Oilseed rape, Brassica napus

Economically, rapeseed is of great importance on the global agricultural market today. However, rapeseed is a young crop. It was harvested wild for centuries before it was first cultivated in Central Europe from the 17th century onwards in order to extract oil for lamps from the seeds. Scientists believe that rapeseed originated from a cross between wild cabbage(Brassica oleracea) and turnip rape(Brassica rapa) in the Mediterranean region.

Yellow flowers with high demands

Rapeseed belongs to the cruciferous family and is related to turnip and cabbage. It is an annual herbaceous plant with an upright, branched stem that can grow up to two meters high. The rape plant is grey-blue in color and forms a taproot underground. In rapeseed-growing areas, the crop is particularly attractive due to the dense sea of yellow flowers during the plants’ flowering period. The fields look so magnificent because each plant bears twenty to sixty flowers. These hermaphrodite flowers are arranged in clusters. The buds of such a cluster bloom one after the other from bottom to top. Depending on the weather, an oilseed rape plant delights onlookers with its flowering splendor for a whole three to five weeks, even if each individual flower is only open for one or two days. However, only about half of the flowers form pods – the plant would probably not be able to develop any more. But even the insects do not manage to fertilise all the flowers and the oilseed rape is dependent on this cross-fertilisation. The dark brown-blackish round seeds grow in the pods. They have a diameter of 1.5 to 2.5 millimetres and remain germinable for a very long time. Rapeseed in the soil can still germinate after up to ten years and thus also disrupt subsequent crops.

The soil requirements of oilseed rape are similar to those of wheat. Both crops require deep soil and do not like waterlogging. Light or shallow soils that dry out quickly also reduce the yield security of rapeseed and are therefore less suitable. Oilseed rape has high requirements in terms of nutrient supply, for example it needs significantly more nitrogen than cereals.

Oilseed rape should not be grown in the same field for several years in a row, as otherwise specific diseases and oilseed rape pests can become rampant. Oilseed rape is therefore dependent on crop rotation with other arable crops. Wheat and other cereals with similar soil requirements are particularly suitable and at the same time benefit greatly from an intermediate crop of rape. This is because when rapeseed is harvested, the harvested plant parts and roots usually remain on the field, which promotes humus formation, soil structure and the biological activity of the soil, from which the cereal crops in the rotation also benefit. In addition, spring oilseed rape penetrates the soil deeply and thus ensures good soil aeration. As a result, oilseed rape has become very popular as an intercrop with cereals, particularly in Europe.

From wild rapeseed to genetically modified large-scale cultivation

The first evidence of the use of rapeseed dates back to 2000 BC in India, where the plant was used for oil extraction, in medicine and as food. In Central Europe, rapeseed was collected wild for a long time, but was only cultivated on a large scale from the 17th century onwards – initially mainly as an important fuel for oil lamps. Because of its bitter taste (due to its high erucic acid content), rapeseed oil was only used to a limited extent as an edible oil, for example in times of famine. In the second half of the 19th century, rapeseed production in Europe fell sharply as cheaper petroleum imports and tropical edible oils came onto the market. This did not change again until the mid-1970s. At that time, new varieties with two new characteristics came onto the market: the oil from this so-called 00 rapeseed (‘double zero’) contains only small amounts of the bitter-tasting erucic acid and is almost free of mustard oil glycosides. Without these toxic substances, the oil can now be used as food or animal feed.

Today, rapeseed is grown worldwide in the mild winter regions of temperate climates. The main cultivation areas are Canada, India and China, but rapeseed is also an important part of agriculture in Europe. In Canada, the world’s most important rapeseed producer, mainly spring rapeseed is grown. Not so in Central Europe, where it is mostly winter oilseed rape. This is sown in the fall and harvested the following early summer. Both winter and summer rapeseed are mainly used for oil production, but there are also leafy rapeseed varieties that are grown as fodder rapeseed.

Unfortunately, there are also some problems that arise from the large-scale cultivation of rapeseed. The monoculture cultivation method displaces and suppresses other native plant species, leading to a decline in biodiversity. The diversity of insects and other animals also declines as the ecosystem is disturbed. This process is exacerbated by the use of genetically modified rapeseed varieties that are immune to herbicides (weed killers), insecticides (insect repellents) and fungicides (protective agents against fungi). If these agents are applied to large areas of oilseed rape fields, all the plants in and around the field will die, with the exception of the oilseed rape plants. Hardly any other crop spreads as quickly and easily as oilseed rape. The pollen usually flies for miles. This means that genetically modified oilseed rape pollen also reaches areas where genetically modified plants are prohibited or restricted, such as nature reserves and protected landscape areas. As a result, the modified oilseed rape starts to grow and spread here too. As a result, there is also a decline in biodiversity here. “If care is not taken in future to ensure that genetically modified varieties and original varieties are cultivated separately, there will soon be no way of removing them from the environment,” warn experts. Globally, the proportion of GMOs in rapeseed cultivation in 2019 was 27%, most of which was in Canada, where 95% of rapeseed is genetically modified. The largest exporter of rapeseed is Canada (crude oil/rapeseed cake/rapeseed) and the largest importer in terms of both volume and sales is the USA.

Feed for humans, animals, tanks and industry

We humans usually eat rapeseed in the form of cooking oil or margarine. The oil is considered healthy as it has a particularly good ratio of the two polyunsaturated fatty acids omega-3 and omega-6, which are important for the body. Refined rapeseed oil has a neutral taste and is often used for frying and roasting or in mayonnaise and dressings, partly due to its high smoke point. Virgin rapeseed oil, on the other hand, has a nutty note. In addition to its use as an oil, rapeseed is also eaten as a leafy vegetable in some regions – special rapeseed varieties are cultivated for this purpose in Zimbabwe and other countries in southern Africa.

But it’s not just us humans who eat rapeseed and oil. It is also used as animal feed – especially the press residue that is a by-product of oil production. This rapeseed meal or rapeseed cake is very high in protein and is therefore well suited as animal feed. Another important application for rapeseed is biodiesel: in Europe, biodiesel is even mainly produced from rapeseed oil. In Germany, for example, half of the rapeseed oil produced is used as vegetable fuel or biodiesel. Rapeseed is also used for special oils, fats and other industrial chemicals or in the form of biodegradable oils and lubricants as a raw material in the production of paints and varnishes as well as for plasticisers and surfactants.

Absolute bee paradise, but hardly any organic cultivation

Rapeseed is an insect-friendly plant and therefore very important for beekeeping. In Germany, rapeseed flowers are one of the most important nectar sources for honey bees. Bees can produce up to 494 kg of honey from one hectare of rapeseed in one season. Because rapeseed requires a lot of nitrogen and is easily attacked by pests, there is still hardly any organic rapeseed. However, due to the ban on neonicotinoids as plant protection products in the EU, there are various research projects for organic rapeseed cultivation. Experiments with undersowing, earlier sowing dates or the targeted promotion of beneficial insects give us hope that it will be possible to produce larger quantities of rapeseed in better harmony with nature in the future.

Sources

Svotwa & Katsaruware (2018): Performance of Two Rape(Brassica napus) Cultivars under Different Fertilizer Management Levels in the Smallholder Sector of Zimbabwe. Link.
Utopia.de: Rapeseed oil in Öko-Test: 12 are “very good” – but almost all contain pesticides and mineral oil. Link.
Utopia.de: Rapeseed wax: Vegan wax without kerosene. Link.
International Society for Horticultural Science: Importance and development of rape (brassica napus l.) as a vegetable in Zambia. Link.