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Group Title: Research report - UF Agricultural Research and Education Center ; CF-75-4
Title: Soil placement of Rhizobium inoculum for soybeans
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Permanent Link: http://ufdc.ufl.edu/UF00075831/00001
 Material Information
Title: Soil placement of Rhizobium inoculum for soybeans
Series Title: Research report - UF Agricultural Research and Education Center ; CF-75-4
Physical Description: Book
Language: English
Creator: Scudder, W. T.
Publisher: Agricultural Research and Education Center, University of Florida
Publication Date: 1975
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Bibliographic ID: UF00075831
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 123072436

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HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida









AGRICULTURAL RESEARCH AND EDUCATION CENTER -
Sanford, Florida lj[]2,E HUBLIWY

Research Report CF-75-4 A2ril 1975
EFF 2 ]97ril
Soil Placement of Rhizobium Inoculum for Soybeans

W. T. Scudder.FA'S. L':'". o Fioridi
Professor (Horticulturist)

Under high temperature conditions in Florida, considerable difficulty
has been experienced in obtaining efficient nodulation of soybeans with
nitrogen-fixing bacteria. Experiments to find better inoculation methods
were begun in 1968 at the Agricultural Research and Education Center, a
unit of the University of Florida at Sanford. These studies indicate that
loss of vitality of the inoculum may be due to several adverse factors,
such as exposure to high temperatures occurring during handling of the
cultures before the inoculum reaches the field and while it is in the
planter hopper, and in the hot dry soil after planting.

In peninsular Florida, soybeans are a new crop. Until recently, good
short-day varieties in late group 7 and group 8 maturity classifications
were not available. Now, with varieties such as Bragg, Hardee, Cobb,
and Jupiter, soybeans can be planted in June and July with a reasonable
expectation of receiving good yields of 40 or more bushels per acre.
Several fields with acre yields between 50 and 60 bushels have been
harvested on farms as well as in experimental plantings during recent
years. To realize these yields, proper care of the crop is essential,
starting out with good inoculation with live nitrogen-fixing bacteria.

Most early attempts at growing soybeans on the light sand soils of
central Florida ended in failure, particularly on fields which had never
grown soybeans before. When conventional inoculation procedures were
used, including both seed and hopper-box treatments at planting time,
only a few scattered dark green well nodulated plants developed in the
field. This occurred even when double or triple the manufacturer's
recommended inoculum rate was used. As the season progressed, the
beneficial bacteria spread throughout the field to the other soybean plants,
but too late to aid this initial crop. When these same fields were planted
to soybeans the next and succeeding years, the plants usually nodulated
early and produced good crops.

It has been shown that the optimum temperature for the production of
nitrogen by the bacteria in the root nodules of soybeans is 75 degrees F.
The rate of nitrogen-fixation decreases rapidly above this temperature.






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A temperature of.122 degrees for only 30 minutes is lethal to the rhizobia.
S6il temperatures up to 108 degrees are not unusual at seed depth at soybean
planting time in Florida. The seed hopper often gets even hotter than this,
closely approaching the lethal temperature for the bacteria. If the weather
is hot and dry, these temperatures may persist for several hours, resulting
in complete inoculation failure when the culture bacteria are applied with
the seed.

To avoid the hazards encountered when the inoculum is applied with the
seed, our efforts have been directed toward application of the inoculum
directly to the soil, in either liquid or dry form. In the early studies, the
powdered inoculum was added to water and then applied either as a spray
followed by disking before planting, or as a high volume drench directly
over the rows after planting. Although both of these procedures resulted
in earlier and better nodulation, the use of peat-base inoculum in this
manner proved to be impractical. It did not disperse uniformly in the
liquid tank, would settle out during use, and would clog the equipment.

In recent years, liquid and granular Rhizobium formulations have
been made available by several legume inoculum producers. These
formulations are very ,;daptable to soil placement using equipment attached
to standard soybean planters. For our Florida studies, a special opening
shoe was constructed and mounted on the planter in front of the standard
seed-opening shoe. This attachment was made adjustable to permit
placement of inoculum at depths from one to two inches below the seed in
the row. To apply granular inoculum at levels beneath the seed, a granule
distributor with drop tubes leading to the special opening shoes was mounted
on the frame of the planter in front of the seed hopper. For placement in
the seed furrow at seed level, the distributor tubes were attached to the
rear of the seed-opening shoe. Many soybean planters are equipped with
granular insecticide distributors behind the seed hopper. When these are
present and not needed for an insecticide, they will function very well for
applying granular inoculum in the furrow with the seed.

For liquid formulations, the inoculum concentrate was diluted with water
and delivered to the soil using a tubing pump and plastic tubes leading to each
row. As with the delivery tubes from the granular distributors, these plastic
liquid-inoculum tubes were readily attached either to the deep-placement or to
the seed opening shoes, permitting liquid inoculum application at the desired
depth as was done with the granules.

