Vergara - 1976 - Physiological and morphological adaptability of ri

520 CLIMATE AND men
fllflfiffli WET $14.17!!’
Grain ylfld lt/hol mmemznr um. 1
6
4
__-§-U-.h-_
g _
§~._
O
0 4O 8O I20 I60 O 4O 80 I20
Nitrogen applied ( kqiha)
7. Nitrogen response of modern (IRK) and traditional
(Sigadis) varieties as atlected by three levels of management
(control of weeds and insects). lRRl. I966 (adapted
tram De Datta and Barker. 1968 and IRRI. 1967).
In the dry season. the grain yield difference betiveen IR8 and Sigadis was 3
tfha. lt is notable that the highest yield of Sigadis. obtained with 8t) kg N/ha,
was lower than that obtained from IRS with no N (Fig. 7). Although the
highest grain yield of 1O t/ha and maximum N response occurred at the
highest management level but beyond management level l. the additional eash
input necessary t0 obtain higher grain yield did not justiffi’ the effort to obtain
maximum nitrogen response.
In the wet season. nitrogen response closely followed the trend of the dry
season. but absolute nitrogen responses were lower for either 1R8 and Sigadis
in the wet season than in the dry season (Fig. 7’). Detailed results from these
experiments have been discussed earlier (De Datta and Barker, 1968).
Experiments conducted during the 1967 dry season showed that even under
high sunlight condition, the degree of insect. disease, and weed control hill