Hard seeded annual legume species such as Biserrula, Bladder Clover, Gland Clover and Medics offer advantages over Lucerne based pastures, particularly in areas with low and variable rainfall.
The most significant advantage of the hard seeded annual legume system is that it will not dry out the soil profile prior to cropping in the same way that Lucerne can. In drier environments, this reduces the risk associated with the transition from pasture to crop and crop to pasture.
Another significant advantage of the system is that the hard seeding characteristic of these legume species allows the pasture to regenerate after the cropping phase without having to be re-sown.
The annual legume system uses a two year pasture phase followed by a two or three year cropping phase.
A typical rotation is outlined below.
Given average seasonal conditions, hard seeded annual legume pastures will fix enough Nitrogen to supply two crops. Grass weed control is achieved by spray fallowing in the second year, followed by canola as the first crop. The system is low risk, as it requires minimal Nitrogen inputs and reduced reliance on selective herbicides.
While a well-managed hard seeded annual legume system provides weed control options through competition, preferential grazing and spray-topping, these species are sensitive to many commonly used herbicides. For this reason, careful planning must go into the management of these species, particularly in the establishment year.
A particular limitation is the sensitivity of Biserrula, Bladder and Gland Clover to winter cleaning with Gramoxone and Simazine.
Grazing management of annual legume pastures differs significantly from Lucerne based pastures. These pasture do not respond to summer rainfall like Lucerne, hence summer grazing revolves around utilising the residual dry matter remaining from spring growth.
The dry plant residue is Nitrogen rich, highly palatable and can decompose rapidly over summer, so grazing pressure must be managed to avoid leaving pasture paddocks bare.
Grazing pure Biserrula can lead to livestock becoming photosensitive. Appropriate grazing strategies, plus an alternative feed source is required to manage this, so Biserrula should be selectively used across the farm.