The development and growth of annual clovers for use in dryland pasture

A series of field and controlled environment experiments aimed to quantify development and growth characteristics of arrowleaf, balansa, gland and Persian clovers for introduction to New Zealand dryland pastures. Thermal time requirements for germination were higher for arrowleaf (34 °Cd) than balansa (32 °Cd), gland (28 °Cd) and Persian (25 °Cd) clovers. Persian clover had an optimum germination temperature (Topt) of 33 °C and a maximum temperature (Tmax) of 45 °C, while all the other species had Topt between 16-20 °C and Tmax of ~34 °C. In field and controlled environment experiments, arrowleaf and gland clovers emerged after 90 and 96 °Cd respectively. Balansa and Persian clovers took ~89 °Cd to emerge when sown at soil temperatures below 12 °C. Above 12 °C, they emerged quicker at 75 °C d for balansa and 55 °C d for Persian clover. Arrowleaf clover produced its first (spade) leaf after 196 °Cd compared with balansa (169 °Cd), gland (175 °Cd) and Persian (154 °Cd) clover. Throughout all sowing dates, phyllochron was the fastest for gland (33-91 °Cd/leaf) and slowest for arrowleaf (53-116 °Cd/leaf) compared with balansa (44-82 °Cd/leaf) and Persian (61-93 °Cd/leaf) clovers. Crops sown into a decreasing photoperiod had a longer phyllochron than those sown into an increasing photoperiod. The influence of photoperiod in modification of the phyllochron affected time to axillary leaf production. A slower phyllochron resulted in longer time to the first axillary leaf. Autumn sown crops that emerged into a decreasing photoperiod had a longer thermal time requirement to flower than spring sown crops and produced more vegetative growth. Therefore, autumn sowing is recommended to maximise dry matter production. The time to flower became shorter with increasing photoperiod until the longest day of the year before it began to slow down as photoperiod decreased towards autumn. All species are long day plants, which only flower when photoperiod increases above 11.3 hours for arrowleaf, 12.6 hours for balansa, 10.3 hours for gland and 15.4 hours for Persian clover. Gland clover flowered earlier (500–1216 °Cd) compared with balansa (600-1733 °Cd), arrowleaf (940-1834 °Cd) and Persian (1047-2610 °Cd) clovers. The differences in flowering time suggests the suitability of gland clover to be grown in areas that dry out quickly in late spring, balansa clover in areas of wet winter and dry summer, and arrowleaf and Persian clovers in areas that receive high spring rainfall. In the establishment year, these annual clovers produced dry matter up to 17.5 t/ha for balansa, 12.5 t/ha for Persian, 11.0 t/ha for gland and 9.4 t/ha for arrowleaf clover. Balansa clover had the highest radiation use efficiency of 2.1 g DM/MJ PAR absorbed followed by gland clover (1.6 g DM/MJ PAR) then arrowleaf and Persian clovers (1.3 g DM/MJ PAR). In the second year, regenerated dry matter production at full flower was up to 11.6 t/ha in balansa, 8.3 t/ha in Persian, 2.9 t/ha in gland and 0.5 t/ha in arrowleaf. Maximum seed production of balansa and gland clovers was 2309 and 2370 kg/ha, respectively in contrast to arrowleaf and Persian clovers which only yielded 914 and 814 kg/ha seeds. In the second year, the percentage seedling emergence from the seed population was 23% for balansa, 19% for Persian, 14% for gland and 10% for arrowleaf clover. These seedlings grew to produce a ground cover up to 91% for balansa, 17% for Persian, 65% for gland and 6% for arrowleaf clover by the end of the second year. Persian clover did not persist because it did not produce any hard seeds. For arrowleaf, balansa and gland clovers, the recovery of hard seeds in the soil after 18 months showed that there was adequate seed production that could sustain on-going regeneration in subsequent years.