Rapeseed
Description
#Rapeseeds - called #canola seeds in North America and other countries - are the seeds of the oilseed rape plant. Rapeseeds are the 3rd source of both vegetable oil (after soybean and oil palm) and oil meal (after soybean and cotton). They are the most widely cultivated crop species in the Brassicaceae family, which also includes cabbages, mustards, turnips, radishes and cauliflowers. There is a very wide range of rapeseed varieties for all types of purposes. Modern rapeseed varieties with low concentrations in erucic acid and glucosinolates (see below) are mainly used for edible oil, biofuel, industrial oil and lubricants. Rapeseeds are also a valuable energy feed for livestock due to their high protein and lipid content.
Low-erucic and low-glucosinolates varieties
Oilseed rape has been cultivated for its oil in Europe since the 13th century, and was a major source of lamp fuel until it was superseded by petroleum in the mid-19th century. Rapeseed oil as a foodstuff used to have a poor reputation, due to the presence of erucic acid, which has a bitter taste and was later found to cause health problems when ingested in large quantities.
The use of rapeseeds and rapeseed oil meal for livestock was limited due to the presence of glucosinolates, which are antinutritional factors detrimental to animal performance. In the 1960-1970s, low-erucic varieties ("0") and low-erucic, low-glucosinolates varieties ("00" and canola) were developed, allowing rapeseed oil to become a major food oil, and rapeseed meal and rapeseeds can now be fed to livestock. Production increased from 5 Mt in 1972 to 72.5 Mt in 2013. Low-erucic, low-glucosinolate varieties are now the main types grown worldwide, though there are also high-erucic varieties grown for specific industrial purposes. In Europe, rapeseed oil is the main source of biofuel
Note: the name "canola" was originally a trademark licensed by the Canadian Canola Council and referring to "00" varieties developed in Canada now used as a generic term for 00 varieties in North America, Australia and other countries. In the text below, the name "canola" is used only when the source of the information actually refers to rapeseeds marketed under that name.
Whole rapeseeds
Plants from the Brassicaceae family produce fruit called siliques, commonly called pods. Oilseed rape pods are 6-9 cm long and contain between 15 and 25 seeds. Rapeseeds are small (1-2 mm in diameter), spherical, light brown to black. There are approximately 280,000 to 300,000 seeds per kg. The seeds are released as the pods dry out and shatter. Because the main livestock rapeseed product is the oil by-product (rapeseed meal or rapeseed cake), whole rapeseeds are often called "full-fat rapeseeds" or "full-fat canola" to distinguish them from the oil meal. The "00" rapeseed and canola seeds can be included in ruminant diets, and to a less extent in pig and poultry diets due to the presence of residual glucosinolates.
SUPPLY
Oilseed rape is thought to have originated from Europe and is now grown worldwide. It is the 4th largest producer of oil seeds after soybeans, oil palm and cottonseeds. In 2013, world rapeseed production was 72.5 Mt: the top 5 producers were;
1. Canada (18 Mt),
2. China (14 Mt),
3. India (8 Mt),
4. Germany (5.7 Mt)
5. France (4.3 Mt),
followed by;Australia,Poland, Ukraine, the UK and the Czech Republic.
Oilseed rape is mostly cultivated in temperate areas but it is also grown in the tropics at high elevations (between 1500 and 2200 m). In regions of Europe and Asia where winters are mild, oilseed rape is mainly cultivated as a winter crop. In Canada, northern Europe and Australia, spring varieties are more suitable. Oilseed rape is prone to heat stress in very hot weather. It is often a good alternative oilseed crop to soybeans in regions where the latter crop does not grow well. Oilseed rape is a versatile plant that does well under a wide range of soil conditions, provided that they are well-drained and that moisture and fertility levels are adequate. It grows where annual rainfall is between 300 and 2800 mm. It responds positively to N and P fertilizers and requires large amounts of sulphur. Optimal growth is obtained in spring-type oilseed rape when the temperature is just over 20°C, and it is best grown between 12°C and 30°C. Winter oilseed rape sown in autumn survives the winter in a leaf rosette form on the soil surface, and resumes growth in the following spring, first developing vertical stems and then lateral branches shortly before blooming. Flowering occurs in spring, and pod development and ripening take place over 6 to 8 weeks. Oilseed rape is frost resistant: unhardened oilseed rape survives -4°C at all stages of growth while hardened spring types withstand -10°/-20°C and winter types can survive down to -15°C/-20°C for short periods. Oilseed rape is sensitive to aluminium and manganese toxicity in acidic soils but it is relatively tolerant of soil salinity (up to 5-6 dS/m).
