Yoshida - 1981 - Fundamentals of Rice Crop Science

16 FUNDAMENTALS OF RICE CROP SCIENCE
1.13. Effect of water regimes on germination and rooting of rice seeds from
sand media (Yokoi 1898).
In lowland direct-sowing cultivation, particularly when the seeds are covered
with soil, lack of oxygen causes poor seedling emergence. Under such conditions,
coating the rice seeds with calcium peroxide is very effective in improving
seedling emergence and subsequent growth (Ota and Nakayama 1970, Mitsuishi
1975). In wet soil, calcium peroxide releases molecular oxygen as it reacts with
water:
Thus, oxygen is made available for seedling growth even in an anaerobic soil.
d. Water regimes. Seedlings for transplanted rice are normally raised in
lowland nurseries. However, experience in northern Japan indicates that uplandgrown
seedlings have better rooting ability and, hence, recover more quickly after
transplanting. The upland-grown seedlings are shorter, have smaller leaves and
more highly branched roots, and contain more nitrogen and starch than the
lowland-grown seedlings (Fig. 1.14). Reduced leaf surface minimizes water loss
during the recovery after transplanting. At the same time, high contents of nitrogen
and starch help seedlings develop new roots (Fig. 1.15). These characteristics
appear to result from the water stress imposed on the seedlings in the nursery.
Upland-grown seedlings perform well when temperatures are cool at transplanting,
the growing period is short, and hence, quick recovery from transplanting is
desirable. At low altitudes in the tropics, however, temperatures are favorable for
rice growth all year round and growth tends to be excessive. Under such condi-