Vegetable Crops Department
University of Florida
April 21, 1960
TO: COUNTY AGENTS
TOPICS COVERED In This ISSUE Are:
I FOLIAR NUTRITION OF VEGETABLES Does it Pay???
II THE USE OF LIQUID FERTILIZERS ON VEGETABLE CROPS An Excellent
Reference Written by W. C. Kelly of Gornell University and
Reproduced here by Permission.
III ADDITIONAL VEGETABLE FIELD DAYS Dates, Times and Places of
Those Set Since Issuring List in Vegetarian of March 16, 1960.
I FOLIAR NUTRITION OF VEGETABLES
The practice of supplying the minor elements like zinc, copper, manganese,
iron, and boron by spraying or dusting them onto the foliage of plants has been
recommended and used with success over a period of time. More recently, much
has been written and said about supplying plants with nitrogen, phosphorus, and
potassium by applications to the leaves of a plant. The practice has been in-
vestigated by research workers throughout the United States. Extensive studies
have also been conducted at several research stations in Florida. RESULTS HAVE
SHOWN RATHER CONCLUSIVELY THAT FOLIAR APPLICATIONS TO VEGETABLE CROPS OF ONE OR
MORE OF THE MAJOR ELEMENTS ARE NO BETTER THAN EQUAL AMOUNTS OF THE SAME MATERIALS
APPLIED TO THE SOIL,
It must be remembered that the major elements, unlike the minors, are re-
quired in relatively large amounts and many applications are generally needed
to supply the needs of the plant. Even under conditions of root damage or
foliage injury from frost or wind, there are no conclusive experimental results
to show that spray applications of the major elements would be any better than
equal applications to the soil.
Here are some direct quotes from Florida Experiment Station Annual Reports
made by workers at several locations in the state on a number of vegetables.
None suggest use of foliar feeding as a primary means of supplying the major
nutrients to plants:
Bradenton, 1951 "Extensive trials on the Station Farm in
Bradenton and on the farm of -a grower- at Ruskin indicate
that crops with high fertility requirements, such as the
tomato, showed little or no response to foliar feeding as
far as the major elements were concerned.
COO-ERATIVE EXTENSION WORK IN AGRICULTUrE AND HOME ECONOMLC5, STATE OF FLOItIDA
CO-LIC' Or r AICULTURE, UNIVERSITY Or FrionDA. UNITED STATES DFPARIMENT OF ACGRCULTURE, AND EOARDS Or COUNTY COMMISS4i8NERS. COOPERATING
FLORIDA AGRICULTURAL EXTENSION SERVICE
UNIVERSITY OF FLORIDA
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
II REPRODUCED BY PERMISSION
Department of Vegetable Crops, Ithaca VC-58
N. Y. State College of Agriculture Revised 1959
THE USE OF LIQUID FERTILIZERS Ct VEGETABLE CROPS
William C. Kelly
The traditional form of fertilizer for vegetable crops is solid, dry materials.
In recent years a number of fertilizers have appeared on the market in a liquid
form or as dry material to be applied as a solution. There are several types of
liquid fertilizers available and each will be discussed. The four major types of
liquid fertilizers are (1) liquid nitrogen materials; (2) soluble fertilizer com-
pounds for starter solutions to be applied to transplants; (3) soluble fertilizer
materials to be applied as foliage sprays and (4) liquid formulations of complete
fertilizers to be used in the same way as conventional dry mixed fertilizers.
Liquid Nitrogen Materials
Types of materials, Each nitrogen source, liquid or dry, has its own advant-
ages and disadvantages. No one material will be the best to use all the time.
There is a place in vegetable farming for all of the various types of nitrogen
materials, but probably not all in a given district or on the same farm. The liquid
nitrogen materials available in New York are anmoniating solutions used in mixing
commercial fertilizers. The two most commonly used are 2A and 32. Solution 2A is
a mixture of ammonium nitrate and ammonium in water and contains 40% nitrogen.
