Yoshida - 1981 - Fundamentals of Rice Crop Science

CLIMATIC ENVIRONMENT AND ITS INFLUENCE 91
Table 2.13. Heat of combustion for different parts of the rice
plant . a
Plant part
Heat of combustion (cal/g)
Leaf blade
Leaf sheath
Root
Panicle
Dead leaf
Whole plant
4036
3569
31 77
3978
3611
3718
a Mean values calculated from Murata et al (1968).
go in our attempts to increase crop yields. Several scientists used different methods
of estimating maximum potential rice yields using different assumptions (Evans
1972, Murata and Matsushima 1975, IRRI 1977).
An estimate of the maximum potential rice yield is given by the product of the
maximum photosynthetic net production per day or per unit of incident solar
radiation and the number of effective days for grain production.
There are two basic methods for estimating maximum photosynthetic net
production. Method 1 estimates the gross production by examining the efficiencies
of component processes in the energy flow of canopy photosynthesis and subtracts
the respiration losses to obtain the net production (Murata and Matsushima 1975).
Method 2 is more empirical and much simpler. It uses the recorded maximum
photosynthetic efficiency of rice crops (IRRI 1977). Both methods implicitly
assume that the sink size is not limiting to grain production and that all the
photosynthates are carbohydrate and contribute to grain carbohydrate.
Method 1
Assumptions:
(a) The period for yield production is 40 days after heading.
(b) The average daily solar radiation is 400 cal/cm 2 per day of which 45% is
photosynthetically active.
(c) Of the photosynthetically active radiation, 5.5% is lost by reflection at the
canopy surface and another 10% through absorption by inactive tissues.
(d) Eight photons are required to reduce 1 molecule of carbon dioxide, corresponding
to an efficiency of 26% in energy conversion,
(e) The loss due to light saturation in the upper leaves is 17% at 400 cal/cm 2 per
day.
(f) The conversion factor for dry matter is 3,900 cal/g.
(g) The respiration loss is the sum of 1.5% of dry weight/day (1.5 kg/m 2 in this
case) and 25% of the gross photosynthesis.
(h) The ratio of husk weight to the dry grain weight is 20%.