HOW TO: ASSESS BRASSICA YIELD

Brassica crops such as kale, forage rape, grazing turnips, stubble turnips, swedes and rape/kale hybrids, can provide nutritious, cost-effective feeds for beef cattle and sheep. They can increase output per hectare, both in terms of dry matter (DM) feed and animal performance. Out-wintering on brassicas can also allow more animals to be kept, with minimal extra capital investment in buildings.        

A break crop of brassicas between reseeds is an ideal solution when trying to reduce pest populations which could prove costly to a new ley. The removal of products containing Chlorpyrifos for leatherjacket control now means that producers also have to look at alternative methods of pest control and using brassicas as a break crop is becoming increasingly popular.

Feed costs can be reduced by grazing brassicas in situ, because high DM yields can be produced quickly and little or no machinery is needed for harvesting and feeding out. The crops can be used for out-wintering, to extend the grazing season or to help to fill a forage gap in dry summers. The aim is always to increase the amount of grazed forage in the diet, rather than relying on expensive supplements.

The energy content of leafy and root brassicas is typically higher than that in other forages and similar to that in concentrate feeds and cereals. They have a high readily digestible carbohydrate content but are low in fibre, which is why they should be fed with a fibre source such as straw or hay to prevent rumen acidosis or bloat. As a general rule, roots tend to have lower protein content than leafy crops. When using brassicas for finishing lambs, supplement root crops with sources of dietary protein and leafy crops with additional energy.

As grass growth drops going into autumn, now may be a good time to assess the amount of brassica crop available for grazing and to develop a feed plan.

Measuring dry matter

For accurate feed planning, it is essential to measure the DM yield of the crop. This can easily be done by using a:

• 1m square frame

• Seed bag

• Pair of garden shears

• Scales

A number of samples should be taken from each field, picking representative sampling points.

1. Place frame in the forage crop

2. Use shears to cut each plant within the frame (about 10cm from the ground). Put the harvested crop in the bag

3. Hook bag onto scales and record the crop weight per metre squared (kg/m2)

4. To calculate DM yield/ha, multiply the fresh weight per m2 by 10,000, then multiply by the expected crop DM percentage

For example:

Kale from 1m2 = 5kg fresh weight x 10,000 = 50,000kg fresh weight/ha

Average kale dry matter = 16%

50,000 x 0.16 = 8,000kg (8t) DM/ha

More information on assessing yields can be found in the BRP manual, Using Brassicas for Better Returns. Information on developing a feed plan can be found in the BRP manual Planning Grazing Strategies for Better Returns.