OREGON STATE UNIVERSITY
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Brassicas
Turnip is one of several species referred to as Brassicas. This group of forbs includes forage rape (Brassica napus L.), kale (Brassica oleracea L.), turnips (Brassica rapa L. subsp. rapa), swedes (Brassica napus L.), and hybrids like Tyfon (a hybrid between Chinese Cabbage (Brassica rapa Pekeninensis Group) and stubble turnip (Brassica rapa Rapifera Group).
Turnip, rape, and kale are distributed over much of Europe, northern Asia, northern North America, and southern Oceania. These crops are grown year-round in cooler and moist climates and as a winter forage in warmer climates. Most brassicas are cold tolerant, and the leaves can withstand light freezes. Moisture requirements are relatively high for most species. Well- to moderately-well drained loamy soils are preferred, but with adequate moisture and fertility, sandy or peaty soils produce adequate yields.
Description and Uses
Turnip is a herbaceous, biennial forb that is used as a pasture forage, alone or in combination with cool-season grasses and legumes. It can be spring-seeded alone or in combination with annual ryegrass or oats following early-maturing corn silage fields for fall/winter grazing. It can also be seeded in August and September in warmer areas to provide grazing in November and December.
Overseeding into existing pastures can be successful with little or no tillage if competition is reduced by close grazing prior to broadcasting turnip seed.
Flowers are small with four light-yellow petals clustered at the top of branched flowering stems 12 to 36 inches (30.5-91 cm) tall. Transition to the reproductive stage, flowering, and seed formation can occur late in the fall of the first year if planted early in the spring. Initial growth habit consists of 8 to 12 erect leaves, 12 to 14 inches (30.5-36 cm) tall with leaf blades 3 to 5 inches (7.6-12.7 cm) wide.
Brassicas are both cold-hardy and drought-tolerant.
[USDA Plant Hardiness zone 4 for most cold-tolerant types; Jan mean minimum of -30 °F, -34.4 °C); American Horticultural Society Heat Zones 1-9 (<150 days above 86 ˚F (30 C)]. Requires 40 inches (1000 mm) of precipitation or irrigation.
Best suited to well-drained to moderately well-drained soil drainage classes. Not tolerant of soils that are of high clay texture, wet, or poorly drained. For good root growth, turnip needs a loose, well-aerated soil. Tolerates moderately acid soils (pH 5.6-7.3). Moderately sensitive of saline conditions (1.5-3 dS/m). Somewhat tolerant of water-soluble aluminum (persisted at 1-2 ppm Al3+).
‘Green Globe’ and ‘York Globe’ are cultivars from New Zealand and ‘Sirius’ was developed in Sweden. Sirius leaves have less glucosinolate than the other two cultivars.
Exceptionally high quality, highly digestible forage.
Due to its exceptionally high digestibility and presence of toxic secondary metabolites, precautions should be taken to prevent animal health problems. Livestock should not be hungry when put on pasture the first time so they do not gorge themselves. If the livestock are moving from a feed low in nutritional value, feed a high-quality diet for two to three weeks prior to grazing turnip, or feed turnip for 30 min/day for one week prior to heavier grazing. This will allow for the development of a rumen microbial population that is adequate to digest the high levels of protein in forage turnips. A lower quality hay should be made available [2-3 lb (0.9-1.4 kg) of dry roughage/head/day for sheep and 10-15 lb (4.5-6.8 kg) for cattle] to provide some fiber in the animals' diet.
Livestock should not feed on turnip during the breeding season or after the plants have begun to flower. Nitrate nitrogen toxicity can be a problem, especially if ruminants are allowed to graze on immature crops or if soil nitrogen levels are high. The risk may remain for a longer period of time in autumn than in summer. Dairy cows should not be fed more than 50 lb turnip/head/day and should not be milked immediately after feeding on turnip to avoid milk tainting.
Srinivas C. Rao and Floyd P. Horn, 1995. Cereals and Brassicas for Forage. Chapter 36. In: FORAGES: An Introduction to Grassland Management. Vol. 1. 5th ed., Iowa State University Press.
Danny H. Smith and Michael Collins. 2003. Forbs. Chapter 10. In: FORAGES: An Introduction to Grassland Management. Vol. 1. 6th ed., Iowa State University Press.
Kenneth J. Moore. 2018. Compendium of Common Forages. Brassicas. In: FORAGES: An Introduction to Grassland Management. Vol. 1. 7th ed., Wiley Blackwell.