Effects of pasture base and species mix complexity on persistence and weed ingress in summer-dry dairy pastures

Basal and canopy cover of sown and unsown species in swards sown with six different mixtures were assessed monthly from autumn 2010 to spring 2014, to test the hypotheses that a) increasing the complexity of the sown mix, or b) sowing an alternative pasture base, improves persistence and reduces weed ingress in summer-dry dairy pastures. Treatments comprised either perennial ryegrass (Lolium perenne) or tall fescue (Schedonorus arundinaceus) to which were added either a legume (‘standard’, 2 species mix), a legume and two forage herbs (‘herbs’, 4 species), or three legumes, two forage herbs and two grasses (‘complex’, 8 species). In the first year, basal and canopy cover of sown species were higher in perennial ryegrass- than tall fescue-based swards, and basal cover of sown species was higher and the percentage bare ground lower in the ‘standard’ (50%) than ‘herbs’ and ‘complex’ swards (42%). By the final year, basal cover of sown species (25%), unsown species (28%), and percentage bare ground (47%) were similar in all six treatments. The decline in basal cover of sown species was less in the ‘complex’ and ‘herbs’ (-16%) than ‘standard’ treatment (-27), and less in tall fescue (-15%) than in perennial ryegrass-based swards (-24%). Although establishment was better in perennial ryegrass than tall fescue-based swards and in the ‘standard’ than in the ‘herbs’ and ‘complex’ mixtures, the loss of sown species in these treatments was greater. These results are contrary to the hypotheses with respect to weed ingress. However, support was provided for the hypotheses in the greater persistence (smaller decline over time in basal cover) in tall fescue than ryegrass-based swards, and ‘herbs’ and ‘complex’ than ‘standard’ mixtures.