I have attended a number of silage events of late at which the issue of grass-cutting height was discussed at length.
For many farmers, this is a black and white issue – it’s a case of setting the mower at ‘ground zero’, thereby getting the maximum amount of forage possible into the silo.
In my opinion, however, this is an approach to silage-making that constitutes total madness.
The issue crystallised in my mind a few days ago while attending a red clover silage farm walk, hosted by Philip and David Clarke.
The father and son team milk a herd of spring-calving cows near the village of Augher in south Co. Tyrone.
Last year saw them establish a new 12ac ley, comprising a mix of perennial ryegrass reed clover and white clover.
Two cuts of silage were taken off the ground in 2023, both baled. However, the spring of this year has seen the field come into full production, with the Clarkes committing to get a number of cuts into a clamp over the coming weeks.
Grass cutting
First-cut silage was made from the new ley at the beginning of May.
Courtesy of his presentation, David made the point that he actually ran behind the mower, so as to make sure that the cutting bar was kept at least 3″ off the ground at all times.
Any lower than this and the contractor ran the risk of cutting the crowns.
His comments stimulated a discussion among those in attendance as to what is the optimal cutting heights for silage crops across the board.
The consensus view was that 3″ seemed to be in the right ballpark.
Going lower than this increases the risk of soil and residual slurry contamination within the resulting silage.
Moreover, leaving a reasonable cover of grass/clover in the field increases herbage regrowth rates while also providing quicker nutrient uptakes, if slurry is applied as a fertiliser source in preparation for the next cut.
A quick look of Ireland’s silage quality figures does not make impressive reading.
Despite all the technical advances achieved over recent years, where the likes of mowing, tedding, raking and harvesting are concerned, forage performance is going in the wrong direction.
I believe, there is one significant factor driving this trend – the use of trailing shoe slurry spreading systems.
No-one is questioning the role of this technology in helping to improve slurry nitrogen utilisation rates. No doubt, these systems also act to reduce nitrogen (N) volatilisation levels to the atmosphere.
However, they also leave ridges of slurry solids in fields. These are most obvious during periods of dry weather, when they stand out like tramlines.
In these specific circumstances, this slurry-based detritus is mixed with cut grass when cutting bars are set at ground zero.
One very simple way around this issue is to raise the height of the mower slightly. 3″ seems a fair enough trade-off height for me.