1. Two experiments are described in which the effects of grazing a lucerne/cocksfoot ley at various intervals throughout the season were examined, together with the effects of a June hay cut and an autumn rest period. The results are discussed.
2. In the year of treatment: (a) The wet year 1954 favoured the grass fraction and the dry year 1955 favoured the lucerne fraction but, in general, the proportion of lucerne in the sward decreased as frequency of defoliation increased. (b) The largest yields of lucerne dry matter were obtained from treatments that included a June hay cut and the largest yields of grass dry matter came from those treatments that included an autumn rest period, (c) Within the chosen programmes of defoliation, there was a tendency for greater yield of dry matter from those treatments defoliated four times when compared with one cut three times, but yields from treatments defoliated more frequently tended to be smaller, with a marked reduction from seven grazings.
3. In subsequent years: (a) Treatments in the wet year had a greater effect on subsequent lucerne vigour than treatments in the dry year, (b) Yields of lucerne dry matter from three hay cuts in the first residual year were reduced by all the grazing treatments, the greatest difference occurring at the first cut. Lucerne yield decreased with increasing frequency of treatment defoliation. There was a tendency for the autumn rest period to increase lucerne yield and for the June hay cut to reduce it. (c) Total grass dry matter yield was greatly increased by grazing treatments, the majority of this difference occurring at the first cut, and it also increased with increasing frequency of treatment defoliation. (d) The proportion of cocksfoot in the grass fraction of the sward was reduced by treatments that included defoliation during the period September–October, and it was further reduced by treatments that included a June hay cut. (e) In the second year following treatment the effect of grazing on the grass fraction had disappeared but reductions in lucerne vigour from too frequent defoliation were still evident, though reduced.
4. Grazing a lucerne/cocksfoot ley reduced the subsequent vigour of the lucerne more than would have been expected from cutting it a similar number of times. This reduction is attributed to increased competition from the grass arising from its response to nutrients in the excreta of the grazing animals. In a wet year four grazings caused a permanent reduction in lucerne vigour and more frequent grazing almost eliminated the lucerne, but in a dry year four grazings caused only a temporary reduction in lucerne vigour and had no lasting effect.
5. The interval between defoliation and the subsequent onset of flowering in the lucerne was very much less in the hot dry year than in the cooler wet year. There appeared to be a relationship between the onset of flowering and the ability of the lucerne to recover from defoliation.