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Predicting Grass Silage Timing 2013

14 May 2013

Irish farmers are being advised to walk silage frequently to assess crops, after a delayed spring has caused growth rates to fall to around a third of average at 20 kg dry matter per hectare for April.

Staff at the Agri-food and Biosciences Institute advise that careful considerations to timing silage cuts is important following late snow fall. After a long and difficult winter, getting silage right may be the best way to manage the fodder crisis situation. 

Predicting Grass Silage Timing 2013

A Year Like No other?

The GrassCheck service, available on the DARD Rural Portal clearly shows how far current grass growth rate has fallen behind the seasonal average. Mercifully, at the end of April growth rates have increased somewhat and at least the shape of the normal growth curve is appearing.

Even so, grass growth is only one third of average at around 20 kg DM per ha per day and is not expected to exceed 60 kg DM per ha per day over the next two weeks. This compares poorly with 2011 growth rates, which at the end of April and start of May were averaging 50 kg per day with an expected rise to 80 kg and above by mid-May. Even in 2012, which most regarded as a poor spring, growth rates at this time of year were already averaging 30-38 kg DM per ha per day.

Rows of early perennial ryegrass varieties sown in plots in 2011, demonstrate the lack of growth just after the snow had cleared at Crossnacreevy.

So this is uncharted territory for most farmers and is certainly the case at AFBI Crossnacreevy where grass heading dates have been recorded every year since the station opened in 1968. Brian Waters, who leads the scientific team doing this work, has said that this is the latest growth he has ever experienced in over forty years! “Currently we’re four weeks behind where we’d normally be at this time of year” he stated with reference to the measurements carried out on new and old ryegrass varieties. So what are the implications for timing grass silage harvests later this May and in June?

Twenty days later and with the addition of fertiliser and an increase in temperature there is growth across these early perennial ryegrass plots.

The ‘Quantity’ versus ‘Quality’ Balance

In a normal year, much of the silage harvesting would be starting within the next three weeks with early cuts being completed by the time of the RUAS show. This is unlikely to be at all possible this year. So is the plan simply to wait for the bulk to accumulate? Sadly it is not that simple.

During March and April silage swards should have been building up a large reserve of high quality leaf. This is essential to buffer the lower quality stems as they extend up into the canopy and so maintain the overall herbage sward quality at cutting. Unfortunately, because daylight hours have now increased considerably, these grasses have turned reproductive. This means that the plants only want to produce stem and finish developing any existing leaves, including the final flag leaf that surrounds the emerging seed head. They will not start to produce any new leaves to replace the ones that are missing. So the normal balance between leaf and stem will not occur and the risk is that grass quality will fall much faster than expected.

The standard guide to timing silage is that when the very first heads are emerging sward quality is around 70-73% D falling to around 67% D when 50% of the seed heads become visible within the sward. This rule of thumb may well not work this year.

The ‘Quantity - Quality’ Compromise

The four week delay in grass development currently at AFBI Crossnacreevy is not expected to translate into a four week delay in silage cutting on farm. More than any year previously, however, keeping a close watch over sward growth and development on each farm will be vital to successful management of a difficult situation. With a low buffer of leaf, sward condition may change very rapidly and cutting decisions will need to be acted upon.

Different farms will have different priorities and so make different decisions. For some the fear of high winter feed costs to supplement shortages in silage supply will mean a loss in quality is less damaging than a loss in bulk. For others the reverse will be true and for most there will be a compromise in the middle. Only with close and regular sward inspections will farmers be able to gauge how their grass is changing and so make the right decision for their enterprise.

It will be important to walk silage swards frequently and open the canopy to inspect the growth and health of the grass plants. For those swards that have taken up their full fertilizer requirements, there could be some very fast growth periods later in May, if weather permits.

Only by examining these swards will it be possible to judge if this bulking is primarily stem. If the grass is very firm to the hand and stems are stiffening, then the quality is probably falling very quickly. The other concern is for those swards that missed the full uptake of fertilizer due to the rain and snow as they will become ‘hungry’ before they are ready to cut. Watch out for yellowing swards and for signs of excessive leaf death at the base of the plants as they try to mobilize nutrients to meet their urge to develop stem. Such swards accumulate little and only change in height but not bulk and so are best cut off, fertilized and hopefully pushed towards a better second cut.

Close inspection into the base of the sward will show the leaf and stem balance and plant condition and help identify when silage harvesting must begin in this very late growing season.

So the dilemma is clear. To get the normal bulk of silage we will have to wait later into the year than normal, but in so doing it will be impossible to hold grass quality at desired levels. The expectation is that correct timing of silage harvests will be more difficult than normal to forecast and so regular monitoring of development is essential. Yields are most likely to be well below normal and with quality being difficult to maintain, compromises will have to be made at the first cut, with plans for a better second and possibly even a third cut of silage needing to be planned for this year.

It is already a difficult growing season, but in so many aspects of farming, it is rising to the challenge by paying close attention to detailed management that will offset the worst effects and achieve the best possible outcome.

May 2013

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