Vergara - 1976 - Physiological and morphological adaptability of ri

430 cut-mm AND RICE
from one year to another at a given location causes a great difference in rice yield
in extremely high-latitude areas (Ishizuka et al.. 1973). On the other hand. in the
tropics temperature changes during the year are smaller. the effect of temperature
on rice growth is not prominent, and temperature variation from one year
to another docs not cause a great difference in grain _vield. An increase of temperature
to a critical point promotes various physiological processes. As the
degree of promotion differs among these processes. the effect of temperature on
growth is complicated. In areas where low temperatures are the limiting factors,
agronomic efforts are being made to increase the temperature in spring or
during spells of low temperatures at critical growth stages. These techniques are
veryf important in increasing and stabilizing the rice yield in such areas.
Solar radiation changes with location and season. The general pattern of
seasonal change at a given place is almost constant, although there are fluctuations
from year to year. In most rice-growing areas there are dry and rainy
seasons. and solar radiation is abundant and limited. respectively’. in these
seasons.
Precipitation changes from place to place and also from year to year in both
total amount and seasonal distribution. In many areas rice is grown only in the
rainy season, except for fields with irrigation facilities. There are also local.
seasonal. and annual changes in the frequency’ of strong winds. We have no
devices to modify these climatic phenomena. We can. hoyvever. adjust ricegrowing
seasons to avoid some hazards or to take advantage ofclimatic conditions,
and control floods and irrigation.
A quantitative description of the relationships between growth and individual
climatic factors during a given growth period can be accomplished by artificially
controlling the factors in question. Statistical quantitative analyses of growth.
grain y'ield. and climatic factors give insights into these relationships. Many
authors have developed their discussions in this symposium from such standpoints.
I intend to emphasize the complex relationship between grotvth and environment.
Individual components of the climatic environment change folloiving
seasonal sequences. with close interrelationships‘. the physiological significance
of these individual factors also interact; and the farmers practice at present
is the one established as an environment-\-'ariety'-cultural practice equilibrium.
For this reason. I am going to discuss the complex relationship from the agroecological
viewpoint. although it is qualitative rather than quantitative.
GROWTH
“(lro\\'th” has two aspects. i.e. dry-matter production (quantitative change) and
phasal development {qualitative change) during ontogenesis. Growth may be
considered as the increase of plant weight with age. We are interested in the
weight of grains produced. Thus. the quantitative aspect of growth is important.
IIou-‘ever. the growth curve of the rice plant cannot be expressed by a simple