About crops and the environment

Crops, suitable for production of biomass

The production of biomass is, in essence, a method whereby sunlight is converted to energy. The conversion happens via plant growth and the greater the plant growth, the more effective the conversion of sunlight into energy.

In Denmark it will be possible to significantly increase biomass yield from farming by switching to new crops. There are different types of photosynthesis in nature, where in warmer conditions the so-called C4 photosynthetic pathway is about 30 percent more efficient at converting solar energy than the C3 pathway used by most of the crops grown in Denmark today.

Miscanthus (elephant grass), which is a well-known feature in many Danish gardens, is one of the few plants using C4 photosynthesis, and since it also has a long growing season it will overall be able to utilise solar irradiance over the year so effectively that it can probably produce twice as much biomass as a common wheat crop currently produces in straw and grain combined. And this is notably with 70 percent less nitrate leaching, lower greenhouse gas emissions and less use of pesticides.

If Miscanthus were to be utilised in a biorefinery, approximately a third of the biomass could probably be used as an animal feed and thus provide as much feed as the wheat field it replaces, in addition to a bioethanol production and fuel for cogeneration. If this could be put into practice, there would be no indirect environmental effects from a lower food production, but only positive effects on the environment, climate and energy supply.

Potential higher yields with a biomass crop

Current yield of wheat: 9 t dry matter/ha
Potential yield of winter rye + maize: 18 t dry matter/ha

Current yield of maize: 12 of dry matter/ha
Potential yield of Miscanthus: 20 t dry matter/ha

Benefits for climate and environment

There are large potential benefits for the climate and energy supply from a conversion from annual crops such wheat and rapeseed to perennial crops such as grass, willow or Miscanthus. Several studies show that perennial crops can lead to an accumulation of carbon in the soil of up to 3 tonnes per hectare per year when the above-ground biomass is used for bioenergy purposes. If this can be achieved in practice, carbon storage on its own would be able to reduce CO2 emissions by 11 t per ha per year. If you grow 100,000 hectares with willow (about 4 percent of the farmed area), the carbon sequestration would be equivalent to nearly 2 percent of total Danish CO2 emissions.

Another viable option is to convert areas to perennial crops (e.g. willow or grass) that currently grow annual cereal crops that contribute to excessive nutrient leaching to water bodies. This is a very effective way of reducing nitrate leaching. Growing perennial energy crops can therefore both provide more biomass, protect the aquatic environment and significantly reduce greenhouse gas emissions.

Benefits to climate and environment of growing perennial energy crops rather than annual crops:

70% reduction in nitrate leaching
60% reduction in pesticide use
60% higher reduction in greenhouse gas emissions