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by G. J. Hochmuth
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste. Dean
S. ercial. Veget able
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3 Soil testing
4 Controlling pH
8 Fertilizer application
G.J. Hochmuth, Associate Professor, Vegetable Crops
Department, IFAS, University of Florida, Gainesville
Modern vegetable fertility programs are very com-
plex in nature, resulting from the interaction of many
factors. One important factor is fertilizer cost, which
is a large portion of the crop production expenses.
Application of unneeeded nutrients contributes to
farming inefficiency and, potentially, to ground-
water pollution. Careful use of fertilizers, therefore,
will save money and ensure freedom from govern-
mental monitoring and regulation.
Adding to the complexity of fertility programs is
the wide array of fertilizing materials, formulations,
methods, and timing of applications, which will vary
depending on the crop and soil used. For example,
technologies are changing fast in methods of apply-
ing fertilizers, such as fertigation, drip irrigation, and
liquid injection wheels. In addition, cultivars of single
crops sometimes differ for nutrient requirements,
although vegetable soil testing has not progressed far
enough to account for this factor.
Because of the complexity, it is imperative that
good soil testing techniques be practiced prior to each
crop. The small amounts of time and money invested
in testing'will pay off handsomely in the long run.
For soil testing kits and guidance, consult the local
county extension agents.
Fertilizer grade The minimum guarantee of
available plant nutrients expressed in terms of total
nitrogen, available phosphorus, and soluble
potassium. For example, a grade of 5-16-8 contains
5 percent nitrogen, 16 percent available phosphorus
(expressed as P2Os), and 8 percent soluble potassium
(expressed as K20).
Figure 1. The modified
porating fertilizer in the
broadcast method of incor-
bed area with a rototilling
Band A narrow strip of fertilizer placed along
the row of plants or seeds on or below the soil
Blend A mixture of several fertilizer sources to
be applied to the crop. Blends may be dry, or in
suspensions or solutions.
Broadcast To spread fertilizer evenly over the
entire soil surface and, usually, thoroughly incor-
porate it. The "modified broadcast" method involves
broadcasting the fertilizer in a 3- to 4-foot swath in
the bed area only (Fig. 1).
Bulk fertilizer Commercial fertilizer, often a
blend, delivered in a non-packaged manner.
Crop nutrient requirement The total amount
of plant nutrients needed by a crop for maximum
productivity in most situations. This amount is sup-
plied by native soil fertility, which is supplemented
as needed by fertilizers.
Filler A substance added to fertilizer materials
to provide weight, prevent caking, etc. Common
fillers are dolomite and sand.
Granular fertilizer Fertilizer present in small,
Homogenized fertilizer Fertilizer manufac-
tured by a complex method. The basic operation is
ammoniation of normal or triple superphosphate
together with sulfuric and/or phosphoric acids
followed by drying, cooling, and screening. The pro-
cess allows plant nutrients, especially micro-
nutrients, to be evenly distributed in each granule.
Also called granulated fertilizer.
Liquid fertilizer Fertilizer nutrients supplied
in true solution.
Micronutrients Essential plant nutrients re-
quired in small quantities. The micronutrients are
iron, boron, chlorine, copper, manganese, zinc, and
molybdenum. In most cases there is a fine line be-
tween sufficient amounts and toxic amounts of these
Figure 2. Watermelons growing on overhead-irri-
gated sandy soils in Sumter County.
Placement Location of the fertilizer in the soil
relative to the plant or seed.
Primary nutrients The term used by the fer-
tilizer trade for nitrogen, phosphorus, and potassium.
Secondary nutrients The term used by the fer-
tilizer trade for calcium, magnesium, and sulfur.
Sidedress Application of fertilizer after the crop
Soil reaction or pH A measure of the acidity
or alkalinity of the soil. The pH is defined as the
negative logarithm of the hydronium ion concentra-
tion. A pH of 7 is neutral; above 7 is alkaline and
below 7 is acidic.
Source The kind or origin of the fertilizer
nutrients. For example, sources of nitrogen include
urea, ammonium nitrate, ammonium sulfate,
potassium nitrate, chicken manure, and sludge. The
source is sometimes important when deciding how
to supply plant nutrients to a vegetable crop.
