Fertilizer is Deeper than N-P-K
We are all aware of
the importance of a good fertilizer for plants, gardens, and lawns. Just as
with animals and humans, plants have to have proper “nutrition” if they are to
be at their best. And most people are aware of the “N–P–K” numbers printed on
all fertilizer bags. These, in order of printing, represent the nitrogen,
phosphorus, and potassium (sometimes referred to as potash) percentages contained in that particular
fertilizer.
For instance, 10–10-10
fertilizer is 10% nitrogen, 10% phosphorus, and 10% potassium. And, on the same
subject, 100 pounds of 10-10-10 is exactly the same as 200 pounds of
5-5-5! No difference.
Let’s briefly review
what the numbers stand for, and the importance of each element.
Primary Nutrients
Nitrogen (N)
Nitrogen is the first, and to some degree the major nutrient for strong, vigorous growth, dark green leaf color, and photosynthesis. Plants that are almost all leaf, such as lawn grasses, wheat, oats, small grain crops, and golf course grasses need plenty of nitrogen. The first number in fertilizers (N) for these crops and others should be especially high, especially for grass since it must continually renew itself due to being mowed often.
When buying
fertilizers for grasses, look for an analysis that starts with a very high
“First number” in the N – P – K numbers. 30 – 0 – 0 is often used, but any
combination with a high “first number” can be used.
Just remember, 100
pounds of 30-0-0 is exactly the same as 200 pounds of 15-0-0. Even if you chose
10-10-10, you could get the same 30 pounds of actual nitrogen by applying 300
pounds. And, with the 10-10-10, you’d also be applying 30 pounds of phosphorus
and 30 pounds of potassium. That would probably be overkill for grass.
Phosphorous is used by
plants largely for root growth and development. Flowers that are well fed with
phosphorus will have more blooms, and fruits ripen better and faster.
Phosphorus is important to flower bulbs, as well as to perennials and recently
established trees and shrubs. Since trees and shrubs do not need as much
nitrogen as grasses and leafy vegetable crops, a small first number and a
larger second number is often seen in fertilizers intended for these plants,
shrubs, and bushes.
Potassium is a general
nutrient for all plants, improving the overall health and strength of the
plant. It improves the plant’s ability to withstand temperature extremes, and
to a lesser degree, stress from drought. Potassium also helps plants resist
diseases.
Because most soils
have some available potassium, the third number is sometimes smaller than the
first two. However, it is important to note that if the soil does not
have available potassium, as some don’t…a smaller third number may not be
desirable.
Secondary Nutrients
Calcium is important
for general plant vigor and promotes good growth of young roots and
shoots. Calcium also helps to build cell walls. As cells weaken,
the vascular system of the plant starts to collapse, reducing the uptake of all
of the major elements. The symptoms show up first at the growing tips of both
the shoots and the roots.
Calcium is an immobile
element, meaning that when there is a deficiency, the plant can’t translocate
calcium from the older leaves to the younger leaves. New growth at the leaf
tips and margins begins to wither and die back, and the new leaves are often
deformed.
Magnesium helps
regulate uptake of other plant foods and aids in seed formation. As it is
contained in chlorophyll, it is also important in the dark green color of
plants and for the ability of a plant to manufacture food from sunlight.
Magnesium is necessary
for formation of sugars, proteins, oils, and fats, regulates the uptake of
other nutrients (especially phosphorous), is a component of chlorophyll, and is
a phosphorus carrier.
Deficiency symptoms
include mottled yellowing between veins of older leaves while veins remain
green. Yellow areas may turn brown and die. Yellowing may also occur on older
leaves. Leaves may turn reddish purple due to low P metabolism, and decreased
seed production often occurs.
Deficiencies most
likely on leached sandy soils and where high levels of N and K have been
applied.
Turf: Green or
yellow-green stripes, changing to cherry red. Older leaves affected first.
Increased winter injury.
Broadleaf:
Leaves are thin, brittle, and drop early. Older leaves may show interveinal and
marginal chlorosis, reddening of older leaves, with interveinal necrosis late
in the season followed by shedding of leaves. Shoot growth is not reduced until
deficiency is severe. Fruit yield is reduced in severe deficiencies; apples may
drop prematurely.
