Yoshida - 1981 - Fundamentals of Rice Crop Science

70 FUNDAMENTALS OF RICE CROP SCIENCE
Table 2.3. Total rice areas, percentage of damaged area, and the cause of damage in
Thailand (1907–1965). a
Totally
Year Cultivated Harvested failed Rice Cause
area area area b production of
(10 3 ha) (10 3 ha) (%) (10 3 t) damage
1917 2223 1757 21.0 2989 Flood
1919 2479 1404 43.4 2270 Drought
1928 2722 2386 16.3 3882 Drought
1929 3036 2445 19.5 3875 Drought
1936 3258 2226 31.7 3380 Drought
1942 4379 2876 34.3 3854 Flood
1945 3762 2847 24.3 3572 World War
1954 5557 4524 18.6 5709 Drought
1957 5075 4287 15.5 5570 Drought
a Isrankura (1966). b
cultivated area – harvested area
cultivated area
× 100.
In studies using controlled temperature facilities, such as the phytotron and
growth chambers, daily mean temperature is normally a weighted mean of day and
night temperatures:
(2.3)
where D = daytime in hours,
t D = temperature during daytime,
N = nighttime in hours, and
t N = temperature during nighttime.
The monthly mean temperatures vary with latitudes, as shown in Figure 2.3.
Generally, the annual mean temperature decreases, and seasonal variation
increases with increasing latitude. One major characteristic of the tropical climate
is seasonal uniformity in temperature. At Los Baños, Philippines, for example,
monthly mean temperatures range from 25.3°C in January to 29.4°C in May, the
difference being only 4.1°C.
Diurnal temperature variation ranges from about 5° to 20°C, or even greater
between the daily maximum and daily minimum. The main factor governing the
diurnal variation is continentality (Fig. 2.4). All marine locations display very
small diurnal changes because the surrounding water has a large value of specific
heat and serves as a buffer to minimize temperature changes. Diurnal changes
increase rapidly with distance from the sea. The maximum values for diurnal
changes are found in the dry tropics at about 15°–25° latitude.