Vergara - 1976 - Physiological and morphological adaptability of ri

NITROGEN RESPONSE OF RICE IN 'l'R()PIt.‘.-‘\L
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2. Nitrogen response of [our rice varieties by month of harvest. plotted with the solar radiation
total for 45 days before harvest (DBH). Date-of-planting experiment. lRRl. l968—69 {De
Datta and Zarate. 1970).
increased‘ inversely‘. as the solar radiation decreased from about 20 kcal/sq em
in tI1e May harvest to about l3 keal/sq cm in the August harvest, the nitrogen
response of [R8 decreased. Nevertheless. this improved variety showed better
response to nitrogen than the traditional tall variety H-4 (Fig. 2). These results
show that at any solar energy level. varieties with good plant type will give higher
response to tertilizer nitrogen over traditional varieties (De Datta and
Zarate.
I970).
During the ripening period of the rice crop. the intensity of solar energy
during an average day in the monsoon tropics approximates 350 ca] - sq cm-l -
day“, which is similar to the values reported during the rice-growing season in
Japan (Mtmakata et aI.. I967} and Korea (IRRI. I972). Similarly. Fukui (IWI)
reported that in the temperate Asian ‘countries. solar radiation during the ricegrotviiig
season is nearly the same as that for the rainy season in humid tropical
regions. that is, 400 cal - sq ems‘ -da_\-'*1. Because the day length is longer
during the main cropping season in Sapporo (43°N) or Konosu (36°N) in Japan
(Moomaw and Vergara.
1964) or Suweon (37°N). Korea (IRRI, I972). compared
with that in Los Bafios in the Philippines tI4°N). the intensity’ of solar energy
per hour is higher in Los Bafios than in Sapporo. Konosu. or Suweon (De Datta.
I973) In temperate Asian countries. gross photosynthesis should he greater
than in tropical countries: Nevertheless, Yoshida and Cock (1971) have pointed