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80 Belle Glade AREC iimeo Report EV-1972-6 July 1972
PLANTING AND THINNING SYSTEMS FOR Sh HIGH SUGAR RETENTION
SWEET CORN HYBRIDS IN EVERGLADES ORGANIC SOILS
V. L. Guzman, E. A. !'olf and 1'. U. Deen, Jr.-
A new experimental high sugar retention corn hybrid for fresh market,
developed at this Center, was tested in commercial plantings during the 1971-72
season. This hybrid, EES 279, contains the shrunken 2 (Sh2) endosperm which
differs from that in regular sweet corn. The shrunken factor causes the fresh
ear of this corn to maintain its good quality for long storage periods. Another
characteristic of Sh2 corn is low starch content in the endosperm resulting in
smaller, more wrinkled seed than regular sweet corn. This relatively low reserve
food supply in the seed hampers germination and makes it more difficult to obtain
a good stand, particularly in cool and/or excessively wet soils. Because it is
difficult to get consistent, high yields planting Sh2 seed to stand, studies were
initiated in the spring of 1972 to investigate methods to assure proper stands
and thus high yields with this type corn.
Working with lobelle and Gold Cup standard sweet corn hybrids, Guzman and
Kahl found that thinning by hand, after drilling the seed approximately 4 inches
apart, improved yields over the "planted to stand" treatment. Further, yield
increase was sufficient to overcome the cost of hand thinning. Since that time,
however, labor costs have increased sharply and, at times, help is difficult if
not impossible to find. OIviously, one method for increasing yield would be to
improve plant population by judicious use of av i le pre-gclalin 1-tM ig and
HUiME LIBRARY
thinning equipment.
SEP 11 1972
1/ Professors and Assoc. Professor respectively. University of Florica, IFAS,
Agricultural Research und Educantion Confter, [4y -C q fGt&Id S430.
inv fF~'d
For this work thinning was performed by a tractor mounted John Deere
synchronous electronic thinner which included an electric energy source, a
sensing probe and a hydraulically activated thinning knife (Figure 1). Contact
of the metallic probe with a plant completes an electric circuit which activates
a solenoid valve, directing hydraulic oil to the knife actuator. The knife is
positioned ahead of the probe to prevent removal of the plant being sensed. The
length of the knife determines the remaining space between plants, A delaying
action mechanism in the electric circuit prevents the knife from swinging again
until sufficient time has elapsed for the activation of the probe by the next
plant. It is a sophisticated machine which requires careful adjustment and opera-
tion to perform satisfactorily.
Experiment 1
In the first field germination test lobelle gave 86% germination and EES
279 76%. Vigor and uniformity were slightly superior for lobelle one week after
planting. Vigor one month after planting was equally good for both lobelle and
279. Conditions for growth were excellent during the test.
The data accumulated represent the mean of four replications of 30-foot
plots. The desired distance between plants was 8 inches or 45 plants per 30-foot
plot. In the first test, summarized in Table 1, thinning of the EES 279 plants
was performed with three different plant sizes. Plants 10 inches tall were
difficult to thin since the large leaves maintained prolonged contact with the
probe resulting in a continuous activation of the cutting knife. With 6-inch
tall plants thinning was appreciably improved, although the number of doubles
(plants closer than 2 inches) was high. With 2-inch tall plants, thinning was
slightly more effective than with the 6-inch plants, but the number of doubles
was still high because plants smaller than 2 inches failed to touch the sensing
probe. Failure to obtain 45 plants per 30-foot plot was partly because the
8-inch cutting knife was too long.
-3-
Table 1. Number of EES 279 corn plants in 30-foot plot in relation to plant size.
Plant height-inches
2 6 10
Before thinning 99 96 96
After thinning 48* 58 27
Doubles after thinning 7* 9* 4
Significant at 0.05 level.
Experiment 2
In the next test seeds were hand spaced in the row 1, 2 and 3 inches apart.