Conifer:
Needle tips are orange-yellow and sometimes red. Primary needles remain
blue-green in young seedlings, but in older plants, older needles and the lower
crown show symptoms first. In affected needles, the transition to green may be
sharp.
Sulfur helps maintain
a dark green color while encouraging more vigorous plant growth. Sulfur
is needed to manufacture chlorophyll. Sulfur is as necessary as
phosphorus and is considered an essential mineral.
What does sulfur do
for plants? Sulfur in plants helps form important enzymes and assists in the
formation of plant proteins. It is needed in very low amounts, but deficiencies
can cause serious plant health problems and loss of vitality. Plants only need
10 to 30 pounds of sulfur per acre . Sulfur also acts as a soil conditioner and
helps reduce the sodium content of soils.
Sulfur in plants is a
component of some vitamins and is important in helping give flavor to mustard,
onions and garlic. Sulfur born in fertilizer assists in seed oil production,
but the mineral can accumulate in sandy or overworked soil layers. Sulfur
deficiencies in soil are rare, but do tend to occur where fertilizer
applications are routine and soils do not percolate adequately.
Trace Elements
We have now
covered primary and secondary elements that plants require for healthy
growth. However, do not make the mistake of thinking the other elements needed are to
be taken for granted. Au contraire! The so-called “trace elements” can
have a far more exaggerated effect on plant growth than just “a trace effect.”
When I ran a 2000 acre
farm, I had a few spots in one farm that have extremely low manganese. Until
the problem was remedied, soybeans completely died in those spots! That’s hardly a “trace”
problem when you’re depending on the soybean crop for your income. Let’s
examine the remaining elements needed to provide everything a plant needs.
Boron helps in cell
development and helps to regulate plant metabolism. It’s a micronutrient
required in very small amounts and there is a narrow range of safety when
applying boron as toxicities can occur if too much is applied.
Boron has important
roles in vegetable plants. It is needed for protein synthesis, development of
cell walls, carbohydrate metabolism, sugar translocation, hormone regulation,
pollen grain germination and pollen tube growth, fruit set, and seed
development. Boron is mobile and readily leached in sandy soils and regular additions
are necessary for many vegetables, but only in small amounts. Boron
toxicity will occur if this element is overly applied.
Chlorine is involved
in photosynthesis. Chloride is necessary for gas exchange, photosynthesis
and protection against diseases in plants. When a plant’s leaf pores, called
stomata, open and close to allow the exchange of gases, the plant sees an increase
in potassium. A subsequent increase in chloride balances out the positive
charge of the potassium to prevent plant damage. The exchange of gases between
the plant and the air around it is critical for photosynthesis; a deficiency of
chloride inhibits photosynthesis, threatening plant health.
Copper is extremely
important in plant nutrition if only for the fact that it aids in forming
chlorophyll. Plants don’t need much copper, but if they don’t get any, results can be disastrous.
It activates enzymes
in your plants that help to synthesize lignin. It’s also part of the
photosynthesis process. On top of that, it’s a key for flavor in certain types
of veggies, and color in certain types of flowers.
Copper is immobile in
plants, so if they are deficient in copper it will likely show up in newer
growth. New leaves will begin to cup and you’ll notice chlorosis between the
veins. If it’s a serious deficiency, small spots of the leaves will die off and
they may wilt and fall off.
Leaf nodes will start
growing closer and closer together, creating a squat look to your plant.
Iron (Fe)
Iron assists in the
manufacture of chlorophyll and other biochemical processes. Iron is a
nutrient that all plants need to function. Many of the vital functions of the
plant, like enzyme and chlorophyll production, nitrogen fixing, and development
and metabolism are all dependent on iron.
Without iron, the
plant simply cannot function as well as it should.
The most obvious
symptom of iron deficiency in plants is commonly called leaf chlorosis. This is
where the leaves of the plant turn yellow, but the veins of the leaves stay
green.
Typically, leaf
chlorosis will start at the tips of new growth in the plant and will eventually
work its way to older leaves on the plant as the deficiency gets worse.
Other signs can
include poor growth and leaf loss, but these symptoms will always be coupled
with the leaf chlorosis.
Manganese is needed
for chlorophyll production.
