Want to know even more about fertilizer and its benefits? In All the
Details you will discover in-depth information that will not only help
you understand more about fertilizer but also show you how its use will
help your garden. Choose one of the topics below to learn about a specific
fertilizer area of interest.
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Nitrogen (N) is a constituent of all living cells and is a necessary part
of all proteins, enzymes, and metabolic processes involved in the
synthesis and transfer of energy. Turf grass fertilizer nitrogen carriers
are available in an array of forms such as granules, pellets, liquids,
powders, and suspensions.
Granules are the most popular and range in size from coarse (1 to 3 mm
in diameter) to fine (< 1 mm in diameter) = greens grade fertilizers.
Over 90% of all nitrogen fertilizers are produced synthetically by
reacting atmospheric nitrogen and hydrogen gas to form ammonia. Large
amounts of energy in the form of temperature and pressure are required
for this process.
Fast-release nitrogen sources are also sometimes referred to as quick
release or water soluble sources. These forms of nitrogen are available
as granules and liquids. Slow-release nitrogen sources are also called
water insoluble sources. These are either coated products (sulfur,
polymer, plastic, resin) or controlled-release reacted products and are
available as granules, powders, or suspensions.
In warm, moist soils with a pH above 5.0, the majority of
ammonium-source nitrogen (NH4+) is converted to
nitrate (NO3-) by soil organisms rather quickly
(within days). Therefore, most nitrogen taken up by plants is in the
NO3- form, although NH4+ is
taken up when present in the soil solution.
The nitrate ion carries a negative charge, which prevents its
retention by the negatively-charged soil colloids. Since it is soluble and
mobile, the nitrate ion is readily and easily available to plants.
Nitrate moves in the soil solution and can be leached below the plant root
zone when soil moisture is excessive. Leaching losses of fertilizer
nitrogen are minimal when rates of application conform to recommendations
consistent with the yield potential for the crop and soil in question.
Nitrate is also subject to denitrification, a process in which the
nitrate ion is reduced through several intermediate steps to a gaseous
nitrogen oxides or to elemental nitrogen.
Urea is a synthetic organic nitrogen fertilizer and one of the most
widely used nitrogen sources due to its low cost and completely soluble
Urea is unavailable to turf grass plants until it is converted to
ammonium. Once urea is applied, it is broken down into ammonium
carbonate ((NH4)2CO3) by the enzyme
urease (produced by soil bacteria). Direct applications of urea to
the turf grass surface can result in the conversion of ammonium carbonate
to ammonia and carbon dioxide, resulting in excess loss of ammonia as a
gas. This loss can be avoided by irrigating immediately after application
of urea fertilizers to incorporate the nitrogen.
Urea has a quick initial release rate of nitrogen with short duration,
and a high foliar burn potential (salt index). Urea-based fertilizer
programs should involve low application rates (< 1/2 pound N per 1000
square feet) made frequently (every two to four weeks) to reduce the loss
Like nitrogen, phosphorus (P) is an essential part of the process of
photosynthesis and is the second most essential element or nutrient for
plant growth. Phosphorus does not move or leach readily due to its low
water solubility; therefore, phosphorus applications are not needed as
regularly as nitrogen applications. A soil test is the best indicator of
the phosphorus level in the soil.
The phosphorus content may range in turf grass tissues between 0.1 to
1.0% by weight with sufficient values ranging from 0.2 to 0.4%. Iron
deficiencies normally result from high phosphorus or alkaline soils. The
highest concentration of phosphorus is in new leaves but is readily
mobile throughout the plant.
Since phosphorus is fairly mobile in plants, deficiency symptoms
normally occur in older tissues. Phosphorus deficiency symptoms in turf
grass plants include slow growth and stunted plants possessing dark green,
lower, older leaves. These older leaves eventually show a dull
blue-green color with a reddish to purple pigmentation along the leaf
margins due to sugar accumulation. Eventually, leaf tips turn red and
may develop red streaks down the leaf blades.
Phosphorus deficiencies usually occur when root growth is restricted
and when soil temperatures and oxygen levels decrease. Early spring and
fall are two seasons when root growth is slowed; hence phosphorus in the
soil is not readily encountered during those times.
The immediate source of phosphorus for plants is dissolved in the soil
solution itself. Plants absorb phosphorus primarily as the
HPO42- ions predominant in most soils.
The H2PO4- ion is more readily absorbed
than the HPO42- by most plants. A soil solution
containing only a few parts per million of phosphate ions is usually
considered adequate for plant growth. Concentrations of phosphate ions in
the soil solution may be as low as 0.001 parts per million. Phosphate
ions are absorbed from the soil solution and used by plants. The soil
solution is replenished from soil minerals, soil organic matter
decomposition, or applied fertilizers.
In young plants, phosphorus is most abundant in tissue at the growing
point. It is readily translocated (moved about) from older tissue to
younger tissue, and as plants mature, most of the element moves into the
seeds and/or fruits. Phosphorus is responsible for characteristics of
plant growth such as utilization of starch and sugar, cell nucleus
formation, cell division and multiplication, fat and albumin formation,
cell organization, and transfer of heredity.
