Topics : Pastures : Strategies for Extending the Grazing Season
Strategies for Extending the Grazing Season
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FALL GROWING FORAGE: Brassicas
Brassicas are annual crops which continue to grow during the fall and into the winter. They are highly productive and digestible and contain relatively high levels of crude protein. They can be grazed 80 to 150 days after seeding, depending on the species and weather (Table 3). In addition, some varieties lend themselves to stockpiling.
Species and Varieties
Several brassica species can provide forage for grazing during the fall. These include:
Kale - The stemless variety `Premier' has consistently survived winters in central Pennsylvania, whereas other varieties of kale usually have winter-killed in December.
Rape - Growth of rape slows or ceases at maturity until leaves senesce and die. Varieties differ in the time this occurs. For instance, `Rangi' rape retains its leaves longer than most varieties, which makes it more suitable for stockpiling and winter grazing than other rape varieties.
Swede - The variety `Calder' has been cold hardy in central Pennsylvania and thus ideal for stockpiling for late-fall or early-winter grazing. However, in general, all swede varieties are recommended for late-fall grazing.
Turnip or Turnip Hybrids - Pennsylvania studies have shown that `Forage Star' turnip is more cold tolerant and retains its leaves longer in the fall than other turnip varieties. Turnip can accumulate dry matter in October as fast as field corn does in August. Growing "out of season" (October and November) makes turnip a valuable crop for late fall grazing.
Proper grazing management is important to optimize the true potential of these crops. Strip grazing small areas of brassicas provides the most efficient utilization.
Rape is more easily managed for multiple (generally more than two) grazings than are the other brassica species. Approximately six to ten inches of stubble should remain after the firstgrazingof rape; this practice promotes rapid regrowth. Regrowth of rape may be grazed at four-week intervals. On the final grazing, the plants should be grazed close to ground level.
When turnips are grazed twice, the first grazing should remove only their tops. Turnip regrowth is initiated at the top of the root, so this part of the plant should not be removed until the second and final grazing. Like rape, regrowth of turnips can be sufficient to graze within four weeks of the first grazing.
Diseases of brassicas are generally not a problem until the plants near maturity. Stockpiling should not be attempted in fields where brassicas have high levels of foliar disease at maturity. Research has shown yield reductions of 40 percent when disease infected brassica crops were stockpiled for 45 days. Generally, `Forage Star' turnip and `Rangi' rape are better suited for stockpiling than other varieties because of lower disease infestation. To reduce club root rot occurrence, brassicas should not be grown on the same field for more than two consecutive years.
Yield and Nutritional Value
Dry matter digestibility at maturity generally exceeds 90 percent for all plant parts except kale stems. Unlike perennial forage crops, the dry matter digestibility of brassicas does not decrease markedly with increasing plant maturity. This characteristic makes them ideal for stockpiling. However, ruminant diets should not contain more than 75 percent brassica forage because the fiber content is too low for maintenance of proper rumen activity. With their high digestibility and low fiber content, brassicas actually should be considered as "concentrates" rather than "forage" in nutritional planning for livestock.
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