Department of Primary Industries' rotational grazing trial finds optimal treatment

The project, carried out by the NSW Department of Primary Industries, began in 2011 following funding from Australian Wool Innovation to look at the influence of intensive rotational grazing on the productivity and sustainability of sheep production systems.

DPI rangelands and pastures research leader Warwick Badgery said the trial was driven by questions from producers around stocking rates and rest periods following a separate EverGraze grazing project.

The trial site at the Orange Agricultural Institute is made up of 11 treatments with different combinations of stocking rates and rest periods.

The high stocking rate averages 14 dry sheep equivalents (DSE) per hectare, while the low rate consists of nine DSE/ha averaged over the trial period. There are also continuous grazing plots as controls.

"We've got 15 paddock rotation and 30 paddock rotation to try and tease apart the intensity of paddocks in rotation," Dr Badgery said.

"We have two different speeds. The fast speed is a 56 day rest on average, it's a little bit shorter in spring and a little bit longer in the non-growing season.

"Then the slow rotation is double that rest length, so 112 days.

"We look at it as a system so we can compare the productivity of those different management approaches."

The trial runs Merino ewes or wethers of a similar type. Productivity is measured by comparing weights and condition scores of the sheep on the treated paddocks to those in the continuous grazing plot.

Dr Badgery said the slow rotations had the biggest impact on production.

"So much so that it doesn't matter what environmental benefit you get out of it, the animal production is just so low," he said.

"The low stocking rate is better but it still impacts on that production. From that production point of view those treatments just don't stack up at all."

Pasture composition declined in the high stocking rate treatments, with the high stocking rate, continuous grazing plot most affected.

"Things like the number of times the pasture is grazed below one tonne of dry matter is highly correlated with the proportion of cocksfoot that's remained in the pasture, as an example," he said.

Dr Badgery said the pasture was primarily cocksfoot with phalaris, fescue and white clover when the trial began.

"Over time that's changed in some treatments, so some treatments still have been able to maintain that existing pasture mix, but others have degraded to have a lot more annual grass and a little bit more sub-clover in them and a few low productive summer perennial grasses.

"Phalaris has generally become more dominant across all our treatments."

The trials indicated the optimal treatment was high stocking rates on fast rotation.

"You get the productivity benefits out of the high stocking rate but there's enough rest in those treatments that you seem to sustain the pastures pretty well," he said.

"Probably the 30 paddock is slightly better than the 15 paddock, but generally any rest is good for maintaining that pasture persistence."

The project has expanded to include agtech devices with the data used for predictive modelling of animal performance. Soil carbon was also baselined at the beginning of the trial and sampling has been carried out every three years.

"We had about a 0.7 tonne of carbon per hectare increase across the site over a 10 year period [to a depth of 30 cm]," he said.

"Most of the treatments have been increasing at a similar rate but the rotational treatments have been about 0.2 tonne higher than the continuous grazing.

"We'll keep testing for that over time because there's a lot of seasonality in the timing of when different treatments change.

"The other things we're trying to put that in context with is the emissions that are associated with those treatments from the animals.

"So really looking at the optimum treatments from greenhouse gas mitigation potential and profitability perspective."

The team was interested to study pasture recovery for the more degraded treatments, he said. Understanding the carbon dynamics was another area that could benefit from further research.

"We're interested in the whole system, like most farmers are. If you were just interested in the soils component, say, you'd do things a lot differently," he said.

"Some of this is going to become really important if things like sustainability metrics are really needed to underpin livestock businesses and the reporting around that."

He noted the work by technical staff and collaborators throughout the trial.