Split application The required fertilizer amount
applied in two or more portions during the growth
Supplemental application Fertilizer (in addi-
tion to the fertilizer portion of the crop nutrient re-
quirements) applied to a crop during the growing
season. The use and number of supplemental applica-
tions depends largely on the intensity and duration
of rainfall and the length of the cropping season.
Suspension fertilizer A fluid mixture contain-
ing dissolved and undissolved nutrient materials and
inert materials often requiring continuous
Timing Coordination of the time periods dur-
ing the crop growth cycle when the fertilizer is to
be applied; for example, pre-plant, at-planting, etc.
Unit One percent (1%) of a ton, i.e. 20 pounds.
A term used by the fertilizer industry to refer to
amounts of fertilizer nutrients. Do not confuse "units
per ton" with "pounds per acre." Growers should
only be concerned with pounds per acre. Be sure that
the fertilizer material purchased can supply the
needed amounts of nutrients in pounds per acre.
Florida vegetables are produced successfully on a
wide array of soil types. For the purposes of simpli-
fying fertilizer recommendations, soils are placed in
three categories: mineral soils, organic soils, and
Irrigated mineral soils. This group includes
sands, sandy loams, and loamy sands, which require
a dependable moisture supply from rains and irriga-
tion (Figs. 2 and 3). Also included in this group for
fertilizer recommendations are the sandy muck soils.
Because of their sandy nature, the above soil types
require careful management of irrigation and fer-
tilizer programs to ensure maximum yields. The san-
dy mucks, because of their higher organic matter
content, require less nitrogen than other mineral
Calcareous soils. These soils are composed largely
of calcareous marine deposits and have a pH in the
range of 7.5 to 8.5. The high pH fixes many plant
nutrients in insoluble form, making special fertilizer
management practices necessary for these soils. Fer-
tilizer recommendations for the calcareous soils,
especially the marl and Rockdale of Dade County,
are lower than other mineral soils mainly because of
reduced plant growth on the high pH soil. The reduc-
ed plant growth results from a variety of reasons, in-
cluding the high fertilizer-fixing capacity of both soils
and the shallowness of the marl and Rockdale soil.
Also, these soils, occurring in southern Florida, are
used for winter vegetable production. The short days
and reduced sunlight intensity during winter also
contribute to reduced plant growth. Based on soil
particle size, calcareous soils can be divided into two
1. Marl soil. This calcareous soil consists of fine,
clay size particles of a narrow size range.
2. Rockdale soil. This calcareous soil is compos-
ed of particles of a very wide range in size. The
soil is very shallow and made of approximately
one-fourth rock (Fig. 4).
Organic soils. These soils include the peat and
muck soils, which are composed largely of organic
matter (Fig. 5). As these soils oxidize, large amounts
of nitrogen are provided to the crop. Therefore, ad-
ditional fertilizer nitrogen is not required except on
winter crops growing under cool conditions.
what amounts can be supplied from the soil. By us-
ing soil testing, the amount of fertilizer to add to sup-
plement the nutrient-supplying capacity of the soil
can be determined.
To receive the most benefit from soil testing,
carefully collect quality soil samples and have them
analyzed by a competent soil testing laboratory. Dif-
ferent laboratories use different methodologies to
Figure 4. Snapbeans growing in the Rockdale soils
of Dade County.
There are 16 elements (C, H, O, P, K, N, S, Ca, Fe,
Mg, B, Mn, Cu, Zn, Mo, Cl) required by for optimum
growth and yield. The soil itself can supply many of
these nutrients in abundance for crop growth. Soil
testing is used to determine which nutrients and in
'1 11' V .
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Figure 5. Radish production on muck soil in the
Belle Glade area of Palm Beach County.
Figure 3. Tomatoes growing on seep-irrigated soil in
analyze soil samples, and therefore not all
laboratories can provide the right fertilizer recom-
mendations for all situations. Be sure to choose a
laboratory that uses methods that were developed
to handle your type of soil, a laboratory that can pro-
vide fertilizer recommendations based on field
calibration research for your soil and production
system. For more information on soil testing and
laboratory selection, consult your extension office
for publications on this topic.
