Yoshida - 1981 - Fundamentals of Rice Crop Science

220 FUNDAMENTALS OF RICE CROP SCIENCE
6.4. Relation between grain yield and
leaf area index at flowering in IR8
(wet and dry seasons, 1966–69)
(Yoshida et al 1972).
indica variety, there is no optimum LAI for dry matter production, although a
critical LAI does exist (see Fig. 5.4, Chapter 5). A LAI as large as 12 at heading is
not detrimental to grain yield unless the crop lodges (Fig. 6.4).
Missing plants due to poor land levelling, insects, diseases, and other stresses
may occur in the field. A high-tillering variety is able to compensate for such
missing plants.
In the wheat ideotype, a single culm is desirable for high yields (Donald 1968).
Similarly, a crop photosynthesis model for corn considers tillering hills the worst
arrangement in plant geometry (Duncan 1968). At high plant densities, however,
multiculm rice plants either would not produce tillers or would produce only a
limited number, thus approaching a single culm plant population. In an experiment,
the effect of plant density on yield was tested for 14–909 plants/m 2
(45–3,000 plants/tsubo) by varying both spacing and plant numbers per hill (Fig.
6.5). Tillering occurred up to a density of 300 plants/m 2 (1,000 plants/tsubo),
beyond which only main shoots grew and produced panicles.
Grain yield increased with increasing plant densities up to 182–242 plants/m 2
(600–800 plants/tsubo). The number of panicles per unit of land area increased
with increasing plant density but the increase was accompanied by a decrease in
paddy weight per panicle. In another experiment, all the plants produced panicles
at a plant density as high as 1,212 plants/m 2 (4,000 plants/tsubo) (Yamada 1963).
Thus, of the three crops, rice is highly tolerant of high plant densities, wheat is less
tolerant, and corn is the least tolerant. In both wheat and corn, grain yield
decreases when the plant density exceeds a certain value (Yoshida 1972).
The above discussion leads to the conclusion that exceptional tolerance for high
densities makes the rice plant flexible in its response to changes in plant density,
and high tillering capacity is desirable for achieving maximum yields in transplanted
rice cultivation.