Step 4. Clamping
Always clean clamps out before refilling.
Next, line the clamp walls with polythene sheeting – leaving a large overlap to ensure proper sealing with the top sheet. Thorough sheeting is vital to keep oxygen out of the clamp because this is what is required for the yeasts that cause aerobic spoilage (characterised by heating) to grow. It is important to take steps to prevent them growing at every stage of silage-making, otherwise they will continue growing and cause major problems later.
Also, keep the area surrounding the clamp clean to avoid soil contamination brought in by machinery. Soil introduces more spoilage organisms into the clamp.
Clamps also need to be filled and sealed within 2 days of cutting to get the fermentation process started and to minimise air exposure.
Filling the clamp evenly in thin layers of a maximum of 15 cm will help with consolidation, since this is the maximum depth that can be compressed effectively.
Use single wheeled packers, and roll continuously for increased packing pressure. And make sure packers can keep up with the speed of arrival of new loads into the clamp. Don’t compromise consolidation, because this is essential for preventing air ingress.
Ideally, calculate the weight of machinery needed to achieve a target bulk density of maize in the clamp of around 750 kg of fresh weight per cubic metre. As an example, estimates suggest that even having two, 14-tonne tractors rolling continuously wouldn’t be enough to achieve this with a fairly typical harvest rate of 120 tonnes per hour.
After filling, in order to protect the shoulders and clamp surface, which are particularly vulnerable to aerobic spoilage, apply salt and fork into the top few inches.
TOP TIP: Clamp correctly to further aid fermentation and starve spoilage organisms of oxygen.
To help keep clamps airtight, seriously consider an oxygen barrier film if you don’t already use one. On top of this, to make the most of resources while getting a tight seal, use two 500-gauge polythene sheets, for example with the bottom layer being new and the top recycled from the previous year’s clamp. Alternatively, a single 1000-gauge sheet can also be used.
After sealing with the plastic sheets, protect them from damage with a woven sheet and weigh down well. Use plenty of mats, gravel bags, touching tyres or silage bales, as the more weight on top the less chance of losses in the top of the clamp. Skimping on this final task can be costly later. Finally, use netting over the top to stop birds pecking through the sheets, and bait to ensure you keep rodents at bay.