Just like in the past, today maize silage is most commonly used to produce biogas in the agricultural. It is particularly popular because of its stable yields and high methane yields. Special, site-adapted maize varieties, such as late-ripening ones, are also available. As the retention time required to break down the maize silage in the digesters of the biogas plants to produce biogas is significantly different to when the maize is used for animal feed, the aim is to have a high content of slowly degradable carbohydrates in the maize silage.
With grass silage, the following applies: a higher crude protein content means a lower methane yield. The number of cuts has a similar effect, the first cut being the most suitable for the production of biogas in the agricultural sector. However, the economic benefits of using grass silage for the farm should be checked by means of a profitability calculation. In addition to cultivation on permanent grassland, arable land can also be used to grow different crop mixtures. One example of this is clover grass which consists of a mixture of legumes added to grass seed. The mixtures can also be adapted to the local conditions on individual farms.
Whole crop cereal silage
As a general rule, whole crop cereal silage is a material that ensiles well. Perennial rye is particularly suitable for producing biogas in the agricultural sector. In total, the crop produces yields of approx. six tonnes of dry matter per hectare. Perennial rye should be planted before the main crop and should not really affect its growth. This can be ensured with a good crop management and a sufficient documentation of crop cultivation activities. The harvesting time also has a significant impact on the yield performance and methane yield. With perennial rye, high energy yields are achieved from the “ear emergence” to “lactic ripeness” vegetative stages. Even though maize offers more advantages, whole crop cereal silage is a good choice for biogas production in the agricultural sector as it can be used to break up crop rotations. This is particularly the case when humus-draining crops such as sweet grasses (sorghum and other varieties) are being used.
Sugar beet has been used by many in the agricultural sector to produce biogas for several years now. In particular, farmers have been using excess beets that they didn’t need to meet their sugar beet quota. Following the reform of the European Sugar Regime in 2017, there has been a decline in the amount of sugar beet directly reaching the digesters of the biogas plants. It is now much more common for shredded beets to be used to produce biogas in the agricultural sector.
Mustard, summer rapeseed, oil radish and wild plant mixes can be used as catch crops to produce biogas in the agricultural sector. The aim is for farmers to obtain a high dry matter yield. The catch crops must be able to establish themselves well in the crop rotation and should not cause any problems during the harvest. The cultivation of turnips is therefore only suitable for specialist farms that have the right harvesting equipment to harvest this crop.
Residual materials, by-products and co-substrates
With regards to the residual materials resulting from biogas production in the agricultural sector, there are many requirements that apply and that must be observed. By-products from livestock farming can pose a major risk through infection chains between animals and animals and animals and humans. As such, appropriate measures must be taken to ensure a safe production of biogas in the agricultural sector. Even co-substrates from the industry should not contain substances that can reach the soils once the fermentation substrate has been spread on the ground and then damage the environment.