effects of frequency of defoliation, date of first cut and heading date of a perennial ryegrass companion on the yield, quality and persistence of diploid and tetraploid broad red clover

The effects of cutting frequency on dry matter yield, crop persistence and herbage quality of representative diploid and tetraploid varieties of broad red clover (Trifolium pratense) were investigated in two trials at Hurley in the period 1975–79. Pure‐sown swards of broad red clover varieties were used in the first trial (A), while both pure‐sown swards and those sown with a perennial ryegrass companion grass were included in the second trial (B). Tria1was cut three or six times per annum, trial B three, four or five times per annum. In both trials, the change from normal management of three cuts per annum to six (trial A) or five (trial B) cuts per annum reduced output, whether in terms of dry matter yield (trial A by 31%; trial B by 33%), N yield (trials A and B by 15%) or metabolizable energy (trial A by 24%; trial B by 28%), and in trial A also led to more rapid reduction in clover plant density. More frequent cutting also raised mean D–value (trial A by 5–3 units; trial B by 3–4 units) and N concentration (trial A by 64 g kg dry matter‐1; trial B by 70 g kg dry matter‐1). Tetraploid (4x) red clover varieties generally out–yielded diploid (2x) varieties, except in trial A in 1976 when, under drought conditions, Granta and Kuhn (both 2x) equalled the yield of Wensum (4x) and out–yielded Norseman and Maris Leda (both 4x). The companion grasses included in trial B formed a sequence from early to late flowering (Aberystwyth S24, Barlenna, Endura), and their inclusion raised dry matter yields and D‐value, though it lowered N concentration in the mixed herbage. Highest annual dry matter yields in this trial, which received supplementary irrigation, were 1641 ha‐1 from a pure–sown crop (Hungaropoly) and 205 t ha‐1 from a mixture (Wensum/ Aberystwyth S24), from three cuts in the first harvest year. Aberystwyth S24 had the greatest effect in raising yields; though least effect on improving digestibility. Endura was the converse, and it was concluded that an intermediate‐maturity variety such as Barlenna was the most satisfactory companion. Both trials A and B suggested that in south–east England, broad red clover can be considered only as a 2–year crop and that ways must be found to prolong its productive life. Strategies to increase the digestibility and hence the economic value of the crop by cutting more frequently than three times per year are unattractive because of the large fall in yield and relatively small improvement in digestibility and hence metabo