Within the GRACE project, two biomass crops will be cultivated: miscanthus and hemp. These were chosen based on their distinctive characteristics, which render them a possible sustainable biomass source, and the quantity and quality of the biomass they produce.
Miscanthus is a perennial C4 grass originating from South-East Asia. It is a very resource-efficient crop which, after a two-year establishment period, can yield up to 25 tonnes of dry matter a year in Central Europe. It can be harvested annually over a cultivation period of up to twenty years. The application of herbicides is only necessary during the establishment phase. Its biomass can be used for a wide range of utilization pathways including combustion, conversion to bioethanol, production of building materials and of basic chemicals.
Efficient Miscanthus nutrient cycle
Miscanthus recycles 40-60% of the nutrients from the aboveground biomass.
General Information Miscanthus
Miscanthus is a genus with more than 15 species. The most important species for biomass production in Europe are Miscanthus sinensis and Miscanthus sacchariflorus. The virtually only commercially available variety is Miscanthus x gigantheus, a natural, sterile hybrid of Miscanthus sinensis and Miscanthus sacchariflorus.
Propagation material – Rhizomes
Miscanthus x giganteus is currently the most widely cultivated genotype. As a triploid interspecific hybrid, this genotype produces no fertile seeds and has to be propagated via rhizomes. Compared with propagation via seeds, this method is very space- and labour-intensive and thus quite expensive. The picture shows rhizomes of Miscanthus x giganteus (picture provided by Novabiom).
Propagation material – Plugs
As propagation via rhizomes is rather expensive for the farmer, there is a trend towards seed based genotypes. The picture shows a seed-based plug.
Propagation – Rhizomes
Rhizomes for propagation purposes are produced through harvesting the rhizomes of so-called ‘mother plants’, which are around 3 to 5 years old. The rhizomes are first cut off using a plough and then picked up with a potato harvester. A propagation field before harvest is shown in the picture on the left (picture provided by Novabiom).
Propagation – Seeds
In seed-based propagation, seeds are collected, the plants are raised in a greenhouse and then planted out as plugs. It is not yet possible to sow seeds directly due to their small size.
Planting – Rhizomes
Miscanthus rhizomes are planted using a rhizome planter, which is comparable to a potato planter. The picture on the left shows rhizomes being planted (picture provided by Novabiom).
Planting – Plugs
Seed-based miscanthus genotypes are planted out as plugs directly in the soil. The plugs are often covered by a planting foil, as shown in the picture on the left. This keeps the soil moist and protects the plugs from damaging effects of late frosts.
Miscanthus is a perennial crop that, after a two-year establishment period, can be harvest annually over a total cultivation period of up to 20 years. Chemical or mechanical weeding is only necessary in the first two years. There are no known pests or diseases that infect miscanthus. In addition, it only requires small amounts of fertilizer. The recommendation is to fertilize the crop with the amount of nutrients removed through the harvested biomass.
Harvest – Chips
Miscanthus can be harvested either as chips or bales. In Central Europe, due to cold winters, the biomass has a low water content of around 15 percent at harvest time. For this reason, harvest is carried out with a self-propelled forage harvester as shown in the picture.
Harvest – Bales
If the biomass is too wet, the whole crop is laid out in a swath and later baled. A miscanthus bale is shown in the picture on the left.
Miscanthus is a low-input crop with a high water, land-use and energy efficiency. Studies have shown that miscanthus is able to produce net energy yields of up to 590 GJ per hectare and year. In addition, it relocates nutrients from the aboveground biomass back to the rhizomes in the autumn, thus before harvest. The rhizomes function as storage organs for resprouting in the next spring. For this reason, miscanthus only requires small amounts of fertilizer.
Hemp is an annual crop, thus sown anew every year. Due to its rapid youth growth and the consequent fast covering of the soil, it suppresses weeds very effectively and thus requires no herbicide application. Hemp is a truly multi-purpose crop and its biomass can be used in a whole range of applications. Composites or building materials can be made from hemp fibres, the seeds can be used to produce bio-herbicides, and medical cannabidiol (CBD) can be extracted from the threshing residues.
General Information Hemp
Genus: Cannabis L.
Hemp (Cannabis sativa, also called Cannabis indica) is one of the oldest crops known to mankind. It can be seen as an ‘on-field biorefinery’: its various fractions (e.g. fibres, shives, seeds) are each used for specific purposes. The seeds have a high oil and protein content. Although hemp is an annual crop, its production has a low environmental impact, since no pesticides are required.
Establishing a hemp crop is relatively simple. Soil preparation is similar to that for other break crops. It requires a fine, homogeneous seedbed to achieve uniform establishment and a crop with the desired plant density (90-150 plants m-2). Hemp seeds (35-45 kg ha-1) are sown in spring using traditional wheat planters.
No management is required during the growth period. Canopy closure is achieved relatively rapidly and no weed control is necessary. Hemp taproots can reach water deep in the soil, so irrigation is not normally needed in European conditions. It has a high nitrogen use efficiency (NUE) and 60 kg ha-1 nitrogen fertilizer are sufficient to achieve maximum biomass yield (up to 20 Mg ha-1).
Traditionally, hemp for fibre production was harvested at full flowering, when the fibre quality is at its best for textile manufacture. Nowadays, multipurpose hemp is harvested at seed maturity, when it can be used both for the production of food-grade seeds and fibre for technical applications. Double headers, mounted on conventional combine harvesters, are used to reap seeds and stems in a single passage.
Retting and processing
Retting is necessary to ease the separation of fibre from shives and maximize fibre quality. Traditionally this was carried out in water, but today it is carried out on the field, where stems are left in swaths after harvesting until retting and drying is complete. The dry stems are then stored and fibre extraction subsequently carried out in industrial facilities.
Hemp is a multi-use, multifunctional crop that provides raw material for a large number of traditional and innovative industrial applications. Hemp raw materials and current applications are: bast fibre (pulp and paper; insulation materials, composites for the automotive industry), shives (animal bedding, building materials), seeds (feed, oil, specialty foods, cosmetics), leaves and inflorescence (pharmaceuticals).
Apart from high yield potential, another important characteristic that an industrial crop should have to make it suitable for modern sustainable production systems is resource-use efficiency. Hemp has a very high NUE and normally does not require irrigation, herbicides or pesticides. Its very favourable environmental impact and “whole-plant exploitation” render hemp an exemplary crop for the bio based economy.