Wholecrop rye is increasing in popularity for good reason. But users growing it for anaerobic digestion are also starting to crimp the grain too.
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.
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 dry matter 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. AD Feedstock Solutions 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 energy 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 clamp or a plastic tube 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.
Learn more about our Crimped Grain Preservation product