Group Title: Mimeo report - University of Florida Everglades Experiment Station ; 58- 16
Title: Testing organic soils
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 Material Information
Title: Testing organic soils
Series Title: Everglades Station Mimeo Report
Physical Description: 4 leaves : ; 29 cm.
Language: English
Creator: Ray, Howard E ( Howard Eugene ), 1926-
Everglades Experiment Station
Publisher: Everglades Experiment Station
Place of Publication: Belle Glade Fla
Publication Date: 1958
Subject: Humus -- Florida   ( lcsh )
Genre: non-fiction   ( marcgt )
Statement of Responsibility: Howard E. Ray.
General Note: "June 20, 1958."
General Note: Caption title.
 Record Information
Bibliographic ID: UF00067566
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 65429016

Full Text

Everglades Station Mimeo Report 58-16


Howard E. Ray**

Four factors are essential to a worthwhile soil testing program. First,
acceptable soil sampling procedures must be worked out. This is a large subject
in itself and will not be discussed further at the present time. Second,
analytical procedures must be developed which will afford rapid and reasonably
accurate means for determining the amounts of plant-available nutrients in a soi7,
Results obtained from such procedures are relative, not absolute, and the numeri-
cal values obtained are important only on a relative basis. Third, using the
procedures that have been developed, minimum or "threshold" soil levels of a
given nutrient required for optimum production must be determined for each crop.
Such information must be obtained experimentally. Fourth, means for calculating
the amount of a nutrient that must be supplied through fertilizer to raise the
soil to any desired fertility level must be determined.

Under Everglades conditions, the problem of developing a useful soil test
is somewhat simplified by the fact that the soils are all highly organic, and of
more or less the same general type. They range in organic matter content from
about 40 to 90 percent, contain as much as 3 percent nitrogen expressed on a dry
weight basis, and furnish adequate amounts of nitrogen for optimum crop produc-
tion in many instances. Due to the limestone underlying the area, these soils
are not highly acid, and are well supplied with calcium and magnesium. Otherwise,
however, they are quite low in mineral content. Phosphorus, potassium, copper,
manganese, zinc, and boron must commonly be supplied through fertilizer to permit
successful crop production.

Methods presently used in the soil testing laboratory at the Everglades
Experiment Station have evolved principally through the work of Dr. W. T. Forsee,
now Chemist in Charge. Soil acidity is measured by means of a glass electrode
pH meter using a 1:2 soil-water ratio (volume basis). Phosphorus is determined
by standard colorimetric procedures on a water extract, and potassium is
determined on a 0.5 N acetic acid extract by means of a flame photometer
(Beckman DU). All samples are measured rather than weighed. Not only does this
increase the rapidity of the procedure, but it is believed to be more satisfactory
for organic soils in the Everglades where bulk density changes as time progresses.
Calcium and magnesium are not routinely determined as these elements are almost
invariably present in adequate amounts. Results are reported in terms of pounds
of elemental phosphorus or potassium per acre.

Needs for phosphorus and potassium on organic soils, together with pH
relationships, have been investigated extensively by Forsee to correlate soil
test results with crop requirements. In this connection, experiments have been
conducted on Everglades organic soils with celery, potatoes, beans, cabbage,
head lettuce, escarole, endive, sweet corn, grasses, and fiber crops. As a
result of these investigations, minimum levels of phosphorus and potassium in
the soil which are necessary for satisfactory production have been worked out
for a number of the crops grown in this area. These levels are&summarized in
Table 1.

Presented at Southern Soil Test Work Group Meeting. Gainesville, Florida,
June 19, 1958.
** Assistant Soils Chemist r :
i;. ''"^ <"'":i .(1 1 ..* ",*
..^j ,;: ,'-"

June 20, 1958


Table 1. Minimum phosphorus and potassium soil test values required for
satisfactory production of some crops grown on organic soils in
the Everglades.