Solution 32 is a mixture of ammonium nitrate and urea dissolved in water and contains
32% nitrogen. In the West a solution of pure ammonia containing 20% nitrogen is
used to some extent. Anhydrous ammonia is usually classed as a liquid nitrogen
material. This is ammonia gas liquefied under high pressures and applied deep in
Nitrogen solutions. The nitrogen solutions such as 2A and 32 are easy and
cheap to apply since they do not require high pressure equipment. They are among
the cheapest sources of nitrogen available today. Solution 32 can be applied to
the surface of the soil, while Solution 2A must be covered with 1 to 2 inches of
soil to prevent the escape of the ammonia gas.
SAnhydrous ammonia. Anhydrous ammonia requires high pressure equipment since
the gas is liquefied under pressures of about 225 pounds per square inch. It must
be applied 6 to 9 inches deep in the soil with rather expensive metering and dis-
pensing equipment. If the soil does not seal properly over the region of application,
ammonia gas will be lost and crop injury may result. Many New York soils may not
seal properly due to stones. Typical stony New York soils also require extra
strong machinery to apply the anhydrous ammonia. In the South and Midwest where
large quantities of anhydrous ammonia are used, it is the cheapest source of
nitrogen available. This is usually a custom operation in New York. To handle tank
car lots of ammonia a grower must have expensive storage tanks. To make it econ-
omical he also must have a large acreage of crops. Poor results have been obtained-
with anhydrous ammonia because the grower neglected to apply the material early
enough to allow for conversion of the ammonia to nitrate.
Foliage Fertilizer Sprays
Major nutrients. Foliage fertilizer sprays are actually dilute starter solu-
tions applied to the leaves of the plants. The same materials that are used in
formulating starter solutions are used in these foliage fertilizers. The foliage
fertilizers usually have a lower total plant nutrient content than standard starter
solution mixes and a higher price. In many cases the starter solution fertilizers
are bought from a large fertilizer company and diluted out with other salts so that
the analysis is changed and sold at a big mark-up. These materials are highly ad-
vertised and receive a vigorous sales campaign. It is easy to see how cuch campaigns
can be conducted since the basic materials would cost less than $200 per ton while
the finished packaged product may be sold for as high as $2000 per ton.
Foliage fertilizers are likely to contain a "magic ingredient" of some type,
such as minor elements, hormones or vitamins. Small traces of minor elements in
these foliage fertilizers have never been shown to be of any benefit when sprayed
on plants in New York. No one has ever shown an increased yield of vegetables due
to spraying vitamins or hormones on the leaves at the concentrations used in foliage
Only small amounts of these soluble fertilizers can be applied to the foliage
since foliage is injured by excessive concentrations. The amount that can be used
on most vegetables supply only 1 to 2 pounds of the major fertilizer nutrients per
acre. Some cases where large amounts of spray solutions are used, the excess
solution runs off and the so-called "foliage application7' becomes a soil application.
The sale of these materials has been greatly stimulated by work that shows absorp-
tion of certain plant nutrients by the foliage. This work has involved radioactive
elements. Dramatic pictures are shown which prove without question that the nutrients
were absorbed by the foliage and translocated to other plant parts. Such photo-
graphs can be made even though only minute amounts of material is presented by in-
creasing exposure time of the film. Actually the leaf works both ways. While
nutrients may be absorbed by the leaf, nutrients may also be leached out of the leaf
during periods of heavy rainfall.
The fact that nutrients are translocated into the roots is of no great import-
ance. The root is also a two-way system and nutrients may move from the root into
the soil. The amount of plant nutrients that are lost to the soil from the roots
and the amount leached from the leaves by rainfall is small, but so is the amount
of nutrients absorbed by the foliage. Recently workers in Michigan measured the
amount of foliar applied phosphorous that was translocated to the roots. Only about
3% of the phosphorous in the roots came from the foliage spray. This represented
less than 5% of the total phosphorous applied to the leaves in four applications.
