In this article from the beginning of April 2013, Padraig O’Kiely of Teagasc Grange helpfully partitions management decisions related to silage-making into nine long-term and short-term strategies.
Longer-term strategies
1. Soil fertility
Having a viable yield of grass to harvest for silage necessitates the soil status of phosphorus (P), potassium (K) and lime being adequate to support sustained good
growth. On many farms, this basic nutrient status has declined in some fields (e.g. they are at soil index 1 or 2, instead of index 3 for P and K) with the following results:
- Grass yields are low on target harvest dates, and the management response to this is often to defer harvest date until yields increase sufficiently. However, the digestibility (feed value) of the sward declines when the crop is allowed to advance in maturity in this way.
- There will be a poorer yield response to nitrogen (N) applied in mineral fertilizer or slurry. This means that the economic reward from applying N is reduced.
- It may be difficult to retain persistence of ryegrass swards. The way to know the P, K and lime status in your fields is to have representative soil samples analysed. Once the status is known, management decisions can be made about the best permitted way to correct deficiencies when they occur.
2. Soil structure and drainage
Grass growth is restricted when soil structure is damaged by compaction or when waterlogging occurs. These problems can develop incrementally over time, but the wet summers of recent years have accentuated the problem in some fields.
The first requirement is obviously to try to prevent such damage occurring.
However, where soil drainage or structural problems have developed and are evidently restricting grass growth or harvesting, it will be necessary to identify the nature
of the problem and then take the steps to correct this.
3. Sward type
Swards that are dominated by perennial ryegrass are the foundation for producing good yields of highly digestible grass. These are the swards that are best suited to successfully preserving as silage.
In some cases, these will be new or recent reseeds, but they can also be several decades old, where consistent good management has retained a productive ryegrass dominant sward.
In contrast, swards with high contents of other grasses or weeds have relatively low sugar contents. This makes them more difficult to preserve as silage.
Swards with high contents of meadow foxtail and, in particular, bent grasses generally have lower feed values at silage harvesting time than ryegrasses. In addition,
weeds such as docks, even when they are at a leafy growth stage, have a low digestibility. The message is that ryegrass swards are preferred for silage production.
But they need to be managed to remain persistent and productive.
Shorter-term strategies
4. Dead butt
If a farmer wants to produce highly digestible silage, then the grass crop harvested needs to have a high content of leaf relative to mature stem. There should be few, if
any, seed-heads present. It must also be relatively free of the dead vegetation that gives rise to a ‘dead butt’ in some meadows.
Dead grass at the base of a meadow typically has a digestibility similar to straw. It will lower the digestibility of what might otherwise be silage of high feed value.
A dead butt is most likely to occur where grass on fields designated for silage was not grazed short last autumn or this spring. This results in the base of the meadow being harvested for silage in late May or early June consisting of very low quality vegetation over six months old.
The scale of this effect was demonstrated by an experiment in which grass was (a) ungrazed in autumn and spring, (b) grazed bare in autumn, or (c) grazed bare in spring (mid-March).
When grass for first cut silage was harvested, the grass that was ungrazed in autumn or spring had accumulated a lot of dead herbage. This grass was over 6% units slower in digestibility than when than when the sward had been grazed bare (i.e. evenly to a 5cm stubble) at one of these times.
Clearly, tight grazing in mautumn or spring is an important part of managing swards to produce highly digestible silage.
5. Spring grazing
In spring, cattle graze the silage fields first on many farms.
This provides them with low cost feed and sets up the sward to produce fresh growth for silage-making (provided the sward is grazed down to the height the mower will cut the meadow in lateMay/early June).
However, a side effect of this spring grazing is that grass yields for silage will be lower in late May.
The yields for silage can be partially retrieved by delaying harvesting for about 10 days. At this stage, grass digestibility will be approximately similar to the nongrazed
sward at the earlier harvest date. However, crude protein values will be about 1.5% units lower.
Since high yields of grass are required for the main silage harvest, the aim is to have a sufficiently long growth interval between closing and harvesting a sward.
