False breaks death on subterranean clovers

Hands on the clovers

FALSE BREAKS occur in almost two of every three WA seasons, making parts of the State a graveyard for subterranean clovers.

CSIRO researchers Senthold Asseng and Ross Chapman drew this conclusion after examining more than 80 years of weather records from 10 WA locations between Mullewa and Esperance. They reviewed the frequency and impact of false breaks on subterranean clovers in WA's southwest and found that they stripped pastures of the species' valuable legume feed herbage and nitrogen-fixing capacity.

False breaks occur when enough rain falls to tempt seeds to germinate, followed by a dry period which kills the seedlings. Such weather betrayal kills many pasture legume species.

Drs Asseng and Chapman found that the riskiest 14-day period for false breaks fell between the 85th and 98th days of the year (late March to early April), with the risk remaining high in neighbouring weeks.

Unfortunately the in-built false break guard of subterranean clovers has often faltered by this danger time, with WA's extreme temperatures baking and chilling the seed's hard shells into submission by February and exposing the kernel to teasing rains.

This means subterranean clovers are not well adapted to resist false breaks, perhaps explaining the species' poor persistence in local pasture systems. Growers should therefore investigate and consider alternative species with more robust late dormancy release strategies to protect against false breaks.

The work was supported by growers and the Federal Government through the GRDC.

Program 4 Contact: Dr Senthold Asseng 08 9333 6615