Vergara - 1976 - Physiological and morphological adaptability of ri

434 CLIMATE AND RICE
CGR during later growth stages (tanaka and Vergara. 1967).
The rate of LA] increase is determined genetically or environmentally’. Some
varieties are more vigorous in vegetative growth, and expand the LAI more
rapidly than others (Kawano and Tanaka, 1967). Higher temperatures and
higher nitrogen levels promote the increase of LAI. There are. moreover, differences
in the optimum LAI depending upon the plant type of varieties and also
upon climatic conditions. Under fEn-‘orzible conditions with a good plant type
there is no optimum LAI. but there is a ceiling LA] (Cock and Yoshida. 1973).
Thus, the time required to reach the optimum or ceiling LAI from date of planting
depends on the nature of varieties and also on environmental and cultural
conditions.
Various growth curves can he classified into a flew types (Fig. 2) :
Type I: A vigorous growth at early stages followed by a weak growth (sometimes
decrease of weight) at later stages; frequently’ observed With old. tall,
leafy varieties ll] the tropics; associated with a large total dry-matter production.
a small grain-straw ratio. and a low grain yield.
Type II‘. A continuous moderate growth rate followed by a slight decrease at
the end; considered to be normal; generally associated with a moderate total
dry-matter production, a large grain-straw ratio_ and a good grain yield.
Total dry mutter production
Days after planting
2. Diagram illustrating various types of growth curves.