Consequently, phosphates are not prone to
leaching and pose little or no threat to groundwater resources.
Phosphorus can also be part of organic material such as manures,
composts, various natural fertilizers, grass clippings, or tree leaves.
In the soil solution, these organic forms of P may not be bound tightly
to soil particles. Thus, they are more prone to leaching or runoff than
the phosphates. Of course, sandy soils will pose a greater leaching
concern than heavier loam or clay soils.
Off-site transport of P to surface waters tends to be associated with
sediment erosion. Phosphorus readily bonds to the very fine soil mineral
and organic matter particles. These very fine particles are easily eroded
by runoff water and wind, thus potentially carrying the P bonded to them
to lakes and rivers. Living plants such as trees, shrubs, and grassy
areas around lakes can help stabilize the soil against wind and water
erosion. Also, they act as filters to help remove these fine soil
particles from the air, thus trapping both the soil particles and any
associated nutrients bonded onto them.
Phosphorus management practices
Phosphorus fertilizer additions to lawn areas should be based on a
reliable soil test. A soil test can usually be obtained from land grant
universities such as the University of Minnesota or through private soil
In established turfgrass areas, runoff potential is quite low due to
dense turfgrass and its extensive fibrous root systems. Therefore, where
P is applied to turfgrass areas, it should be watered into the soil where
it is immobilized and generally protected from loss by runoff.
During the winter months, freezing and thawing can break down leaves,
dead grass plants, and other organic debris and release soluble forms of
phosphate and nitrates. These nutrients potentially can run off from
frozen ground, especially slopes, during spring snowmelt and early spring
rains and could be carried into surface water areas.
Grass clippings, leaf litter, and other forms of organic debris should
be removed and kept off hard-surface areas where they could be carried in
runoff to surface water areas. Obviously, these same materials should not
be dumped on or near shoreline areas where nutrients released during
decomposition can move directly into the water.
It is often advisable to add some P when establishing a lawn even though
soil P levels may be adequate for turf. This ensures that P will be
available near the soil surface for the young developing grass roots.
Protecting newly seeded areas, especially slopes, with some type of mulch
cover during establishment helps prevent runoff and erosion of soil and
possible nutrients. Applying P to an established turf following core
cultivation helps get P down into the soil, thereby protecting it from
loss by runoff.
General fertilization practices
In addition to the specific N and P management practices already
mentioned, following are some general lawn fertilization practices that
can help reduce potential water pollution.
Never directly deposit or inadvertently apply fertilizer materials into
Fill granular fertilizer spreaders on a hard surface where any spills
can be easily cleaned up. NEVER
wash off fertilizer spills into
the street or other hard-surface areas where they can easily enter storm
sewers and ultimately surface water areas. Wash off granular fertilizer
spreaders over turfed areas to prevent runoff of fertilizer from hard
surfaces. Fill and clean liquid fertilizer applicators over turfed areas
for similar reasons.
Close the gate on the fertilizer spreader when crossing hard-surface
areas or go back and sweep up the material. Reuse it another time or put
it back into the spreader.
Try to use a drop spreader, which is more precise but slower than a
rotary type spreader near surface water. Next to shoreline areas, apply
fertilizer around the perimeter of the property with a drop spreader to
create a safety zone. The rest of the area farther away from the
shoreline can be fertilized with a rotary spreader. Since the perimeter
has already been done with the drop spreader, it is not necessary to hug
the shore because fertilizer may get into the water. The same kinds of
precautions should be taken when using liquid fertilizer.
Avoid getting fertilizer into natural drainage areas or pathways on a
property. These areas may not necessarily be hard-surface areas, but they
can carry fertilizer directly into the surface water before having the
chance to infiltrate into the surrounding turf/soil area.
Leave a buffer zone of unmanaged grasses or possibly natural vegetation
growing around the shoreline. This can help prevent soil erosion and may
retain some of the nutrients that might otherwise enter the lake.
Leave grass clippings on the lawn area to decompose and recycle
nutrients back to the turf area. They should not be blown or raked into
street gutters or onto sidewalks and driveways where they may be carried
with runoff water to surface water. Nutrients released in water through
decomposition may cause undesirable algae and vegetative growth.
apply N fertilizers to water resources directly or to
Improper management or use of turf fertilizers may contribute to
potential pollution of surface water and groundwater. However, combining
appropriate landscape management practices with a modest lawn fertilizer
program may further reduce surface water pollution.
Prepared by Robert J. Mugaas, Hennepin County Extension
horticulturist, University of Minnesota; Michael L. Agnew, Extension
horticulturist-turf; and Nick E. Christians, professor of
horticulture, Iowa State University.
Originally a joint publication of the Minnesota Extension
Service, University of Minnesota, and Iowa State University
This material is based upon work supported by the U.S.
Department of Agriculture, Extension Service, under special project
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.