Vergara - 1976 - Physiological and morphological adaptability of ri

RICE cRowni as DIFFERENT Eminomunstrs 445
transplanted seedlings. and limited use of nitrogen fertilizer. Since prior to
planting it is almost impossible to predict weather conditions throughout the
rice season. recommendations by government agencies are somewhat conservative
and intended to secure a stable, reasonable yield. rather than aimed at an
extremely‘ high yield when the weather condition happens to be favorable.
Destructive GOOl-\V€3ll'l¢f damage is failure of fertilization of spikeleLs
caused by a low temperature at a certain growth stage. An extremely low tempcrature
may occur any time during the rice season. Rice is most susceptible
to low temperature during spikclet differentiation and development. If a critical
low temperature hits the critical growth stage. the spikelets become sterile. This
type of damage cannot be compensated for even if weather conditions are
favorable afterward. There are varietal differences in susceptibility to this type
of damage. To avoid this type of damage, use of various varieties with different
growth durations is recommended to make sure that at least some varieties will
escape from a critically low temperature. It is also recommended that water in
the fields be kept deep enough so that the surface is above the developing pai1icleprimordia,
to protect them from critical low temperatures which generally’
occur at night.
In many riec-groyving areas tytphoons or floods often cause low grain yields.
The incidence of these climatic phenomena is unpredictable. The only way’ to
minimize damage from these hazards is to use shtirt-statured. lodging-resistant
varieties (against typhoons) or floating varieties (against floods).
Solar radiation is often a critical factor which controls grain yield in the
tropics. The fluctuation of solar radiation in a given season from year to year is
large. and the grain yield fluctuates accordingly‘. There is an interaction between
the optimum rate of nitrogen application or the optimum planting density‘ and
the amount of solar radiation. Thus. the decision on cultural methods becomes
complicated because of the fluctuation of solar radiation.
CONCLUSION
The relationship between the environmental condition and the rice yield is
complex. because yield is the overall result of the growth. A phenomenon which
occurs when the plant is at a certain growth stage may be magnified or
compensated for during the subsequent process. depending upon the environmental
condition. It may‘ have a beneficial effect on grain yield under some
circumstances. but may have an adverse effect under others.
The reason for this fundamental statement is that while significant infonnation
is obtained from experiments where precise artificial treatments are given
at certain growth stages under well controlled conditions. it is not sufficient to
demonstrate the relationship between an environmental factor which is represented
by the treatment and grain yield under practical farm conditions.
Agroectiltigical interpretation of the relationship between the environmental
condition arid growth may be qualitative. but is a useful tool in synthesizing into