April 14th - 2021

Silage production Part 3

Harvesting crops for silage

Do you use a contractor or run the foraging team yourself? An often asked question as the timing of the harvest is often up to the diary of the contractor so you may miss the ideal window for your crop. However, the economics or labour available may require outside help so forming a good relationship with the contractor and getting them booked in to suit you is vital.

As with all the stages of this process attention to detail is vitally important. Again these points we have put together will help this process.

Assessing dry matter in the field

Aim to harvest at the target dry matter.

Dry matter can be assessed with a microwave or Koster oven.
Observe the crop in field in the days prior to planned date of harvest and use.

Target dry matter at harvest

Harvest at 30% DM or higher to avoid loss of nutrients from liquid effluent.
Aim to harvest close to the target DM for the crop.

Theoretical length of cut (chop length)

Avoid the common pitfall of not paying enough attention to chop length.

Using the optimum chop length is crucial when harvesting grass, because it has a big impact on how good a consolidation you can ultimately achieve in the clamp.

Silage is produced when beneficial bacteria ferment some of the sugars in grass to lactic acid. This ‘pickles’ the grass, preventing the growth of spoilage micro-organisms and so preserving nutrients. However, fermentation only starts once there is no air left in the clamp. So the quicker you can achieve this, the better.

The Silostop system of using an Oxygen Barrier Film to effectively seal the clamp relies on good crop consolidation. If the crop hasn’t had this consolidation the air left in once covered allows an elongated respiration period and so uses up valuable sugars and starch.

Short chopping aids compaction of the crop in the silo, increases speed of fermentation, increases silage DM intake and reduces sorting (selection) by livestock.
Keep knives sharp at all times to ensure uniform length of cut.
Avoid variable particle/chop lengths.
Make sure all kernels are damaged or cracked.
Aim to chop to the theoretical length of cut.
Measure chop length regularly during harvest.
Longer particles stimulate rumination which reduces risk of sub-clinical acidosis and helps to sustain milk fat levels.
Optimum chop length for anaerobic digestion is 8 to 10 mm.

Top tip: Ensure knives are kept sharp and adjusted.

Too long a chop makes it more difficult to squeeze all the air out of the spaces between the grass, particularly at higher dry matters. But too short a chop can also cause problems. So as well as keeping knives sharp, ensure they are correctly adjusted according to the crop’s % dry matter.

As a guide, if grass is > 30% DM, chop to 1.5-2.5 cm chop length to improve consolidation (though if grass silage is being fed as part of a high maize diet, chop length should be increased to ensure sufficient effective fibre in the complete diet).

If grass is at 20-30% DM, use a chop length of 2.5-5.0 cm.

If grass is less than 20% DM, you may need to increase up to 10cm to reduce effluent and prevent clamp slippage.

Poorly chopped crop

Well chopped crop

This video from AHDB gives a good overview on the whole silage making process.click here

Tim Brewer