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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 × cultivar or N × 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. [ABSTRACT FROM AUTHOR]

Herbage accumulation (HA) data from four sites were combined to (1) address the hypothesis that adjustments to the New Zealand Forage Value Index to account for grass-clover interactions are not required and (2) explore the main effects of clover and nitrogen (N) fertiliser treatments on pasture productivity. In summer and autumn, pastures based on mid-season heading ryegrass cultivars consistently supported a greater clover content than pastures based on late heading cultivars. However, the clover ×  cultivar interaction was significant in only 2 of 17 HA data sets available for analysis. Thus, the hypothesis is supported. Compared with ryegrass monocultures, mixtures yielded an additional 2.4 (in the Low-N treatment) and 1.2 (High-N treatment) t DM/ha/year. Apparent N transfer from clover to grass was 79 (Low N) and 27 (High N) kg N/ha/year, derived from estimated N fixation efficiencies of 66 (Low N) and 50 (High N) kg N/t clover DM grown. [ABSTRACT FROM AUTHOR]