The measurement of perennial ryegrass persistence

Poor persistence in perennial ryegrass has been identified as a major limitation to pasture productivity, particularly in the upper North Island. Persistence can best be defined as the continuity of forage yield relative to a cultivar’s potential. Though there is limited evidence of differences in persistence between cultivars, there is interest in including persistence in the DairyNZ Forage Value Index. This requires an agronomically robust metric of persistence, measured over a suitable time frame and connected to economic value. Five candidates are evaluated: plant populations, tiller populations, basal cover, ground score and annual dry matter yield. Scarcity of long-term data is a major limitation to development of performance values for persistence, and must be addressed. The four abundance-based measures also lack a clear connection to economic values, from the limited data available. A persistence metric is proposed, that relates medium-term dry matter yield to short-term dry matter yield, for which perennial ryegrass functional type and cultivar differences are demonstrated.