Development and growth characteristics of Caucasian and white clover seedlings, compared with perennial ryegrass

Seedling competition for resources during establishment affects the potential success of individual species within a pasture. Germination, emergence and leaf expansion are key characteristics that contribute to the competitive ability of species. In this study, development and growth characteristics of Caucasian clover, white clover and perennial ryegrass (PRG) seedlings were quantified. A base temperature of < 4 degrees C and an optimum temperature of similar to 27 degrees C were found for development in each species. Thermal time (Tt) requirements for 75% of final germination were lower for Caucasian clover (46 degrees C d) and white clover (40 degrees C d) than for PRG (76 degrees C d), but Tt requirements for 50% of final emergence were similar (similar to 110 degrees C d). The phyllochron (degrees C d leaf(-1)) for primary stem leaves was slower for Caucasian clover (109 degrees C d) than for white clover (94 degrees C d) and PRG (101 degrees C d). Appearance of the first PRG tiller, which indicates the initiation of secondary leaf development, occurred after 373 degrees C d, compared with 532 degrees C d for the first white clover stolon. Caucasian clover crown shoots did not develop until > 1180 degrees C d. Consequently, white clover and PRG had more leaves (similar to 15 plant(-1)) and faster shoot relative growth rates (similar to 0.062 mg mg(-1) d(-1)) than Caucasian clover (5 leaves plant(-1), 0.049 mg mg(-1) d(-1)).