SEEDLING VIGOR AND RHIZOME DEVELOPMENT IN TRIFOLIUM-AMBIGUUM M-BIEB (CAUCASIAN CLOVER) AS AFFECTED BY DENSITY OF COMPANION GRASSES, FERTILITY, DROUGHT AND DEFOLIATION IN THE FIRST YEAR

Trifolium ambiguum was grown from seed in a mixture with Festuca arund inacea and Phalaris aquatica at four grass densities under high fertil ity, and at two intermediate grass densities under low fertility, with frequent or infrequent defoliation imposed from week 15 to week 31, i n large pots for 1 year. Selective defoliation of the clover at week 3 5, and 3-4 weeks drought were imposed on high and low fertility treatm ents in the post-cutting period. The impact of these treatments was as sessed by destructive harvest of shoots, roots and rhizomes. Plant den sities of T. ambiguum and grasses were unaffected by the treatments; h owever, rhizome numbers were reduced by increasing density of grasses, by frequent defoliation, and at high fertility compared with low fert ility where grass vigour was very poor. Selective defoliation of T. am biguum and short-term drought temporarily reduced the contribution of T. ambiguum to harvested herbage, but had no permanent effect on growt h rate. Final root and rhizome biomass of T. ambiguum was reduced by i ncreasing density of grass, by frequent defoliation and at high fertil ity where grass competition was vigorous. We conclude that early growt h of T. ambiguum, in particular root and rhizome development, may be b etter where the density of companion grasses is low, or grass vigour i s low due to low fertility, provided soil P and S are not limiting for clover growth. Defoliation in the presence of vigorous grass competit ion reduces root and rhizome development and may not be effective in m inimizing competition. Options for inclusion of T. ambiguum in mixed s wards are discussed.