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Abstract
The objectives of this investigation were to:
I) evaluate the effects of GA3 and CCC as seed-soaking treatments at
different rates and their interactions with N rate on growth, yield, and
grain N uptake of cv. Giza-2 com.
2) compare the effects of ethephon vs. Primo on vegetative growth, crop
quality, and distribution of total yield among organs of com plant shoot at
harvest.
3) determine optimum time and rate of application of ethephon and Primo to
minimize stalk lodging and to maximize yields of hybrid com.
4) study the agronomic and economic responses of com to different levels of
N, P, and K as a balanced fertilizing management.
5) evaluate the yield and economic responses of hybrid com to eight N rates
under unmanured and manured com conditions.
To accomplish the first objective, a 2-year (1988, 1989) field study
was conducted at the Agric. Res. Center. of Faculty of Agric., Moshtohor,
Zagazig University (Benha Branch). The soil of the experimental field was
clay textured with a pH of 7.97, had an organic matter of 2.3 %, and a total
N of 0.14 %. The experiment was laid out in a strip plot design with four
replications. The treatments were a factorial combination of five PGR
treatments and three N rates for a total of 15 treatments. Treatments of
PGRs were applied as seed-soaking solutions which were in 1988 and 1989
as follows: 1988 1989
1) Check (no-POR added) 1) Check (no-POR added)
2) GA3 at 150 ppm 2) GA3 at 75 ppm
89
3) GA3 at 300 ppm
4) CCC at 600 ppm
5) CCC at 1200 ppm
3) GA3 at 150 ppm
4) CCC at 300 ppm
5) CCC at 600 ppm
Results of this experiment can be summarized as follows:
1) Treatments of GA3 and CCC did not significantly affect plant height, ear
height, stem diameter, active leaves number, leaf area, days to mid-silk,
percentage of barren, and lodged plants in 1988 season. However, in
1989, the treatments significantly modified ear height, active leaves
number, and barren plants percentage.
2) In 1988, the highest level of 1200 ppm CCC significantly reduced the
number of harvested plants/fa by 6000 plants compared to the control.
However, the number of harvested plants/fa was not significantly affected
by PGR treatments in 1989.
3) Number of ears/plant significantly increased by increasing CCC
concentration from 600 to 1200 ppm in 1988, while the treatment of 150
ppm GA3 significantly had more ears/plant as compared to either CCC at
300 ppm or the control in the second season.
4) The treatment of 600 ppm-CCC significantly reduced number of
kernels/ear in comparison with all other treatments, and also reduced
weight of kernels/ear as comp.ared to 300 ppm of GA3 or 1200 ppm of
CCC in 1988. However, both parameters in 1989, and 100-kernel weight
in both seasons were not significantly changed by all PGR treatments.
5) The PGR treatments had no significant effects on grain yield, grain N
percent, and grain N uptake in both seasons, and stover yield estimated
only in 1989. Yet, there were slight increases in grain yield with 150
ppm-GA3 in 1988, and with GA3 and CCC applied at both rates of each
in 1989.
6) Changing levels of either GA3 or CCC did not significantly affect all
parameters measured in both seasons except for harvested plants/fa,
number of kernels/ear, and weight of kernels/ear with both CCC levels in
1988.
7) Increasing N rate from 70 to 130 kg/fa significantly increased both stem
diameter and active leaves number, but reduced percentage of barren
plants in same direction in 1989. Meanwhile, all other vegetative
parameters checked in both seasons were not changed by N rate
treatments.
8) Harvested plants/fa, number of ears/plant, number and weight of
kernels/ear, 100-kernel weight, and stover yield were not significantly
affected by N rate treatments in both seasons. However, ear and kernel
characteristics were slightly improved, and stover yield was increased
with the increase in N rate.
9) Grain yield, grain N percentage, and grain N uptake were significantly
increased as N rate increased from 70 to 100 kg Nzfa, but not from 100 to
.130 kg N/fa in 1989 only.
10) Except for plant height, and leaf area of prime ear measured in 1988, the
PGR by N rate interaction effects were not significant for all other
parameters studied in both seasons.
To achieve the second and the third objectives, a field experiment
was performed in 1992 at the Penn State University’s Farm, USA. Findings
of this experiment can be summarized as follows:
I. The PGR treatments meaningfully altered vegetative growth characters
of com plants.
a) Both plant height and stalk lodging were reduced.
b) The ethephon at 450 and 750 g/ha rates increased ear shank length at
VI0 stage. On the other hand, it was decreased with the Primo
treatments at 800 and 1200 g/ha at the same stage.
c) A 29 and 13% delay occurred in silking with using Primo at 800 and
1200 g/ha, respectively.
d) The Primo 400 g/ha applied at either V6 or VlO increased leaf area,
and leaf area index.
