Subterranean clover

This is more commonly known as Sub clover or Sub.

Subterranean clover is an annual legume that underpins most of south-eastern and south-western Australian broadacre agriculture. It is an amazing legume that buries its seed, hence the "subterranean" (it means underground), after flowering.

Its international or scientific name is Trifolium subterraneum and there are some other varieties called Trifolium yanninicum and Trifolium brachycalycinum.

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Sub clover is a good example of most of the reasons why pasture legumes are special.

The sub part of the name refers to the fact that after the flowers are fertilized the seed stalk reaches down and into the ground. This allows it to bury the seed where it has the greatest chance of survival and germination. The varieties that do not bury their seed often find a convenient crack to drop it into in the cracking or self-mulching clays that they are adapted to.

The species evolved in the Mediterranean, western Europe and southern Britain and Ireland. It is an annual that dies off in late spring to early summer and as a result doesn't need to survive the hot dry summers of the Mediterranean climate throughout the growing area.

The excellent sub clover improvement programs based mainly in Western Australia have bred dozens of varieties of sub, all suited to different conditions through having such characteristics as:

a mix of hard and soft seededness so that
- not all the seeds germinate at the same time particularly on summer storm rains and
- the seed bank isn't exhausted when there is a poor year for winter legumes such as when there has been a late break
massive seed production (more than half a tonne of seed per hectare or 450 pounds per acre) to ensure its long-term survival and to provide extra feed. Sheep are the main grazing animal in this area and they are able to pick up the tiny seeds left on the surface. This seed reserve can carry sheep through droughts and summer feed gaps
high rates of nitrogen fixation to boost the quality of surrounding and following grasses and crops (boosted by the rhizobium inoculum that most varieties share and so it is in the soil of most farms, regardless of which varieties of sub that farm grows)
the ability to be grazed hard and grazed hard, again and again
resistance to a variety of pests and diseases
high production of high digestibility feed.

Much improvement of native pastures in these areas has been based on "sub and super" - sub clover and superphosphate topdressed over the existing native grass-based pastures to add phosphorus, sulphur, nitrogen and enhanced digestibility.

This was a low-cost, highly effective way to improve pastures dramatically. It often trebled pasture production.

An organic farmer wanting to achieve similar results could use a suitable rock phosphate instead of the superphosphate. They would need to increase the application rate to as much as three times but would need to apply it less often, provided they maintained a high level of organic matter and biological activity in the soils.

Using rock phosphate requires local knowledge as well as a good understanding of the different processes involved in phosphate availability and how these processes operate in local soils and under local climatic conditions. You also need to have a reasonable understanding of the differences between superphosphate and the particular rock phosphate that you choose.

The availability of phosphate in the short-term is dependent on the amount of available phosphate applied. This applies to both superphosphate and rock phosphate.

However, with rock phosphate, the amount of phosphate available longer term is set by

the nature of the rock phosphate itself
the soil acidity
the amount of iron in the soil
organic matter levels in the soil
the level of biological activity and
various other factors.

This is why some specialist local advice will make it easier to get the best results with rock phosphate. And this applies whether you are

farming organically
wishing to use fewer artificial chemicals
wanting to make better use of soil phosphorus
aiming to reduce your costs
setting out to improve profits.

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This page was updated on December 27, 2007