lb Mg/A will satisfy the Mg CNR. If lime is also needed, Mg can be added
by using dolomite as the liming material. If no lime is needed, then the Mg
-
um-magnesium sulfate. Blending of the Mg source with other fertilizer(s) to
be applied to the soil is an excellent way of ensuring uniform application of
Mg to the soil.
corrected by using S-containing fertilizers such as magnesium sulfate,
ammonium sulfate, potassium sulfate, normal superphosphate, or potassium
magnesium sulfate. Using one of these materials in the fertilizer blends
MICRONUTRIENT SOURCES
It has been common in Florida vegetable production to routinely apply
these nutrients were inexpensive and their application appeared to be
insurance for high yields. In addition, there was little research data and a
lack of soil-test calibrations to guide judicious application of micronutrient
fertilizers. Compounding the problem has been the vegetable industry’s use
of micronutrient-containing pesticides for disease control.
Copper (Cu), manganese (Mn), and zinc (Zn) from pesticides have
tended to accumulate in the soil. This situation has forced some vegetable
producers to over-lime in an effort to reduce availability and avoid micronutrient
toxicities. Data have now been accumulated which permit a more
accurate assessment of micronutrient requirements (Table 10). Growers are
encouraged to have a calibrated micronutrient soil test conducted and to refrain
from “shotgun” micronutrient fertilizer applications. It is unlikely that micronutrient
fertilizers will be needed on old vegetable land, especially where
micronutrients are being applied regularly via recommended pesticides. A
micronutrient soil test every 2 to 3 years will provide recommendations for
micronutrient levels for crop production.
MANURES AND COMPOSTS
Waste organic products, including animal manures and composted organic
matter, contain nutrients for enhancing plant growth. These materials
applied to the soil decompose releasing nutrients for vegetable crops to
utilize. The application of these materials has to comply with food safety
requirements, such as Produce Safety Alliance (PSA). The key to proper
use of organic materials as fertilizers comes in the knowledge of the nutrient
content and the decomposition rate of the material. Growers contemplating
using organic materials as fertilizers should have an analysis of the material
before determining the rate of application. In the case of materials such
as sludges, it is important to have knowledge about the type of sludge
to be used. Certain classes of sludge are not appropriate for vegetable
production, and in fact, it is not permitted for land application in vegetable
production. Decomposition rates of organic materials are rapid in warm
sandy soils in Florida. Therefore, there will be relatively small amounts of
residual nutrients remaining for succeeding crops. Usually application rates
of organic wastes are determined largely by the N content. Organic waste
materials can contribute to groundwater or surface water pollution if applied
in rates in excess of the CNR for a particular crop. Therefore, it is important
to understand the nutrient content and the decomposition rate of the organic
waste material, and the P-holding capacity of the soil. For more information
about using manure for vegetable production, see “Using Composted
Poultry Manure (Litter) in Mulched Vegetable Production” at <https://edis.
.
As a soil amendment, compost improves soil physical, chemical, and
biological properties, thus making soil more productive. To eliminate or
minimize human and plant pathogens, nematodes, and weed seeds, the
composting temperature must be kept in a range from 131 and 170oF for 3
days in an in-vessel or static aerated pile. Nitrogen in compost is basically
organic. Thus, before being mineralized, compost N is not as readily
bioavailable as synthetic N fertilizers. Compost N mineralization rate varies
with feedstock, soil characteristics, and composting conditions. Compost N
On the contrary, compost P and K are as bioavailable as chemical fertilizers.
Composting converts raw organic materials to humus-stable forms and
hence minimizes possibly adverse impacts on the environment.
RIGHT PLACE
FERTILIZER PLACEMENT
Fertilizer rate and placement must be considered together. Banding low
amounts of fertilizer too close to plants can result in the same amount of
damage as broadcasting excessive amounts of fertilizer in the bed. Because
P movement in most soils is minimal, it should be placed in the root zone.
plants than broadcasting. This is especially true on the high P-immobilizing
calcareous soils. Where only small amounts of fertilizer P are to be used, it
is best to band. If broadcasting P, a small additional amount of starter P near
the seed or transplant may improve early growth, especially in cool soils.
Micronutrients can be broadcast with the P and incorporated in the bed
area. On the calcareous soils, micronutrients, such as Fe, Mn, and B, should
be banded or applied foliarly. Since N and, to a lesser extent, K are mobile
in sandy soils, they 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. Hence, up to one-half of the N and K 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 early part of the growing season. Split-appli-
as leaf scorch resulting from over-fertilization.
When using plastic mulch, fertilizer placement depends on the type of
irrigation system (seepage or drip) and on whether drip tubing or the liquid
fertilizer injection wheels are to be used. With seepage irrigation, all P and
micronutrients should be incorporated in the bed. Apply 10% to 20% (but not
more) of the N and K with the P. The remaining N and K should be placed
in narrow bands on the bed shoulders, the number of which depends on the
crop and number of rows per bed. These bands should be placed in shallow
(2- to 2 1/2-inch deep) grooves. This placement requires that adequate bed
moisture be maintained so that capillarity is not broken. Otherwise, fertilizer
will not move to the root zone. Excess moisture can result in fertilizer leaching.
Fertilizer and water management programs are linked. Maximum fertiliz-
In cases where supplemental sidedressing of mulched crops is needed,
applications of liquid fertilizer 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.
RIGHT TIME
SUPPLEMENTAL FERTILIZER APPLICATIONS AND BMPS
In practice, supplemental fertilizer applications when growing conditions
require doing so, allow vegetable growers to stay within BMP guidelines
while numerically applying fertilizer rates higher than the standard UF/IFAS
recommended rates. The two main growing conditions that may require
supplemental fertilizer applications are leaching rains and extended harvest
2019 Vegetable Production Handbook of Florida 7