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Field silage heaps - What you need to know

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With silage season now upon us, Technical Director Chris Bentley gives us the low down on how to plan and manage silage heaps.

Storing silage in field heaps is not ideal with levels of wastage likely to be higher than in a properly constructed clamp. Fetching the silage often makes a mess, even if conditions are good when you make the heap. However, with careful site selection, and management procedures, if you run out of clamp capacity, making silage in a field heap is still an option.

Field silage heaps - What you need to know

Choice of site

The choice of site is dictated by a combination of legal, environmental and operational constraints and most importantly you need to make sure the site is suitable and won’t cause pollution.

Fundamentally you need to be able to get the crop to the place where it is to be stored and you need to be able to get it out again. This may sound obvious, but we’ve seen heaps where getting the laden feeder wagon out of the gate was almost impossible in wet weather.

When selecting a site the basic requirements are to ensure that the site is not under-drained, is at least 10m from a ditch or watercourse that any effluent could enter, and 50m from a spring well or borehole. You may well also not get regulatory approval for a heap in a groundwater source protection zone 1 (SPZ) either. You can check MAGIC maps to see if your proposed site is in an SPZ, which can be accessed via the following internet link:

Once you are happy with the location you’ll need to download and submit via email (or print and post) a copy of WQE4 form and a location map to the EA / NRW. Be aware one of the boxes on the form doesn’t always work properly when trying to fill in the PDF version. The WQE4 form can be accessed via the GOV.UK website

Constructing a heap

Ideally the heap should be on level ground without too many stones and with a decent covering of turf. The key requirement of the regulatory guidance is that other than levelling minor ruts, you can’t do any site preparation – digging out or laying a hard surface for instance. The principle is that should any effluent be generated by the ensiled crop it should be absorbed by the soil underneath and broken down by soil micro-organisms.

Putting a sheet underneath to keep the soil out of the silage is therefore not a good idea, but a layer of straw can be. The straw will help to absorb any effluent, protect the soil, and can be fed out if it is clean enough, or put to one side and treated as an organic manure if not.

When making the heap try to keep wheels and therefore silage clean and uncontaminated – lay the straw layer (if being used) as you go, and tip the crop onto it, or lift and carry into position, spreading the crop and consolidating the wedge as normal. Care is needed to ensure heap edges / sides are safe and not too steep, and if you include a straw bale wall to keep things tidy, this should be used as a guide / absorbent and not subjected to significant lateral loading when rolling the clamp.

If you have the option, wetter forage should go into a clamp with effective effluent containment. Making the field heap when ground conditions are good will lessen the risk of getting soil in the silage at clamping, and of subsequent problems, and the approach is much better suited to dry maize or wholecrop than lush second cut grass for example.

If the site slopes you really need to access the heap from the downhill end or ideally across the slope, this ensures that any surface water from the cleared part of the site doesn’t drain into the remaining silage, but it is equally important to ensure that the muddy run off doesn’t end up direct in the ditch or draining straight down the wheel ruts onto the road. Providing an area of grassland to one side where run off can be allowed to soak away can help avoid this problem. The use of bog mats or temporary tracking can also help if you are operating on a significant scale.

Silage heaps

Keep an eye on where any run off is going – it’s probably worth walking round the heap at least on a weekly basis to check for any problems, and making a note of the fact that you have done so. If you start to get problems, divert any run off to a sump and tanker it back to the slurry store if conditions aren’t fit to spread. If things go wrong and effluent gets to a watercourse, ring the EA or NRW immediately, block it off as soon as possible to contain any pollution and get the tanker out.

At the end of the season the site is likely to need a bit of tidying up – cultivating out the ruts and reseeding, even if (or particularly if) you intend to re-use the location another year. Unlike field heaps of manure, field silage heaps can be made in the same place more than once, and the notification form includes provision for this. However it is important that the topsoil / turf doesn’t get dug away with each successive use, increasing the risk of drainage from the site or pollution of ground water.

In the long term more clamp capacity back in the yard is likely to be a more satisfactory approach, and baled silage is more flexible, but as a temporary solution whilst additional capacity is planned and financed, a field heap can make sense.

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