2. The Primo 400 g/ha at V6 increased grain yield by 7% as compared to that
of the control. However, at VIO; there was a 17% reduction in grain
yield by using 1200 g/ha of Primo.
3. Delaying the application time of ethephon and Primo from V6 stage to
VlO stage improved com quality.
4. Total shoot dry weight reflected the mode of action of both ethephon and
Primo as growth retardants. Moreover, the PGRs affected grain yield via
their impact on dry matter distribution among plant shoot organs.
5. Concentrations of total Nand N03-N were inversely proportional to dry
matter accumulation.
To fulfill the fourth objective, a 2-year field trial was carried out in
the same time and at the same field, previously mentioned, for GA3 and
CCC Experiment. The most important results are:
1. Effect of N rates
a) Plant height, stem diameter, number of leaves, and leaf area were
increased by increasing N rate from zero to 60 kg/fa.
b) Barren plants percentage as well as number of days to mid-silking
decreased with the 0 - 60 kg/fa N increment.
c) The 60 kg N/fa gave the greatest leaf area.
d) Lodged plants percentage was not affected by N rates.
e) Increasing N rate up to 60 kg N/fa increased grain yield, however;
it was not affected much as N rate increased from 60 to 120 kg N/fa.
f) Increasing N rate up to 120 kg N/fa increased grain N percentage.
g) Grain N uptake was increased with increasing N rate up to 60 kg N/fa,
and up to 90 kg N/fa in 1988 and 1989, respectively.
T
2. Effect of P20S rates
a) Forty kg of P20S/fa increased both leaf area and ear height than those
of the control.
b) There were no significant responses in yield, yield components, or
grain N uptake in 1988. In 1989, grain yield, grain N uptake, and
weight of kernels per ear were significantly higher at 40 kg P20S/fa
rate as compared to the control.
3. Effect of K20 rates
All measured parameters for vegetative growth, yield, yield components,
or grain N uptake did not significantly respond to the application of 40 kg
K20 vs. zero K20 in both seasons of study.
4. NPK interactions
Except for P x K interaction effect on kernel number per ear in 1989, and
N x P x K interaction effect on grain N content in 1988, there were no
significant effects observed in both years for other possible interactions
on all other estimated parameters.
Two field experiments were conducted during 1992 in Penn State,
USA to study the yield and economic response of com to eight N rates under
unmanured and manured soil conditions (the fifth objective). Four
randomized complete blocks were used for both experiments. The used N
rates were 0, 40,80, 120, 160,200,240, and 280 kg/ha for each experiment.
The most important results can be summarized as follows:
1. The application of 200 kg N/ha to unmanured com resulted III 66%
increase in com grain yield compared with that of the control. On the
other hand, grain yield of manured com was negatively affected by
applied N rates.
2. The quality of unmanured com was improved by applying inorganic N.
While; stover N03-N was, the only parameter among those measured for
crop quality, significantly increased by increasing N rate for manured
com.
3. Manuring com without inorganic N addition produced as much grains as
120 kg N/ha applied to unmanured com. This suggests that manuring
com can efficiently replace inorganic fertilizer N.
Economic analysis’
1. Economic optimum N fertilizer rates were 77,91, and 60 kg/fa for 1988,
1989, and 1992, respectively, and all were lower than that needed to
reach the yield plateau in each trial.
2. The difference between the economic optimum N rates and the maximum
used N rates were 43, 29, and 58 kg/fa in the same three years,
respectively. This result reflects the importance of supplying the
optimum N rate to minimize N loss and to maximize com profitability.
3. Every one kg N applied at the economic level contributed an average of
27.5 kg for 1988 and 1989, and 65 kg for 1992 of the total grain yield
production.
Conclusions
1. The effects of GA3, and CCC as seed-soaking treatments were almost
slight on vegetative growth and yield of com under conditions of this
study.
2. Ethephon, or Primo can be used as folliar applications for controlling stalk
lodging, improving ear characters, enhancing harvest index, or for
breeding targets. However, such PGRs must be applied at the optimum
time and proper rate to fully achieve these objectives.
3. The commonly used N rates for com (by farmers in Egypt) are considered
high not only from the agronomic standpoint but also from the economic
viewpoint. Therefore, economic studies for fertilizing com should be
established with using different genotypes, and variety of management
systems at other locations of’ com production in Egypt. These
suggestions would help in producing more grains, maximizing com
profitability, and limiting the harmful impact ofN03 on environment.