What Is Oilseed RapeCurrent Crop StatusHistory Of Cultivation In The UKMain Varieties Currently Grown
It is grown specifically for the oil contained within the seed (mainly used for cooking oils and margarines),
however the meal left after oil extraction is utilised as a high protein animal feed. Both parts of the
seed contain unwanted compounds, primarily the oil has high levels of erucic acid and the
meal contains glucosinolates. These are harmful to their respective consumers, although
plant breeders have largely succeeded in reducing or removing them, illustrated by the 'double low'
(00) glucosinolate and erucic acid varieties.
The 'double low' glucosinolate varieties are not of economical importance to the farmers growing the rapeseed, however it is of great importance to the farmers using rapeseed meal in their animal feed as the lowered level of glucosinolate allows an increased, maximum level of meal that can be consumed by the animals to remain in a healthy state.
Rapeseed oil is also suited to a range of industrial applications, shown in recent years with high erucic and lauric acid cultivars that have been cropped on set-aside, creating an important alternative in a new non-food market.
The protein content of oilseed rape meal is around 20-25 percent, but crucially it has a high feed
value because it contains high levels of many essential amino acids, relative to cereal
crops and most legumes.
Throughout the world there are four main Brassica species grown for oil; B. napus (Swede rape), B. rapa (Turnip rape) [formerly B. campestris], B. juncea (Mustard rape) and B. carinata. Oilseed rape (Brassica napus) is thought to have originated from a cross between B. rapa and B. oleracea in southern Europe before being introduced into Asia in the 18th century (Kimber & McGregor, 1995). In Europe, B. napus is the predominant species although B. rapa is grown in some areas where its superior cold tolerance offsets its inferior yield potential (eg. Scandinavia). In the UK, both B. napus and B. rapa are referred to by the generic term, oilseed rape.
It is believed that B. napus was first introduced into the UK for cultivation in the 17th century, to aid fenland land reclamation and provide oil for lighting, green fodder and seed meal for animal feeds. By the 19th century the amount of rape grown declined due to cheap imports, coupled with the widespread development and availability of mineral oils by 1850 it meant that rapeseed oil had been replaced and the crop was instead used primarily as a forage crop. At the beginning of the 20th century, oilseed production was effectively nil, although the demand for fats and oils was increasing rapidly. However, the Second World War induced disruption of world trade, giving a small boost to UK rape production as the need for lubricating and edible oils soared, and it was also introduced as a break-crop for intensive spring barley cultivation (Bunting, 1984). By the mid-1960's, large-scale growing of rapeseed began, as its adoption into modern agricultural rotations resulted from the specialisation into intensive arable farming, thus leading to the requirement of break-crops within cereal based rotations (Inglis et al, 1989). Spring sown varieties were ideal as they grow well in a range of soils (Archer, 1981), aren't susceptible to cereal fungal diseases (Labuda, 1981) and do not require extra investment into farming machinery above that used for cereals (Goetz, 1979).
Cheap, imported oilseeds stifled production until Britain joined the EEC in 1973, when UK farmers qualified for guaranteed minimum price support, which subsequently doubled their seed value and oilseed rape became a valuable cash-crop, as well as early entry for cereals (Inglis et al, 1989). As a result the area cropped increased ten-fold by 1980, and continued to rise until reaching its peak of 496,000ha in 1994. Now in the 1990's, the area aid applicable to the crop, combined with a world market (oilseed rape accounts for 25% of world oil production) gives it the stimuli for its continued cultivation (Skinner, 1998).
In 1970, roughly 75% of the oilseed crops were spring grown, although they were soon replaced with the preferred winter rape varieties, due to their superior productivity (20% higher), oil content, drought tolerance and earlier maturing nature. By 1984 the spring varieties had declined to only 1% (Inglis et al, 1989), whereas oilseed rape as a whole had increased to occupy 6% of the 'total crops' area in the UK (Bunting, 1984). Varietal development has led to many important changes in oilseed cultivars in recent years. Its position as the major European vegetable oil was secured in the mid 1980's after the introduction of double-low varieties (Bearman, 1989), with reduced levels of erucic acid and glucosinolates, as high levels had been associated with heart disease and thyroid dysfunction respectively (Rowan & Lawrence, 1982). The lower glucosinolate levels also permitted the increased use of rapeseed meal in animal feed (Rowan & Lawrence, 1982), thereby increasing its value further.
However, due to further improvements in spring cultivars, more are now grown as improved yields combined with lower variable cost inputs have dramatically narrowed the gross margins between spring and winter crops (SAC, 1997).
Yields over the past 10 years have remained relatively constant, at about 3t/ha, but with the rigours
of 'Agenda 2000' approaching, yield improvement will be essential if oilseed rape is to survive. The much improved
hybrid cultivars and a new generation of genetically
modified varieties with specific quality traits, will hopefully ensure that oilseed rape remains
as an integral part of crop rotations (Skinner, 1998). This market is poised to expand if genetically
modified rape, with such features as manipulated fatty acid profiles can be grown, from which plastics, detergents
and cosmetics can be derived (Murphy & Mithen, 1995).
