Renewed Focus on Grass Silage 

After the difficult grass management year in 2012, silage yields and quality led to forage shortages and expensive feeding in the winter just past. There is therefore a renewed interest in making more silage, and better quality silage, in 2013.

Key point: The target should be to make 50% more than your expected winter requirements; allowing a buffer against poor summer weather, an early winter or a late spring 2014.

Good yields spread the costs of making silage over a greater tonnage. Quality is equally important dictating animal performance, be that milk production or recovering cow condition. Winter milk producers have always had a requirement to make good quality silage but now there are good reasons why spring calving herds also should be focusing on grass silage, outside of the memories of the winter just past:
-Higher stocking rates as a means of expansion mean greater demand for high quality forage in the ‘shoulders’ of the year.
-Earlier calving driven by expansion and/or to benefit from improved efficiencies also drives demand for high quality forage in early spring.
-The relatively high cost of concentrates makes silage DMD an important economic factor.


Below are the key factors in achieving good silage first-cut yields and quality:

Soil Fertility
Ensure soils are well drained and free from compaction.  Maintain soil P, K and lime levels based on up to date soil analysis. Organic manures are very useful in helping to balance P and K levels on silage ground. 

Sward type
A large-scale experiment conducted at Teagasc Grange over a number of years highlights that swards with high levels of perennial ryegrass (recently reseeded ground); have two key advantages over swards with low levels of perennial ryegrass in silage making:
1. Better digestibility (DMD)
Weed grasses such as meadow grasses etc. tend to have lower digestibility than perennial ryegrass. This difference is very significant in the order of 6% DMD.
2. Easier preservation
Perennial ryegrass swards have about twice the sugar content of many grasses which means you are four times more likely to get good preservation with perennial ryegrass than with a weed grass like red fescue.

Sward management and closing date
If ground is not grazed at all in the late autumn or in the spring, dead material accumulates at the base of the grass reducing the DMD by 6-7% points. However, grazing silage ground in the spring can cause yield reductions of up to 50% from grazing in April. Therefore the target is to graze silage ground tight (to at least 5cm) in late autumn. If the ground has to be grazed in spring, it should be grazed as early as possible with harvest date delayed slightly (by 10 days) to recover the majority of yield loss.


Nitrogen (N)
Apply 100-125 Kg N/ha (80-100 units/acre) with high perennial ryegrass content swards (recently reseeded ground) requiring higher levels of N. Make sure to allow for any organic manures used and any fertiliser applied before spring grazing (expect circa 20% to be remaining). Apply all fertiliser as early and evenly as possible.

N fertilizer reduces grass sugar levels & increases buffering capacity, therefore allow enough time for any N applied to be utilized to ensure good crop preservation. Approximately 2 units of N per day are used up by the crop. Therefore if 100 units/Ac are spread, at least 50 days should be left between N applications and mowing. Note bad weather will reduce the uptake of N and more time may be required to reduce N levels.

Cutting date
The target yield and quality depends on individual farm requirements as there is an inverse relationship between yield and quality i.e. grass digestibility decreases as grass DM yield increases. Digestibility is relatively stable until the 20th May but it then declines by about 2.5% DMD in late May-early June when the grass begins to go to seed. This is a much quicker decline than in July-August when the plant is in the vegetative state. Plan to mow the crop when seed heads begin to emerge; this is typically shortly after the mid-point in May.

Preservation aids
In order to preserve silage, lactic acid bacteria need high sugar levels (minimum 2.5%, preferably >3%), to ensure a rapid drop in pH and good preservation. Sugar levels tend to be erratic in crops depending on the time of day (highest in the afternoon/evening) and weather conditions (increase with sunshine and cool nights). But in general over time it increases as the grass crop matures, hence making low digestibility silage easier to preserve.  

Wilting is a useful preservation aid as it will help to increase sugar levels. Benefits are greatest after a wet spell but ensure the crop is reasonably dry before mowing (all dew disappeared) and spread rows of grass out over the field. There is no benefit in wilting crops for more than 24 hours prior to pick up. 

The use of an additive will help greatly in the preservation of young leafy crops or where N levels or sugar levels are not ideal. They are less relevant for relatively mature, wilted crops given adequate time to use any N applied.

Pit management
The aim is to achieve anaerobic conditions as quickly as possible and completely maintain until the pit is opened. This involves quick filling of the pit ensuring the grass is well compacted and sealing carefully beneath a double black polythene layer followed by a full covering of tyres and sandbags. Inspect frequently (at least once every two weeks) and immediately repair any damage to the polythene. At feed-out; try to move across the pit face quickly and evenly, preferably using a sheer-grab, to minimize heating losses.

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