In general, the most suitable pH range for many
vegetables is 6.0 to 6.5. However, some vegetable
crops will tolerate slightly acidic soils (Table 1). Lim-
ing acid soils will avoid aluminum and manganese
toxicities. It is in the aforementioned pH range, on
mineral soils, that most fertilizer nutrients are in
greatest availability. There are cases where crop pro-
duction at less-than-optimum pH is unavoidable. An
example is the use of acid soils for potato scab con-
trol. Another example is the alkaline Rockdale and
marl soils of Dade County, where adjustments in
rates and placement must be made for that portion
of the fertilizer that is fixed by the soil.
Table 1. A general guideline to crop tolerance of
mineral soil acidity. 1
Slightly tolerant Moderately tolerant Very tolerant
(pH 6.8-6.0) (6.8-5.5) (6.8-5.0)
Beet Bean, snap Endive
Broccoli Bean, lima Potato
Cabbage Brussels sprout Shallot
Cauliflower Carrot Sweet potato
Celery Collard Watermelon
'From Knott's Handbook For Vegetable Growers, 2nd ed.
Table 2. Effect of some fertilizer materials on the
Fertilizer material equivalent (Ibs)1
Ammonium nitrate -1200
Ammonium sulfate -2200
Anhydrous ammonia 3000
Diammonium phosphate -1250 to -1550
Potassium chloride 0
Sodium-potassium nitrate +550
Nitrogen solutions 750 to -1800
Normal (ordinary) superphosphate 0
Potassium nitrate +520
Potassium sulfate 0
Potassium-magnesium sulfate 0
Triple (concentrated) superphosphate 0
'A minus sign indicates the number of pounds of calcium carbonate
needed to neutralize the acid formed when one ton of fertilizer
material is added to the soil.
Liming. On some newly cleared land, soil tests
have indicated that lime is required to achieve a
suitable pH. Raising the pH to 6.0 to 6.5 increases
the availability of most fertilizer nutrients on these
soils and also increases the activity of soil
microorganisms such as the nitrifying bacteria. On-
ly small amounts of lime are required to change the
pH of sandy soil. Therefore, use of a soil test will
guide the grower to correct liming and will reduce
the possibility of overliming.
Avoid overliming. This can be a problem in Florida
where routine limestone applications are made
without reference to soil testing and/or where
alkaline irrigation water is applied. Overliming can
lead to nutrient deficiencies, especially with
micronutrients, and it can reduce the accuracy of soil
testing programs and resulting fertilizer
Many fertilizer materials lower the soil pH when
added to the soil. The effect of some fertilizer
materials on the soil pH is shown in Table 2. The ap-
proximate calcium carbonate equivalent is a measure
of the acid-producing potential of the fertilizer. Fer-
tilizer applications should therefore be considered in
all good liming programs.
When adding lime, it is critical that it be thoroughly
incorporated in the soil throughout the plow zone.
The amount of lime to use is specified in the recom-
mendations by the Florida Extension Soil Testing
Laboratory in Gainesville. It is usually best to apply
the lime several months prior to planting; however,
if time is short, then it is better to apply the lime any
time before planting than to not apply it at all.
The most commonly used liming materials (Table
3) are calcite (CaCO3) and dolomite (CaCO,.MgCO,).
Dolomite is an excellent lime material having a
neutralizing value slightly higher than calcite (calcic
or "hi-cal" lime). Dolomite also supplies magnesium,
a nutrient often low in Florida soils. Fast-acting lim-
ing materials such as hydrated lime and burnt lime
are to be used with extreme caution since they can
cause severe crop damage if used in excess.
Alkaline soils. The most commonly used material
for reducing soil pH is elemental sulfur, which is ap-
plied like lime. Amounts needed are estimated by
methods similar to those for lime requirement. The
use of sulfur to reduce soil pH is practical only on
mineral soils that have been overlimed. This might
occur through the use of very alkaline irrigation
water. Soils normally high in pH, such as the marls
and Rockdale, cannot be economically changed. On
the latter soil types, increased rates of fertilizer and
band placement are more economical approaches to
combating the effect of the high pH.
