Yoshida - 1981 - Fundamentals of Rice Crop Science

84 FUNDAMENTALS OF RICE CROP SCIENCE
2.11. Relationship between grain number
and amount of nitrogen absorbed by heading
(Yoshida et al 1972. Data for Japan are
adapted from Murayama 1967).
Table 2.10. Effects of temperature on spikelet number and efficiency
of nitrogen to produce spikelets (minicrop experiment in
the phytotron). a
Day/night
Spikelets
temperature Spikelets (10 2 /m 2 ) (no./mg N absorbed)
(ºC)
150 N b 100 N 50 N 150 N 100N 50 N
35/27 278 280 244 1.4 2.0 2.9
32/24 299 308 275 1.6 2.2 3.0
29/21 376 313 288 2.1 2.3 3.3
26/18 482 409 326 2.2 2.5 3.2
a lRRl (1978). b Kg N/ha.
c. Low temperature-induced sterility and phosphorus. The adverse effects of
high nitrogen under low temperatures during the reproductive stage can be
alleviated by increasing the amount of phosphate applied (Fig. 2.13). This experiment
confirms a common observation in northern Japan that the effect of phosphorus
on rice yield is more significant in cool than in warm years (Ishizuka
1971).
2.4. SOLAR RADIATION
2.4.1. Physical aspects
Most of the radiant energy from the sun has a wavelength between 0.3 and 3 µm,
often referred to as short-wave radiation. The earth emits radiation with
wavelengths ranging from 3 to 50 µm, which is referred to as long-wave radiation.
Solar radiation penetrating the earth’s atmosphere is reflected, absorbed, and
scattered by clouds, gases, and aerosols in the form of soil and salt particles,
smoke, insects, and spores. The reflection and scattering occur at all angles, and the
downward component is usually referred to as diffuse sky radiation. Thus, incoming
solar radiation takes the forms of direct radiation and diffuse sky radiation. The
sum of these two is called global radiation or simply incident solar radiation.