Yoshida - 1981 - Fundamentals of Rice Crop Science

214 FUNDAMENTALS OF RICE CROP SCIENCE
Table 6.1. Response of a traditional tall variety to graded doses
of nitrogen, with and without farmyard manure (FYM). a
0 33.6 67.2 100.8 134.40
kg/ha kg/ha kg/ha kg/ha
No manure 2.08 2.59 2.49 2.49 2.22
Farmyard manure 2.44 2.72 2.47 2.17 1.92
at 8.89 t/ha
a Chandler (1963). b Added as ammonium sulfate. Converted from
Ib/acre.
Rough rice yield (t/ha) at nitrogen doses b of
mal water and weed control at moderately wide spacing.
High yielding japonica rices have short, narrow, erect, dark-green leaves; thin,
but short and sturdy culms; and short, dense panicles. They respond to increased
application of nitrogen, and produce high yields (Jennings 1964). Such observations
may suggest that japonica rices be grown in the tropics. In fact, ponlai nces,
japonica rices developed in Taiwan and adapted to subtropical climates, perform
well in tropical regions. However, the direct introduction of japonica rices into the
tropics was not favored for several reasons. First, most japonica varieties mature
very early because of daylength and temperature sensitivity, resulting in stunted
growth and low yield. Only ponlai rices are adapted to tropical climates; consequently,
the amount of genetic resources is quite limited. Second, people in
tropical Asia prefer the cooking quality of indica rices. Third, japonica rices lack
the grain dormancy desirable for tropical varieties that mature toward the end of
the monsoon season.
With this consideration, it was logical to make hybrids between japonicas and
indicas to transfer the good characters of japonica rices to indica rices. In the
1950s, the Food and Agriculture Organization (FAO) organized an indicajaponica
hybridization program with its headquarters at the Central Rice Research
Institute (CRRI) in Cuttack, India (Parthasarathy 1972). From this program came
ADT27 in India and Mahsuri and Malinja in Malaysia. However, the over-all
results made little impact on rice improvement programs in South and Southeast
Asia.
The warm tropical climate was considered another factor responsible for low
yields. Because high temperatures increase respiratory losses, net dry matter
production — as a balance between photosynthesis and respiration — was thought
to be inevitably lower under higher temperatures. Low rice yields in southwestern
Japan were attributed to warm climates. For example, yields were correlated with
solar radiation and air temperature by the following formula (Murata 1964):
Y = S [1.20 – 0.021 ( t – 21.5) 2 ],
(6.1)
where Y is grain yield (kg/10 a [ a = 0.01 ha]), and S and t are solar radiation
(cal/cm 2 per day) and daily mean temperature (°C), in August and September. The
equation indicates that temperatures higher or lower than 21.5°C will decrease