Fertilizer sources and formulations. There are
many fertilizer sources of the various nutrients need-
ed by plants (Table 4). Some are more economical
than others. However, certain situations arise where
the cost of using more expensive materials might be
offset by the increased yield and crop value.
1. Nitrogen The most commonly used nitrogen
sources are ammonium nitrate and urea. On
most soils fumigated with a general purpose
fumigant, or for crops planted in cool soils, at
least 40 to 50 percent of the nitrogen applied
should be in the nitrate form, the preferred
form for plant uptake. Diammonium phosphate,
when banded with micronutrients, has been
shown to reduce certain micronutrient uptake
when high rates of phosphorus were needed
and the soils were low in micronutrients. Diam-
monium phosphate should be used cautiously
for only part of the nitrogen and phosphorus
supply if it is to be banded with micronutrients.
Table 3. Liming materials.
Material Formula value (%)
Calcium carbonate, calcite, CaCO3 100
Calcium-magnesium CaCO3.MgCO3 109
Calcium oxide, burnt lime CaO 179
Calcium hydroxide, hydrated Ca(OH)2 136
Calcium silicate, slag CaSiO3 86
Magnesium carbonate MgCO3 119
1The higher the neutralizing value, the greater the amount of acid-
ity that is neutralized per unit weight of material.
2. Phosphorus Normal (ordinary) super-
phosphate and triple (concentrated) super-
phosphate are excellent sources of phosphorus,
both contributing calcium as well. Normal
superphosphate also contributes sulfur and
3. Potassium Potassium chloride is the most
common source of potassium; however, its use
increases, over other sources of potassium, the
risk of soluble salt injury. On some crops, for
example Irish potatoes, about one-half of the
potassium should be replaced by potassium
nitrate, potassium sulfate, or potassium-magne-
sium sulfate, since potassium chloride might
reduce the tuber specific gravity.
Micronutrients. On most native soils brought in-
to production and on cropped soils showing low
micronutrient test values, a micronutrient fertilizer
is recommended. This fertilizer (depending on soil
test and crop) should contain, per acre, 3 to 6 pounds
of copper, 2 to 4 pounds of zinc, 6 to 12 pounds of
manganese and iron, and 1 to 2 pounds of boron sing-
ly or in combinations. The micronutrients can be sup-
plied as sulfates, oxides, chelates, or "frits."
Micronutrients are more thoroughly incorporated
in the fertilizer when the fertilizer material is
homogenized or liquid. One of the problems with dry
bulk blends is that the micronutrients, present in
such small quantities and particle sizes, tend to set-
tle out and are difficult to mix uniformly.
Table 4. Some commonly used fertilizer sources.
Nutrient Fertilizer source Nutrient content (%)
Nitrogen (N) Ammonium nitrate 34
Ammonium sulfate 21
Calcium nitrate 15.5
Diammonium phosphate 18
Potassium nitrate (nitrate of potash) 13
Sodium-potassium nitrate (nitrate of soda-potash) 15
Normal (ordinary) superphosphate
Triple (concentrated) superphosphate
Potassium chloride (muriate of potash)
Potassium sulfate (sulfate of potash)
Potassium-magnesium sulfate (sulfate of potash-magnesia)
Copper sulfate, monohydrate
Copper sulfate, pentahydrate
'Mention of a trade name does not imply a recommendation over similar materials.
Homogenized and liquid fertilizers are manufactured
in a manner that ensures uniform distribution of
nutrients in all granules.
The amounts of micronutrients in pesticides used
on crops should be considered when planning a
micronutrient fertilizer program. Micronutrients
from pesticides can accumulate in the soil from leaf
runoff and from decaying plant material. In many
production areas, micronutrients have built up in the
soil to levels such that no additional micronutrients
from fertilizers are needed.