This is like feeding a pig one grain of corn at a time.
Much of the work on foliage sprays has involved urea. Urea is a good source
of nitrogen for vegetables and is commonly used in starter solutions, in dry
fertilizer mixes, and as a sidedressing material. Most vegetables tolerate only
about 5 pounds of urea (about 2 lbs. actual nitrogen) per acre as a foliage spray.
However, potatoes and carrots tolerate as high as 20 pounds per acre in 1 application.
The amount of nitrogen that can be applied to the foliage is considerably less than
in a normal sidedressing of 30 pounds of nitrogen per acre.
Nitrogen deficient plants are pale green in color and a spray with urea re-
sults in a deeper green color within a few days. However, no one has ever shown
an increase in yield of any crop with an application of 5 pounds of urea per acre
to the leaves. Some work by Hester and Isaacs on carrots in New Jersey showed
definite plant responses to several foliage applications of 20 pounds of urea per
acre. The greatest response occurred when no notrogen was applied in the fertilizer.
The yields obtained with these foliage sprays were no better than with normal soil
applications of nitrate.
In the field, nutrients applied to the leaves washes off with subsequent rains
and becomes effective as a soil application, not as a foliage application. In
field studies it is not possible to differentiate between the foliage effect and the
soil effect when fertilizer is applied to the leaves. The urea absorbed by the
leaves is taken up within an hour or two after the spray is applied. There is
essentially little or no uptake after that period of time even though the urea re-
mains on the leaves. In other words, moisture is needed for uptake of nutrients
on the leaves just like the roots. The material that is not taken up immediately
by the leaves is then subject to washing by rainfall and subsequent uptake by the
The maximum uptake of plant nutrients from, the soil occurs during the period
of maximum growth which lasts usually about four to six weeks. About half of the
nutrients absorbed by the plant are absorbed during this short period of time.
Foliage sprays for the most part are too little and too late to supply this big
demand for nutrients. Restrictions in growth that occur during this period of time
can never be recovered even though fertilizer is added in large amounts later. If
you consider the total amount of nutrients that the crop contains you can easily
see that small amounts of nutrients applied to the foliage cannot have much effect
on the growth of the plants. The nutrient content of the tops of four vegetable
crops for one set of analyses are given below:
Pounds removed per acre
Crop Yield Nitroen Phosphoric Potash
Tomatoes 10 ton 100 35 175
Cabbage 15 ton 100 25 100
Dry beans 30 bushel 95 30 55
Celery 350 crates 80 65 235
Even if foliage applications of fertilizer were completely absorbed by the plant,
how much of the total nutrient content could be furnished by such spraying? The
amount that can be furnished by sprays is so small that a grower is not warranted
in spending appreciable amount of money per acre to apply the material. Some argue
that as long as he has to spray the crop with insecticides and fungicides, why not
dump some of these materials in the tank, too? However, with the results that the
majority of Experiment Station workers have obtained, the yield responses from these
materials would not pay for the labor of dumping it into the tank if the material was
furnished free of charge.
Some careful experiments were conducted in Delaware to eliminate the effects of
foliage fertilizer washing down to the soil. Tomato plants were grown in sand cul-
tures that were protected so that none of the run-off could enter the root zone.
Repeated foliage sprays could not furnish enough plant nutrients for normal tomato
growth under these conditions. The foliage is not an efficient nutrient absorbing
One possible use of foliage spray applications is to obtain a better color of
the foliage of the crops shortly before harvest. If the foliage is a pale green
color due to lack of nitrogen, the color can be improved in a few days by a urea
spray. If the foliage is pale due to some other cause, the nitrogen or urea sprays
will not influence the color of the leaves.
Minor elements. In Florida and elsewhere, minor element sprays are used or
many crops as standard practices on certain soils. The materials used are standard
fertilizer materials applied at concentrations established by research in the area.
