Hybrid rye is coming into its own, according to agronomy, bioenergy and feedstock preservation specialists. They say that, although the crop may take second place to maize when it comes to biogas per hectare, it still offers huge yield potential and many further advantages to its growers and the environment, and more flexibility for anaerobic digestion.
Today, some five million hectares are grown worldwide, and in the UK well over 20,000 hectares are grown specifically for AD. Almost all of the AD acreage is preserved as wholecrop rye silage, a massive yielding forage which offers numerous agronomic advantages over maize. These include its long drilling window which can run from September to early November, ground cover over winter which protects against soil erosion, simple agronomy and, perhaps most important of all, a far earlier harvest, generally in July.
But there’s another way of using rye, according to Charlie Bowyer who offers independent nutrition advice for AD plants through Biologic Biogas Solutions Ltd.
He says that although the freshweight yield of wholecrop rye is huge – reported to approach 50 tonnes/ha (20t/acre) on some farms – and its biogas yields impressive, at 200-250 cubic metres per tonne of freshweight which is on a par with forage maize, the crop’s usefulness and flexibility can be extended even further.
This can be done by crimping, a process by which high moisture grain (from 25-45% moisture) is rolled through a mill, treated with a preservative and stored – just like wholecrop – in anaerobic conditions.
Driving any switch from forage to crimp is the declining digestibility of wholecrop as the growing season progresses.
“Like any cereal, rye becomes more lignified as it matures, which means it becomes increasingly difficult for the straw and seed coat to be digested,” says Mr Bowyer.
“This means the more mature the crop, the more challenging the rye can become in the digester, particularly where retention time is short or where there is no maceration.”
Once the DM of the wholecrop increases to over 50% he says it is much more likely to cause these problems. These also include the formation of floating layers, which may have detrimental effects on mixing and efficiency.
“If your crop is approaching this level of maturity, I would recommend considering switching to crimping from whole-cropping,” he says.
Kelvin Cave Ltd concur and say that crimping moist grain offers numerous advantages over harvesting it dry.
“Crimping is commonly used for wheat, barley and maize by livestock farmers and also used for maize for anaerobic digestion,” says the company’s MD, Kelvin Cave.
Advantages of crimping include the lack of a need to dry grain, an earlier cereal harvest and a higher nutritional value than dry grain.
“Crimp has been proven to be higher yielding than dry grain, not just because freshweight yield per hectare is higher but dry matter yield is higher too,” he explains. “This is because the grain is harvested in better condition, usually before there’s any disease or shrivelling, which also avoids the grain losses which can occur when the crop is dry.”
The crimped grain is then stored in a plastic tube or clamp in a similar manner to forage.
“Whilst your yields will inevitably be lower than if you had harvested wholecrop, the energy value per tonne is massively higher and you have the by-product of plenty of straw. This could be chopped and ploughed in to return nutrients and structure to the soil or baled and sold,” he says.
“Crimping will certainly overcome the problems of an over-mature wholecrop rye,” adds Mr Bowyer. “The grain is an energy-dense feedstock with a shorter retention time than wholecrop rye so it gives more flexibility from the same crop.
“Although its biogas yield per tonne has yet to be calculated in practice, its composition is such that it is expected to be similar to crimped maize grain at around 500 cubic metres per tonne of freshweight.
“It certainly has a place in an AD plant with a short retention time or you could use it to complement feedstocks which may not be yielding as well as you’d hoped,” he says.
Cutting edge contractor now crimping rye
West Sussex farmer and contractor across the south of England, Frans de Boer crimped hybrid rye for the first time last year.
As the owner of a 500kW digester he is already familiar with crimping cereals and maize and processes around 6,000 tonnes for himself and his clients each year.
So crimping rye was a logical progression which he decided to do when his forage stocks peaked last year.
Frans says: “We use wholecrop forage rye in our digester but if we feed too much it can be difficult for our technology and we can end up with a crust and problems in the tank.”
So it was a logical progression to switch from whole-cropping to crimping last summer, which he did when the grain reached 35% moisture.
He says: “We combined the rye in early July and applied Crimpsafe 300 at the time of rolling to preserve the grain.”
Using a Korte roller he says he was very happy with the freshweight yield of 5 tonnes/acre (12t/ha) and the look of the feedstock.
“It looks like a really attractive crop and although we have yet to have it analysed, we expect its biogas yields to be similar to crimped maize.
“We don’t plough any more but wanted to incorporate the straw to return nutrients to the soil but this was hard work so on reflection we may have been better off rowing and baling, especially when there’s a good market for straw.
“The grain produces at least 80% of the whole rye plant’s biogas yield so crimping the grain can definitely be a viable solution.
“If the crop gets too bulky and you have to haul a long distance, or if you need to shorten your retention times crimping can also be a better option than wholecrop.
“I’ve always been a fan of the process because of crimp’s high feed value, easy storage and keeping qualities,” he says. “I’ve never understood why you’d incur the fuel cost for drying grain when you are only going to make it wet when you either feed it to livestock or put it in the digester.
“Our customers tend to take delivery of full lorry-loads of crimped maize which may need to last them outside the clamp for a week to 10 days,” he says. “They report that the crimp keeps really well and stays cold – right down to the dregs at the end, so I have no hesitation in preserving rye in the same way.”