Effect of cultivar of white clover on plant morphology during the establishment of mixed pastures under sheep grazing

The establishment of white clover from seed is characterised by two distinct morphological growth forms, a seminal tap-rooted stage with radiating stolen systems lasting 1-2 years, followed by a clonal growth form. Transition of a plant from tap-rooted to clonal form occurs when the tap root and primary stem axis die, releasing a variable number of stolen systems as independent clonal plants. The purpose of this study was to investigate any effect different cultivars of white clover may have on the morphology of plants during the transition of populations from tap-rooted to clonal growth form when establishing in mixed pastures based on either perennial ryegrass or tall fescue. Cultivars studied ranged from small-leafed to large-leafed cultivars in the order of Prop, Prestige, Demand, Huia, Sustain, Le Bons, Kopu, and Aran. During the tap-rooted phase there were no differences between cultivars in shoot growth apart from the small-leafed cultivars (Prop, Prestige, Demand, and Huia) having a higher plant branching order and lower partitioning to leaf than the large-leafed cultivars (Sustain, Le Bons, Kopu, and Aran). After one year, tap-rooted plants were 4-5 times larger than plants in the subsequently formed clonal populations. Tap root death and fragmentation to form clonal plants commenced one year after sowing and initially occurred at a faster rate in small-leafed than in larger-leafed cultivars. By 15-18 months later, loss of all tap-rooted plants in all cultivars was complete. The mean characteristics of clonal plants and populations were similar for all cultivars, and similar to those reported in other studies. It took two years of differential grazing management to achieve the balance in plant DW structure reported in older pastures. The possible role of changes in plant form in cultivar performance is discussed.