Processes
Rapeseeds can be ground and heat-processed to improve their digestibility and reduce their residual glucosinolate content for cattle, pigs and poultry.
Forage management
Establishment
Oilseed rape plants can either be sown during autumn for winter types or during spring for spring types. Note: oilseed rape is a major crop with a large number of specialised cultivars.
Harvesting
Rapeseeds can be harvested through direct combining or they can be cut, swathed and then combined. When direct combining is intended, harvest should be done when seeds contain between 15% and 9% moisture and when the straw is yellow in colour. Earlier harvesting can reduce yield as green seeds may remain in the pods and pass through the combine harvester with the chaff. If the seeds are too dry (below 9% moisture), they may shatter before combining. When swathing is intended (for example in areas where the growing season is short), the crop can be cut and left on the ground for 8 to 10 days so that uniform drying occurs. Once the seeds are dried to about 8-10% moisture the swathed crop can be threshed.
Yield
The worldwide average seed yield for oilseed rape was 2 t/ha in 2013. However, yields range between very low (0.3 t/ha in Tunisia) and very high values (4.2 t/ha in Belgium).
Storage
For optimal storage, seeds should be clean, healthy and not broken. They should be below 10% moisture (8% being at lower risk) and allowed to cool before entering storage bins. Ideal temperature for storage is 15°C or below. Under such conditions, rapeseeds have a long shelf-life (over 6 months). Under less optimal conditions, storage should not be longer than 6 months.
Environmental impact
Genetically-modified canola seeds
Many genetically-modified canola cultivars have been developed and are widely used in Canada (95% of the crop) and in the USA (82%). In the European Union, GM rapeseed crops are banned but rapeseeds, rapeseed oil and rapeseed oil meal resulting from the cultivation of certain cultivars can be imported and used as feed and food. Harmonisation of GM rapeseed labelling has been recommended so that livestock farmers can make an informed choice. However, no compulsory labelling is required for livestock products resulting from feeding GM oilseed rape products.
Cover crop, mulch and stubbles
Winter oilseed rape covers the soil for 10-11 months. It has high nutritional demands in autumn and is able to scavenge soil nutrients (especially N), thus reducing N nutrient losses. Plant cover also reduces soil erosion in winter and the taproots alleviate soil compaction. Oilseed rape plants are known to reduce root nematodes. During winter, crop residues left on the soil after harvest help to trap snow and subsequently reduce snow melt run-off, wind and water erosion. Oilseed rape is increasingly recommended for soil conservation as well as for minimal or no-till practices, provided it is combined with adequate weed control.
Nutritional attributes
#Rapeseeds are a source of protein and lipids. They contain about 21% of protein (17-24% DM). They have a lower protein content than soybeans (40%) and linseeds (24%), are similar to cottonseeds (22%), and are richer in protein than sunflower seeds (17%). They have a high oil content of 46% of the DM (40-50% DM), which is slightly lower than the oil content of sunflower seeds (48%), and much higher than that of linseeds (37%), soybeans (21%), and cottonseeds (20%). Rapeseeds and canola seeds have a relatively low fibre content (crude fibre 10% DM; NDF 21% DM; ADF 15% DM), which is much less than in other oilseeds except soybeans (crude fiber 6% DM). Rapeseed oil is rich in polyunsaturated fatty acids (60% oleic, 21% linoleic and 10% linolenic), which makes it valuable for human and animal diets.