Yoshida - 1981 - Fundamentals of Rice Crop Science

GROWTH AND DEVELOPMENT OF THE RICE PLANT 45
Table 1.12. Yield of traditional tropical rices in relation to transplanting time. a
Variety
Yield b
(kg/ha)
July August September October November
Bangkhen 293 229 3478 4791 b 3386 2435
Luang Tawng 101 67 2455 4121 3098 2234
Nang Mon S-4 155 2222 2971 2010 1174
Puang Nahk 16 4136 4104 4769 3492 2388
Jao Luang 11 158 1791 3571 2120 2681
Khao Dok Mali 105 66 1219 3031 3020 1820
Bai Lod 104 388 1758 3519 2241 2019
Khao Pak Maw 17 265 1537 3820 2187 1528
a
Takahashi et al (1967). b ltalic figures indicate highest yields.
Photoperiod sensitivity may function as a safety mechanism when the onset of
the rainy season is considerably delayed (Oka 1958). In most of tropical Asia, the
onset of the rainy season is unpredictable and varies from year to year, whereas its
end is fairly fixed. Thus, when planted late, a photoperiod-sensitive variety may
still mature at its usual time regardless of shortened growing periods. On the other
hand, a photoperiod-insensitive variety requires a specific growing time before
flowering, and hence, maturity. Thus, such a variety will suffer from water stress
at later growth stages after the rain ceases.
Most traditional rice varieties in the tropics are sensitive to photoperiod, have
long maturity periods, and are tall. When they are grown with high levels of
applied nitrogen, they tend to lodge at later growth stages, and their grain yields
are extremely low. When these varieties are planted later than usual, they have a
shorter growth duration and usually are shorter in height, and consequently,
have increased lodging resistance.
Table 1.12 shows the results of delayed-planting experiments using
photoperiod-sensitive varieties. The September transplanting, 2 months later than
usual, gave the highest yield for all varieties. Delayed planting of photoperiodsensitive
traditional indica rice varieties prevented excessive growth and lodging,
and resulted in high grain yields.
1.8.2. Response to temperature
a. The temperature summation concept. Temperature summation is a summation
of daily mean temperatures over a certain period of growth or development. When
the temperature drops to a certain level, growth or development may stop.
Temperatures below this threshold are considered ineffective.
TWO ways of calculating temperature summation have been used for rice
(Asakuma 1958, Copeland 1924, Nagai 1962):
Temperature summation = S (Daily mean temperature) (1.12)
Temperature summation = S (Daily mean temperature
- threshold temperature). (1.13)