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Oregon Cover Crops: Rapeseed(Brassica campestris/Brassica napus)EM 8700 Do you want to print a copy? We recommend downloading the print version (67 K). First download the free Adobe Reader, if you don't already have it. ContentsQuick facts Rapeseed is a large, stemmy, winter or spring annual. It is related to mustard, cabbage, broccoli, cauliflower, and turnip. B. campestris is primarily a spring annual, and B. napus a winter annual, although both have winter and spring varieties. Rapeseed grows from 3 to 5 feet tall. It has bright yellow, four-petaled flowers, a deep taproot, and a fibrous near-surface root system. Seeds are small (90,000-150,000/lb), round, and brown-black. Environmental preferences and limitationsRapeseed does well on a wide variety of well-drained soils. It prefers a pH between 5.5 and 8.3 and is moderately tolerant of saline soils. It will not tolerate poorly drained or flooded soils, especially during establishment. Rapeseed is able to grow at relatively low temperatures. The minimum soil temperature for planting is 45°F, and the maximum is 85°F. Winter hardiness is excellent if plants reach a rosette size of six to eight leaves before the first killing frost. If they experience a hard frost or wet soils before they reach this stage, losses are likely. The small taproot of young seedlings is susceptible to breakage by frost heaving. Rapeseed is very sensitive to planting date in all areas. In western Oregon, rape crops have failed entirely when planted after October 1. UsesRapeseed is grown for its oil and meal, and as a cover crop. Rapid fall growth captures part of the available soil nitrogen, which otherwise might be lost to leaching, and provides good ground cover over winter. Rapeseed produces large amounts of biomass and is good at suppressing weeds. Its root system can help loosen plow pans and improve soil tilth. Dry matter and N accumulationIn a mid-Willamette Valley replicated trial over 4 years, Dwarf Essex rapeseed planted in mid-September accumulated a maximum of 4.8, minimum of 0, and average of 2.6 tons dry matter/acre and a maximum of 136, minimum of 0, and average of 67 lb N/acre by mid-April. The crop failed entirely 1 year due to a late planting date and cold, wet fall weather.
ManagementWhen you plant rapeseed, the seedbed should be smooth, firm, and packed. However, overtilling can cause crusting that interferes with emergence. The recommended seeding rate is 5-8 lb/acre if drilled, and higher if broadcast. Drill seed in 6-10 inch wide rows, no deeper than 3/4 inch. If moist soil is deeper than 3/4 inch and irrigation is not available, use a hoe opener to push dry soil aside to allow deep placement, but shallow soil coverage of seed. Most grain drills can be used. Alfalfa calibration settings usually work if rapeseed calibrations are not provided. Seeding should occur from mid-August to mid-September so that plants achieve the six-to eight-leaf stage before cold weather begins. Fall irrigation, if necessary, speeds up establishment and improves crop stand and winter hardiness. Incorporate rapeseed during spring bloom. It usually needs to be mowed or chopped before being turned under. Due to the relatively low C:N ratio of rapeseed residue, decomposition is rapid (except for fibrous stems), and soil organisms involved in the decomposition process do not compete with the following crop for N. Volunteer rapeseed can cause problems harvesting some green vegetables and seed crops. Separation of rapeseed residues is difficult because the bulk density of stems and/or the size and shape of pods are similar to the harvested crop (e.g., green beans, dry sugar beet seed). Rapeseed can be a serious weed in sugar beet seed production. The percentage of hard seed varies among varieties. Canola varieties have fewer hard seeds than industrial varieties. Hard seed may be acceptable for self-reseeding covers in orchards and vineyards. Rapeseed may be sensitive to residual herbicides, including sulfanated ureas and triazines.
Production restrictionsRapeseed production is regulated in Oregon and other
Pacific Northwest states. The Oregon Department of Agriculture
(ODA) has established rapeseed production districts. In order
to grow rapeseed, even as a cover crop, you may need to Pest interactionsRapeseed normally competes well with weeds, especially grasses. When followed by a cereal crop, volunteer rapeseed can be killed with broadleaf herbicides. Rapeseed fits well into rotations with non-brassica crops; it is immune to many of the diseases that attack them. However, rapeseed itself is susceptible to pathogens that can build up in the soil rapidly. Therefore, plant rapeseed in the same field only once every 4 years. Other brassica crops also are susceptible to the diseases
of rape-seed. If brassica crops are part of the summer rotation,
you probably should not use rapeseed as a cover crop. Rapeseed
is susceptible to sclerotinia stem rot, which also infects potatoes,
beans, and carrots. Be sure to consider sclerotinia effects on
crops in your Flea beetles can seriously damage seedlings. If flea beetles are a problem during establishment, you may need to use seed insecticide treatments or foliar sprays. A winter rapeseed cover crop can be used as part of a
rotation to lower soil populations of Columbia root-knot nematode
(Meloidogyne chitwoodi), which infects potatoes. Rapeseed
is a non-host of Columbia root-knot nematode, and its Note that the ability of rapeseed to decrease nematode populations is specific to the nematode type. For example, Dwarf Essex has not successively reduced the populations of root lesion or dagger nematodes in berry field trials. Using rapeseed as a break crop in wheat can greatly reduce the incidence of the disease take-all (Gaeumannomyces graminis). Rapeseed flowers have been observed to attract several species of hoverflies (Syrphidae), the larvae of which are predators on aphids. Varieties/cultivarsCanola is a term for rapeseed varieties that contain low levels of both erucic acid (in their oil) and glucosinolates (in their meal). These characteristics increase palatability for human and animal consumption. Oil from other varieties generally is used only for industrial purposes. All varieties grow similarly and provide biomass and N uptake. However, industrial types are most likely to reduce nematode populations. This effect results from their higher levels of glucosinolate, which is believed to be the active agent in nematicidal activity. Prepared by Robert Sattell, faculty research assistant in crop and soil science; Richard Dick, professor of soil science; Russ Ingham, associate professor of botany and plant pathology; Russ Karow, Extension cereals specialist; Diane Kaufman, Extension agent, North Willamette Research and Extension Center; and Dan McGrath, Extension agent, Willamette Valley; Oregon State University. January 1998. |
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