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Grass is good in more ways than one

Production of biomass from grass performs well with regard to yield and protein levels, as well as environmental footprint.

[Translate to English:] Flerårige græsser har stor potentiale som produktiv og effektiv afgrøde. Foto: Janne Hansen

Would it not be nice to have a crop that uses the sun’s energy efficiently to produce lots of biomass, contains substantial amounts of protein, and is beneficial to the soil’s nitrogen balance? Sound too good to be true? It is not! The answer lies in grass.   

Researchers from the Department of Agroecology at Aarhus University have studied novel biomass production systems under the auspices of the research platform BioValue SPIR. One of the projects in the platform involved investigation of innovative biomass production systems, harvest and conservation technologies.  

The results from the project indicate that perennial grasses have a number of advantages compared to traditional annual crops. Among other things, fertilised perennial grasses outperformed all the other systems in the study by doubling biomass nitrogen uptake and reducing nitrate leaching by 70-80 percent compared to the traditional systems.  

Novel cropping systems tested

The researchers compared novel cropping systems optimised for high maximum biomass production with traditional systems. The trials were carried out at two sites in Denmark differing in soil type and climatic conditions and comprised three main cropping systems: 

  • Optimised rotation of annual crops (maize, beet, hemp/oat, triticale, with winter rye and winter rapeseed as second crops)
  • Perennial grasses that were either intensively fertilised (festulolium, reed canary, cocksfoot and tall fescue), low-fertilised (miscanthus) or unfertilized (grass-legume mixtures)
  • Traditional systems (continuous monocultures of maize and triticale, and a rotation of spring barley-winter barley-winter rapeseed)

Good biomass and protein yields

As described in an earlier article about the study, “Grasses are good at using the sun to be productive”, intensively fertilised perennial grasses produced high biomass yields. Although the grasses did not always outperform the other systems with regard to biomass yield, they had added benefits. One of these is that the grasses contained plenty of extractable protein.  

The fertilised pure grasses thus produced the highest amount of crude protein annually, ranging from 2.6 to 3.7?ton per?ha irrespective of the year, of which 0.9–1.6?ton?per ha was neutral-, i.e., easily- extractable protein. The unfertilised grass-legume mixtures yielded crude protein amounts comparable to the annual crops in the optimised and traditional systems. 

Easily extractable true protein ranged from 34 to 46 per cent of the crude protein in pure grasses and comprised 48 per cent of the crude protein in the grass-legume mixtures. The researchers predict that the potential extractability of crude protein can be further increased by 14-35 per cent if the cell wall-bound protein can also be extracted. 

Satisfactory environmental footprint

One might perhaps think that intensively fertilised crops have a greater environmental impact, notably with regard to nitrate leaching. This was not the case with the intensively fertilised grasses.  

At each of the study sites, the fertilized perennial grasses outperformed all the other systems with regard to nitrate leaching. Compared to the traditional systems at the two sites, nitrate leaching in the fertilised grassed was 70-80 per cent less, in addition to producing more biomass with a high protein content.


- Production of a broad spectrum of products from biomass is of key importance for an economically viable and sustainable biorefinery sector. For example, the quality of the protein from grasses is often high in lysine and methionine contents, making the grasses particularly interesting source to substitute the environmentally costly imports of soya bean protein. However, growing crops with high biomass yields and high nitrogen levels can significantly alter the agricultural landscape. Understanding the fate of nitrogen in these novel land uses is vital for product optimisation and environmental protection, say Senior Scientist Uffe Jørgensen and postdoc Kiril Manevski from the Department of Agroecology at Aarhus University.

 - And we are currently following up on studying the development in soil nitrogen contents, as well as gaseous losses of nitrogen, they add. 

Read the article “Grasses are good at using the sun to be productive”.


You can also read the following scientific articles:

Biomass productivity and radiation utilisation of innovative cropping systems for biorefinery

Crude protein yield and theoretical extractable true protein of potential biorefinery feedstocks

Nitrogen balances of innovative cropping systems for feedstock production to future biorefineries

For further information please contact:

Head of Aarhus University Centre for Circular Bioeconomy (CBIO), Senior researcher Uffe Jørgensen, Department of Agroecology, email: uffe.jorgensen@agro.au.dk, telephone: +45 8715 7729, mobile: mobile: +45 2133 7831 

Postdoc Kiril Manevski, Department of Agroecology, email: kiril.manevski@agro.au.dk, telephone: +45 8715 7795