The yield and chemical composition of Sabrina hybrid ryegrass and RvP Italian ryegrass were compared, with special reference to regrowth after defoliation in spring and early summer. Initial cuts were taken on 6, 20 April and 4. and 18 May; subsequently a conservation crop was harvested at either 5 or 7 weeks, and a second regrowth 30 days later. There were four fertilizer treatments. Tiller density, stem development and individual tiller dry weight were recorded in selected treatments.
At the initial cuts and in the conservation crops after the first three initial cuts, varietal differences in yield and dry-matter digestibility (DMD) were relatively small. In all other harvests, RvP was appreciably higher yielding than Sabrina, and it showed greater responses to fertilizer in all second regrowth harvests. The water-soluble carbohydrate (WSC) content of RvP was consistently higher than that of Sabrina in regrowth harvests; the DMD was higher in Sabrina.
In primary growth of the two cultivars, tillering was suppressed at the time of head emergence, but active tillering was resumed earlier in RvP, the later-heading cultivar. In RvP, tillers arising early in the regrowth periods attained head emergence within 5 weeks. In Sabrina there was a marked decline in head production during June, and an increase in the size of individual vegetative tillers.
In regrowth harvests both the yield and the % WSC were markedly reduced when drought conditions were most severe; the most marked varietal differences occurred at this time, both in terms of yield of dry matter and % crude protein responses to fertilizer treatment.
In the two cultivars the DMD of 7-week conservation crops harvested in late May was at least equal to that of 5-week crops harvested later during drought conditions. A distinctly more advanced stage of development was attained in the earlier, heavieryielding crops.