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New medic pasture systems to increase production in pasture/cereal rotations in the Victorian mallee

C. M. J. Williams and N. A. Valiance

Mallee Research Station, Walpeup, Victoria 3507

Cropping in the Victorian Mallee largely follows a fallow-cereal-pasture rotation. Wheat, the major cereal grown, is subject to very considerable losses from both cereal cyst nematode (Heterodera avenae) and the take-all fungus (Gaeumannomyces graminis). In 1978/79, for example, it was estimated that yield reductions caused by the two diseases represented about $40 million (1, 2).

As well as infecting cereal crops, both diseases are hosted by grasses and are carried over during the pasture phase, in which Hordeum leporinum, Lolium rigidum and Bromus species are dominant. By the use of higher seeding rates and appropriate herbicide applications it should, therefore, be possible to produce medic–dominant pastures that will reduce the levels of disease and weed infestation in all phases of the rotation.


Medic pastures (Medicago truncatula cv. Jemalong) were sown on 18th June, 1981, at rates of from 1 to 256 kg seed/ha with 13 kg P/ha on a sandy loam soil at Walpeup, on a site with no history of medic. Trifluralin was applied at 1 i/ha and incorporated the day before sowing and Diclofop-methyl (1 k/ha) and Methabenzthiazuron (550 g/ha) were applied on 30th July for control of L. rigidum and broadleaf weeds, respectively.

Results and Discussion

There were no increases in dry matter (DM), seed yield or pod numbers at harvest by sowing at rates greater than 16 kg/ha (Table 1).

Table 1: Effects of medic seeding rates (kg/ha) on medic and weed densities (plants/m`) and on medic DM and seed yields (kg/ha)


Furthermore, where pastures were sown at rates of 8 kg/ha or higher, winter weed infestation (Brassica tournefortii and Sisymbrium orientale) was greatly reduced compared to that in lower density pastures. The mat of senescent medic pasture also reduced the density of summer weeds (Chondrilla juncea and Lactuca serriola, Table 1). These results indicate that the sowing of dense medic swards coupled with strategic herbicide applications may enable highly productive, weed-free pastures to be established. Wheat will be direct–drilled into the medic plots in 1982 to assess whether the different sward densities influence cereal yields.

1. Brown, R. H. 1981. Proc. Cereal Cyst Nematode Seminar, Department of Agriculture Victoria, Horsham, pp.1-6.

2. Griffiths, J. B., and Walsgott, D. N. 1982. Proc. Australian Agronomy Conference (in press).

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