CHANGES INDUCED BY DEFOLIATION IN THE YIELD AND DIGESTIBILITY OF LEAVES AND STEMS OF PERENNIAL RYEGRASS (LOLIUM-PERENNE L) DURING REPRODUCTIVE DEVELOPMENT

Ten identical perennial ryegrass plots (cv. Frances) were sequentially harvested for first cut silage at 7 day intervals, with second cuts a fter 6 weeks regrowth and further cuts until the growing season ended. Total herbage dry matter and digestible organic matter yields increas ed and digestibility decreased with delayed cutting, as was expected. The opposite and counterbalancing response occurred at the second cut. This pattern of yield change was mirrored by changes in the amount of stem tissue, whereas leaf yield did not change significantly at the f irst harvest but declined at the second, in response to delayed cuttin g. Furthermore, stem digestibility declined at the first cycle of harv ests from ca. 75 to 62-64% in the most delayed cutting treatments. In contrast, leaf digestibility remained high (ca. 70%) until after seed- head emergence but then decreased rapidly to ca. 56%. This decline may have been associated with accelerated leaf senescence and redistribut ion of assimilates, though this needs to be examined. It was concluded that although manipulating first harvest date determined the proporti oning of yield and digestibility in the first and second cuts, the obs ervation that the combined yield and digestibility in these two harves ts did not vary substantially is an important result for fanning pract ice. (C) 1997 Elsevier Science B.V.