Yoshida - 1981 - Fundamentals of Rice Crop Science

CLIMATIC ENVIRONMENT AND ITS INFLUENCE 69
2.2. Effect of technical improvement on average brown-rice yields in Hokkaido, Japan, during
the past 90 years (Satake 1976).
managed, the dry season crop usually produces higher yields than the wet season
crop because it receives more sunlight.
Stability of crop yields is affected by several factors. In Hokkaido, which is the
northern limit of rice cultivation in Japan, low temperatures frequently cause crop
failure. Between 1880 and 1970, 22 crops were affected by cool summer temperatures
(Fig. 2.2). In addition, low sunlight associated with excessive rainfall during
ripening causes low yields. Too little or too much rainfall at any stage of rice
growth can cause partial or total crop failure. In Thailand, more than 15% of the
cropped area totally failed because of either drought or flood during 8 of the 58
years from 1907 to 1965 (Table 2.3). In 24 of the 58 years, more than 10% of the
cropped area was not harvested at all.
In both the tropics and the temperate region, typhoons are unavoidable hazards.
One way to minimize crop damage by typhoons is to shift crop seasons so that
ripening proceeds when typhoons are least frequent.
2.3. TEMPERATURE
2.3.1. Physical aspects
Average temperatures for a month or a year are computed from daily mean
temperatures, which are usually calculated by averaging the daily maximum
temperature plus the daily minimum temperature.