Many of the extensive pasture systems in the central west contain the annual legumes subterranean clover or annual medics. While these are very high quality plants for livestock production, they have quite shallow root systems. This means that they often struggle during hot-dry periods in spring and may not recover and continue to grow if rainfall occurs later in spring. Even in good growing conditions, subterranean clover and medics have usually reached their maximum production by mid spring and from then on, they begin to senesce and ultimately die off by late spring-early summer.
Some of the deeper rooted annual legumes such as biserrula, French serradella, yellow serradella and arrowleaf clover are very capable of surviving periodic dry spells often experienced in spring and then being able to respond to later spring rainfall. This also means such species are more reliable in setting seed and therefore in regenerating reliably in following years. The ability to recommence growth following a dry spell also means provision of higher quality green forage for livestock later in the spring-early summer period which can result in higher levels of livestock production.
The picture (below) shows a paddock sown to biserrula in late autumn this year. Three weeks before this photo was taken, the entire paddock had browned off. Prior to this, the biserrula had been able to produce and fill pods. Since rainfall a couple of weeks ago, the biserrula has recommenced growing and has produced more flowers which will result in a second round of seed production.
If you are planning to sow pastures next year, keep these deep-rooted annual legumes in mind as they also fit very well in flexible crop-pasture rotations.