Potassium is absorbed by plants in larger amounts than any other
mineral element except nitrogen and, in some cases, calcium. Potassium is
supplied to plants by soil minerals, organic materials, and inorganic
fertilizer. Potassium, unlike nitrogen and phosphorus, is not found in
organic combination with plant tissues. Potassium plays an essential role
in the metabolic processes of plants and is required in adequate amounts
in several enzymatic reactions, particularly those involving the
adenosine phosphates (ATP and ADP), which are the energy carriers in the
metabolic processes of both plants and animals. Potassium also is
essential in carbohydrate metabolism, a process by which energy is
obtained from sugar. There is evidence that potassium also plays a role
in photosynthesis and protein synthesis.
Potassium is directly involved in maintaining the water status of turf
grass plants, the turgor pressure of its cells, and the opening and
closing of stomata. As the potassium concentration increases, cell walls
thicken and the water content of tissues decreases and plants become more
turgid (swollen, distended).
Cold tolerance is also influenced by the plants P to K relationship.
A 1:2 P to K ratio in the leaf tissue increases the cold tolerance of turf
The critical level of potassium in plants is about four times that of
phosphorus. Leaf tissue analysis by weight for potassium consists of 1 to
5%. Sufficient levels range from 1.5 to 3%. Potassium deficiency occurs
when tissue levels drop below 1%.
Potassium deficiency symptoms include interveinal yellowing of older
leaves and the rolling and burning of the leaf tips. Leaf veins finally
appear yellow and leaf margins appear scorched. Potassium is a mobile
element and can be translocated to younger tissues if a shortage in
Muriate of potash (KCl) is the potassium-containing fertilizer source
most often used. Other sources of potassium include sulfate of potash
(K2SO4), potassium magnesium sulfate
(K2Mg(SO4)2), and potassium nitrate
Three other nutrients that are needed by the plant are calcium,
magnesium, and sulfur.
Seven of the sixteen elements necessary for plant growth are needed
in such small quantities that they are referred to as
micronutrients. These elements include Manganese, Iron,
Copper, Zinc, Boron, Molybdenum, and Chlorine.
Applying limestone to the soil raises the pH. Before putting
limestone on your soil, test your soils current pH level. The
soils pH level shows the amount of limestone needed to raise
your soils pH to your desired level. You should always
test before applying limestone to make sure that your soil isnt
In some soils, lowering soil pH permanently is almost
impossible because of naturally-occurring lime in the soil, such
as sea shells, marl, or limestone. Soil at construction sites may
contain large amounts of mortar and concrete, which are both
alkaline. In situations like the ones mentioned, too much lime
exists that can be neutralized. Choose plants that tolerate a
high soil pH.
Yes, but there is a lot of work involved in maintaining the
necessary pH level. Applying sulfur will temporarily lower your
soils pH, but will last only as long as it takes for the
microorganisms in the soil to break down the elemental sulfur.
With some forms of sulfur, this process may only take a few
weeks and then the soil pH rises to its original level.
Applying a large amount of sulfur may also burn and damage
Follow the instructions given on the product you purchase;
however, the maximum amount of sulfur applied should be between 5
to 10 pounds per 1000 square feet. Repeated annual treatments may
acidify the soil enough to protect against micronutrient
deficiencies caused by high soil pH. Carefully watch your plants
responses to the sulfur before beginning a sulfur treatment
program for your plants.
When you purchase sulfur, be aware that most sulfate sulfur
does not affect soil pH. While ammonium sulfate, iron sulfate,
and aluminum sulfate will acidify the soil, gypsum (calcium
sulfate), Epsom Salt (magnesium sulfate, and potassium sulfate
will not lower your soils pH level.
Organic matter, such as manure, peat, and composted leaves, may
help reverse the alkalinity of your soil when they are applied in
heavy amounts such as 200 pounds per 100 square feet. Semiannual
or annual applications will be sufficient since these materials
take time to be broken down.
Do not set a predetermined pH level that you must reach at all
costs. Also, make sure you test your soils pH level before
trying to adjust the level. Applying lime or sulfur when it is
not necessary will damage plants just as much as not applying
these compounds when they are needed.
In soil that is already acidic, this fertilizer will lower the
soils pH. However, this fertilizer will not lower the pH of
soil with naturally-occurring limestone or shells.
Even though all nutrients are taken up by plants through their roots,
the availability of nitrogen to the plant varies.
- Hydrolysis involves dissolving fertilizer with water.
Fast-release fertilizers are readily available to the plant when they are
applied. No chemical decomposition is required for the release of these
sources of nitrogen.
