Comparative Pre-Emergence Heat Tolerance of some Seeded Grasses and of Weeds

Abstract

1. Evidence was obtained demonstrating that soil temperature may determine which weedy plants emerge in competition with seeded grass. A comparison of species was made by subjecting seeded grasses and weeds to several levels of soil heat in a controlled temperature chamber. The relative differences in heat tolerance so obtained agreed with the seasonal emergence pattern of these weeds in the field. 2. The winter annual grasses possess a lower pre-emergence temperature tolerance than do several perennial grasses used in range reseeding, while certain forbs possess a higher pre-emergence temperature tolerance. 3. A degree of regulation of the weedy competition resulting from seed resident in the soil may be attained by timing preparatory tillage operations and the date of seeding with regard to prevailing temperatures. 4. It is proposed that physiological studies of weedy species may reveal means of altering the environment in ways disadvantageous to the weed and suggest additional methods of control.