Amount and quality of grass harvested for first-cut silage for differing spring-grazing frequencies of two mixtures of perennial ryegrass cultivars with contrasting heading date

Abstract

There are potential advantages and disadvantages associated with grazing spring perennial ryegrass swards designated for first-cut silage. These may differ for intermediate-heading (0·50 ear emergence in the second half of May) and late-heading (0·50 ear emergence in the first half of June) cultivars. The interactions between cultivar type, spring-grazing frequency, silage-harvest date and year were examined in an experiment with a randomized complete block (n = 4) design with a factorial arrangement of treatments, conducted in Ireland. The factors were (i) two perennial ryegrass mixtures: intermediate- vs. late-heading cultivars, (ii) three spring-grazing regimes: no grazing, grazing in mid-March or grazing in both mid-March and mid-April, (iii) four first-cut silage-harvest dates that were at c. 10-d intervals from 19 May and (iv) 2 years (1998 and 1999). The effects of cultivar mixture on herbage mass of the swards in spring were small and not statistically significant. The late-heading cultivars provided lower amounts of herbage dry matter for harvesting for first-cut silage but herbage with higher in vitro organic digestibility values compared with intermediate-heading cultivars. To achieve the same amount of herbage for silage, the late-heading cultivars needed to be harvested 8 d later than the intermediate-heading cultivars. Even with this delay in harvest date, the late-heading cultivars had higher in vitro organic digestibility values than the intermediate-heading cultivars. The late-heading cultivars could be harvested up to 30 d later and produce a higher amount of herbage for first-cut silage with similar digestibility values compared with the intermediate-heading cultivars.