Alfalfa is a high-protein perennial legume with a crude protein content of about 18-20%.
It usually lasts four to five years and is predominantly used for silage or hay, with some aftermath grazing. It has an energy value of about 10-11ME and average dry matter yield of 15t/ha.
Alfalfa grows off a taproot that stores nutrients to help the plant regrow after it has been cut or grazed.
Like other legumes such as clover, peas and beans, there are nodules on its roots that contain nitrogen-fixing bacteria, so the crop needs no additional applied nitrogen (N) to grow.
There have been some reports of alfalfa roots going down as far as 15m in search of water.
Alfalfa requires a free-draining soil with a pH of 6.2 or more. It does not tolerate heavy soils, waterlogging or acidity.
Alfalfa should be established when the soils are warm and at a consistent 7-8C or above. It can be sown from the end of April until mid-August.
The crop is slow to establish in the first year, so later autumn sowing should be avoided, as it can lead to a patch establishment into winter.
Undersowing can be a useful way to establish alfalfa, as it means the field is not out of production while the crop establishes.
When undersowing, the general rule of thumb is to reduce the cereal component by one-third – for example, reducing the cereal rate from 187.5kg/ha to 125kg/ha – to give the alfalfa seedlings space and light to develop.
Alfalfa should be sown when soils are warm into a fine and firm seed-bed, no deeper than 1cm. Very small seeds can fail to emerge when sown too deep. Fields must be rolled before and after drilling to ensure good soil-to-seed contact.
Alternatively, it can be grown with non-aggressive grasses that will not outcompete the seedlings, such as Timothy or meadow fescue.
Based on 2018 figures, a rough establishment cost per crop per year (over five years) would be £105/ha (see below for a cost breakdown).
Alfalfa requires no N once established, but it can be beneficial to apply 25kg N/ha to an autumn sowing to promote rapid plant development. P and K should be kept at Adas index 2 to maintain yields.
In the year of sowing, a light cut may be taken in mid-August at the early flowering stage. If conditions are favourable, a second light cut, or grazing, may be taken in mid-autumn.
If it has been sown during midsummer, it’s unlikely there will be much to cut that year.A rotation of five years is recommended between Alfalfa crops, to reduce the likelihood of disease issues.
The crop should be cut to a stubble length of 10cm minimum.
In the first full harvest year, it should be ready for cutting in May/June at almost full flowering. Thereafter, cut at the bud stage, every five or six weeks. This provides the best balance between yield and forage quality.
After cutting, the crop must be wilted to a minimum dry matter content of 30% (40-50% if baling) to concentrate the sugar content.
Up to 70% of the protein and 90% of the minerals and vitamins in the plant reside in the leaf, so it is important to minimise leaf losses.
As the leaf dries out more quickly than the stem of the plant, overwilting or extensive handling can result in large amounts of leaf shatter.
The use of roller-type mower conditioners, which cut and condition the alfalfa by crimping or crushing the stem, is advisable when harvesting. These will speed up the rate of moisture loss from the stem without extensive damage to the leaf.
Alfalfa can be silaged as either bales or chopped and put into the clamp. It can then be fed as part of a ration with other silage, such as grass or maize. It can also be made into hay or haylage.
The target freshweight (FW) production a year is 40t/ha, with a target annual DM yield (at 30% DM for silage) of 12t DM/ha.
The high protein content of alfalfa silages make it a good replacement for soya bean meal in diets. It is also a good complement to maize silage.
For ruminants, the lower readily available starch content and higher buffering capacity of alfalfa compared with maize silage also has a beneficial effect on rumen pH. Hard grazing can cause excessive damage to the plant crowns.
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