nium phosphate (MAP), and monopotassium phosphate. All sources can be
effective for plant nutrition. However, on soils that test very low in native micronutrient
levels, DAP in mixtures containing micronutrients reduces yields
when banded in large amounts. Initial soil reaction pH with DAP is about 8.5
which favors ammonia production and volatilization. This produced ammonia
causes seedling injury and inhibits root growth. Adequate separation of seed
and DAP is needed to eliminate any seedling damage. DAP should not be
used on calcareous or high pH soils. MAP’s reaction pH is 3.5 and doesn’t
have the above problems.
Potassium (K) can also be supplied from several sources, including potassium
chloride, potassium sulfate, potassium nitrate, and potassium-magnesium
sulfate. If soil-test-predicted amounts of K fertilizer are adhered to,
there should be no concern about the K source or its relative salt index.
CA, MG, S NUTRIENT RATES AND SOURCES
The secondary nutrients calcium (Ca), magnesium (Mg), and sulfur (S)
have not been a common problem in Florida. Calcium usually occurs in
adequate supply for most vegetables when the soil is limed. Since we don’t
have an interpretation for Mehlich-3 soil Ca yet, we still have Mehlich-1 soil
Ca interpretation. If the Mehlich-1 soil Ca index is above 300 ppm, it is unlikely
that there will be a response to added Ca. Maintaining correct moisture
levels in the soil by irrigation will aid in Ca supply to the roots. Calcium is
not mobile in the plant; therefore, foliar sprays of Ca are not likely to correct
point of the plant on a timely basis.
however, when the Mehlich-3 soil-test index for Mg is below 23 ppm, 30–40
Table 2.5. Target pH and Nitrogen (N) fertilization recommendations for selected vegetable crops in mineral soils of Florida.
Crops Target pH N (lb/acre)
Tomato, pepper, potato, celery, sweet corn, crisphead lettuce, endive, escarole, romaine lettuce and eggplant 6.0 (potato) and 6.5 200
Snapbean, lima bean, and pole bean 6.5 100
6.5 175
Radish and spinach 6.5 90
Cucumber, squash, pumpkin, muskmelon, leaf lettuce, sweet bulb onion, watermelon and strawberry 6.0 (watermelon) and 6.5 150
Southernpea, snowpea, English pea and sweetpotato 6.5 60
Kale, turnip, mustard, parsley, okra, bunching onion, leek and beet 6.5 120
Table 2.6. Mehlich-1 (double-acid) and Mehlich-3 interpretations for vegetable crops in Florida.
Mehlich-1 (double-acid) interpretations Mehlich-3 interpretations
Very low Low Medium High Very high Low Medium High
Nutrient (parts per million soil) (parts per million soil)
P <10 10–15 16–30 31–60 >60 <25 26–45 >45
K <20 20–35 36–60 61–125 >125 <35 36–60 >60
Mg1 <10 10–20 21–40 41–60 >60 <20 21–40 >40
Ca2 <100 100–200 201–300 301–400 >400
1 Up to 40 lbs/A may be needed when soil test results are medium or lower.
2 Ca levels are typically adequate when > 300 ppm.
Table 2.7. Phosphorus (P, expressed as P2O5) and potassium (K, expressed as K2O) fertigation recommendations for selected vegetable crops in mineral soils for Florida
based on low, medium, and high soil test index using MEHLICH 3 SOIL EXTRACTANT METHOD.
P2O5 K2O
Low Medium High Low Medium High
(lb/A/crop season) (lb/A/crop season)
Celery
150-200 100 0 150-250 100 0
Eggplant
130-160 100 0 130-160 100 0
onion, watermelon, pepper, sweet corn, crisphead lettuce, endive, escarole, strawberry, and romaine lettuce
120-150 100 0 120-150 100 0
Tomato
120-150 100 0 125-150 100 0
Cucumber, squash, pumpkin, snapbean, lima bean, pole bean, beet, radish, spinach, and sweetpotato
100-120 80 0 100-120 80 0
Bunching onion and leek
100-120 100 0 100-120 100 0
Potato
120 100 0 150 -- --
Southern pea, snowpea, and English pea
80 80 0 80 60 0
6 2019 Vegetable Production Handbook of Florida