As mentioned above, micronutrients can be pro-
duced in fritted form. Frits are made by mixing
micronutrients with molten glass, then cooling and
grinding. The micronutrients are, therefore, slowly
available to plants and are less likely to leach. This
form of micronutrient fertilizer is not widely avail-
able. If you want fritted micronutrients, be sure that
the fertilizer you are purchasing is actually fritted,
since mislabeling has been a problem in this area. For
more information on this, see Vegetarian 85-1, a
Vegetable Crops Department monthly newsletter.
For information regarding specific articles, consult
your local agricultural extension office.
Table 5. Average nutrient content of selected
Product N P206 K20
dry weight basis
Blood 13 2 1
Activated sewage 6 3 0.2
Fish meal 10 6 0
Bone meal 3 22 0
Cotton seed meal 6 3 1.5
Peanut meal 7 1.5 1.2
Soybean meal 7 1.2 1.5
dried commercial manure products
Stockyard 1 1 2
Cattle 2 3 3
Chicken 1.5 1.5 2
Hog 2 2 1
Organic fertilizers. Organic fertilizers, such as
manure, can be good fertilizers (Table 5). Not only
do they supply nutrients, but also they add organic
matter to the soil to increase its water-holding capaci-
ty and tilth if applied in large quantities. However,
for most situations, transportation cost reduces the
economic return from the use of organic fertilizers.
In addition, most organic sources cannot readily
supply enough of all nutrients so that, in most cases,
supplementing with "chemical" fertilizers is needed.
Slow release fertilizers. Several brands of slow-
release fertilizers are available for supplying
nitrogen. Research at Gainesville has shown in-
creases in yields of some vegetables when slow-
release fertilizers, such as sulfur-coated urea or
isobutylidene-diurea, were used to supply a portion
of the nitrogen requirement. Although more expen-
sive, these materials may be useful in reducing fer-
tilizer losses through leaching, in decreasing soluble
salt damage, and in supplying adequate fertilizer for
long-term crops such as strawberry or pepper.
Fertilizer movement in the soil. Nitrates,
chlorides, and sulfates move readily with the upward
or downward movement of water in the soil. These
salts can accumulate at the soil surface where water
evaporates or can be leached from the root zone by
heavy water application. On very sandy soils, potas-
sium, magnesium, and boron also may be subject to
leaching. Phosphorus, however, does not readily
move in most soils. Because of this, phosphorus fer-
tilizer needs to be placed in the root zone.
Soluble salts. Overfertilization or placement of
fertilizer too close to the seed or root leads to solu-
ble salt injury or "fertilizer burn" (Fig. 6). Fertilizer
sources differ in their capacity to cause soluble salt
injury (Table 6). Therefore, where history has shown
soluble salt problems, or where irrigation water is
Figure 6. Soluble salt injury from improper fertilizer
placement for cabbage near Immokalee in Collier
high in soluble salts, choose low-salt index fertilizer
sources for example, potassium sulfate instead of
potassium chloride and broadcast or split-apply the
Fertilizer placement (general). Fertilizer rate
and placement must be considered together. Placing
low amounts of fertilizer too close to plants can result
in the same amount of damage as placing excessive
amounts of fertilizer in the bed.
Because phosphorus movement in most soils is
minimal, it should be placed in the root zone. Ban-
ding is generally considered to provide more efficient
utilization of phosphrous by plants than broad-
casting. This is especially true on the high phos-
phorus-fixing calcareous soils. Where only small
amounts of fertilizer phosphorus are to be used, it
is best to band. However, in most other situations,
broadcasting and thorough incorporation in the bed
area prior to planting is satisfactory. If broadcasting
phosphorus, a small additional amount of starter
Table 6. Relative salt effects of fertilizer materials
on the soil solution.
Material Salt index'
Anhydrous ammonia 47
Ammonium nitrate 105
Ammonium nitrate-lime 61
Ammonium sulfate 69
Calcium carbonate 5
Calcium nitrate 53
Calcium sulfate 8
Diammonium phosphate 30
Monoammonium phosphate 34
Monocalcium phosphate 15
Nitrogen solution, 37% 78
Potassium chloride 116
Potassium nitrate 74
Potassium sulfate 46
Sodium chloride 154
Sodium nitrate 100
Potassium-magnesium sulfate 43
Normal superphosphate 8
Triple superphosphate 10
From Knott's Handbook for Vegetable Growers, 2nd ed.
