The effect of continuous grazing on the seed production of Subterranean clover (Trifolium subterraneum).

Abstract

Three pure swards of subterranean clover were either (a) left ungrazed with a leaf area index (LAI) of 4.6, or (b) continuously grazed leniently to leave 1 600 kg DM/ha herbage mass equivalent to an LAI of 1.0, or (c) hard grazed to leave 1 400 kg DM/ha herbage mass equivalent to an LAI of 0.6 throughout the flowering period. These swards yielded 1 250, 320 and 70 kg/ha of seed, respectively. One intensive sampling during the middle of flowering showed that seed yield was positively correlated with plant weight, leaf area per plant, and area per leaf, specific leaf area and leaf area ratio. Grazing reduced numbers of both inflorescences and burrs and hence seed yield. Whilst reduced leaf area and plant weight may have also been partly responsible, under hard grazing, only 58% of potential reproductive sites were occupied which suggests that grazing animals also reduced seed yield by consuming these. It is recommended that continuous grazing during flowering and seed maturation should be controlled to leave at least 1 600 kg DM/ha of residual herbage mass, equivalent to an LAI of 1.0, if adequate seed is to be produced to be ensure the establishment of a high producing sward in the following growing season. Key words: flowering, grazing, herbage mass, leaf area, seed production, Trifolium subterraneum