Oil seed rape (OSR)
- Oilseed rape (OSR) is well-suited to the Irish climate with good yield potential (4-6 t/ha for winter and 2.5-4 t/ha for spring varieties). 7500 ha grown in 2015
- A good break-crop that boosts the succeeding cereals in rotations.
- National and international markets for all production. Food and industrial markets for pressed oil. Animal feed markets for whole seed and pressed cake following oil extraction. Scope for developing high-value edible oil speciality markets.
- Variability in yield, disease prevalence and impact, and climate specific management are key research deficits.
- Delivering critical-mass levels of production while developing all market outlets are necessary actions to increase production.
- OSR is a brassica grown primarily for its oil. The commonly grown winter and spring crop types are swede rape (Brassica napus), but turnip rape (Brassica rapa) is grown to a limited extent as a spring type. OSR is an erect, annual plant with branched stems (up to 1.5m) and with a stout taproot. Brassica napus is generally self-fertile, although insects improve seed setting.
- Varieties can be classed according to their seed production (conventional or hybrid), seed fatty acid profile (double low, HEAR, HOLL) and canopy structure (e.g low biomass).
- The OSR crop has diverse end-uses (Fig. 1) including human nutrition; renewable vehicle fuel; environmental friendly lubricating oil; or as raw material in the chemical industry. Following oil extraction the expeller cake is a high protein and energy animal feed source.
Fig. 1: Possible uses of oilseed rape from a yield of 5 t/ha (From UFOP, 2001)
OSR oil for human consumption
- In human nutrition the high levels of unsaturated fats in OSR makes it attractive compared to animal fats and most other plant oils (Fig 2).
- The use of variety types with different oil profiles can satisfy specific market sector needs (e.g. ‘double low’ or HOLL types). The market for food oils is significant with Ireland importing 201,000t annually for food use.
Fig. 2: Fatty acids composition (% of total) (HGCA 2014)
- OSR oil and the extracted cake can also used for industrial purposes, including biofuels, fuel additives, lubricants, surface coating agents, polymers, functional additives, adhesives, cosmetics and as a source of medical compounds.
- Whole seed and oil-extracted rape meals are high-value animal feed components. The oil-extracted cake is a particularly useful protein and energy source.
Suitability for Ireland
- OSR is well suited to the Irish climate and soils, with good growth and yield potential and few moisture limitations.
- Over-winter bird damage is common and diseases such as stem canker (phoma), light leaf spot and sclerotinia are significant.
- The field equipment required is common with cereals and sowing and harvest dates allow efficient use of labour and equipment.
- While drying and storage facilities are available, there is no large-scale crushing plant.
- The whole crop and expellor cake are valuable high protein feed constituents.
Rotation/break crop benefits
- OSR is a good-break crop with the subsequent cereal crop typically yielding 0.5-1.5t/ha more than continuous cereals, due mainly to disease breaks but also other benefits which brassicas bring to rotations.
- OSR provides weed control options for problematic grass weeds.
- With early sowing and harvest dates and strong tap root development, OSR can help improve soil structure.
- Autumn N uptake and good soil cover helps reduce N leaching and soil erosion.
Research and development status
- Internationally OSR is a significant crop with good breeding support. In addition to oil yield, traits of particular interest to Ireland, requiring more development, would include resistance to disease such as phoma and light leaf spot. Breeding for specific oil profiles may improve markets.
- Irish research on crop establishment and basic agronomy provides a good basis for production systems, but there is a significant deficit in OSR research generally with a greater understanding of yield variability in our climate required.
- Autumn and early spring crop management need to be tailored to our climate.
- Factors influencing disease development and disease control strategies need to be studied.
Crop production summary
- Select a variety type suitable for climate and markets
- Sow mid-August to mid-September with reduced cultivation or conventional establishment systems with seed rates of 50 – 60 seeds/m2
- Weed control important and best achieved with pre-emergence herbicides for broad-leaves and graminicides for grass/cereals
- Disease control for stem canker (phoma) and light leaf spot is essential with ; sclerotinia and occasionally alternaria also causing problems
- Fertiliser P and K should be applied on the basis of soil status with N applied on the basis of cropping history and early season crop development. Fertiliser S is important with OSR.
- Pests such as slugs, flea beetle and pigeon grazing can all damage OSR
- At harvest the crop is usually desiccated to give an evenly ripe crop