Appreciable amounts, usually 3 to 5 pounds of specific salts are applied to the
foliage of the vegetables. These sprays are necessary due to the nature of the
soil in those areas. Fortunately, in New York we do not have any of this type of
soil. Vegetable minor element needs can be satisfied by standard soil applications
in most cases. The only exception is the magnesium chlorosis of Utah strains of
celery on alkaline mucks. It cannot be economically corrected by soil application,
but responds well to spray applications of magnesium sulfate. There is some justi-
fication for minor element foliage sprays in New York as an emergency when soil
applications were not made. In cases where this is necessary, the specific minor
element compound should be applied at rates high enough to do some good. The
traces of minor elements present in these foliage fertilizers will not be enough to
do the job.
Liquid Complete Fertilizers
Comparison of liquid and dry fertilizers. Most of the publicity on these
materials has come from the midwest where a few growers are using standard analysis
fertilizers applied as a liquid instead of dry materials. These are applied at the
same rates per acre as dry fertilizers. That is, 500 pounds of a 5-10-10 liquid
formulation is exactly comparable to 500 pounds of a 5-10-10 dry mix. The main
advantages attributed to this type of fertilizer are the convenience in handling
liquids and the ease of application with simple equipment. The liquid can be hauled
in tank trucks and handled with pumps and applied with easily calibrated inexpensive
equipment. Apparently a grower near the source of manufacture can obtain these
materials at a price competitive with dry fertilizers. However, in New York, most
of these materials are much more expensive than dry fertilizers. Actually the main
impetus in the use of liquid fertilizer is not due to poor results with dry fertili-
zer, but to poor machinery for distributing the dry fertilizer. Growers object to
frequent filling, the bridging and clogging, etc. that result with most types of
fertilizer distributors. The designs of machines to dispense liquids are simpler
and there are fewer things to go wrong with the machinery.
How do these liquid fertilizers differ from dry fertilizers? Why can't we
just dump regular 5-10-10 in the tank and apply it to the soil? The nitrogen and
potash in liquid fertilizers are usually exactly the same materials as in dry ferti-
lizers. All sources of nitrogen used in fertilizers (except organic, such as
tankage) are completely water soluble. Therefore, they can be applied either as a
liquid or as a dry material. The potash materials used in dry fertilizer are all
water soluble, both the chloride-and sulfate. These same materials can be used
in the liquid fertilizer. The only real difference in the liquid and dry fertilizers'
is the source of phosphorous.
Forms of phosphorous. Most phosphorous sources are insoluble. The term
"available phosphorous" in a fertilizer includes water soluble phosphorous and citric
acid soluble phosphorous. Both of these forms are considered to be available to
plants when applied to the soil. In the liquid fertilizers only the water soluble
phosphates are used. The most commonly used sources of soluble phosphorous are
mono-ammonium phosphate, di-ammonium phosphate, mono-potassium phosphate and di-
potassium phosphate. Mono-calcium phosphate is also water soluble, but is not
used in liquid fertilizers. Actually, the sources of phosphorous in these liquid
fertilizers are exactly the same as those used in starter solutions and foliage
The most common source of phosphorous in dry fertilizer is 20% super-phosphate.
This is generally considered to be an insoluble material, but this is not entirely
true. Superphosphate is half gypsum which is insoluble. The available phosphate
in superphosphate is about 90% water soluble mono-calcium phosphate. The rest of
the available phosphate is the citric acid soluble di-calcium phosphate. Therefore,
even 20% superphosphate furnishes large amounts of water soluble phosphate to veg-
etables when applied to the soil. A part of the nitrogen used in mixed fertilizers
comes from the nitrogen solutions previously mentioned. These solutions are added
to the superphosphate as a cheap source of nitrogen. This is called ammoniation and
involves some rather complex chemical reactions. When a nitrogen solution is added
to superphosphate, chemical reactions occur so that only about 50% of the available
phosphorous in superphosphate is water soluble. This now represents mono-ammonium
phosphate rather than mono-calcium phosphate. The other 50% is citrate soluble
di-calcium phosphate. In regular dry fertilizers usually about half the total
phosphorous is water soluble.
