Implications of grass–clover interactions in dairy pastures for forage indexing systems. 3. Manawatu

The implementation and monitoring of the treatments in the core experiment (eight perennial ryegrass cultivars grown under four combinations of plus/minus clover and high/low nitrogen (N)) at a dryland Manawatu site are described. Herbage accumulation (HA) was significantly greater for high N than for low N in 14 out of 21 annual and seasonal totals. There were no significant main effects of clover and there were no interactions between clover and N level. With the exception of autumn 2016, there were significant differences among ryegrass cultivars in all seasons, but no clover x cultivar or N x cultivar interactions for HA or nutritive value (NV). With the caveat that successive droughts reduced the proportion of white clover to low levels, the hypothesis that relative HA or NV rankings of ryegrass cultivars do not differ when ryegrass is grown in monoculture or in mixtures with white clover is supported.