Vergara - 1976 - Physiological and morphological adaptability of ri

538 CLINIATE AND RICE
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DISCUSSION
Evan's (Chairman): One major advantage of the dwarf riees compared with the rslder tall
cultivars is their capacity for yield response up to high levels of nitrogen fertilizer application.
De Datta and li-Ialabuvoe give many examples of this advantage for both irrigated and rainfed
lowland rice, and for upland rice.
For lowland rice under irrigation, the yield response to high levels of feflilizer is greater the
higher the incident radiation during the reproductive 1nd ripening periods, hut with rainfed
rice this may not be so when high radiation levels are associated with water stress. as they often
are.
Climatic factors also interact with nitrogen supply in determining the incidence of pests and
diseases. These are encouraged by high nitrogen supply, although possibly to a lesser extent
in rice than in cotton. They are also more devastating to rice in the wet season, when yield
response to fertilizer application may be slight even when pests and diseases are controlled.
Weeds must also be controlled if yield response to high rates of fertilizer application is to
be obtained. as the authors show with many examples drawn from farmers‘ crops in India.
the Philippines. and other countries.
Taken together. the data presented by De Dalia emphasize how much the yield response of
rice to climatic factors, such as radiation. is dependent not only on cultivar. hut also on the
level of fertilizer application and control of pets. diseases. and weeds. Ellective simulation of
these complexities would be no mean achievement.
KATO: Your data on the relation between nitrogen applied and the outbreak of diseases are
very interesting. As a plant pathologist, l think we should discuss this relation on the basis of
the amount of absorbed nitrogen in each plot. It would be useful it" you considered the data on
absorbed nitrogen.
De Dana: I agree with you that studies on the relationship between absorbed nitrogen and
degree of susceptibility to diseases and insects should provide useful information. However. no
such data are available in the studies we have reported.
ALLES: ls not the mode of application of nitrogen another important factor influencing
nitrogen response, as you in fact so nicely showed us on our first day at IRRI‘?
De Dario.‘ All factors that atlcct the efiiciency of nitrogen fertilizer will also afiirct nitrogen
response of upland and lowland rice. 'll1ese data are summarized elsewhere.
PCINNAAIPERUMAI Don't you think that absence of injurious substances and the presence of