'The term "salt index" is the salt effect of the material in relation
to sodium nitrate, which is given an index of 100. Materials with
high salt indexes must be used with great care to avoid plant injury.
Figure 7. Sidedress fertilizer applicators.
phosphrous near the seed or transplant may improve
early growth, especially in cool soils. For wide-row
crops such as watermelons, the modified broadcast
method provides more efficient use of fertilizer than
Micronutrients can be broadcast with the phos-
phorus and incorporated in the bed area. On the
calcareous soils, micronutrients, such as iron,
manganese, and boron, should be banded or applied
Since nitrogen, and to a lesser extent, potassium,
are mobile in our sandy soils, these nutrients must
be managed properly to maximize crop uptake.
Plastic mulch helps retain these nutrients in the soil.
Under non-mulched systems, split applications of
these nutrients must be used to reduce losses to
leaching (Fig. 7). Here, up to one-half of the nitrogen
and potassium may be applied to the soil at planting
or shortly after that time. The remaining fertilizer
is applied in one or two applications during the ear-
ly part of the growing season. Splitting the fertilizer
applications also will help reduce the potential for
soluble salt damage to the plants.
Another technique to reduce leaching losses is to
use the strip mulch method. In this case, incorporate
all phosphorus and micronutrients pre-plant along
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Figure 8. Liquid sidedress fertilizer applicators.
with approximately 20 percent of the nitrogen and
potassium. Place the remaining nitrogen and potas-
sium in a band in the bed 1 to 2 inches deep and cover
with a strip of polyethylene mulch. The mulch strip
(10 to 12 inches wide) is placed over the fertilizer
band in an inverted "U" fashion. The fertilizer place-
ment and mulch application can be mechanized.
Supplemental applications. The use of sup-
plemental fertilizer depends mainly on the amount
of rainfall and the length of the season. The need for
supplemental fertilizer will be minimized when the
soil-test-predicted fertilizer requirements are proper-
ly managed to reduce losses to leaching. In most
cases, nitrogen and potassium are of most concern
because of leaching, although sidedressing of
phosphorus might be needed on the phosphate-fixing
calcareous Rockdale, especially during cool periods.
If required, supplemental applications of nitrogen
and potassium should be made as a band or swath
just ahead of the advancing root system. Place the
fertilizer deep enough in the soil to be in contact with
moisture. In many cases, liquid fertilizers are easiest
to use and can be easily knifed into the soil (Fig. 8).
Sidedress applications must only be made when there
is no danger of shoot or root damage from the fer-
tilizer application machinery.
Fertilizer placement (mulched crops). When us-
ing plastic mulch, fertilizer placement depends on
the type of irrigation system (seep or overhead) and
on whether drip tubing or the liquid fertilizer injec-
tion wheel are to be used.
With overhead irrigation, all fertilizer can be in-
corporated in the bed before mulch application.
However, when high amounts of fertilizer are re-
quired, such as on virgin soil, a portion of the fer-
tilizer can be banded to reduce salt damage. The fer-
tilizer for crops grown on Rockdale soils can be band-
ed, although recent research has shown equal or bet-
ter yields by some crops with incorporation in the
With seep irrigation, all phosphorus and micro-
nutrients should be incorporated in the bed. Apply
10 to 20 percent (but not more) of the nitrogen and
potassium with the phosphorus. The remaining nitro-
gen and potassium should be placed in narrow bands
on the bed shoulders, the number of which depend
on the crop and number of rows per bed. These
bands should be placed in shallow (1- to 1/2inch deep)
grooves (Fig. 9). This placement requires that ade-
quate bed moisture be maintained so that capillari-
ty is not broken. Otherwise, fertilizer will not move
to the root zone.
However, excess moisture can result in fertilizer
leaching. Fertilizer and water management programs
are linked. Maximum fertilizer efficiency is achiev-
ed only with close attention to water management.
Under either system above, fertilizing with drip ir-
rigation or with a liquid fertilizer injection wheel
might be suitable alternatives to the placement of all
nitrogen and potassium in or on the bed prior to
Figure 9. Placement of nitrogen and potassium fer-
tilizer in bands in surface grooves for seep-irrigated,
full-bed mulched tomatoes in Collier County.
