Ten years of producing a diverse range of crops to feed a large-scale gas to grid business has reinforced the critical importance of efficient forage conservation at St. Nicholas Court Farms near Birchington in Kent.
Growing nearly 2200ha of energy crops a year and ensuring these stay in the best condition possible to drive maximum gas production has been a huge learning curve for the previously arable-based business, says senior farm manager Iain Moss.
“Forage management and silage clamps are not really part of the mindset for arable producers but when you’re involved in renewable energy production, they become the foundation of the business.
“After harvest, we’ve probably got nearly £4 Million worth of forage sitting in our clamps so the decisions we make to ensure it’s going to store well and be simple to manage over the following year are of critical importance.
“Our target is zero loss from field to digester and that requires a very specific approach to the harvest process, managing and sealing the clamp at filling and how we remove material through the year to feed the digesters.”
Just a decade ago, the business was based around 1300ha of conventional arable production but the addition of the energy business has seen total enterprise size grow to nearly 3500ha, he explains.
“During the evolution of the AD plant, CHP has given way to gas with two gas to grid digesters with full CO2 recovery now in operation.
“Whilst we grow wholecrop rye and triticale plus some grass silage to supply these, we’re pretty much focused on maize with up to 1500ha of the crop grown each year and this has taken a bit of getting used to in terms of management.
“At first we thought - great, it’s really going to help with controlling black grass, but we soon learned the growth habit of maize does not make it particularly effective at this, although it does provide some opportunity for cultural control ahead of drilling.”
The area’s near continental climate allows the use of later maturing varieties with KWS Amaroc, Grainseed’s Cathy and RAGT Indexx being some of the highlights in recent years, but drier growing conditions are becoming a concern, Iain Moss says.
“Soil moisture conservation is a priority for us, so we’re very careful with cultivations and how much land we open up before drilling. Everything is rolled once the seed is in and we’re making more use of cover crops to return organic matter back to the soil.
“We’re learning to deal with the variability in yields, too. We target 42t/ha freshweight but it has been as low as 33t/ha and as high as 51t/ha.
“The gas production process needs a constant supply of forage so we always aim to grow 15% more than we technically need in any one year, allowing for carry-over stocks and helping even out any production hiccups.
”Dry matter drives gas production so as well as high yields, we’re also aiming for 32 – 35% DM at harvest and in the clamp.”
Such an approach puts a high emphasis on quality and quantity of storage facilities with the addition of new purpose-built ARK clamp built in 2014 being a great example of this.
“We saw the ARK clamps in operation in Germany and were impressed. Ours is a two-bay construction measuring 40m across by 140m long and capable of storing over 50,000 tonnes of forage,” Iain explains.
“The 23o sloping walls of the clamp also allow for safe piling of material above the height of the panels plus they allow for improved compaction along the shoulders of the clamp as machinery can work right up to the edge.”
Assistant farm manager Luke Robison says compaction is one of the most important objectives of the clamp filling operation.
“We aim to complete all the maize harvesting and clamp filling in a three week period, usually in the middle of September so we can get a first wheat in, so this means we’ve got to approach it with almost military precision.
“We’ve run two contractor teams with at least one tractor and buck rake for each team at the clamp to consolidate material properly. The aim is to keep a steady flow of material entering the clamp at all times.
“Side walls are sealed with 150 micron thick side sheet to eradicate the possibility of air entering through the walls once sealed and our aim is to minimise joins in the top sheet as we progress.
“We’ve used a single-layer Silostop Max oxygen barrier sheet for the last four years as we’ve found this to be the best way of achieving this whilst being the simplest approach to use.
“Double sheeting is a nightmare from a practical perspective and smaller sheet sizes mean there are many more joins to try to make airtight. This adds time to the sheeting process and increases the clamps vulnerability to the high winds we often experience here.
“We can use a 27m wide Silostop sheet which is 150m long so we go right across the 80m width with a single sheet. That way we can cover the entire 140m long clamp with 6 – 8 sheets in total.
“Any offcuts of sheet are used to cover our smaller silage clamps, so no plastic is wasted. Using this method makes it easier to sheet individual sections of the clamp as they are completed and doing it in bitesize chunks is far less daunting for everybody!
“As we move down the clamp, the side sheets are folded under the top sheet and an ARK secure cover is placed on top with gravel bags used to seal the joins.
“We’ve found we get zero wastage of forage due to air ingress and spoilage this way, which is pretty impressive for a clamp this size.
“When we open the clamp up, we then simply roll the whole sheet back as much as we need to, with the single layer making the whole operation much easier than with a two layer approach.
“It also means we‘re using a lot less plastic than we would be doing with a more traditional two sheet system.”
Iain Moss believes the combination of the right silage clamp to optimise capacity and consolidation together with a single-layer sealing system provides a solid foundation for the energy business.
“The single biggest thing under our control to ensure the long-term viability of the energy business is to make sure we know how to grow the right type and amount of crops and that we can keep these in as good a condition as possible before we need to use them.
“None of this has been easy. We are primarily an arable farm that has transformed into an energy business too.
“In some ways that has allowed us to take a slightly sideways look at the best technology available for the job and not just go along with traditional thinking at the time.
“But we are moving forward all the time and the area of forage production and its conservation is one where we have learned some very important lessons and doubtless will continue to do so in the future.”