Crop P K
Lbs/A Lbs/A

Celery 30 300
Potatoes 12-15 150
Sweet Corn 8-10 150
Lettuce 8-10 120
B. E. Peas 8 120
Cabbage 8-10 86-100
Snap Beans 6-7 75-100
Pasture 4-6 75-80

A summary of results of 200 samples of virgin soil and 4000 samples of
crop soils (not including pastures) analyzed in the soil testing laboratory
during the past five years indicates that approximately two-thirds of the virgin
soils contain too little phosphorus for satisfactory production of most vegetable
crops. As can be seen in Table 2, the average phosphorus content tends to in-
crease somewhat on cultivated land.

Table 2. Levels of water-extractable phosphorus in the organic soils of
the Everglades*.

Water-extractable P Percent of total samples
Lbs/A Virgin Cropped

0.4 18.8 18.6
5-6 16.4 11.4
7-10 31.3 18.3
11-20 25.0 30.1
21-30 6.5 13.1
S30 2.0 8.5

Summary of analyses of 200 samples from virgin, and 4000 samples
from cropped, organic soils analyzed by soil testing laboratory,
Everglades Experiment Station, 1953-57.

On the basis of the summary mentioned above, more than 80 percent of the
virgin soils contain insufficient potassium for satisfactory production of any
commonly grown field or vegetable crop (Table 3). On land that has been cropped
for a number of years, however, only 40 percent of the soils are deficient in
potassium for such crops as pasture, beans, and cabbage.

Table 3.

Levels of 0.5N acetic acid-extractable potassium in the organic
soils of the Everglades*.

HAc-extractable K Percent of total samples
Lbs/A Virgin Cropped
0-40 41.5 14.6
41-80 41.6 24.6
81-120 3.9 21.6
121-160 1.5 14.6
161-300 4.5 9.5
> 300 4.o 5.1

Summary of analyses of 200 samples from virgin, and 4000. samples
from cropped, organic soils analyzed by soil testing laboratory,
Everglades Experiment Station, 1953-57.

The last factor involved in a soil testing program is the fertilizer
recommendation. It has been found experimentally that for organic soils in the
Everglades approximately 20 pounds P205 per acre must be applied in fertilizer
for each pound of phosphorus that a soil is below the necessary minimum accord-
ing to the soil test. Similarly, two pounds K20 per acre must be applied for
each pound that a soil is deficient in potassium. There are, of course, many
factors to consider in arriving at a fertilizer recommendation, but the basic
recommendations for phosphorus and potassium are worked out on the basis of the
minimum values previously discussed, and the above factors for converting soil
test results into fertilizer needs.
Acidity is a little more difficult to interpret quantitatively than phos-
phorus and potassium levels. As shown in Table 4, nearly 90 percent of the
organic soils in the Everglades range in pH between 5.1 and 6.6. Limestone is
not recommended on such soils. Conversely, minor element deficiencies often
appear when the soil pH is above 6, so sulfur for lowering the pH is often
applied in much the same manner that lime would be used in other areas.

Table 4. Acidity levels in the organic soils of the Everglades*.

Percent of total samples
H .irgin Cropped

5.0 or below 5.0 5.4
5.1 5.6 22.0 25.1
5.7 6.0 26.2 35.0
6.1 6.6 39.8 26.2
6.7 or above 7.0 8.3

Summary of analyses of 200 samples from virgin, and 000 samples
from cropped, organic soils analyzed by soil testing laboratory,
Everglades Experiment Station, 1953-57,

No determinations for nitrogen or minor elements are made on routine
samples. Levels of available nitrogen change so rapidly that a soil test would
be of little value in arriving at a fertilizer recommendation. Results obtained
from minor element determinations would also be of doubtful value as no corre-
lation data are available to aid in interpretation. Recommendations for these
elements are made on the basis of past experience and land history.

Correlation work with soil testing is never completed. New varieties and
types of crops, new farming practices, and aging agricultural soils result in
a constantly changing picture of soil fertility. Thus, minimum values of
phosphorus and potassium must be adjusted from time to time, and methods for
arriving at fertilizer recommendations must be constantly re-examined.

EES 58-16
200 copies

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