Farmers looking at past rainfall records continue to wait for the ‘autumn break’, but late summer rain is becoming more common and is useful for cheaply reinvigorating Australian pastures, said a Charles Sturt University (CSU) researcher.

 

Dr Roshan Thapa, who recently completed this research as part of his PhD with CSU supervised by Professor David Kemp, said these late summer rains that sometime extend into early autumn, offer the best chance for regenerating perennial grass pastures in south-eastern Australia.

 

“I found Australian native and introduced grasses germinated after late summer rains, even during years of drought. As long as there was sufficient moisture in the surface soil for ten to15 days after the rain event and there were enough seeds in the soil, native grasses such as Austrodanthonia sp. and Bothriochloa macra and the introduced grass Phalaris aquatica would establish and survive into winter when more reliable rain normally falls,” Dr Thapa said.

 

“’Roughing up’ or ‘lightly harrowing’ the soil surface in summer around existing plants on most soils when the grass seed heads are mature further increased the young seedling numbers. Better still for farmers, fewer management practices are needed,” he said.

 

“I also found no seedlings emerged after autumn or winter rain fell, showing that there is usually only one germination event after grass seeds have matured in summer.”

 

Australia has over 400 million hectares of grazing lands that cover 70 per cent of the continent, most of which include native grasses. “These grasslands are vital for livestock production and the environment and we need better ways of improving them.”

 

Much Australian livestock production depends on existing pasture species, as it is not profitable or practical to sow new pastures, except in more fertile regions in higher rainfall districts. Many existing pastures have a low proportion of perennial grass, the main part of a pasture that affects livestock productivity.

 

“There has been little research into low-cost ways of encouraging new and desirable perennial grasses to ‘rehabilitate’ existing pastures, which would reduce the need for farmers to re-sow pastures with these grasses,” said Dr Thapa. He also noted these techniques could be used in regenerating native grasses in conservation and recreation areas.

 

Dr Thapa, originally from Nepal, said because his work was done during the recent severe drought in sites near Orange, Wellington and Trunkey Creek in central NSW, seedling survival in the pasture through the following summer was limited. However, seedlings that survived six to nine months after they established means that normally these seedlings survive and thicken up without the need to re-sow the whole paddock.

 

“We know many native pasture species often regenerate naturally on their own along roadsides, but it is now clearer how this occurs and how to manage the grasses to encourage recruitment at low cost,” said Professor Kemp.

 

Dr Thapa found that over the last 30 years, late summer rains fell in Orange nearly every year, over 90  percent of the time at Trunkey Creek and over 70 per cent at Wellington .

 

From his work, Dr Thapa has developed a set of recommendations for farmers wanting to renew their perennial pastures. “Paddocks earmarked for improvement in perennial grass content need to be selected in spring and locked up from grazing so if it is a good season there will be a good seed set and mature seed will be ready for late summer rains. If the season is dry, there will be little seed and the paddock can be grazed. If there are lots of seedlings, farmers can manage the paddock like a newly sown pasture,” he said.

 

Dr Thapa said future research needs to investigate the interaction between plant competition in the pasture and soil moisture conditions on seedling survival in the following summer, as well as the impact of when to encourage nitrogen fixing legumes, and the effects of managing sheep and cattle grazing on renewing perennial grass pastures.