Some companies are producing extra high analysis fertilizer such as 10-20-20
in which the source of phosphorous is ammonium phosphate. These fertilizers with
an amnophos base could be completely dissolved in water to produce a liquid fer-
tilizer. There are usually a few insoluble impurities in a regular fertilizer and
a small residue might be left on the bottom of the tank. Since these materials
differ only in phosphorous, let us consider some of these various types of phos-
phorous. Water soluble phosphorous applied to the soil in either liquid or dry
fertilizer is rapidly taken up by vegetables providing roots are present in the zone
Phosphorous availability. Phosphorous is rapidly fixed by the soil and tied
up in relatively unavailable forms. The particular form in which it is tied up
depends on the soil reaction. In very acid soils, aluminum and iron phosphates
are formed and in alkaline soils, tri-calcium phosphate is formed. While water
soluble phosphate may be rapidly taken up by the plant, it also may be rapidly
fixed by the soil and rendered unavailable to the plant. The citrate soluble phos-
phate, di-calcium phosphate, is slightly soluble in water and slowly dissolves in
the soil solution. This material supplies water soluble phosphorous over a some-
what longer period of time than the completely soluble materials. The plant there-
fore has a continuing source of phosphorous when some of these citrate soluble
sources are used.
Some manufacturers make granulated superphosphate and granulated fertilizer.
The principle behind this practice is that granulation slows down the rate of
solution, so that the nutrients are available over a longer period of time. Granu-
lation tends to prevent the immediate soil fixation of large quantities of soluble
phosphate. Some recent work comparing granulated and powdered superphosphate in
the laboratory has shown that the granulated superphosphate is superior. Immediate=
ly upon addition to the soil, more water soluble phosphate could be extracted from
the soil where the powdered superphosphate had been added. After waiting two or
three weeks, more water soluble phosphate was found in the soil where the granulated
superphosphate had been added. The theory advanced was that the area immediately
around each particle of granulated material was saturated in so far as the soils
capacity to tie up the phosphorous was concerned. Here was a zone where water
soluble phosphate could exist without being fixed rapidly. Some of the companies
manufacturing high analysis fertilizer with an ammophos base are pelleting or
granulating the fertilizer to slow down the solubility of the ammophos and prevent
rapid fixation. The amount and rate of fixation of phosphorous by the soil varies
with the soil type and no one material will be superior on all soil types.
Liquid fertilizers in dry soil. Some claim that liquid fertilizers are already
in solution and would be more available in a dry soil. If water is limiting vege-
table growth only water will give increases in growth. The water used in liquid
fertilizers is usually less than 100 gallons per acre. An average loam soil that
is dry enough to need irrigation contains about 25,000 gallons of water per acre
in the furrow slice. How then can 100 gallons of water be of any possible benefit
to vegetable growth?
Future of liquid fertilizers. There is a place for all forms of fertilizer
materials. As far as supplying plant nutrients are concerned there is no great
advantage in either liquid or dry forms. The main thing to consider is the cost
of the fertilizer on a plant nutrient basis and the ease of handling and application.
While we have traditionally used dry fertilizers, there is no reason we should
have to use them if we can obtain liquid mixes as cheap and handle them more effi-
ciently. However, expensive storage facilities are needed for liquids and it is
rather unlikely that liquid fertilizers will replace dry fertilizers to a very great
extent. You must consider too that for the most part the water soluble sources of
phosphorous are more expensive to manufacture than ordinary superphosphate. It will
probably be some time before the two are strictly competitive over a very large
part of the country. While liquid fertilizers are a novelty, this is no basis for
paying excessive prices for plant nutrients that can be supplied much cheaper with
conventional fertilizer materials.