The Testing of Grass Varieties in Swards With Clover: The Effect of Grass Seed‐rate on Comparisons of Gross Yield

Three experiments were carried out to examine the influence of grass seed‐rate upon the amount of clover growing with different varieties of perennial ryegrass. The bred varieties S23 and S24 were compared with Irish ryegrass. A larger quantity of clover grew with Irish ryegrass than with bred varieties at any given seed‐rate. If the varieties were to be compared in terms of herbage of similar clover content, then Irish ryegrass sown at 20 lb/ac had to be compared with S23 or S24 sown at about a quarter of that rate. Reducing the seed‐rate of the bred varieties from 20 to 5 lb/ac had only a small effect upon yield of ryegrass, and this was offset by an increase in yield of clover. Since weed grasses also took advantage of low grass seed‐rate, it is concluded that other factors in the management of variety trials must be so controlled as to produce a satisfactory clover content without too drastic a reduction in the seed‐rate of any variety. The relationship between grass seed‐rate and yield of clover varied markedly with the availability of moisture.