Vergara - 1976 - Physiological and morphological adaptability of ri

4 CLINIATE mo) RICE
agricultural and related sciences. as much as on his own increased experience of
techniques and management.
Of all the factors which affect agricultural productivity. the most powerful.
and at thc same time least modifiable. is the climate. or its principal components.
temperature and rainfall. Rainfall can. of course. be supplemented or replaced
by irrigation where suitable ivater is available. but even the rice crop. the traditional
ccreal of irrigation agriculture. is grown on large areas under rainfcd conditions.
Temperature control is a great deal more costly‘. hence restricted to the
cultivation of high-cost horticultural products.
On a world scale. temperature presents the most general, and the least tractable,
restriction on productivity’. although this is less marked in the tropics.
ln general terms. productivity‘ is correlated xivith temperature; subject to the
availability of an adequate moisture supply. Most climates are punctuated by
temperature peaks and troughs. Their incidence and duration. and the relationship
to moisture supply. condition the productivity of a region. Temperature
in tinze is thus the predominant environmental parameter determining growth".
and where thc moisture supply" is irregular. as in a monsoon climate. growing
seasons may be further attenuated.
Cropping seasons, since time imrnemonal, have evolved to fit into the prevailing
climate pattern. To raise the efficiency of the system means to utilize to the
maximum the available time, and, within its limits, the investment in fertilizers,
cultivation, improved seeds, irrigation. weed control. and plant protection. all
of which are components of the essential intensification of crop production.
Thus temperature, and in some important instances temperature in interaction
with the length of daylight, is the main controlling factor which determines
whether any or all of these investments will be profitable. Hence the desire to
understand in precise and predictable terms the effects of temperature and day
length on the development of crop plants. on their fertilizer and water use. on
the tvay they resist or succumb to diseases and pests, and form. shed, or retain
leaves and seeds. Clearly, the (iverall aim must he to devise systems uthich ivill
use to the full the blessings of sun energy, but escape its ravages. As agriculture
advances from primitive to intensive levels of production. this increasingly
demands precise adjustment 0f heredity and environment, and hence a detaiieti
zmderstunciirzg oft/re developmental pilrases of the plant ‘which determine its productivity‘.
as of those phases which are susceptible to injury or breakdown.
It has been claimed that controlled environment facilities could greatly
accelerate this process of adjustment. and this is very likely indeed. But it must
be understood that the road to “applied phytotrtmics." i.e. to the use of a phytotron
in plant selection or agronomy, leads as a rule through a fuller understanding
of the physiologv of the plant, i.e. of those phases which are critical for
development and reproduction. The temperatures during both day and night,
the daily period of illumination, and the intensity and spectral composition of
daylight. all have profound effects on the growth of plants. In the field these