Botanical survey of perennial ryegrass-based dairy pastures in three regions of New Zealand: implications for ryegrass persistence

Abstract

A botanical survey of 24 commercial dairy pastures ranging in post-sowing age and perennial ryegrass type (mid-season diploid, late-season diploid, tetraploid) was undertaken in each of Waikato-Bay of Plenty (BoP), Taranaki and Canterbury during autumn/winter. The mean perennial ryegrass proportion (85% of total DM) and tiller density (3252 m−2) was greatest in Canterbury and the broadleaved weed proportion lowest (2%). Conversely, Waikato–BoP had the lowest ryegrass proportion (59%), tiller density (1817 m−2) and greatest proportion of broadleaved weeds (15%), with Taranaki intermediate. Tiller density was greater in pastures sown with diploid rather than tetraploids (averaging 3033 vs. 1784 m−2). Grass grub (Costelytra zealandica, 11 m−2) populations were lowest in the youngest age category pastures where nematode populations were highest (80 g−1 dry soil). The soil seedbank was dominated by unsown species (with total species emergence averaging 4594 seeds m−2), with negligible ryegrass emergence.