'Wen the plants were approximately 6 inches tall, thinning was performed using
a 6-inch cutting knife. The data presented in Table 2 indicates that the best
thinning was accomplished with the 3-inch spacing. It should be noted that
although the 40 and 50 plant stands are equally spaced from the desired 45 plant
stand, the 2-inch spacing resulted in more doubles.
Table 2. Number of EES 279 corn plants in 30-foot plot in relation to planting
distance.
Seed spacing-inches
1 2 3
Before thinning 192 153 99*
After thinning 62 50 40*
Doubles after thinning 16 6 3*
Significant at 0.05 level.
Experiment 3
In the following tests the corn was seeded using different planters. In
one test the Cole planter, with 42 and 32 pockets per plate, was used. Due to
heavy rains and poor drainage of the plot area, it was not possible to thin these
plants at the proper stage of growth. At thinning time the plants were over 10
inches tall and leaning slightly to one side due to wind damage. Under these
conditions thinning with the electronic thinner was far from satisfactory. It
was observed again that tall plants are almost impossible to thin properly and
that failures can occur when inclement weather delays thinning too long. A
comparison of plant spacing was made using a John Deere plateless seeder and an
International Harvester 400 cyclone seeder. The cyclone seeder was adjusted to
give a 2.5-inch seed spacing in the row at a 2 mph planting speed. The plateless
seeder was adjusted to give a 3.5-inch seed spacing at a 1.5 mph planting speed.
This was the closest distance permitted by this planter with the sprockets avail-
able. Thinning was performed at a 1.2 mph travel rate and a 1500 rpm tractor
engine speed. Table 3 gives the data for the 4 tests.
Table 3. Number of EES 279 corn plants in 30-foot plots planted with the plate-
less and cyclone planters and thinned with the John Deere electronic
thinner.
Plateless Cyclone
Before thinning 90 99*
Doubles before thinning 8 15*
Test 1
After thinning 38 40
Doubles after thinning 2.5 3
Test 2
After thinning 33 33
Doubles after thinning 2.5 2.6
Test 3
After thinning 32 34
Doubles after thinning 2.5 3
Test 4 1/
After thinning 42 41
Doubles after thinning 2.5 2.5
/ After adjusting delayed action mechanism.
Significant at 0.05 level.
For the intent of these tests, the plateless and the cyclone seeders are
excellent planters and no major differences were noted in the final stand of
EES 279 corn plants using either planter.
The John Deere electronic thinner, after proper adjustment, performed
satisfactorily. Certain precautions are imperative. The planting operation
should leave a flat or nearly flat surface as ridges and depressions interfere
with thinner performance. lWhen the planter leaves a shallow furrow (which it
usually does) rolling the ground is necessary to leave the ground level and
compacted. Shallow flat planting of the seed about 1 inch deep facilitates
emergence and improves uniformity but at the same time facilitates lodging if
the soil is not properly accumulated around the plants after thinning. Best
plant spacing for thinning appears to be 2 to 3 inches. Near perfect weed control
is very necessary since the sensing mechanism cannot distinguish between weeds
and corn plants. Four pounds per acre of Vegadex plus 2 pounds of Randox gave
the desired weed control. The corn plants should be no taller than 6 inches and
no less than 2 inches. Probe and knife height adjustment are critical. It is
necessary that the operator maintain the thinner in proper row alignment and
that he check frequently for malfunctions. His task is simplified if the
thinner is front mounted.
Acknowledgment
The authors would like to thank the Everglades Farm Equipment Company,
Belle Glade, for the loan of the tractors and plateless planters; the Glades
Equipment Company, Belle Glade, for the loan of the tractor and cyclone seeder;
and the S. N. Knight Farm for the loan of the electronic thinners without
whose help these studies would not have been possible.
EV-1972-6
450 Copies
SOLENOID \
ELECTRICAL
CONNECTION
TO
SOLENOID .
FIGURE
SCHEMATIC OF
KNIFE ON JOHN
THINNER
SENSING MECHANISM AND
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