Vergara - 1976 - Physiological and morphological adaptability of ri

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DISCUSSION
ISHIZUKA (Chairman): ln Southeast Asian countries. it is very difficult, or almost impossible.
t0 control the excessive rainfall of the monsoon season. However. from ancient times traditional
practices have developed excellent rice cultivation methods adapted to severe conditions,
which are far beyond the control of human beings.
Moderately satisfactory yields of rice have been secured by in effect accepting the limiting
conditions imposed by nature. Floating rice cultivation is a good example of the wisdom of
nations.
However. the recent population explosion and economic pressure have threatened to disturb
this peaceful balance with nature and make it irecessary to seek higher yields from rice.
Thus we are obliged to seek new techniques which can increase yields under the same difficult
circumstances. and this paper reports efibrts to find a possible solution.
The characteristics of the cultivation of floating rice in dcep water are:
1. Direct seeding of the area before it is flooded.
2. Allow" at least 4 weeks for growth before flooding commences.
3. As flooding develops the gmwth of the rice must keep pace with the increase of water depth
so that the top of the plant is always above the water surface.
If the flooding is so rapid that the ricc cannot elongate in parallel. it must bc able to tolerate
some submergence. and survive.
As a consequence the authors have concentrated on these two different characteristics (l) the
rapidity of intemode elongation under water. and (2) the ability to survive when submerged.
When evaluating these qualities they suggest that the following need to be considered: (l) the
age of the plant at the beginning of inundation; (2) temperature of the water. (3) duration of
submergence; (4) turbidity of the water". (5) light penetration into the water: and (6) nitrogen
nutrition.
The consideration of these qualities. separately. is reasonable and adequate. But. of course in
practice, it‘ ability to elongate is high. the time of submergence would be reduced and this would
compensate tor any intolerance of submergence and vice versa.
Moreover. when we examine the effect on elongation and on tolerance of the six conditions
mentioned above. we find that only water temperature produces conflicting efTects.
lf water temperature is high, it encourages elongation but reduces tolerance of submergence.
It is therefore very important to make clear whether water temperature favors one ability or
the other.
If the temperature is favorable for elongation. then the rice would require a greater degree of
tolerance to survive and vice vcrsa.
Llnfortunately". as the authors report. there are no reliable records of water temperature
throughout growing seasons. and these must be obtained before an answer to this problem can
he provided.