No abstract

Studies of the germination of subterranean clover (Trifolium subterraneum L.)

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

An attempt is made to establish a relationship between herbage utilization, pasture production, and animal performance per unit area. When pastures are rotationally grazed, it appears that the highest pasture yield and animal production per unit area will result only if feed demand is closely matched with supply so that little stubble is left after grazing. Experimental data indicate that the aim should be to achieve at least 60% single grazing utilization of the total herbage on offer as long as in so doing overgrazing does not occur. Future work is likely to show the need for an even greater degree of utilization if per-hectare production is to be maximized. Limited data suggest that overgrazing of ryegrass pastures commences when they are grazed below 2 cm, while with more upright grass species this starts when defoliation is closer than 10 cm.

This review covers the history of subterranean clover (Trifolium subterraneum) and its present occurrence in New Zealand; a review of research and conclusions to be drawn from this; and examines past and future research directions. Subterranean clover has been important in terms of area of use in New Zealand since the late 1930's. Today it makes a significant contribution to pasture production on steep, north-facing North Island hill country where effective rainfall is low, and in other areas where soil moisture drops below wilting point for between 2 weeks and 5 months of the year. Research has identified the superiority of cultivars possessing a compact, ground-hugging habit of growth, and flowering late, in late October - early November, for use in North Island hill country. In drier areas, more research is needed to identify superior cultivars, although there is evidence that lines in the mid-season or early mid-season flowering groups may be appropriate. A major problem for the use of subterranean clovers in New Zealand is the slow breakdown of hardseededness. About 7 M ha of land in New Zealand is mapped as being subject to slight to severe moisture deficit (an area which could with advantage support subterranean clover), but further research is needed to identify appropriate cultivars for 4.8 M ha or more of this area. Key words: history, New Zealand, research, Trifolium subterraneum