In Denmark climate changes are important with regard to which crops farmers choose to grow. Grain maize will spread to the whole country and there will be more focus on robust and environmentally friendly crop rotations.

There is every indication that Denmark will become warmer due to global climate changes. The changes will affect which crops will be grown in Danish agriculture. With the aid of models, climate experts are busy calculating just how much and how quickly the changes will occur.

- For each degree the average temperature increases, the climate zones move approximately 200-300 km northwards. Up to the year 2050 temperature increases of 1.5-2.0 °C are expected. That would give us a climate that is similar to the present climate in Holland or central Germany, says research professor Jørgen E. Olesen from the Department of Agroecology and Environment at the Faculty of Agricultural Sciences, University of Aarhus. He is a member of the UN Intergovernmental Panel on Climate Change (IPCC), which shares the Nobel Peace Prize with Al Gore.

Temperature is not the only factor determining which crops can be grown and their yield. Many factors play a part such as the length of the growing season, the amount of CO2 in the air and the amount of rainfall.

An enhanced CO2 concentration increases production in most crops with maize being one of the exceptions. For crops that do not mature, such as grass and sugar beets, a higher temperature will increase the length of the growing season, resulting in a higher yield provided that there is no drought.

Easier and more productive

There is good news for organic farmers, since it will probably be easier to grow organic protein crops if the Danish climate becomes warmer. Many legumes will mature earlier and may thus be grown more reliably.

There will also be openings for new protein crops such as sunflowers and in the long run soybeans. Growing these crops will most likely require temperature increases of 3-5 °C. Organic grain rotations will also be favoured by milder autumns that make it possible to increase production of nitrogen-fixating catch crops that can fertilize ensuing crops.

Denmark will still have a favourable climate for growing winter rapeseed and with an earlier harvest of winter wheat it could be attractive to sow winter rapeseed after winter wheat. New seed crops such as sunflowers require a temperature increase of about 2 °C before being interesting for widespread growing in Denmark. However, there is no doubt that sunflowers and soybeans will be grown in smaller amounts in Denmark within the next few decades.

A temperature increase of 1-2 °C will make it possible to grow maize to maturity in Denmark. An increasing area with maize will increase the focus on the crop’s impact on the environment and on the greater need for growing catch crops in order to avoid nitrogen and phosphorus losses.

Good Danish tomatoes, wine and apples

With a longer growing season, Danish outdoor vegetable production will cover market demand for a longer period. A warmer summer climate also enables new production types such as tomatoes and cucumbers in unheated greenhouses or perhaps even outdoors.

Increasing temperatures can also result in larger fruits and better quality and there will be better growing conditions for Danish wine production.

Climate changes will probably not have any appreciable effect on cattle farming, which has to a great degree already switched to feeding with grass-clover and maize. However, the yields in the pastures will be stimulated not only by a longer growing season but also by a higher level of CO2, which is particularly beneficial to clover and legumes. This can make it even more attractive than now to combine nitrogen-rich grass-clover with cob corn.

Few disadvantages

In a warmer climate winter wheat will develop more quickly. In order to avoid a loss in yield, varieties that develop more slowly and flower around the same time as now must be chosen. In any case, the crop will mature earlier. This will result in a longer period in the autumn with bare soil and a greater risk of nitrogen leaching in the autumn and winter. There will therefore be a greater need to grow catch crops. Drier summers can make it difficult to establish the catch crops when sowing in July or August. It can be necessary to undersow the catch crops in the spring.

In annual agricultural crops such as maize, rapeseed and potatoes, plant development depends on temperature and day length. For these crops, an increase in temperature will reduce the length of the active growing period because the crops will mature earlier. All other things being equal that will reduce the yield. Yield reduction is greatest in autumn-sown crops and less in spring-sown crops, where it is possible to counteract some of the effect using earlier sowing so that the crops have a better chance of utilising the favourable light conditions in the spring. An increased yield could be achieved especially by changing crops species and varieties.

For more information please contact: Research professor Jørgen E. Olesen, Department of Agroecology and Environment, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 1659, e-mail: jorgene.olesen@agrsci.dk