Delayed autumn closing and its effects on silage dry matter production and sward quality

The effects of delayed autumn closing of perennial ryegrass-based swards on silage dry matter production and quality from first cut silage harvest the following season were evaluated in a plot experiment conducted at Hillsborough, Northern Ireland. Last defoliation as a simulated grazing cut was completed in mid-September, mid-November or mid-January in 2018/2019 and in 2019/2020. Silage dry matter yields from plots defoliated in September were significantly higher than those from plots defoliated in January in both seasons. Defoliation in January resulted in silage with significantly lower ammonia nitrogen as a fraction of total nitrogen compared with defoliation in September in both seasons, with a significant timing × year interaction. Silage metabolisable energy was significantly higher for plots defoliated in November 2018 and January 2019 compared with those defoliated in September 2018. There were statistically significant effects of defoliation timing for acid detergent fibre and volatile corrected organic dry matter but not for other silage quality parameters.