The vegetative and reproductive development of balansa clover

Abstract

The vegetative and reproductive development of balansa clover (Trifolium michelianum Savi.) were quantified in relation to the environmental drivers of each phenophase in field and controlled environments. In a grazed experiment over 6 years, balansa clover sown with cocksfoot (Dactylis glomerata) contributed 1.6 t DM/ha/year, or ~20% of the total DM production. However, grazing management for increased seed production during flowering in the establishment year strongly influenced balansa clover regeneration. The earliest closed plot (September) averaged between 2.2 and 4.3 t DM/ha/year of balansa clover across all six years.

In an incubator, balansa clover required 29°Cd for germination with an optimum temperature of 14°C and a maximum of 40°C. The base temperature for germination was 0°C. A field experiment determined that 38°Cd were required for emergence with an optimum soil temperature (Topt) of 8.5°C. The time from emergence until the first leaf appeared, the phyllochron and timing of axillary leaf appearance were compared with perennial ryegrass (Lolium perenne) and white clover (Trifolium repens L.). The rate of each was found to increase linearly with temperature. The balansa clover cultivar ‘Frontier’ required 97°Cd from sowing for the first leaf to appear, had a phyllochron of 47°Cd and secondary leaves appeared after 490°Cd. For each vegetative stage, the base temperature was 2.5°C.

The timing of flower appearance depended on the quantity and direction of change of the photoperiod at emergence. A balansa clover plant, cv. ‘Bolta’, which emerged on 1 December into an increasing photoperiod of 15.6 hours flowered after 574°Cd (Tbase = 2.5°Cd) or 58 days after emergence. In contrast, if the plant emerged on 16 January into a similar but decreasing photoperiod it took 1503°Cd or 227 days to flower. This length of time became progressively shorter until remaining constant after the shortest day. In contrast, ‘Frontier’ took a constant 390 and 690 °Cd in increasing and decreasing photoperiods, respectively. The time which an individual inflorescence took from pollination until seeds were physiologically mature was 250 °Cd for both ‘Bolta’ and ‘Frontier’.

The re-establishment of balansa clover each year relied on a large seed set (>1000 kg/ha) in the establishment year. The continued survival of balansa clover would then depend on a similar seeding event within a 4-5 year period to maintain the seed bank. Management considerations for balansa clover persistence and survival are discussed.