Tropical Grasslands (2001) Volume 35, 226–234

Growth and persistence of 17 annual medic (Medicago spp.) accessions on clay soils in central Queensland

M.J. CONWAY1, N.J. BRANDON2, R.L. CLEM3, R.M. JONES2, B.A. ROBERTSON4 and J.R. WILLCOCKS5

1Department of Primary Industries, Emerald
2CSIRO Tropical Agriculture, Brisbane
3Department of Primary Industries, Brian Pastures Research Station, Gayndah
4Formerly Department of Primary Industries, Roma Research Station, Roma
5Department of Primary Industries, Toowoomba, Queensland, Australia

Abstract

Seventeen accessions of annual medics were evaluated on clay soil sites at Emerald, Theodore, Biloela and Mundubbera, central Queensland. Successful medics could have a role in both permanent and ley pastures. However, these are marginal areas for medics with winter (June–August) rainfalls of 80–100 mm. The accessions were selected on the basis of results in southern Queensland, a more favoured area for medics. There were 9 accessions of Medicago truncatula (barrel medic), 4 of M. scutellata (snail medic), 2 of M. polymorpha (burr medic) and 1 each of M. aculeata (keg medic) and M. orbicularis (button medic). Lucerne (M. sativa) cv. Trifecta was sown at 3 sites. All sites except Theodore were irrigated in the year of establishment (1993). The medic seedlings at Theodore died in 1993 and the trial was resown in 1994. Measurements were made of seed set in the first year and whenever it occurred in later years, seedling density in most years and yield when there was adequate growth. Selected measurements were made of soil seed reserves. Measurements ceased in 1998.
Despite moderate to high levels of seed production in the first year at all sites except Theodore, vegetative yields in subsequent years were very low until 1998 at Mundubbera. This was primarily due to well below average winter rainfall. During 1994–1997, there was no seed set at Mundubbera and only low levels of seed set at Theodore and Biloela. There was no single best line of barrel medic although Paraggio and SA11292 were consistently poorer. M. orbicularis SA8460 sometimes yielded as well as the better barrel medics and had the highest seed reserves in all 4 sites at the end of the experiment. At the end of the trial, the density and soil seed reserves of snail medic were low at all sites, with cv. Sava snail medic being as good as or better than the other accessions of snail medic. Lucerne did not persist into the second year at any site. Based on yields and soil seed reserves measured in 1998, the better medic lines showed good promise of persisting in the long term at Biloela and Mundubbera, and possibly Theodore, but their potential at Emerald is lower. The results showed the importance of achieving a substantial seed set in the year of sowing in these marginal subtropical environments with low and unreliable winter rainfall where there can be consecutive years without any seed set.
There is potential for some of the current barrel medic cultivars to persist in marginal medic environments in central Queensland. M. orbicularis SA 8460, with its early flowering, high seed set and relatively slow rate of hard seed breakdown, warrants consideration for release so that it could be included as one component of a mixture of annual medics for use in this region.

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