Topics : Species and Forage Variety Trials : Species Fact Sheets : Brassica
Additional brassica information via the Forage Information System (FIS)
Characteristics & Adaptation of Brassica Crops
Cool-season perennial grass and grass-legume pastures typically become less productive as the grazing season advances from June to November. Forage brassica crops such as turnip, swede, rape, and kale can be spring-seeded to supplement the perennial cool-season pastures in August and September or summer-seeded to extend the grazing season in November and December. Brassicas are annual crops which are highly productive and digestible and can be grazed 80 to 150 days after seeding, depending on the species. In addition, crude protein levels are high, varying from 15 to 25 percent in the herbage and 8 to 15 percent in the roots depending on the level of nitrogen fertilization and weather conditions.
Adapted Brassica Species & Varieties
Kale (Brassica oleracea L.)
Varieties of kale differ markedly in rate of establishment, stem development, time required to reach maturity, and in winterhardiness. The stemless type kale (e.g. Premier) has a faster rate of establishment than varieties which produce stems. Crop height of the stemless type is approximately 25 inches, whereas that of marrow stem kale is 60 inches with primary stems often 2 inches in diameter. Stemless kale attains maturity in approximately 90 days, allowing two crops/year, whereas varieties that develop stems require 150 to 180 days to attain maximum production (Table 1). Premier has consistently survived winters in central Pennsylvania, whereas other varieties of kale usually are winter-killed in December.
Rape (Brassica napus L.)
Mature forage rape is one of the best crops available for fattening lambs and flushing ewes. Rape is a multistemmed crop with fibrous roots. The stems vary in length, diameter, and in palatability to livestock. Forage yields of spring- planted rape increase until plants become physiologically mature. Growth slows or ceases at maturity and yields plateau until leaves senesce and die. Varieties differ in when this occurs, however, Rangi rape retains its leaves longer than most varieties. Generally, yields of rape varieties in Pennsylvania are maximized with two , 90-day growth periods (Table 1). However, performance of Emerald and Winfred rape varieties, is best with one 180-day growth period, and yields of rape hybrids were greatest with 60 days of growth before the first harvest and a 30-day growth period before the second harvest.
Swede (Brassica napus L.)
Like turnip, swedes produce a large edible root. Yields are higher than those of turnip, but they grow slower and require 150 to 180 days to reach maximum production. Swedes usually produce a short stem (neck), but can have stems 2 1/2 feet long when grown with tall crops which shade the swede. Unfortunately, stem elongation is at the expense of root development. The variety Calder was found to be cold hardy in central Pennsylvania and thus ideal for stockpiling and late fall or early winter grazing (Table 1). In general, all swede varieties are recommended for late fall grazing.
Turnip (Brassica rapa L.) or Turnip Hybrids
These crops grow very fast, reaching near maximum production levels in 80 to 90 days (Table 1). Studies in southwestern Pennsylvania showed that turnip can accumulate dry matter in October as fast as field corn does in August. Growing "out of season" (October/November) makes turnip a valuable crop for late fall grazing.
The proportions of tops and roots varies markedly depending on variety, crop age, and planting date. Research by the USDA Pasture Laboratory showed that turnip crops can vary from 90 percent tops/10 percent roots to 15 percent tops/85 percent roots. Some hybrids have fibrous roots which will not be readily grazed by livestock. All varieties produce primarily tops during the first 45 days of growth. Sixty to 90 days after seeding, turnip varieties such as Savannah and All Top continue to produce a high proportion of tops. During the same period, other turnip varieties have nearly equal top and root production and Purple Top has a greater root than top production. The significance in the proportion of tops and roots is that the crude protein concentration (8 to 10%) of roots is approximately one-half of that in turnip tops. Therefore, greater root production tends to reduce the crude protein yield of the total crop. On the other hand, stockpiled tops appear to be more vulnerable to weather and pest damage than roots. Varieties differ in resistance to diseases, but this often is not evident until the crop is more than 80 days of age and the plants are reaching full production.
Other Forage Brassicas
Several hybrids of brassica species are also used as forage crops, however, there is limited research information on the production and management of these hybrids. The more common hybrids include a cross between Chinese cabbage (Brassica campesteris sensulato L.) and rape (Perko), turnip (Tyfon, Buko), and swede (Wairangi).