Improving the power of pasture cultivar trials to discriminate cultivars on the basis of differences in herbage yield

Abstract

A review of 7 recently published perennial ryegrass cultivar trials (from 6 contrasting environments) with data expressed as an aggregate of seasonal harvests (autumn, winter, spring, and summer) revealed that the 1.s.d. (P = 0.05) varied between 4 and 255% of the mean herbage yield of the trial in a given season, with 56 of 72 data points having an 1.s.d. (P = 0.05) > 10% of the trial mean. Power analysis of a perennial ryegrass trial that was conducted at Heywood (Vic.) from 1997 to 1998, with a 16% apparent difference in the total yield of a new synthetic and commercial cultivars, demonstrated that this difference would have only been detected 45% of the time. However, if the number of re..