Vergara - 1976 - Physiological and morphological adaptability of ri

RICF. PRt)l')L.'(f‘l‘t\r'lTY 1N ('.‘l.l.\.tA']‘lC REGIONS OF JAPAN 465
mineralization of iritrogen in the soil and its absorption by plants. Temperature
also affects the decrease of leaf area in the later growth periods by its influence on
the speed of senescence of leaves or physiological aging of the plant. In addition
to these, in northern areas a low temperature affects the ability to produce dry
matter through its influence on the development of photosynthetic activity just
after transplanting.
On the other hand. solar radiation affects dry-matter production mainly
through its direct effect on photosynthetic rate and parth/ through leaf area
development by the supply of photosy-"nthates and the regulation of specific
leaf area.
At Sendai some peculiarity in the ability for dry-matter production not seen
in the six other stations was observed. The peculiarity appeared at later growth
stages in the form of acceleration of leaf area decrease due to the toxic substances
produced in the peaty clay soil, in addition lo the commonly observed
acceleration of leaf withering caused by higher temperature. At earlier grotvth
stages, the peculiarity did not necessarily appear as depression of the ability to
produce dry matter; sometimes it even induced the increase of the function. This
is shown in the slope of the regression of NAR on S - N. The slope of that line at
Sendai was considerably higher (0.114) than that for the pooled regression line
(0.078).
LOCPIFIONAL DIFFERENCES
IN GRAIN YIELD AND CLIMATIC FACTORS
As shown in Table l, significant differences were observed in the 5-year average
grain ydeld among different stations and varieties. although the plants were
grown under optimal conditions
locational differences may lie in the differences of yield capacity. production
of the yield content, or both, and a considerable part of these differences apparently’
can be explained by climatic factors.
The yield capacity of rice plants depends on the total number of spikelets per
square meter and the average size of individual husks (c.f. Murata. 1969). In
the IBP field experiment, the average husk size of the varieties used did not differ
greatly. so that it may be assumed that yield capacity depended mainly on
the total number of spikelets per square meter. Analysis using some of the data
of that experiment enabled Murata and Togari (1972) to report that three
climatic factors showed comparatively high correlation coefficients with the total
number of spikelets in the data pooled for 3 years and six stations. The first was
solar radiation during the 6 weeks after transplanting. through its effect on the
number of ears per square meter. The second and the third are solar radiation
and mean temperature, respectively’, during the 6 ‘weeks up to heading‘ through
their effect of increasing the number of spikelets per ear.
However, using data for the whole 5-year period, Kudo (1975) found that.
presumably because of the heavy participation of varietal characteristics. the