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Energy Crops Are Sustainable in Many Ways

25 March 2011

DENMARK - Growing energy crops not only benefits the environment by increasing Denmark's production of sustainable energy. It can also help improve the aquatic environment by removing excess nutrients from agricultural soil.

Growing energy crop such as miscanthus can benefit the environment in several ways. Photo: DJF

Is it good or bad for the environment when the farmer switches from growing annual crops such as cereals and rapeseed to growing perennial energy crops such as willow and miscanthus?

A survey carried out by scientists from the Faculty of Agricultural Sciences, Aarhus University, shows that growing energy crops can be a win-win situation. Not only do the crops provide environmentally friendly energy. Growing perennial crops can also protect the aquatic environment against excess nutrients such as nitrogen and phosphorous.

The scientists reviewed the consequences of changing from regular crop rotation to growing perennial crops on lowland and highland soils. The results have been published in a report that focuses on nitrogen and phosphorous loss via leaching or drainage transportation to the aquatic environment.

Energy crops mop up N and P

An improved nutrient balance on highland soils can be achieved by producing energy crops on land that was previously included in a regular crop rotation. Planting energy crops will on average reduce leaching by 15-35 kg N per ha on clay soils and 40-60 kg N on sandy soils.

With regard to phosphorous it is assumed that such a change will reduce the risk of P erosion on erosion-threatened land as is the case when a change is made to growing permanent grass.

On lowland soils it is more difficult to draw clear conclusions. This is partly because they cover a wide range of soil types and hydrological patterns and partly because not many studies have been carried out. However, the scientists believe that on certain kinds of lowland soils it would be beneficial to grow perennial energy crops.

Certain kinds of lowland soils have a high phosphorous content and there can be a great risk of mobilising phosphorous by allowing drained agricultural land to return to wetland conditions. On land like this growing energy crops, without P fertilisation, can be one of the only ways to mop up the large amounts of accumulated phosphorous and reducing the loss to the environment, says one of the authors of the report, senior scientist Uffe Jørgensen from the Department of Agroecology and Environment at the Faculty of Agricultural Sciences.

Seen as a whole, growing perennial energy crops can be an important instrument in helping to fulfil the requirements of the Water Framework Directive and EU's climate and energy strategy. And it would be an instrument that does not limit the possibilities of continuing to farm the land, Uffe Jørgensen points out.

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