Vergara - 1976 - Physiological and morphological adaptability of ri

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NITROGEN RESPONSE or RICE m TROPICAL coimmosis 511
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l. ElTeet of plant type on nitrogen response of lR8-288-3 (IRS) and tall tropical
varieties. IRRI. 1966 (adapted from De Datta et al.. 1968).
which meant 69 kg rough rice for each kilogram ofN added. At 120 kg N/ha,
IRS produced about 30 kg rice/kg N.
During the cloudy wet season. 1R8 gave a modest increase of 0.9 t/ha of rice
with 60 kg Nlha (Fig. l). Nevertheless. it outyielded all other tropical varieties
by at least 1.6 t/ha (De Datta et al.. 1966).
1n the wet season of 1966. line 1R5—47—2 (later named 1R5) gave positive response
to N up to I21) kg/ha with the highest yield of 7.3 t/ha at an experiment
station (veflisol, p11 6.9, organic matter 1.5%, and CEC 36 meq/‘IOO g soil)
located in the principal rice-grouting area in the Philippines. 1R5. an intennediate-statured
variety (about 130 cm tall) has given stable yield and stable nitrogen
response under less favorable moisture conditions since it was introduced
in the Philippines in 1966 13P1-76. an improved variety widely grown in the mid~
sixties in the Central Luzon area. gave lower nitrogen response than either 1R8
or 1R5 (116-47-2). The tall tropical variety Peta responded to up to 90 kg
N/ha with a maximum yield of 3.9/11a (IRRI. 1967).
The results from India (Shastrfvi et al.. 1974) are similar to the results reported
from the Philippines. On the new varieties, plant habit has been changed to
enable a more efficient utilization of sunlight and fertilizer N. Data from the
All India Coordinated Rice Improvement Project (AlCRlP) have abundantly
illustrated the greater efficiency of the new varieties in utilizing native fertility
and fertilizer nitrogen (Shastrjr et al.. 1974).
Similarly in Peru at 6°42’ S latitude. Sanchez ct al. (1973) reported marked
response oflR8 to up to 320 kg N/ha on an alluvial clav loam soil under intennit-