There was no measurable competition among plants before the four-leaf stage of growth. Competition among plants after the four-leaf stage reduced their average weight and their capacity to store assimilates in the ear after anthesis. As competition intensified total dry-matter yield at lower plant populations approached progressively the yield at the highest plant population. Total whole plant yield per unit area showed an asymptotic response to increase in plant population. Ear yield per unit area showed a parabolic response. On a unit leaf area basis, the top three leaf laminae apparently contributed about 66% more to cob (rachis + grain) dry weight than the three adjacent leaf laminae immediately below them. Ear weight per plant was reduced, either (a) by increasing plant population, or (b) by partial defoliation, or (c) by both treatments. In situation (c), i.e. where high plant populations were partially defoliated, cob weight per plant was apparently determined by the amount of available assimilates, and not by ear storage capacity. © 1969, Cambridge University Press. All rights reserved.
