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-" I)6 Gulf Coast Research and Education Center
IFAS, University of Florida
5007- 60tHifStree t-Eas t._
Bradenton,a F.jrida !'4203i7

Bradenton GCREC Research Report BRA1984- D December 1984

CORRELATION BETWEEN-ALUMINUM. COUTEIT;
OF MEDIA AND TOMATO SEEDLING DEVELOPMENT

S. S. Woltz

Transplant production in various media (natural and synthetic) depends
on the physical and chemical qualities of the media. Among the important
chemical features are pH and aluminum content. High aluminum levels in
combination with low p1H's frequently cause problems in plant growth that
are more severe than either factor alone. Tomato foliage samples from
transplant operations as well as grower's fields have shown occasional
high aluminum levels, indicating a possible problem. Aluminum may at times
be a growth-limiting factor in transplants and field operations. This
possibility was investigated with young Red Cherry and Walter tomato seedlings
grown in 11 media variants in the greenhouse. Tomatoes were seeded, 8
seeds per 4-inch pot, into a variety of soil media (Table 1). A complete
nutrient solution (200 ppm N) was applied each Monday, Wednesday, and Friday
at the rate of 50 ml per pot for the two-week period. Seedling heights
were measured after 18 days, and root development and phosphorus deficiency
symptoms were noted at that time.

The data on aluminum extractable from 11 media (Table 1) indicate that
4 of the 11 may cause aluminum problems, namely unlimed Canadian and Florida
peats and unlimed Myakka topsoil and subsoil. Serious growth depression
occurred with unlimed peats and unlimed subsoil. These treatments had
symptoms of acute aluminum toxicity as shown by severely stunted root systems
and symptoms of phosphorus deficiency in the leaves.

Tomato plants are sensitive to soil aluminum content under acid conditions.
If the soil (medium) is well-limed, the effect of aluminum is generally
negligible except when large amounts of chlorides are present. Then the
aluminum may be activated, possibly resulting in phytotoxicity. Chlorides
form soluble complexes with aluminum which are active in entering plant
roots even in the presence of phosphate and hydroxide ions which usually
inactivate aluminum. If the pH is raised from native levels of 4.0 to
5.0 up to pH 5.5, the aluminum activity declines markedly. Phosphate reduces
aluminum activity by precipitating alumino-phosphate compounds. Cations
present (calcium, magnesium, potassium, and minor elements) also reduce
aluminum toxicity, with calcium being the most effective. Aluminum, when
present in excess of 3 ppm in the soil solution severely restricts root
growth. These very damaging effects most likely are caused by the substitution
of aluminum for calcium in the developing root, which prevents root elongation.
Also, aluminum causes acute phosphorus deficiency by the formation and
precipitation of insoluble forms of phosphorus.

Table 1. Media pH's, aluminum extractable with two reagenct and seedling

height of two tomato cultivars grown on the media, 18 days from seeding.

Soil
Mdcia

Aluminum
... mg/L media_
Soil extractants

oH Double acid 1 M KC1

Canadian peat

Canadian peat L*

Florida peat

Florida peat L

Myakka topsoil

Myakka topsoil L

Myakka subsoil

Myakka subsoil L

Perlite

Sand

Vermiculite

LSD, 5%

3.9

6.7

3.6

5.8

4.3

7.3

4.0

5.7

6.4

8.1

6.2

25

16

112

40

25

18

518

282

7

18

20

18

1

70

3

4

0.1

44

2

0.1

0.3

1.2

Varieties
Seedling height

Red Cherry Walter
mm mm

10 7

140 40

19 9

171 87

119 87

125 89

41 32

77 50

51 38

70 57

98 68

15 12

*L = Limed

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