Farmers intending to direct drill, oversow, or broadcast subterranean clovers into their dryland pastures this autumn should now be grazing those pastures down to 700-1000kgDM/ha.
A hard grazing in February will open up the pasture and aid the germination of both resident and oversown subterranean (sub) clover seed. If necessary, herbicide can also be used to reduce drymatter before broadcasting or drilling seed.
Sowing and establishment
The preferred method of clover seed establishment is drilling, this is because sub clover has adapted to germinate from burrs buried 10mm in the ground.
While not ideal, broadcasting is often the only option on hill country sites because of the nature of the terrain. Sub clover seed germination is triggered by rainfall of over 20mm, so ideally seed should be spread before a prolonged wet spell in March or April. These can be difficult to predict. Immediately after broadcasting, stock can be used to trample the area and facilitate seed to soil contact.
Sub clover should be sown at a rate of 10kg/ha either by itself or in combination with significantly reduced rates of grass-seed plants (e.g 8-10 kg/ha of perennial ryegrass or 2kg/ha of cocksfoot and plantain). A sowing rate of 10kg/ha will generate around 100 established sub clover plants per metre square.
Another option is to sow sub clover with rape (at 1kg/ha or less if the soil is fertile). The brassica will act as a nurse crop for the clover and provide a couple of grazings over winter. Grass can be over-sown the following autumn, after the sub clover has set-seed.
For successful establishment, legumes need a soil pH greater than 5.5, an Olsen.P of over 15 and Sulphate-S of over 8.
Grazing management
After the sub clover seeds have germinated, the area should be spelled to allow the seedlings to reach the trifoliate leaf stage.
The area can be lightly grazed over winter, preferably by cattle, to keep the pasture at around 2000 kg DM/ha. This ensures the clover is not shaded. The area can be grazed by lambing ewes before being shut up for re-seeding in late spring.
Cultivar selection
Sub clover cultivars vary in flowering dates, leaf size, pest and disease tolerance and hard seed ratings. A mix of at least two complementary cultivars will compensate for site and climate variability.
Earlier flowering cultivars are better suited to low rainfall areas (under 500mm) whereas later flowering cultivars are adapted to higher rainfall areas (over 700mm).
Hard seed
A proportion of sub clover seeds will be hard seeds. These seeds, which germinate one or two years later than most, are an adaptation that help protect the plant from false strikes, where early germination is followed by drought and loss of seedlings.
Sub clover cultivars which have a lower percentage of hard seed in summer are more susceptible to false strikes than cultivars with a higher hard seed rating. But even with a major false strike, only around 10 per cent of the total seed bank will be lost.
Sunny hill faces with a high proportion of bare ground in summer will require cultivars with a higher hard seed rating than shady faces.