- Microbial activity, which involves soil microorganisms
breaking down nutrients in the soil into forms that are usable by the
plant. Microbial activity is dependent on the environment due to the
need for soil microorganisms to function. Extreme environmental
conditions (too hot, cold, or dry) may reduce or delay nitrogen release
from microbial degradation.
|Nitrogen Sources ||Hydrolysis ||Microbial*|
| || |
|IBDU ||x || |
|Organic || ||x|
|Milogranite || ||x|
|Urea Formaldehyde || ||x|
|Poly-coated Urea ||x || |
|Methylene Urea || ||x|
|Sulfur-coated Urea || ||x|
|Ammonium Nitrate ||x || |
|Ammonium Sulfate ||x || |
|Urea ||x || |
|Calcium Nitrate ||x || |
|Mono- or Diammonium Phosphate||x || |
*Microbial nitrogen release generally increases with
increasing soil temperatures, moisture, oxygen levels, and neutral soil
PolyonŽ is a polyurethane coated fertilizer manufactured by Pursell
Industries, Inc. Gardeners who use plant foods containing PolyonŽ-coated
nutrients enjoy season-long feeding with one application. PolyonŽ is
distinguished by a unique green coating that bonds to fertilizer
Depending on the thickness of the coating, the green PolyonŽ-coated
granules are timed to release for 2, 3, 6, or 9 months (measured at
72°F soil temperature). The length of timed-release varies depending
on each products formula. That means that you can choose a fertilizer
that lasts as long as you need it. This steady, predictable release feeds
plants slowly, as they can use it.
Pound per pound, fertilizers containing PolyonŽ-coated nitrogen are a
better value than fertilizers that release all of their nitrogen quickly,
only to be washed away. PolyonŽs timed-release approach to feeding
reduces waste, fertilizer runoff or pollution, and saves both time and
Most plant foods containing PolyonŽ-coated nutrients feed plants both
now and later, so some of the granules in the bag are not coated at all.
This is by design. The thoughtful mix of both fast and timed-release plant
food provides some instant feeding and planned, long-lasting nutrition.
Fertilizers potential harm to the environment has received
considerable attention over the past few years. When fertilizer is used
excessively, nutrients wash off into nearly lakes, streams, and ponds.
Since fertilizer encourages growth, the algae in the water multiply
quickly, causing excessive algae blooms. Fish and other organisms will
no longer be able to survive in the polluted waters. Groundwater may
also become contaminated and made unsuitable for drinking.
Fertilizers like PolyonŽ decrease the amount of runoff that ends up
going into the groundwater due to its controlled-release formula. By
releasing the exact amount of fertilizer the plant can use, the nutrients
end up in the plant as opposed to running off the soil and into the water
Follow these steps when shopping for fertilizer:
Perform a Soil Test.
This is the only way to be sure of the level of nutrients
currently in your soil. Only after you conduct your soil test will
you truly know the nutrients lacking in your soil that you need to
boost through applying fertilizer.
Buy nutrients, not "fertilizer.
Know the nutrients your soil needs before you go to buy
fertilizer. If you buy a fertilizer that contains a wide variety of
nutrients that you do not need, you may be spending more money and
getting less of the nutrients you want. Remember, nitrogen is
necessary for new, green growth and most soils do not provide enough
to plants. Phosphorus and potassium, however, may exist in levels
that are sufficient for the plants you are growing.
Examine the Cost per Pound.
Since bags of fertilizer are not the same weight, and their
concentration of nutrients differs as well, it can be difficult to
compare the costs. Comparing the cost per pound of the three major
nutrients is one way to generally compare the different products.
Add the nitrogen, phosphorus, and potassium percentages given on the
bag. Multiply that number by the number of pounds in the fertilizer
to find the number of pounds of nutrients in the fertilizer.
Divide the the cost of the bag by this number to determine
the average cost of nutrients per pound. For example, suppose you
choose a 50-lb bag of 10-10-10 fertilizer. This bag would contain
15 pounds of nutrients (30% N-P-K total in 50 pounds). If the bag
costs $5.00, the cost of nutrients would be a little over $0.33
All Fertilizers are NOT created equal.
One of the major deterrents against purchasing the new
controlled-release fertilizers like PolyonŽ is the increased cost
per pound of these fertilizers. However, you must look past the
price and examine the actual nutrients the plant receives.
For example, many water-soluble fertilizers release their
nutrients into the soil all at once. At this time, a tremendous
amount on nitrogen is available to the plant. However, there is
only so much nitrogen the plant can absorb during the initial
application. Once the water-soluble fertilizer sinks down below
the drip line, the plants roots are unable to absorb the rest of
the nutrients. Those wasted nutrients then seep into the groundwater.
Also, heavy concentrations of water-soluble fertilizers may pull
water out of the plant, causing burning.
With controlled-release fertilizers like PolyonŽ, water-soluble
nitrogen pellets are coated with different amounts of polyurethane.
When this fertilizer is applied to the soil, only a portion of the
fertilizer is readily available to the plant. The plant is able to
absorb these nutrients while the other coated portion of the
fertilizer still remains near the plants roots. As time passes and
soil temperatures rise, water is allowed into some of the coated
fertilizer and some of the fertilizer is diffused back into the soil
where it is absorbed by the plant. This process results in steady
nutrition available when the plant can use the nutrients.
Controlled-release fertilizers release amounts of nutrients the
plant absorbs when the plant can do so. When buying fertilizer, do
not simply purchase the fertilizer with the most nutrients. Purchase
the fertilizer with the necessary nutrients that will be fully
absorbed and utilized by your plants.