Manganese and Magnesium
It’s necessary to note
the difference between magnesium and manganese, as some people tend to get them
confused. While both magnesium and manganese are essential minerals, they have
very different properties.
Magnesium is
a part of the chlorophyll molecule. Plants that are lacking in magnesium will
become pale green or yellow. A plant with a magnesium deficiency will show
signs of yellowing first on the older leaves near the bottom of the plant.
Manganese is
not a part of chlorophyll. The symptoms of manganese deficiency are remarkably
similar to magnesium because manganese is involved in photosynthesis. Leaves
become yellow and there is also interveinal chlorosis.
However, manganese is
less mobile in a plant than magnesium so that the symptoms of deficiency appear
first on young leaves. It’s always best to get a sample to determine the exact
cause of the symptoms.
Other problems such as
iron deficiency, nematodes, and herbicide injury may also cause leaves to
yellow.
Molybdenum helps
plants to use nitrogen. In non-legumes (such as cauliflowers, tomatoes,
lettuce, sunflowers and maize), molybdenum enables the plant to use the
nitrates taken up from the soil.
Where the plant has
insufficient molybdenum, the nitrates accumulate in the leaves and the plant
cannot use them to make proteins. The result is that the plant becomes stunted,
with symptoms similar to those of nitrogen deficiency. At the same time, the
edges of the leaves may become scorched by the accumulation of unused nitrates.
In legumes such as
clovers, beans and peas, molybdenum serves two functions:
1.
The plant needs it to
break down any nitrates taken up from the soil—in the same way as non-legumes
use molybdenum.
2.
It helps in the
fixation of atmospheric nitrogen by the root nodule bacteria. Legumes need more
molybdenum to fix nitrogen than to utilize nitrates.
Zinc is used in
development of enzymes and hormones. It is used by the leaves and needed
by legumes to form seeds. The function of zinc is to help the plant produce
chlorophyll.
Leaves discolor when
the soil is deficient in zinc and plant growth is stunted. Zinc deficiency
causes a type of leaf discoloration called chlorosis, which causes the tissue
between the veins to turn yellow while the veins remain green. Chlorosis in
zinc deficiency usually affects the base of the leaf near the stem. Chlorosis
appears on the lower leaves first, and then gradually moves up the plant.
In severe cases, the
upper leaves become chlorotic and the lower leaves turn brown or purple and
die. When plants show symptoms this severe, it’s best to pull them up and treat
the soil before replanting.
It’s hard to tell the
difference between zinc deficiency and other trace element or micronutrient
deficiencies by looking at the plant because they all have similar symptoms.
The main difference is
that chlorosis due to zinc deficiency begins on the lower leaves, while
chlorosis due to a shortage of iron, manganese or molybdenum begins on the
upper leaves.
The only way to
confirm your suspicion of a zinc deficiency is to have your soil tested. Your
cooperative extension agent can tell you how to collect a soil sample and where
to send it for testing.
How to Test Your Garden’s Soil
By now, it should be obvious that plants are actually miniature
chemical factories that require a strict balance between primary, secondary,
and trace nutrients.
And, they will perform
poorly when these chemical nutrients are not in correct balance. The obvious
question is…
How do I know how to fertilize my garden?
The answer seems
impossible for the average person to know. Well, the good news is….it isn’t
hard at all! Many laboratories and even most state extension offices offer soil
testing that can pinpoint exactly what any garden needs and even modify their
recommendations for specific crops.
So, to get your
garden, lawn, or farm ready for a new season, do this:
Take soil samples. You will need ½ to 1 pint of soil per sample. Now, don’t take
one sample from one spot in your garden and send it in. Rather, take
multiple samples over the area go get a representative sample of the entire
area.
Send the sample to a trusted and established laboratory for
their recommendations. There are always forms
to be filled in, so contact the lab of your choice first to get the proper
forms.
Fill in the forms very specifically, indicating what crops you intend to grow,
any known problems from previous years, any concerns that you have.
When the report comes back…it may be difficult for you to read and interpret, so never
hesitate to re-contact the lab with your questions. They will be glad to
help.
Apply exactly what is recommended. Everything. Exactly. And, you should
do it as early in the spring as possible because the added nutrients will not
be readily available to the plants until they undergo certain chemical
reactions in the soil. Earlier is better.
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