Seedling vigour 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

Abstract

Trifolium ambiguum was grown from seed in a mixture with Festuca arundinacea and Phalaris aquatica at four grass densities under high fertility, and at two intermediate grass densities under low fertility, with frequent or infrequent defoliation imposed from week 15 to week 31, in large pots for 1 year. Selective defoliation of the clover at week 35, and 3-4 weeks drought were imposed on high and low fertility treatments in the post-cutting period. The impact of these treatments was assessed by destructive harvest of shoots, roots and rhizomes. Plant densities of T. ambiguum and grasses were unaffected by the treatments; however, rhizome numbers were reduced by increasing density of grasses, by frequent defoliation, and at high fertility compared with low fertility where grass vigour was very poor. Selective defoliation of T. ambiguum and short-term drought temporarily reduced the contribution of T. ambiguum to harvested herbage, but had no permanent effect on growth rate. Final root and rhizome biomass of T. ambiguum was reduced by increasing density of grass, by frequent defoliation and at high fertility where grass competition was vigorous. We conclude that early growth of T. ambiguum, in particular root and rhizome development, may be better where the density of companion grasses is low, or grass vigour is low due to low fertility, provided soil P and S are not limiting for clover growth. Defoliation in the presence of vigorous grass competition reduces root and rhizome development and may not be effective in minimizing competition. Options for inclusion of T. ambiguum in mixed swards are discussed.