Arrabawn | Making Quality Silage
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Making Quality Silage

Following on from a difficult 2018, silage stocks on farms have run low and farmers must ensure they have a significant buffer of stock to see them through the coming wintering period. Silage Dry Matter Digestibility (DMD) is a key indicator of silage quality. DMD is directly linked to harvest date so early harvesting equates to a higher DMD percentage. A crop harvested on June 2 verses a harvest date of May 20 can result in a DMD drop of as much as 5pc.

High nitrate levels in grass inhibit good fermentation and nitrate levels should be tested on farms if there are any concerns about the interval between fertilising and harvesting. Grass should be wilted to more than 28% dry matter to help overcome the effects of high nitrogen. If ideal conditions aren’t achieved at the time of harvest, then use of an inoculant or an additive should be considered. Inoculants have been shown to increase DMD by as much as 5% when used when conditions are not ideal. A rule of thumb is that a silage crop uses two units a day of N. However, the crop can be cut earlier if weather conditions are dry and sugar levels are good. Test a sample rather than ‘waiting for the N to be used up’.

The fermentation process typically begins once the pit has been sealed airtight. Once it is sealed tightly then the pH drops dramatically and grass sugars are converted to lactic acid. For adequate fermentation the level of sugar in the grass at time of harvest should be at 3%. Conditions are key with dry sunny weather, cool nights and evening mowing all vital.

Fill the silo quickly and seal tight in order to achieve air-free conditions, necessary for good preservation and preventing mould growth. The use of a heavy duty tear resistant silage cover should also be considered on farm. Ensure that effluent channels are in good order and channel all effluent quickly from pits or clamps to a suitable storage tanks. Silage costs twice as much as grazed grass so it must be preserved and protected.

Six inches of waste on an average size pit (30x50x10 ft.) @ a feed cost of €25/ tonne of silage = €1250 loss in feed for upcoming winter period. During periods of high grass growth rates, removing surplus bales as baled silage will help to keep good quality grass in front of livestock and make some valuable reserves of good quality silage. The table below shows units of N, P and K removed per acre depending on the number of bales per acre.

In general, the N removed in the bales is not a problem, as N fertiliser will have been applied before cutting and applied again after cutting for the next grazing. The P and K removed is what needs to be considered. For example, four to five bales/acre will remove around six to eight units of P/ac and 40 to 50 units of K/ ac. This is important, as a rough rule of thumb is that 50 units K/ac is enough to change a soil K index, i.e. to go from index 2 to index 3 or vice versa. If no slurry and only straight N, such as CAN or protected urea, was applied before and after cutting the surplus bales, there will be a large shortage of P and K in this paddock. Best practise is to apply slurry to these paddocks after cutting to put back what was taken off. 1000 gallons of slurry equates to 6 units N, 5 units P, and 30 units K. Where slurry is not available, a P and K compound could be used, but you must ensure you have a P allowance before you spread P. Where you have no P allowance and no slurry is available to spread on these paddocks, a compound such as 19:0:15 is an option. When making a choice to select one paddock among three or four paddocks to take out for bales, some farmers are selecting the paddock with the highest K index when everything else is equal.