Competition between cocksfoot (Dactylis glomerata L.) and companion species: Evidence for allelopathy

Cocksfoot (Dactylis glomerata L.) is a widely grown temperate perennial grass for livestock production worldwide. Recent studies have observed that cocksfoot plants inhibit the growth and development of companion and volunteer species. However, there has been little research on how this inhibitory effect happens and whether it occurs widely or on a limited number of species only. The aim of the study was to quantify the inhibitory or allelopathic effect and its possible role in the effect of cocksfoot on the growth and seed germination of a range of grass, legume and volunteer species. Three experiments were conducted: Experiment 1 was a greenhouse experiment that used 4 grass and legume monocultures and 9 mixtures with 3 mixtures ratios; Experiment 2 was a lab experiment that used different concentrations of cocksfoot rhizosphere extracts to test the germination and seedling growth of 5 commonly sown pasture species; Experiment 3 was a field experiment to validate the inhibitory effects of cocksfoot as shown in Experiments 1 and 2 under field conditions. The results demonstrated that cocksfoot had strong inhibitory effects on all the species tested in this study although the magnitude varied between species. On average, the cocksfoot percentage in mixtures was increased by 120% for herbage accumulation, and 168% for tiller density relative to its designed proportions in mixtures under field conditions. Cocksfoot rhizosphere extracts considerably reduced the germination and seedling growth of all tested species except lucerne that had lower seedling vigour. It is concluded that cocksfoot roots may have produced metabolites that inhibit the seed germination and plant growth of companion or volunteer species. This could be a contributor to the superior persistence of the species and have significant practical implications on weed control. The biochemical compounds of cocksfoot root metabolites and their functions deserve further investigation.