Renovating paspalum pastures by direct drilling ryegrass - is it worthwhile?

Abstract

A 5-year experiment at Ruakura Agricultural Centre measured the effects of blanket application of glyphosate herbicideand direct drilling ofperennial ryegrass and white clover on seasonal pasture composition and production. Plots were sprayed in autumn 1985 with 6,4,2 and 0 l/ha of glyphosate before direct drilling with a mixture of 'Ellett' ryegrass and 'Grasslands Kopu' white clover. These treatments werecompared with plots of the original paspalum pasture which was not sprayed or drilled. Plots were arranged at random in 6 replicate blocks that were rotationally grazed by dairy cows. Applying high rates (4-6 l/ha) of glyphosate completely eliminated paspalum from the pasture and subsequently, treatment differences between the 6 and 4 l/ha treatments for most variables were small. Differences in winter/spring herbage accumulation between the 4 l/ha treatment and the control plots were highest in the first year and declined with time, representing 1.9,0.8,0.8.0.6 and 0.4 t DM/ha, respectively, over the S years of the trial. The declining growth response was paralleled by an increasing level of paspalum in the previously sprayed plots, which exceeded 30% of DM by the fourth summer. Over the same period, their summer ryegrass contents had declined by more than half (46-20% of DM). These results suggest that for this site further renovation using glyphosate (at 4 l/ha) would be beneficial after 4 years to recapture the immediate superior growth responses, and since the costs of renovation could be met within 2 years. Keywords Paspalum dilitatum, Lolium perenne, seasonal herbage accumulation, renovation methods, glyphosate herbicide, dairy pastures, volunteer paspalum invasion, pasture botanical composition stability