Energy Beet Guide
Maximising Beet yield in the Field
Growers need to maximise †DM yield in the field and to use this in the AD plant to ensure the highest level of efficiency.
It is important to harvest as much of the beet as possible, in practice this means just defoliating the leaf so that the crown is retained. This alone increases dry matter yields by around 6–12%.
In addition, the leaf can be harvested and used within the digester however the low dry matter content (10– 2%) makes ensiling challenging and with the relatively low additional dry matter yields of approximately 5t/ha it may not be practicable to harvest and utilise the leaf.
Energy Beet - Breeding
The primary target for biogas feedstock production is a high dry matter yield per hectare.† This provides both an effective feedstock supply and the most efficient use of land.†
Both of these key characters can be secured through the selection of specialist Energy Beet varieties from KWS’ specialist E-beet breeding programme.
Energy Beet is very fast to ferment, has very high methane yields per tonne of dry matter and provides a high percentage of methane within the biogas that is generated., In addition, there are many agronomic traits that make Energy Beet suitable for growing in all types of conditions and varieties with resistance or tolerance to Rhizomania or beet cyst nematode (BCN) will help ensure high yields in traditional beet growing areas.
Continued, innovative breeding and trial assessment ensures that overall Energy Beet performance will improve year-on-year as each new variety comes to the market, maximising gas yields.
Energy beets are specifically bred and designed to optimise performance in the biogas plant and are not suitable for delivery to sugar factories.
Fodder beet is not suitable for biogas production primarily due to its low dry matter content of 16–20%.† Also, most fodder beet offer no resistance to Rhizomania or BCN, so†their use in most parts of the UK is limited.† This, combined with their high water content, will lead to relatively poor performance in the AD plant as well as high transport costs †
KWS will continue to target high agronomic field performance of Energy Beet suitable for the UK, with high DM contents, high methane yields and low dirt tares to ensure growers have access to one of the highest performing AD feedstocks available.
Soil and stones in the substrate
The biggest challenge is the removal or minimisation of stones and soil.†While clay will remain in solution and travel through with the digestate, sand tends to sediment out within the digester.†
Beet grown on lighter sandy soils will be lower in dirt tare and this will be relatively easy to remove.†
However, growers should attempt to manage harvest to minimise levels of dirt tare in the clamped crop.
KWS beet washing
There are now several technology manufacturers who are designing and building beet washers for the AD market.
The main benefit of washing beet is to remove stones.† The whole process is most efficient when harvesting and washing activities are synchronised to ensure best use of manpower and logistics.
The beet firstly goes through a dry cleaner to remove most of the soil and stones.† Then, a wet wash is used to remove a high proportion of the remaining soil but primarily to allow the separation of stones from the beet by allowing the beet to float and the stones to sink, a solution commonly employed in the sugar processing industry.† Subsequently, a conveyor belt transports the beet into the clamp for ensiling.† †
It is important that once washed, the beet is not left to sit for long as, depending on the temperature, the beet will deteriorate after 5–10 days.† Therefore, ensiling should begin soon as soon after wet washing as possible.
Obviously, wet washing adds to the cost of processing beet.† Therefore, when dirt tares are low and there are minimal amount of stones and/or sand, then dry cleaning should be considered.†
Storage of fresh beet
In UK conditions, biogas producers can use fresh beet between September and March.
Just as beet for sugar production, beet for energy production should be clamped to allow air flow through the clamp to keep beet cool and prevent it from overheating.†
During periods of very low temperatures beet should be fleeced and possibly covered with straw to help prevent frost damage.†Again, when temperatures warm up then the clamp should be uncovered and allowed to ‘breath’.
Ensiled Beet – easily digested and fast gas!
Having achieved the optimum harvest date and highest dry matter yields, the next step is to preserve this quality by ensiling the beet.†Ensiled beet brings significant advantages during digestion such as increasing the speed of digestion and organic loading rate.
It is important to capture the beet effluent (25-40% of the incorporated fresh matter) otherwise, due to its high energy content, significant losses are experienced.† This effluent should be captured and pumped into the digester.
The beet effluent has a very low pH, around 3.5, and therefore clamp materials should be robust and acid resistant to ensure long life.
Collect as much effluent as possible using methods that minimise contact with oxygen.† It is through contact with oxygen that the effluent becomes corrosive.
Ensiling of whole beets
For long term feedstock provision, beet needs to be clamped either as a ‘mixed’ silage, for example with maize, or alternatively as whole beet on its own.
Perhaps the most important step is to use quality covers and to cover the beet as quickly as possible to achieve a secure anaerobic environment.† The quality of covers and secured weights, so as to avoid any oxygen contamination, is crucial, as unlike other crops, such as maize or wholecrop cereals, the beet cannot be rolled to achieve compaction.† Speed of covering will allow the beet to respire, use up existing oxygen and create anaerobic conditions.
During the ensiling process the bulk density of the beet changes.†The clamp will reduce in height as the beet compact together.
The beet will ensile very quickly, in approximately 10 days, reaching a steady state with a low pH of 3.5.
One cost-effective option is the use of a lagoon.† Whole beet can be crushed and fed into the lagoon and, when needed, the beet pulp pumped directly into the digester.† There is no risk of loss of the leachate and rainwater is collected and recycled into the digester, which improves the pumping ability of the substrate. †
Experience shows that a floating layer or crust is formed after some time.† However, such as system leads to some gaseous loss.
Ensiling of mixed silage
The use of existing clamp capacity is an affordable solution from an operational point of view.†Mixed silage has been used for many years on livestock farms with very good success.
The challenge here is to find an optimal harvest date of both the beet and maize crop and to co-ordinate the harvesting and combined ensiling of the two crops.†Maize is typically harvested in during September in the UK, however the beet yield will peak in mid to late November, so combined clamping may not always be practicable.
One approach for those looking to use this storage method is to grow a late maturing Energy Maize variety so that both beet and maize yields can be optimised as much as possible to ensure maximum methane yields.
Talk to your KWS consultant for advice on variety selection to achieve this.
Ensiling of beet and Corn Cob Mix (CCM)
A later harvest window can be utilised to supply maize processed as CCM. CCM has significantly higher dry matter content than maize silage.†The high dry matter content allows a much higher proportion of beet in the mixed silage (up to 70% CCM and 30% beet are possible).
This mixture is a very energy-rich substrate for the biogas plant.†Due to its low lignin content and high starch, gas can be produced very quickly.†The retention time in the digester at high loading rates is shorter than where wholecrop maize is used and KWS and our research partners have seen excellent results from this mix.†
Perhaps the only downside of this method is that because the whole maize plant is not utilised, methane yield per hectare is reduced.