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The effect of grazing on the seed production of a range of annual medic species

C.W. Thorn and C.K. Revell

Western Australian Department of Agriculture, Katanning. W.A. 6317.

Burr Medic (Medicago polymorpha var brevispina) is well adapted to hardsetting grey-clay soils with neutral to slightly acid pH reaction in the Great Southern region of Western Australia. The ability of pasture legume species to set seed under grazing is an important factor in their long-term persistence. This paper describes the seed yield response of a range of pasture legume species to grazing.


A total of nineteen varieties of nine pasture legume species were sown in 27m x 1.4m plots on a grey-clay soil type and replicated three times. All seed was inoculated and lime-pelleted and sown at 10 kg/ha with 150 kg/ha of single superphosphate (9.1% P). The plots were fenced into three equal sections during the growing season and grazed as part of a whole paddock at 16 sheep/ha. The grazing treatments employed were ungrazed (G1), grazed for 60 days, starting 33 days after cowing (G2) and continuous grazing for 165 days, starting 33 days after sowing to seed harvest (G3). Spring pasture production (5 x 0.1m2 quadrats/section) and seed yields (5 x 0.2m2 quadrats/ section) were measured, with burrs being collected from the surface for all varieties except Dalkeith which was sampled to 4 cm.


Serena burr medic was the earliest maturing line tested, being 9-10 days earlier than four intermediate lines and 27 days earlier than Circle Valley. All other lines tested were of similar maturity to Circle Valley (Table 1). Total dry matter and seed yields were reduced by extending the grazing period. The intermediate lines of M. polymorpha set more seed under continous grazing than either Circle Valley or Serena and as a group the burr medics set more seed than all other species under all grazing conditions (Table 1). In terms of dry matter production T. cherleri appeared to best tolerate heavy grazing, however, seed production was severely reduced by continuous grazing beyond flowering.

This data shows that there is scope to select medic lines with higher seed production under conditions of hard grazing.

Table 1. Total dry matter and seed yields of nineteen pasture legume varieties under grazing.

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