As silage is the main winter feed on most Irish farms, it is essential that it gets the appropriate attention to detail for all aspects of its production, storage and feeding to ensure that a reliable and cost-competitive feed is produced.
Utilising research from Dr. Padraig O’Kiely, formerly of Teagasc, who dedicated his work as a researcher at the Teagasc Animal and Grassland, Research and Innovation centre in Grange, we focus on the long and medium-term guidelines which impact the quality of the silage made on Irish farms. Next month we will concentrate on the shorter-term guidelines so you can optimise the quality of your silage for 2020.
Digestibility and preservation are the two main components of silage quality. Silage digestibility depends mainly on how much leaf is present and how few seedheads and dead vegetation were in the harvested crop. Highly digestible silages support much better and more efficient animal performance (Table 1), but are more expensive to produce, than silages of low digestibility.
Table 1. Silage digestibility effects on kg energy-corrected milk/cow/day, at a range of rates of concentrate input
Concentrate input (kg/cow/day)
Source: Randby et al. (2012)
Long term guidelines
The species of plants in silage swards are very important. If you require high yields of silage that have superior digestibility and are relatively straightforward to preserve, then perennial ryegrass dominant swards are an essential long-term investment. For silage swards already in place some guidelines include:
- Avoid soil compaction when grazing, applying slurry and when fertiliser spreading. Compaction can reduce yields, ryegrass persistence and trafficability on land.
- Manage slurry and inorganic fertiliser application based on regular soil analysis to ensure you are working with appropriate soil P and K status, and pH. Deficiencies of soil P, K and/or pH are the main cause of sub-standard silage quality on many farms.
Medium term guidelines
Manage livestock to sensibly graze silage swards in spring (before late March), to avoid the accumulation of low quality dead/stemmy herbage at the base of the silage crop. A substantial dead butt can drop crop digestibility by 5 – 6 percentage units in May. If adopting spring grazing, make sure to remove the cattle early enough to permit adequately high silage yields be achieved. Similarly, if rolling silage fields in spring, complete the job before grass starts to elongate, as late rolling can crush the stems and impair growth.
Avoid excess input of N, be it from inorganic fertiliser (e.g. urea or CAN), slurry or both, as this can predispose well advanced heavy-yielding silage crops to lodging, if weather conditions turn wet and windy. A lodged crop lying in continuously wet conditions can lose up to 9 percentage units digestibility in a week; compared to the normal expected loss of 2 to 3 percentage units.
Apply up to a total of 110 – 125 (reseed) kg N/ha, between the combined contributions of inorganic fertiliser and slurry. High or late application of N from inorganic fertiliser and/or slurry can greatly reduce grass sugar concentration and increase buffering capacity (Table 2), thereby making it harder to preserve as silage. Similarly, late or uneven application of slurry that leaves the grass contaminated at harvest time makes the silage quite difficult to preserve.
Table 2. Ensilability of grass in response to nitrogen fertiliser application
Rate of N applied (kg/ha)
Dry matter %
Sugars (% in juice)
Buffering capacity (mEq/kg DM)
Source: Teagasc, Grange
As we get closer to harvest, we will bring you a list of short-term guidelines that are important when making high quality silage.