Yoshida - 1981 - Fundamentals of Rice Crop Science

CLIMATIC ENVIRONMENT AND ITS INFLUENCE 93
synthetic efficiency recorded for a short period during the vegetative growth stage
should continue during ripening when senescence occurs.
Figure 2.17 shows a linear relationship between incident solar radiation and
potential yield. This is because the same E µ value is used at all levels of incident
solar radiation. However, E µ value is expected to decrease with increasing level of
incident solar radiation. As a consequence, the relationship between incident solar
radiation and potential yield would likely be curvilinear but not linear. However,
information as to how E µ relates to incident solar radiation in rice is lacking.
Therefore, the potential yields calculated by equation 2.13 are likely to be underestimates
at lower levels of incident solar radiation and overestimates at higher
levels.
The estimated potential yield shown in Figure 2.17 indicates that the temperate
region, where the effective grain-filling period is longer. is more productive than
the tropics on per-crop yield basis. The estimated maximum yields may be
compared with recorded maximum yields: 13.2 t/ha in Japan with an estimated
solar radiation of 400 cal/cm 2 per day and 11.0 t/ha at IRRI with an estimated solar
radiation of 550 cal/cm 2 per day.
At IRRI and with good management, about 6 t/ha is normally obtained in the wet
season when incident solar radiation is about 300 cal/cm 2 per day during ripening
2.17. Relation between potential
yield and incident radiation-
during the grain-filling
period of rice (IRRI 1977).