Vergara - 1976 - Physiological and morphological adaptability of ri

282 CLIMATE AND RICE
Brown rice yield It/hcl)
5
_
O — Average year
I -— Cool injured year
o
Q 1 1 1 ' 1 1 1 1 1 1
I880 I890 I900 l9|0 I920 I930 I940 I950 I960 I970
1. Effect of technical improvement on average brown rice yields (tfha) in Hokkaido
during the past 9t) years.
were practically no harvests in 1902 and 1913. Such a great decrease in yield does
not occur today due to progress in agricultural techniques. Even nowadays.
however. the difference in yield between an average year and a cool-injury year
amounts to about 1.5 tonsfha. Thus, the development of countenneasures to
reduce cool injury‘ is a fairly important problem for rice cultivation in Hokkaido.
Expansion ofcool-injured areas
For several years after World War II. shortage of food was the greatest social
problem in Japan. To increase rice production, paddy fields have been expanded
into high mountainous. cool locations. and new cultural methods such as early"-
season culture have been developed in the southwestern warm regions (iflapan.
Field expansion in high locations and the development of early-season culture
have brought about much rice production and simultaneously caused cool injury
in the southern warm regions of Japan (Sato, 1967). Thus. cool injury has become
an important problem of rice culture throughout Japan.
Kinds ofcool injury in the world
Cool injury of rice plants has been occurring not only in the temperate region.
but also in the tropical region. Kaneda (1972) questioned correspondents in
some 20 countries, mainly in lower latitude areas. and confirmed that cool
injury" has occurred in many countries including Australia, Bangladesh. Colombia.
Indonesia. Kashmir, Korea. Nepal. Pakistan, Peru. Sri Lanka. Iaivtran. and
the USA.