Brassica crops are best used in a system, where you can build in the benefit of successive crops, to give better year-round feed supply.
Advantages a prior crop
Often paddocks are chosen for a brassica crop because of their poor pasture growth. This may be caused by underlying problems such as poor soil fertility, drainage, weeds, pests or diseases. A prior crop (e.g. a winter ryegrass) allows any issues to be corrected before sowing the brassica, helping ensure high crop yields.
Double cropping has real advantages if the paddock has turfy, fibrous grass weeds such as browntop, fescue or cocksfoot. Much better long-term control of these is achieved through multiple crops and herbicide applications. Using a prior crop also gives time for turf to break down, allowing a better seedbed for the brassica crop in spring.
Crop rotation examples
Kale or swedes
Prior to a winter kale or swede crop, a winter ryegrass crop can be sown, to produce extra winter and early spring feed.
Prior to a summer turnip crop, a winter ryegrass crop can be sown, to produce extra winter and early spring feed.
A winter rape crop could be sown after a cereal crop.