Vergara - 1976 - Physiological and morphological adaptability of ri

‘HELD AND YIELD (,7()l\-ll‘()l\'l£.\l'l'S 0F LUViFLANl) RICE IN THE 'l‘l{(,)l’l(75 4?9
Groin yield
s
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tt/ho}
Y=|3+OB|X
r=O90t**
I l l | I | l I
4 5 6 7 8
Chmunc productivity index time:
5. Grain yield in relation to climatic productiviQ/ index.
Since the computed yield is expressed in terms of solar radiation and temperature
it may be called a climatic productivity index (Murata, 1964; Hanyu et al., 1966).
This index is highly correlated with actually measured yield (Fig. 5) which iinplies
that yield of the IR74? line at Los Bafios is positively correlated “Iith daily
solar radiation and negatively’ with the daily mean temperature during the
reproductive stage, i.e. the 25-day period before flowering (Fig. 6).
To examine the effect of solar radiation during the ripening period on ykield.
the correlation coefficient was computed for ripening grade and solar radiation
during the ripening period. Ripening grade is the product of filled grain percentage
and LOGO-gain weight. and is considered a good indication of degree of
ripening. Ripening grade. however. was only lmiseljt’ correlated with solar radiation
during the ripening period (r = 0480*).
The evidence tve have presented here
ber per square meter is the most important factor limiting grain yield of IR747-
132-6 at Los Bafios, and it is highly correlated with solar radiation and temperature
during the reproductive stage. that is the 25-day period before flowering.
Solar radiation during the ripening period has a slight correlation with degree
of ripening.
So far we have been depending on correlation studies. Such studies may not
reveal a direct influence of climatic factors on rice yield.
As shmvn in Table 2. shading from 75 to 25 % sunlight during the vegetative
stage, ie. first 25 days after transplanting, had only a slight effect on yield and
yield components. SOlZiT radiation did not have tiny effect on yield when it was
more than 300 cal-sq em-“dayM (Fig. '5'). Dry-matter production at the end of