Yoshida - 1981 - Fundamentals of Rice Crop Science

28 FUNDAMENTALS OF RICE CROP SCIENCE
1.26. Air space in a lower internode.
Unusual environments, such as deep seeding and deep water, induce internode
elongation even at early growth stages. Seed placement 2 cm deep in soil does not
induce internode elongation but the placement deeper than 3 cm may induce
elongation of the first and second internodes (Sekiya 1953).
In deepwater and floating rices, internode elongation occurs in response to
increased water depth. The maximum observed rate of internode elongation is 25
cm/day but about 2–10 cm/day is more common (Vergara et al 1976).
1.5.3. Culm characteristics related to lodging
Physically, lodging can be examined in terms of the bending moment and the
breaking strength of the culm and sheath (Chang 1964). The bending moment is
the product of shoot weight and the height of the main axis (culm height). After
heading, the panicle weight increases as the grains grow, and hence the bending
moment increases. If other things are equal, a tall variety has a greater bending
moment than a short variety because it has a greater culm height.
The shoot’s breaking strength is greatly affected by 1) length of lower internodes,
2) strength or stiffness of the elongated internodes, and 3) strength and
tightness of the leaf sheath.
Lodging usually results from the bending or buckling of the 2 lowest internodes,
which have elongated more than 4 cm. The strength of elongated internodes