As an example, if the plan is to take a first cut silage harvest in late May, then the last of the silage fields would be closed by the start of April.
6. Slurry and nitrogen application
A permanent meadow intensively managed for first cut silage will have a target application per hectare of about 125kg N, 20kg P and 120kg K (maintenance on soil P and K index 3). Recently reseeded swards may have up to 150kg N/ha applied.
Good quality (e.g. undiluted) slurry can provide the P and K requirement in fields with soil index 3 for both P and K. It also provides a worthwhile input of N.
For example, if 28 tonnes of slurry were applied per hectare (2,500 gallons/acre), there would be about 41kg N available to the grass from the slurry (plus 22kg P and
118kg K), and the amount of inorganic fertilizer N to be applied would be reduced to allow for this.
It is important that slurry spread on silage fields is applied evenly to bare stubble or short grass to avoid residual contamination carrying through on the grass to silage-making time. For this reason the first opportunity for spreading should be used to apply slurry, with mineral fertilizer to follow afterwards.
Once slurry is applied, advice from TeagascJohnstownCastle is that the application of inorganic N in the form of urea or calcium ammonium nitrate (CAN) should wait
until about five days have passed after slurry spreading.
This is to ensure the efficient capture and use of the mineral fertilizer N. A rule-of-thumb is that about 20% of N applied for early grazing remains available for the silage crop. The amount of fertilizer eventually applied to the crop closed for silage should be reduced to allow for this.
Closing dates and slurry/fertilizer spreading need to be managed to give sufficient time between applying N fertilizer and harvesting the crop for silage for two reasons.
Firstly, it allows the full yield response to applied N to occur, and secondly, it improves the likelihood of proper silage preservation. The general aim, therefore, is to have at least six to seven weeks between applying N and harvesting grass for silage.
7. Managing the silage harvest
Highly digestible silage made from intermediate-heading ryegrass is harvested when grass seed-head emergence is starting. A comparable digestibility target for late-heading ryegrasses involves harvesting at an earlier growth stage than this. Each one-week delay in harvest date beyond these optima results in an approximately 3% unit drop in digestibility.
Be prepared to begin harvesting when weather and other conditions permit, even if this means starting a few days earlier than expected. However, only start mowing the silage fields if you are confident you can complete the harvest quickly.
Measure grass sugar content the day before harvesting to find out how easy or difficult the crop will be to preserve. In some cases, it may be appropriate to apply a silage additive.
Be careful to ensure that no soil contamination occurs to the grass during harvesting or silo filling (or baling). Preferably, mow meadows after the dew has risen as this means that 2.5 tonnes water/ha (one tonne/acre) has been removed. Successful wilting means that mown grass dries quickly on the ground (usually within 24 hours).
To be successful, this process requires wide (or tedded) swaths and good drying weather. If this is not feasible, then harvest the grass soon after mowing. Fill the silo quickly, and shape the top surface to facilitate proper sealing and appropriate removal of rainfall.
Seal the grass using a ‘wall sheet’, plus two cover layers of black polythene sheeting. Fix the sheeting edges with a continuous layer of sandbags, etc, and cover edge-toedge with tyres. Check the covering and sealing as the silage settles, and intervene as necessary to maintain the seal.
Similarly, wrap bales within an hour or two of baling, and ensure the integrity of the plastic seal is not breached.
Periodically throughout the storage period, inspect the plastic cover and repair damage that has occurred.
8. Safety
Silage-making and slurryspreading pose a series of dangers. Plan to avoid any mishaps.
9. Inventory
Once silage is made, calculate the amount of silage dry matter (DM) in storage. Compare this with the expected requirement for your livestock. About three weeks
before silage-feeding begins in autumn, take at least two core samples from each silo (these can be mixed to produce a single sample).
At a minimum get the DM, digestibility (DMD), crude protein, ammonia-N and pH measured. Use the amount and quality of silage produced to help you evaluate the management practices used.
(Source – Irish Farmers Journal – Padraig O Kiely – 03/04/2015)