The 2020 UK maize harvest look like it’s going to produce good yields and maybe you’re in the tricky position of not having enough clamp space. In days gone by it was easy to find a bit more space for some silage, just clear a corner of a field and build a heap before sheeting up. But with rules and regulations ever tighter and the threat of prosecution from SSAFO regulations are those days long gone?

Are field silage clamps still allowed?

Well if you study the SSAFO regulations then you will find the requirement that any silage clamp needs to have an “impermeable floor”. It used to be argued that some high clay soils could be “puddled” to form an impermeable layer. An alternative could be to lay a membrane under the silage, either in the soil layer or between the silage and the earth. Unfortunately both these options have been eliminated by the latest version of the SSAFO regs that state the floor must be constructed of either concrete or hot rolled asphalt. So to comply, you need a floor.

Can I store silage on a concrete slab?

The basic answer to that is yes you can – but, and there is always a but, the slab need to be impermeable, and have a perimeter drain, oh and you have to have an effluent tank. So building a stack of silage on an old concrete yard or roadway or (if you’re lucky enough to have one) an old runway is possible but it’s tricky to stay within the rules that way.

So a field clamp is no longer allowed – but when is a clamp a clamp and when is it a heap?

Temporary field storage of crops is still allowed and silage can be stored temporarily in the field. This might seem crazy, you can’t store silage on a concrete pad but you can heap it up in the field! But the thinking is that if you do this correctly any effluent will be absorbed into the soil and will be broken down by the soil micro organisms before it can do any damage. This is a risky operation so there are lots of things to consider and you do need to get permission to form a temporary field silage store.

Firstly you need to consider the siting of the store in exactly the same way as you would for a new silage clamp. Therefore all of the store must be at least 10m away from any watercourse or drainage. That includes under the heap itself; if the area has field drains then you can’t use it to store silage. You also need to be at least 50m away from any spring, well or borehole. As you can’t excavate the site you should choose a level site to minimise the chances of effluent run off.

In addition to this you need to think about the access to get at the silage once the harvest is over. How are you going to get it to the point of use and what sort of mess are you going to make on the way? You also need to think about the water table once the monsoon season starts. The last thing you need is your precious extra silage becoming a new Tracey Island sitting proudly in a new lake!

Once you have answered all these points you need to identify the site on a map and complete the WQE4 form on the government website to apply for Environmental Agency approval. Be aware – if this is a store to feed an AD plant, your approval process may be a bit more stringent than for a livestock only farm.

How to form a field silage clamp

Perhaps contrary to your expectations, you can now just start building a heap of silage. You might be tempted to think about stripping off the topsoil or placing some hardcore or road planings – but you shouldn’t and you can’t. Likewise you can’t use a membrane either. A field store is exactly that, it must be built on the field and not in the field. The organisms that are (hopefully) going to save you from a pollution prosecution are in the topsoil and around the plant roots so you need to leave them in place.

So what can you do to minimise the risk of effluent pollution from a field store?

Firstly choose your site with a good soil health status, ideally with a good grass turf cover. This will help resist breaking up with traffic and provide the best conditions for effluent breakdown. The most important element is the silage dry matter. You can spread an absorbent layer such as straw on the bottom of the clamp before the silage goes in, but getting the DM right is so much more important. We have seen elsewhere in this series how effluent production is directly associated with the crop DM, so if you get the dry matter at the high end of target then the effluent problem will be eradicated.

Field clamp downsides.

The downsides of field storage will be well known to most, firstly you can expect much higher losses. Compared to a permanent silage clamp, you might expect clamp losses to be 15%-20% higher in a field store, Obviously the bigger the heap the lower the percentage loss as there is more of the silage in the protected body of the store away form the vulnerable edges.

Secondly there is the damage the store and the traffic will do to the area of land sacrificed for the store. This can recover with time but don’t expect there to be an overnight solution.

And finally there is the risk, the risk of prosecution. Just because you have been given permission to produce a field store by the EA, this doesn’t protect you prosecution should a pollution incident occur. You might think “what is the point of getting EA approval in the first place” but if you don’t get approval you may get a prosecution even if there is no pollution!

In summary you can still store silage in the field but it’s a risk and you should only think of it as a temporary solution. If you need further information or help on how plan your silage storage, or for any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com