In cases where supplemental sidedressing of
mulched crops is needed, applications of liquid fer-
tilizer can be made through the mulch with a liquid
fertilizer injection wheel. This implement is mounted
on a tool bar and, using 30 to 40 psi pressure, injects
fertilizer through a hole pierced in the mulch.
Research is under way to determine the benefits of
using the wheel for supplying seasonal nitrogen and
potassium as well as for fertilizing used mulched beds
for double cropping.
For more details on fertilizer placement for specific
crops, consult the individual crop production guide.
These guides are available from county extension
Drip irrigation. The combination of mulch and
drip irrigation often provides an excellent yield-
boosting system (Figs. 10 and 11). The drip irrigation
method results in substantial water savings and can
be used to supply fertilizer. When fertilizing through
the drip, apply all phosphorus and micronutrients
and 20 to 40 percent of nitrogen and potassium pre-
plant. Use the lower rate where seep irrigation will
be used to provide a portion of the irrigation water
at the beginning of the season. Apply the remaining
nitrogen and potassium through the drip system in
increments corresponding to the growth of the crop.
For more information on drip irrigation, see Exten-
sion Circulars 606 and 607.
. & .
Figure 11. Filter system
and computer control for drip
Fertigation. Supplying fertilizer through overhead
irrigation systems may provide an economical
method of fertilizer application and increase the ef-
ficiency of the irrigation system. Fertigation is most
applicable to sandy soils that require small, but fre-
quent water applications. Fertigation of vegetables
is new, and there is very little data on rates and tim-
ing of fertilizer applications. In general, it is most
useful on crops with close row spacing, such as leafy
greens or corn, rather than on crops such as
watermelons. Fertilizer application of nitrogen or
potassium should coincide with the growth rate of
the crop. For more details, see Vegetarian 85-2, 4,
Starter fertilizer. A true starter fertilizer is a solu-
ble fertilizer, generally high in phosphorus, used to
help establish young seedlings and transplants.
Starter fertilizers generally work best if a small
amount of nitrogen and potassium is present along
with the phosphorus. Starters represent a very small
percentage of the overall fertilizer amount but are
very important in establishing crops in cool, damp
soils. They can be applied with the planter at 2 in-
ches to the side of the seed and 2 inches deep or can
Figure 10. Drip irrigation on tomatoes in Gadsden
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Figure 12. Applying soluble starter solution (from
tanks) as vegetables are transplanted.
be dissolved in the transplant water and applied in
the furrow (Fig. 12). For more information, see
Foliar applications. In general, foliar applications
of nitrogen, phosphorus, or potassium are not effec-
tive where a good soil fertility program is followed.
It is difficult to place enough of these nutrients on
the leaves, especially early in the growth cycle, to
be of benefit. Foliar applications of micronutrients
can be effective in correcting micronutrient deficien-
cies (Table 7). Nutrients such as calcium and boron,
which are immobile in the plant, should be applied
in small amounts at high frequency rather than in
one application for correcting temporary deficiencies
in some leafy vegetables.
Nutrient deficiency symptoms. Nutrient defi-
ciency symptoms are sometimes hard to identify
(Table 8). Usually a tissue analysis will help identify
the cause. Collect most recently-matured leaves,
wipe clean of dirt with a damp cloth, dry, and send
to the tissue-testing laboratory. When sampling, be
sure to include a tissue sample from a plant appear-
ing normal. Soil samples from around normal and ab-
normal plants might help diagnose the problem.
Table 7. Recommendations for foliar applications
of plant nutrients.
Nutrient Source (Ib product per acre)
Boron Borax 2 to 5
Soluborl 1 to 1.5
Copper Copper sulfate 2 to 5
Iron Ferrous sulfate 2 to 3
Chelated iron 0.75 to 1
Manganese Manganous sulfate 2 to 4
Molybdenum Sodium molybdate 0.25 to 0.50
Zinc Zinc sulfate 2 to 4
Chelated zinc 0.75 to 1
Calcium Calcium chloride 5 to 10
Calcium nitrate 5 to 10
Magnesium Magnesium sulfate 10 to 15
From Knott's Handbook For Vegetable Growers, 2nd ed.
