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Two rates of N (80 and 160 kgsjha) were
used and each variety was replicated twice at
each fertility level for each planting date.
Rate
of planting was 44,000 plants per hectare.
Days-to-flower, ear height, and grain-tostover
ratios were measured on ten competitive
plants in each. plot, as indicators of the response
to changes in daylength.
Ear height and grain-to-stover grain-ta-stover ratios give
some indication of relative vegetative growth
under varying photoperiods. The grain-tostover
ratio is a measure of plant efficiency
which may be useful as an indicator of stability
under changing daylengths.
In general, for the trait days-to-flower, the
trend was toward a longer period as daylength
(at planting) became shorter. This does not
agree with the premise that maize is a shortday
plant. However, the maximum difference
in daylength at the different planting dates was
2 hours, 31 minutes. Also, the maximum daylength
was 13 hours, 12 minutes, which is still
a photoperiodically short day for maize.
It appears that at these intermedi3.te intermedi"lte daylengths,
some other environmental factor exerted
an effect strong enough to override the
effect of small changes in daylength (possibly
temperature). The importance of interactions
between photoperiod and temperature in controlling
flowering
in maize have been emphasized
by several
investigators.
With respect to ear height there was no
clear effect of photoperiod. It was not possible
to pinpoint a direct relationship between
photoperiod at planting or temperatures following
planting, and yield of grair per plant.
However, in general, the longer tHe time from
planting to flowering, the greater the plant
height, and the greater the grain weight per
plant.
The grain-to-stover ratio, although useful
as a measure of plant efficiency, integrates
many of the responses of a plant to its environment.
It is obvious that this ratio was
not a very meaningful
indication of response
to photoperiod in this particular experiment.
Taller and later varieties, high in grain production,
did not show high grain-to-stover
ratios. On the other hand, the shorter, early
varieties, lower in grain production, showed a
high ratio. Different relationships could exist
at higher population
levels.
An experiment to follow up these earlier
findings on days-to~flower,
using artificial illumination
to extend
daylength, was planted at
EI Batan Experiment Station, in 1970.
Twentynine
varieties, including the 17 varieties in the
Photoperiod experiment using uSing artificial lights to
extend daylength.
Two rows of a variety of Zapa­
lote rote chico are shown. Note plastic, lower right.
previous experiment, were planted in rows
perpendicular to the light source.
Dissections
were made of the developing tassel on single
plants of each row at distances of 5 to 7
meters, 14 to 16 meters, and 44 to 46 meters
from the light source. Indications were that
development of the tassel was delayed in those
plants under long days (close to the lights), as
compared to plants under natural short-day
conditions.
Immediately after emergence, a clear plastic
sheet, with holes for growth of the plants was
placed on the soil surface along the length of
one row of each variety as a means of increasing
the minimum night soil temperature. Vegetative
growth of all entries in the rows with
plastic was greater than in the rows without
plastic. The dissections showed that tassel
development was hastened by this treatment,
also.
Temperature changes are obviously involved
in the effects of altitude on the daysto-flowering
of a maize variety. These experiments
suggest that temperature may be
as important as photoperiod when latitude
changes are involved. Production of a variety
of maize possessing the degree of temperature
insensitivy (in terms of its effect on
time to flowering) necessary for wide adaptation,
may be neither possible possibl~
nor desirable.
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