Seedling development and growth of white clover, caucasian clover and perennial ryegrass grown in field and controlled environments

Autumn sowing on 4 February (SD1) and 31 March (SD2) 2000 was used to compare the establishment success of white and caucasian clovers sown with 0, 3, 6 or 12 kg seed/ha of perennial ryegrass. Total dry matter (DM) production from sowing to 3 October 2000 averaged 5770 and 3470 kg DM/ha for the two sowing dates, respectively. Clover species did not affect herbage production in monocultures which averaged 2610 kg DM/ha. The total DM increase from the addition of ryegrass was 87, 109 and 114% for 3, 6 and 12 kg/ha, respectively. On 3 October 2000, white clover content averaged 15% when sown with 3-12 kg/ha ryegrass on SD1 but less than 2% for SD2. Caucasian clover never exceeded 9% in either sowing and weed content was 2% when ryegrass was included for SD1 but 18% for SD2. A complimentary controlled environment study examined seedling development and growth of the three species. For each species the leaf appearance interval (phyllochron) in days differed across temperatures but was constant in thermal time at 94ºCd for white clover, 109ºCd for caucasian clover and 101ºCd for ryegrass. Axillary leaves and tillers of ryegrass first appeared after 375ºCd compared with 439ºCd for axillary leaves of white clover and 532ºCd for stolon initials. No secondary leaf development or rhizome initiation was detected in caucasian clover up to 774ºCd. At this time ryegrass seedling shoots were 635 mg/plant compared with 167 and 184 mg/plant for white and caucasian clovers, respectively. Thus, the success of ryegrass seedlings during autumn pasture establishment was explained by its high relative growth rate, and rapid onset of axillary leaf and tiller development compared with white and particularly caucasian clovers. Successful caucasian clover establishment is most likely to occur in the absence of either ryegrass or white clover