Vergara - 1976 - Physiological and morphological adaptability of ri

452 CLINIATE AND RICE
the late-maturing variety than in the early'-maturing one, while the situation
was the reverse as to mean CGR.
Grain yield
The locational order of grain yield in dry weight roughly coincides with that of
nct production. The highest 5-year average value, 600 g/sq m. was attained by
Manryo at Nagano; the second highest, 567 g/sq m. by the same variety at
Takada and Fukui; and the third, 564 g/sq m, by the normal season culture of
IIoyoku at Chikugo. The lowest value, 483 g/sq m, was obtained at Akita.
The highest single-year record grain yield was 694 g/sq m attained by Manryo
at Nagano in 1968. Nagano Prefecture, to which the Nagano Experimental
Station belongs, is well known for its highest average rice yield per hectare
among all the prefectures in Japan.
The locational difference in grain yield is even smaller than that in net production.
because the ratio of the smallest value to the highest in grain yield is 80.5%.
This is also reflected in the smaller cv value. 6.8 %, in grain yield compared
with 8.1 %, in net production.
No clear relationship was found between grain yield and geographical location
or climatic conditions for the whole growth period at a given station; however, a
positive correlation coefficient with solar radiation (0.429. not significant) was
obtained. The present reporter has SlIOWII earlier (Murata. I964) that the average
rice yield per hectare of individual prefectures shown by the statistical data ofthe
5 years. 1957-1961. was very closely correlated positively‘ with solar radiation and
negatively with mean temperature in the August-September period. During this
period average rice crops in Japan pass through the yroung-car-formation and
grain-filling stages. Thus, the highest yield in Nagano Prefecture was attributed
to its highest SO13!‘ radiation coupled with the relatively cool mean temperature
in the August-September period.
It seems possible to explain a considerable part of the locational difference
in grain yield in the 5-year experiment with a more reliable basis than before by
the difference in solar radiation. This will be discussed later in more detail.
Other climatic factors, including temperature, do not seem to have any great
influence. at least directly. on the locational differences in grain yield.
DEVELOPMENT AND MAINTENANCE
OF PIIOTOSYNTIIETIC ORGANS AND CLIMATE
Increase of leaf area
The increase of leaf area starts at germination. Usuallgr the tillering of a rice
plant begins at the 4-leaf stage and proceeds at a definite speed and order sgxnehronized
with the emergence of new leaves on the main eulm (Katayama. 1951).
'l‘illers which emerge in the nursery’ usually die at transplanting, but following
the establishment of the seedling in the field. new tillers are produced at the
higher nodes of the eulm. with developing new leaves on thcin. In this way’. as