Effects of perennial ryegrass cultivar, duration of lock up and nitrogen fertiliser application on dairy pasture dry matter yield and quality for silage in south-western Victoria

A study in south-western Victoria determined effects of 3 perennial ryegras s (Lolium perenne L.) cultivars (Vedette, Impact and Nevis) with differing maturities, duration of lock up and nitrogen (N) application on the dry mat ter yield and nutritive characteristics of pasture for silage. Treatments w ere cultivar (3), N (0 and 50 kg N/ha) and duration of lock up (5-10 weeks) arranged in a completely randomised design in 3 by 5 m plots replicated 3 times. Plots were mown to a uniform height (5 cm) on 14 September 1998 (fir st day of lock up) and 1 week later N was applied as urea (46% N) at either 0 or 50 kg N/ha to the respective plots. Weekly sampling commenced on 19 O ctober (week 5 of lock up), and continued until 23 November. For each treat ment and harvest date, dry matter yield and botanical composition were dete rmined, and samples of total pasture and the ryegrass fraction were collect ed and chemically analysed for dry matter digestibility, concentrations of crude protein, neutral detergent fibre, water-soluble carbohydrates and min erals. Metabolisable energy was derived from dry matter digestibility. All pasture types were predominantly ryegrass (>90%) with no differences in the nutritive characteristics of total pasture swards or the respective ry egrass fraction. Nitrogen at 50 kg N/ha significantly (P<0.05) increased dr y matter yield for all cultivars. Metabolisable energy (MJ/kg DM) of the pa sture declined with time for all treatments, with Vedette having a signific antly (P<0.05) greater rate of decline than the other cultivars. Vedette re ached early ear emergence about 3 weeks earlier (week 7) than the other cul tivars. The harvestable metabolisable energy yield (MJ/ka) at ear emergence was highest for Impact, followed by Nevis and Vedette. In conclusion, there is potential to use later-maturing cultivars of ryegra ss in south-eastern Australia to allow for later harvesting of forage for s ilage, while maintaining metabolisable energy and maximising dry matter yie lds. Furthermore, the use of N fertiliser can also increase dry matter yiel ds without impinging on pasture quality provided the time between N applica tion and harvest date does not exceed 5-6 weeks.