Vergara - 1976 - Physiological and morphological adaptability of ri

474 crntiiyrls mo RICE
Groin yield
tt/ho)
'0 T Dry season
o
1 I | 1 I
0 2 4 6 8 l0 l2
Leaf urea index
1. Relationship between grain yield of [R8 and leaf area
index at heading in wet and dry season. 196641.
a wider range of yield. Figure l shows a close correlation between grain yield
and leaf area index (LAT) at flowering. Within the same season, there is some
degree of yearly variation in temperature and incident solar radiation. Nevertheless.
the grain yield for each season is stable. and the dry-season yield is
consistently higher than the wet-season yield. Clearly. the yield difference between
dry and wet seasons is pronounced only when LAI is high. Thus. co1iclusions
from the results obtained with [R8 are: (a) spikelet number per square
meter is the most important for yield up to 9 t/ha. and (b) climatic influence on
yield can be detected only when large leaf-area indices are insured by good
agronomic practices along with adequate supply of water and nutrients.
The climatic environment of Los Bafios is described elsewhere (UPCA. 1959-
1972; Moomaw and Vergara, I964". IRRI, 1967-4973). Briefly. monthly average
of daily mean temperature (mean of daily maximum and daily minimum) ranges
from about 24° to 30°C". monthly average of daily maximum-minimum temperature
difference, from 7° to 11°C. Thus, temperature difference between day and
night is greater than seasonal variation in the monthly average of daily mean
temperature. The monthly average of daily solar radiation ranges from about
300 cal - sq cm‘ - day‘ in December to about 600 cal - sq cm‘ ~ day"
in April (Appendix).
To study climatic influence on rice yield at Los Bafios. we grew one variety’.
early-maturing lR74l-B2-6, in the Institute field every 2 weeks from July 1972
to September 1973. This variety develops l3 leaves on the main culm and
matures in 96 days regardless of planting time throughout the year. The growth