Overview
- Reliance on slow, ageing HB harvesters is a major threat to Australia’s capacity to produce enough medic seed.
- Harvesting pods from standing crops with modern grain harvesters is promising, but commercial-scale testing of harvest timing, windrowing, desiccation and pod recovery is still needed.
- Machinery development must be matched by breeding for pod retention, larger pods and seeds and suitable seed-softening characteristics.
Annual medics provide valuable livestock feed and nitrogen for following crops, particularly on alkaline soils across southern Australia. However, seed production is increasingly constrained by slow harvesting, high labour requirements and reliance on ageing machinery.
Research suggests harvesting pods above ground with modern grain harvesters could provide an alternative. The system is not yet commercially ready, but it offers a potential pathway to faster, less disruptive harvesting.
Ageing machinery is limiting production
Medic pods traditionally fall to the ground before harvest. Growers remove plant material, lightly till the soil and use a Horwood Bagshaw (HB) harvester to suction up and thresh the pods.
HB harvesters are at least 30 years old, increasingly unreliable and difficult to replace. They harvest about 0.3 hectares per hour, compared with around 8.3 hectares per hour for a combine harvester. Medic harvesting can also require five workers, compared with two for lentils. These constraints have contributed to a 60% decline in medic seed growers over the past 25 years.
Harvesting before pods fall
One alternative is to harvest pods directly from standing plants using a grain harvester, then thresh them separately. Pod-retaining cultivars such as Jaguar, Lynx and Cheetah have been bred for this purpose, and some growers already harvest Lynx and spineless Penfield using grain harvesters.
Earlier trials recovered 790 to 2,500 kilograms of pods per hectare from barrel and strand medics. Burr medic produced up to 3,200 kilograms per hectare in a wet season.
Desiccating or windrowing crops before pods drop could also extend the approach to other varieties and reduce losses from summer rainfall. The key challenge is identifying when seed is mature while enough pods remain attached.
Threshing remains the missing link
Conventional grain harvesters cannot readily thresh hard medic pods, so above-ground harvesting requires a separate stationary thresher. A modified HB processed around 1,000 kilograms of pods per hour and achieved an 83% clean-out rate, compared with 60% under the conventional system. Warm pods also appear easier to thresh, suggesting grain dryers may help prepare pods for processing. Developing a reliable, high-capacity threshing system is now a key research priority.
Machinery and breeding must move together
Harvestability varies considerably between cultivars. Cavalier burr medic is relatively easy to harvest because it has large pods and seeds, while Seraph strand medic is more difficult because its pods and seeds are small.
Breeding for stronger pod retention and larger pods and seeds could make above-ground harvesting more practical. The Australian Pastures Genebank contains more than 250 accessions with seed larger than 3.5 milligrams, providing useful breeding material.
Selling cleaned pods rather than fully threshed seed may offer another option. Scimitar burr medic pods can be stored for two summers and then sown at around 30 kilograms per hectare, although this approach requires further testing.
