Lucerne - the plant
Lucerne or alfalfa (Medicago sativa) is a deep-rooted, temperate, perennial pasture legume which is well adapted to mixed farming systems in southern Western Australia.
Due to its high water use and deep roots (>two metres on suitable soils) it is able to address rising watertables and associated salinity.
Lucerne will provide additional green feed at the start and at the end of the normal winter growing season with peak production in spring and early summer.
It has the ability to respond quickly to significant summer rainfall (>10 millimetres) but requires 20-25 millimetres (mm) to produce substantial growth.
A rain-fed lucerne pasture produces between 4-8 tonnes (t) of dry matter per hectare per year (DM/ha/yr) which is similar to annual pasture, but production is spread more evenly over the year.
Once established, lucerne has good drought tolerance and is well suited to irregular rainfall patterns, but it will appear to go dormant during extended dry periods.
It grows in areas receiving as little as 325mm annual rainfall but also provides good summer production in areas up to 700mm rainfall. Out-of-season production can be used to reduce supplementary feeding requirements.
Lucerne produces high quality green feed. It has high energy — digestibility of 65-72% with a metabolisable energy of 8-11 megajoules per kilogram (MJ/kg) DM — and high protein (12-24%).
The quality of feed remains relatively constant throughout the year while it is active. Lucerne is also a source of calcium, magnesium, phosphorus and vitamins A and D.
Lucerne can be grown as a pasture phase, removed and followed by a crop phase or it can be over sown with crops (pasture cropped).
Lucerne fixes between 10 and 20kg/ha of nitrogen for every tonne of dry matter produced, increasing soil nitrogen levels for subsequent crops.
Once established, it can help manage herbicide resistant weeds with its competitiveness and tolerance of some broad-spectrum herbicides.
Effective weed management will increase the legume component and nitrogen accumulation from a lucerne based pasture. Also, grain crops following a lucerne phase produce better yields and quality than unimproved pasture.
The principles for integrating lucerne into broadacre dryland farming systems are described in the Department of Agriculture and Food, Western Australia's (DAFWA) Bulletin 4785 - Lucerne Guidelines for Western Australia. The bulletin is available in hard copy from department offices or can be emailed in PDF format on request.
In brief, lucerne can:
- provide a high quality feed for livestock and improve animal health
- reduce groundwater recharge and help to alleviate the effects of salinity
- even out seasonal livestock feed and produce fodder opportunistically out-of-season
- improve soil fertility and structure
- reduce weed burden and manage herbicide resistance for cropping.
Lucerne’s limitations are:
- the cost, and slow rate (6-12 months) of establishment
- low winter production
- requirement for rotational grazing for long-term persistence
- greater monitoring for insects and susceptibility to being over-grazed
- variable out-of-season production
- the pasture phase needs to be at least three years to overcome the high upfront costs of establishment
- can be difficult/costly to remove if going into a crop phase
- can reduce crop yields in the year following the lucerne phase due to a dry soil.
- Growth habit varies with winter activity. The less winter active types have a lower set crown and a more prostrate growth habit, while more winter active types have an erect growth habit (50-70 centimetres high).
- Plants are hairless with many stems originating from the crown.
- Leaves are trifoliate with leaflet length greater than the width.
- New stems emerge from the crown following grazing. These stems may branch from the lower axillary buds as they develop.
- Flowers are compact racemes with purple florets.
- Pods are coiled spirally with two to five kidney-shaped, yellow or brown seeds.
- Seed count is 400 000/kg (very small).
- Rainfall: >325mm.
- Drought tolerance: very high.
- Frost tolerance: moderate to high.
- Soil type: grows well on a wide range of well drained soils including deep loams, deep yellow and brown sands, loamy sands over clay or gravel, deep sandy duplex soils and uniform clays. It is not suited to deep pale sands and shallow soils.
- Soil fertility requirements: moderate to high.
- Soil pH (CaCl2): 4.8 to 8.0 in the top 30 centimetres (cm) — note optimum pH >5.5.
- Aluminium tolerance: low.
- Waterlogging tolerance: low.
- Salt tolerance: moderately low (if not waterlogged).
- Nutritive value: digestibility of 65-72% whole plant, 75-80% leaves and 45-70cm stems. Metabolisable energy of 8-11 MJ/kg DM and crude protein (12-24%).