Vergara - 1976 - Physiological and morphological adaptability of ri

484 cunmrs mo RICE
Tabla 4. Graln yields of four crops wlthln 1 year rnt Los Bafios, Phlllppines, 1971-1973.
Crop no. Planted Variety Yield (1,113)
19H
1 January IRB 8.8
2 May lRT47-B2-fi 5.4
3 July lR747t-B2-6 6.4
4 October IR667—96 5.2
Total 26.8
1972
1 January IRS 9.1
2 May |RT47—B2-6 4,2
3 July lR1561-22B-3 5,1
4 October lRTfl-BZ-fi 4,7
Total 24.1
1973
1 January IRE 7.7
2 May lRT4'i'-B2 -6 5.0
3 July lR1561-22B-3 5.1
4 October lR747-B2-6 3.3
Total 21.1
3 years‘ average of annual production 23.1
In Sri Lanka, Murakami (1968) found that spikelet number per square meter
was linearly correlated with grain yield of the variety H4 up to 6 t/ha.
An overall examination of these data seems to indicate that WhClhCf spikelet
number or filled-grain percentage is more limiting to grain yjield. or whether
weather conditions before or after flowering have a greater effect on yield. is
location- or season-specific. Therefore, it is highly important to examine causes
of variations in ykield components. particularly spikelet number per square meter
and filled-grain percentage, under a given condition.
CLIMATIC FACTORS AFFECTING YIELD COMPONENTS
Spikelet number per square meter
Under subnormal cultural practices. spikelct number per square meter can be
increased by increasing plant densityn An optimum plant density or spacing
maximizing spikelet number varies xvith tillering capacity and growth duration
of a variety. and with nitrogen application. A higher plant density is required
for lonr-tillering, early-maturing varieties and at low nitrogen levels.
Within a moderate range, low temperature during the reproductive stage appears
to favor increasing spikclet number. In the northern regions of Japan, a
larger number of spikelets can be produced per unit amount of nitrogen alasorbed
or per unit weight of vegetative part than in southern Japan (Murayama. 1967).
In other words. the efficiency" of producing spikelets per unit nitrogen or dry
weight is much higher in cool regions than in warm regions. In a controlledenvironrnenl
experiment ivhere light ititetisity was kept high and constant
and plant nutrients were abundantly supplied, lower temperature during the
reproductive stage produced more spikelets (Yoshida. 1973b).
Solar radiation during the reproductive stage also has a pronounced effect on
spikelet number per square meter (Matsushima, 1957; Stansel et al.. 1965;