1 Mention of a trade name does not imply a recommendation over
1. Anderson, D. L. 1985. Crop soil fertility recom-
mendations of the Everglades Soil Testing
Laboratory EREC-Belle Glade Mimeo.
2. Bottcher, D., and R. D. Rhue. 1984. Fertilizer
management-key to a sound water quality pro-
gram. Fla. Coop. Ext. publication Sp-28.
3. Hanlon, E. A. (editor). 1986. Proceedings of the
Florida Fertilizer and Lime Conference. Volume
16, p. 40.
4. Harrison, D. S. 1974. Injection of liquid fertilizer
materials into irrigation systems. Univ. Fla. Coop.
Ext. Bull. 2765.
5. Lorenz, O. A., and D. N. Maynard. 1980. Knott's
Handbook for Vegetable Growers, 2nd ed. Wiley-
Interscience, New York.
Table 8. Fertilizer nutrients required by plants.
Nutrient Deficiency symptoms Occurrence
Stems thin, erect, hard. Leaves small, yellow; on some
crops (tomatoes) undersides are reddish. Lower leaves
Stems thin and shortened. Leaves develop purple col-
or. Older leaves affected first. Plants stunted and
Older leaves develop gray or tan areas on leaf margins.
Eventually a scorch appears on the entire margin.
Growing tips die and leaves are distorted. Specific
diseases caused by boron deficiency include brown
curd and hollow stem of cauliflower, cracked stem of
celery, blackheart of beet, and internal browning of
Growing point growth restricted on shoots and roots.
Specific deficiencies include blossom-end rot of tomato,
pepper, and watermelon, brownheart of escarole, celery
blackheart, and cauliflower or cabbage tipburn.
Yellowing of leaves, stunting of plants. Onion bulbs are
soft with thin, pale scales.
Distinct yellow or white areas between veins on
Initially older leaves show yellowing between veins,
followed by yellowing of young leaves. Older leaves
Yellow mottled areas between veins on youngest
leaves, not as intense as iron deficiency.
Pale, distorted, narrow leaves with some interveinal
yellowing of older leaves, e.g. whiptail disease of
Small reddish spots on cotyledon leaves of beans; light
areas (white bud) of corn leaves.
General yellowing of younger leaves and reduced
Deficiencies very rare.
6. Rhue, R. D., and G. Kidder. 1984. Lime require-
ment test in Florida. Notes in Soil Science, No.
13. Fla. Coop. Ext. Service.
7. Rhue, R. D., and G. Kidder. 1983. Procedures us-
ed by the IFAS Extension Soil Testing Laboratory
and interpretation of results. Univ. of Fla. Coop.
Ext. Circ. 596.
8. Volk, G. M., and J. B. Sartain. 1980. Fertilizers and
fertilization. Univ. Fla. Coop. Ext. Bull. 183-C.
9. White, W. C., and D. N. Collins, eds. 1984. The Fer-
tilizer Handbook. The Fertilizer Institute,
On sandy soils especially after heavy rain, or after over-
irrigation. Also on organic soils during cool growing
On acid soils or very alkaline soils. Also when soils are
cool and wet.
On sandy soils following leaching rains or
On soils with pH above 6.8 or on sandy, leached soils,
or on crops with very high demand such as cole crops.
On strongly acid soils or soils where excessive
potassium has been applied, or during severe droughts.
On organic soils or occasional new mineral soils.
On soils with pH above 6.8.
On strongly acid soils or soils where excessive
potassium has been applied, or on leached sandy soils.
On soils with pH above 6.4.
On very acid soils.
On wet, cold soils in early spring or where excessive
phosphorus is present.
On very sandy soils, low in organic matter, especially
following continued use of sulfur-free fertilizers and
especially in areas that receive little atmospheric sulfur.
Usually only under laboratory conditions.
Graphic design and illustration by Katrina Haufler
Reprinted August 1990
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, John T.
Woeste, director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the
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