A comparison of diploid and tetraploid Lolium perenne L. sown alone and in mixtures with particular reference to the effect of treading

Abstract

SUMMARYDiploid and tetraploid perennial ryegrass (Lolium perenne L.) cultivars were compared sown alone and in mixtures, with and without cattle treading for 4 years after the year of sowing. Data were also obtained on the survival of tetraploid ryegrass in mixtures under farm conditions.The overall effect of treading was not large but annual yield of dry matter was reduced by cattle treading every year (mean 9%). Sheep grazing and treading also reduced yield below that of cut plots. The reduction depended on the sampling date and varied from 40% to nil. In two instances treading increased yield.Interactions between cultivars/mixtures and treading occurred in 22% of the occasions when treading influenced yield. In the first harvest year the tetraploid Reveille was more resistant to treading than the diploid S. 24. In older swards (3rd and 4th harvest year) the situation was reversed. The occurrence of cultivar/mixtures × treading interactions and the effect of mixing diploid and tetraploid ryegrass on resistance to treading were unpredictable.The evidence from the main trial and the farm survey showed that tetraploid ryegrass could persist for at least 3 years after the seeding year when exposed to periods of high stock density. In addition, in mixtures there was no initial domination of the sward by either component when cut or when subjected to severe treading. In the third harvest year of the experiment the proportion of tetraploid ryegrass decreased considerably. Total yield of the mixtures was not significantly different from that of pure swards of the components though seasonal distribution of yield could be modified. The contribution of tetraploid ryegrass to swards up to 4 years old was in proportion to the percentage of tetraploid in the seeds mixture. Evidence from both the experiment and farm survey demonstrates that it is possible to exploit advantages claimed for tetraploids in mixtures for three harvest years without detrimental effect on sward performance.