Tests using this equipment during 1974 resulted in significantly improved
yields where soil placement was used in comparison with conventional inoculum
application along with the seed in the planter hopper. Table 1 shows the
response with two varieties, Bragg and Hardee, when used with the three
different formulations of inoculum. In all cases, the liquid and granular







-3-


inoculum, which was placed in the soil either at seed level or beneath it,
out-performed the powder inoculum which was applied along with the seed,
either on the seed or stirred into the hopper box. Table 2 shows a better
comparison for each of the placement methods. Whenever the Rhizobium
bacteria were placed directly in the soil, better plant color, root
nodulation, and yields were obtained. In this particular test, where rain-
fall was adequate and the soil remained relatively cool and moist during
the first few weeks after planting, there was no significant benefit from
placing the inoculum below seed level in the soil. Also, the granular and
liquid formulations performed equally well.


Table 1.- The Effect of Formulation of Inoculum on Plant Color, Root
Nodulation, and Yield of Bragg and Hardee Soybeans.


Formulation Plant Colorb Root Nodulationc Yieldd
of Inoculuma Bragg Hardee Bragg Hardee Bragg Hardee

None 1.5 b 2.0 b 4.0 b 3.2 b 24.2 c 33.4 c
Powder 3.6 b 3.6 b 3.5 b 3.8 b 34.2 b 45.0 bc
Granules 10.Oa 9.5a 10.Oa 9.Oa 43.4a 51.4ab
Liquid 9.4a 8.9a 10. Oa 9. Oa 40.7a 56. a

Treatment averages not followed by the same letter are significantly different
at odds of 19:1.
aAll data are averages of 4 replications and of all treatments within each of the
formulation groups.
Plant color ratings, recorded on August 13, 1974, are based on a 0 to 10 scale;
10=dark green.
CRoot nodulation ratings, August 13, 0 to 10 scale; 10=maximum nodule development.
dyield of seed in bushels per acre.



Apparently, most of the loss of vitality of the bacteria occurred when it was
placed on the seed or in the hopper-box due to exposure to hot dry conditions
before it reached the soil. The growth of the plants throughout the season, as
revealed by the measurements of plant color, plant height, and nodule counts on
the roots, showed the same contrasts due to inoculum type and placement.







-4-

Table 2.- The Effect of Placement of Inoculum on Plant Color, Root Nodulation,
and Yield of Bragg and Hardee Soybeans.

Placement Plant Colorb Root Nodulationc Yieldd
of Inoculuma Bragg Hardee Bragg Hardee Bragg Hardee

None 1.5 c 2.0 c 4.0 b 3.2 b 24.2 c 33.4 c
On Seed 4.0 b 3.9 b 4.2 b 3.9 b 37.4ab 47. 5ab
Stirred in Hopper 2.8 c 3.0 bc 2.0 b 3.8 b 27.9 bc 40.0 bc
In Row Over Seed 9.9a 9.4a 10. Oa 8.6a 42.9a 52.9a
1 Inch Below Seed 9. 6a 9. Oa 10. Oa 9. la 41. 5a 50. 6a
2 Inch Below Seed 9. 6a 9. 2a 10. Oa 9. 3a 41. 9a 58. Oa

Treatment averages not followed by the same letter are significantly different
at odds of 19:1.
aAll data are averages of 4 replications and of all treatments within each of
the placement groups.
Plant color ratings, recorded on August 13, 1974, are based on a 0 to 10
scale; 10=dark green.
cRoot nodulation ratings, August 13, 0 to 10 scale; 10=maximum nodule
development.
dyield of seed in bushels per acre.



This test also included a study of inoculation rate with each of the methods
of inoculum placements. The results of this are summarized in Table 3. In
all cases where soil placement was used, increasing the rate of application
failed to improve nodulation or yields. Doubling the manufacturer's
recommended rate proved to have no effect onthe efficiency of the inoculation.

Studies on inoculation methods to improve the nodulation of soybeans
with nitrogen-fixing bacteria and thereby increase the yields of soybeans
grown on the warm sub-tropical soils of central Florida are being continued
during 1975. It is essential that living Rhizobium bacteria be delivered into
soil that remains moist and cool until the soybean plants become established.
If this is done, good early-season nodulation is possible even on new land
which has never grown soybeans before. In our Florida tests, direct soil
placement at seed depth or below proved to be superior to methods of applying
the inoculum through the seed hopper. This can easily be accomplished by
the farmer using the new Rhizobium bacteria formulations available. Both
granular and frozen liquid inoculum will be available to the grower from
several sources during 1975.








-5-


Table 3.- The Effect of Rate Inoculum on Plant Color, Root Nodulation,
and Yield of Bragg and Hardee Soybeans.

Rate of Plant Colorb Root Nodulationc Yieldd
Inoculum Bragg Hardee Bragg Hardee Bragg Hardee

None 1.5 b 2.0 b 4.0 b 3.2 b 24.2 b 33.4 b
SX 7.4a 7. la 7.6a 6.9a 37.7a 52. la
2X 7.9a 7.6a 8. la 7.7a 41.3a 49.2a


Treatment averages not followed by the same letter are significantly different
at odds of 19:1.
Inoculum rates were as follows: 1 X = manufacturer's recommended rate;
2 X = double the recommended rate. All data are averages of 4 replications
and of all treatments within each of the rate groups.
plant color ratings, recorded on August 13, 1974, are based on a 0 to 10
scale; 10=dark green.
CRoot nodulation ratings, August 13, 0 to 10 scale; 10=maximum nodule
development.
dyield of seed in bushels per acre.




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