Brassicas: How forage crops can play a valuable role?

Without doubt, grass has to be the first priority when feeding livestock efficiently.

However, forage crops can play a valuable role both for out-wintering livestock and overcoming grass shortages during the summer months.

There are a number of options available to farmers when choosing forage crops.

Before deciding on the most cost-effective type of forage crop for your livestock production system, Germinal is reminding farmers to answer three fundamental questions:

• When do you want to utilise the crop?
• When will the land for growing the forage crop become vacant?
• How many animals do you need the crop to feed?

Site selection

When choosing a field to grow forage crops for out-wintering, choose a field that will dry out quickly and does not have an extreme slope.

The field should not be close to watercourses or water supplies, in order to adhere to cross compliance.

Ideally, choose fields where grass production is falling so it can be incorporated into a grass reseeding program.

Club root is a threat to brassicas. A one-in-five year rotation is advised to keep club root levels low.

Sowing advice

• Soil test prior to sowing. Soil pH is critically important and should be at least 6.0; the optimum is between 6.2 and 7.0. Crops will perform best under good soil pH and fertility status.
• Spray off the old sward with glyphosate.
• If min-till sowing techniques are being used, apply a minimum of two bags of granulated lime per acre.
• Seed is generally sown into a cultivated seedbed, but can also be direct-drilled or broadcast. If broadcasting it is important to note that you will need to increase the seed rate.
• Sow seeds into a fine, firm seedbed at a maximum depth of 10mm. This will help ensure uniform germination.
• Roll after sowing.
• Monitor the crop closely for weeds and pests and control as appropriate.

Benefits of brassicas

Brassicas are low in fibre; therefore supplementing with a fibre source, for example, baled silage, is critical for animal health.

It is also important to ensure animals have constant access to fresh water when grazing the crop.

Kale and the hybrid brassicas (rape/kale cross) are among the most common brassica forage options used by Irish farmers.

Kale – suitable for sheep and cattle

Kale is suitable for sheep and cattle grazing. Maris Kestrel is the most popular variety of kale in Ireland. This is due to its exceptionally high leaf-to-stem ratio and high feed value. It has high digestibility and a long utilisation period, along with animals being able to utilise the entire plant.

Friesian bulls grazing kale on a farm in Moyne, Co. Tipperary

Kale/rape hybrids

The hybrid brassica, Redstart (rape/kale cross) offers the highly beneficial combination of rapid growth ability and good all-year-round performance.

Its ability to grow quickly derives from the forage rape, while the kale genes deliver excellent winter hardiness.

Redstart is mainly used as a high-energy protein crop for out-wintering cattle and sheep. It can be grazed more than once if sown early. However, care must be taken with the first grazing in order to ensure the main stem remains intact to protect the crop for future regrowth.

Fertiliser for brassicas

Brassicas have a high requirement for nitrogen (N) and phosphorous (P). An adequate supply of these nutrients is critical to maximise the yield potential of the crop.

According to the Teagasc Green Book, at soil Index 3, kale and Redstart will require: 100kg of N/ha (split dressing); 30kg of P/ha; and 170kg of K/ha.

It is advisable to fertilise a crop of Redstart after grazing. This will help to ensure sufficient nutrients for regrowth. However, keep in mind your N and P allowances within the nitrates directive.

Grazing management

When it comes to grazing the crop, there are a few guidelines that should be followed so that the stock really benefit from the crop and don’t experience any setbacks:

• Introduce stock slowly. Allow 1-2 hours access; then build up to full-time access after 7-10 days.
• Provide access to roughage, for example, silage bales. Place the bales in the field during the summer or at sowing. This will avoid machinery travelling the field in winter, therefore reducing soil damage and workload.
• Strip grazing will maximise utilisation and minimise wastage.
• Graze in long narrow strips to ensure all animals can graze at the same time. This will also help to minimise trampling of the crop at feeding.
• Provide minerals or bolus animals. Speak to your vet to ensure stock receive the necessary minerals.
• If sown on a hill, always graze down-hill.
• Ensure constant access to fresh water.

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