Information reprinted by permission from the Ohio State Agronomy Guide - Bulletin 472 http://ohioline.ag.ohio-state.edu/b472/forage.html
Forage brassicas are fast-growing annual crops that are highly productive and digestible. Crude protein levels range from 15 to 25 percent in the herbage and 8 to 15 percent in the roots, depending on nitrogen fertilization rate and weather conditions. The most commonly used forage brassica crops are rape, turnip, kale, and swede. They can be grazed from 80 to 150 days after seeding depending on species (Table 13-8). These crops offer great potential and flexibility for improving livestock carrying capacity from August through December. Spring-seeded brassicas boost forage supply in late summer. Summer-seeded brassicas extend the grazing season in late fall and early winter.
Rape is a short-season, leafy crop whose stems and leaves are eaten by the grazing animal; rape can also be greenchopped. It has fibrous roots, and each plant produces many stems. Rape re-grows after harvest and is the easiest brassica species to manage for multiple grazings. Mature rape is excellent for fattening lambs and flushing ewes.
Turnip is a fast-growing crop that reaches near maximum production 80 to 90 days after seeding. Roots, stems, and leaves are grazed. The relative proportion of tops and roots varies markedly with variety, crop age, and planting date.
Kale is a long-season, leafy brassica that produces some of the highest yields of the brassica family when it is spring-seeded. Some varieties are very cold tolerant, which allows grazing of leaves and stems into December and January most years. Stem less varieties reach about 25 inches in height, whereas narrow stem kale grows to five feet with primary stems two inches in diameter. Stem less kale (e.g., 'Premier') establishes quickly and reaches maturity in about 90 days. Narrow stem kale is slower to establish and requires 150 to 180 days to reach maximum production.
Swede is a long-season brassica that produces a large edible root. Swede produces higher yields than turnip, but it grows more slowly and requires 150 to 180 days to reach maximum production. Swede produces a short stem when not shaded. If plants are shaded, it produces stems 30-inches tall. Swede does not re-grow after harvest.
Hybrids of Chinese cabbage with either rape, turnip, or swede can also be used for forage. Research information on the production and management of these hybrids is limited.
Brassica crops germinate quickly, and can be planted to provide either summer or late fall/winter grazing:
- Plant rape, turnip, and stemless kale in the spring (mid-April through May) to provide pasture in August and September.
- Plant rape and turnips in July and August to provide grazing in Nov. and Dec.
- Plant swede and kale in the spring for grazing in November and December.
Brassica crops require well-drained soils with a pH between 5.3 and 6.8 for good production. Seed rape and kale at 3.5 to 4.0 lbs/A and turnip and swede at 1.5 to 2.0 lbs/A. In the spring, use the higher side of the suggested seeding rates. Plant seeds in 6- to 8-inch row spacings at 1/4- to 1/2-inch deep in a firm seedbed. Apply 50 to 75 pounds of nitrogen per acre at seeding to stimulate establishment and seedling growth. Weed competition should be limited during establishment, otherwise stand establishment failures are likely.
On conventionally prepared seedbeds, brassica seed can be broadcast and incorporated with cultipacking. No-till seeding into grain stubble or grass sod is recommended, but weeds and sod must be suppressed for two to three weeks to allow the brassicas to establish. Apply either Gramoxone Extra or Roundup for sod suppression. Another alternative is to apply a manure slurry or liquid nitrogen solution to burn the sod back, then no-till plant the seeds. Brassicas can also be seeded with rye to protect the soil after brassicas are consumed by animals.
Determine lime and fertilizer needs by a soil test. Adequate phosphorus and potassium are important for optimum growth. In addition to the nitrogen applied at planting (50 to 75 lbs/A), another 70 lbs/A should be applied when multiple grazings are planned with rape and turnips. This second application should be made from 60 to 80 days after seeding. Nitrogen application in a chemically suppressed grass sward tends to increase the efficacy of the suppressing herbicide. This reduces the proportion of grass in the brassica-grass sward, which is not always advantageous. Avoid excessive nitrogen and potassium fertilization to prevent animal health problems (see below).
Although brassicas can be harvested for green chop, they are most often grazed. Rotational grazing or strip grazing helps reduce trampling and waste by livestock. Graze small areas of brassicas at a time to obtain efficient utilization. Rape is most easily managed for multiple grazings. Leave 6 to 10 inches of stubble to promote rapid re-growth of rape. When turnips are to be grazed twice, allow only the tops to be grazed during the first grazing. Turnip re-growth is initiated at the top of the root. Both rape and turnips should have sufficient re-growth for grazing within four weeks of the first grazing.
Stockpiling these crops for grazing after maturity should only be attempted when plants are healthy and free of foliar diseases. Some varieties are more suited for stockpiling because they possess better disease resistance. Do not grow brassica crops on the same site for more than two consecutive years to prevent the buildup of pathogens that limit stand productivity.