Southeastern U.S. Vegetable Crop Handbook - 2021 - 18

Potassium Management. Crops are very likely to respond to K
fertilizer when the soil test indicates that K is deficient-very low
or low. A soil testing deficient-medium in K may or may not respond
to K fertilizer. Crops are more responsive to K when growing
under drought stress than when growing under favorable conditions.
Soils testing optimum or exceeds crop needs are unlikely to
respond to K fertilizer, but K may be applied to maintain the soil
fertility level in the optimum range.
In general, most of the K fertilizer should be broadcast. When
the fertility level is deficient, it may be advantageous to apply a
portion of the total K application as a band. There is generally no
benefit to applying banded K when soil fertility levels are optimum
or exceeds crop needs. Crops remove larger amounts of K than
P from the soil during a growing season. In addition, sandy soils
have low reserves of K, and K is susceptible to leaching. Therefore,
frequent applications of K are needed to maintain K at an optimum
fertility level.
Secondary Nutrients. Calcium (Ca), magnesium (Mg), and sulfur
(S) are included in the secondary element group. Calcium
may be deficient in some soils that have not been properly limed,
where excessive potash fertilizer has been used, and/or where
crops are subjected to drought stress. Magnesium is the most likely
of these elements to be deficient in vegetable soils. Dolomitic
or high-magnesium limestones should be used when liming soils
that are low in magnesium. Magnesium should be applied as a
fertilizer source on low-magnesium soils where lime is not needed
(Table 4). Magnesium may be applied as a foliar spray to supply
mag nesium to the crop in emergency situations (2 TBSP of Epsom
salts per gallon of water).
Sulfur is known to be deficient in vegetable crop soils in
coastal plain soils. Sulfur deficiency is often mistaken for lack of
nitrogen because the symptoms are similar. Onions are one crop
that will need additional sulfur over what vegetables normally require,
particularly on coastal plain soils.
Micronutrients. Boron is the most widely deficient micronutrient
in vegetable crop soils. Deficiencies of this element are most likely
to occur in the following crops: asparagus, most bulb and root
crops, cole crops, and tomatoes. Excessive amounts of boron can
be toxic to plant growth. This problem can occur when snap beans
(a sensitive crop) follow sweetpotatoes (a crop where boron is applied
late in the season). Do NOT exceed recommendations listed
in Table 2.
Manganese deficiency often occurs in plants growing on soils
that have been overlimed. In this case, broadcast 20 to 30 pounds
or band 4 to 8 pounds of manganese sulfate to correct this. Do
not apply lime or poultry manure to such soils until the pH has
dropped below 6.5, and be careful not to overlime again.
Molybdenum deficiency of cauliflower (which causes whiptail)
may develop when this crop is grown on soils more acid than
pH 5.5. An application of 0.5 to 1 pound of sodium or ammonium
molybdate per acre will usually correct this. Liming acid soils to a
pH of 6.0 to 6.5 will usually prevent the development of molybdenum
deficiencies in vegetable crops.
Deficiencies of other micronutrients in vegetable crops in the
Southeast are rare; and when present, are usually caused by overliming
or other poor soil management practices. Contact Exten18
2021
Vegetable Crop Handbook for Southeastern United States
sion if a deficiency of zinc, iron, copper, or chlorine is suspected.
Sources of fertilizers for the essential plant nutrients are found in
in Tables 3A and 4.
Municipal Biosoilds. Biosolids Should Not Be Applied to Land
on Which Crops Will Be Grown That Will Be Entering the Human
Food Chain. Municipal biosolids are the solid material removed
from sewage in treatment processes. Biosolids treated by
one of the digestive or similar processes to reduce pathogens is a
low-analysis fertil izer suitable for application to nonfood crops
under specific soil conditions. It should not be applied to sloping
land, to highly leachable soils, to poorly drained soils, to soils with
high water tables or near surface water, or to soils having a pH less
than 6.2. Check with your local or state department of environmental
management for latest regulations. The time required to wait
prior to planting a food crop varies from state to state.
Foliar Fertilization. Foliar feeding of vegetables is usually not
needed. Plants usually obtain their nutrients from the soil through
their roots. It is known that plants can also absorb a limited amount
of some nutrients through aerial organs such as leaves. Properly
managed soils will supply the essential mineral nutrients the crop
will need during its development. If, for some reason, one or more
soil-supplied nutrients becomes limiting or unavailable during the
development of the crop, foliar nutrient applications may then be
advantageous but likely only with the micronutrients.
Southeastern U.S. Vegetable Crop Handbook - 2021

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