Trial to unearth where the grass is greener

A future where dairy farmers no longer have to use high levels of nitrogen on their pastures could become a reality as a three-year research project by the Tasmanian Institute of Agriculture (TIA) enters its final 12 months.

The Dairy HIGH 2 program is a $7.7 million partnership between TIA and Dairy Australia.

Four farmlets have been set up at the TIA dairy research facility at Elliott, with each having varying pasture mixes and nitrogen application:

• Farmlet one: 80 per cent perennial ryegrass and 20 per cent white clover – with 300kg of nitrogen per hectare
• Farmlet two: 80 per cent perennial ryegrass and 20 per cent white clover - with 150kg of nitrogen per hectare
• Farmlet three: 40 per cent perennial ryegrass, 30 per cent white clover and 30 per cent plantain - with 150kg of nitrogen per hectare
• Farmlet four: 40 per cent mixed grasses, 30 per cent mixed legumes and 30 per cent mixed herbs - with no nitrogen application

TIA research fellow Peter Raedts said that the dairy industry is highly reliant on nitrogen for cow pastures, as it is considered a crucial nutrient source for grass growth.

“But it is expensive, and in other places around the world, legislation has come into place to make sure that the right balance is found between trying to make pastures grow and losing nitrogen to the environment.”

The trial aims to achieve 20 tonnes of dry matter production from each of the four farmlets, which TIA pasture feedbase research fellow Zac Beechey-Gradwell said was very high compared to dairy industry averages.

“In the first season, we exceeded that, and in the second season, we got very close,” Dr Beechey-Gradwell said.

“We got within about a ton for farmlets one, two and three, and we were short by 2.53 tonnes for farmlet four.”

Mr Raedts said the research team had deliberately made farmlet four a challenging pasture to maintain by using no synthetic nitrogen and white clover.

“What everyone would expect is that you grow a little bit less grass in the first year, which was not the case - but in the second year, we did start to see less grass growth.

“But, of course, it also has a lower cost structure.”

The grass still needs nitrogen to grow, which is why TIA researchers have used varying amounts of white clover on the remaining three farmlets.

“It has a symbiotic relationship with rhizobia bacteria on its roots, which can grab nitrogen out of the air,” Mr Raedts said.

“What we have seen over the first two years of the trial is that if you incorporate white clover into fields, you can see the pasture and milk production per hectare kept at a high level.”

Mr Raedts said the dairy industry had a high level of interest in the work TIA had been doing.

“Everybody tries to have as environmentally sustainable a production as possible by not needing to buy as much synthetic nitrogen, which is quite often made using gas stored in underground soil that releases carbon into the air.

“We have started a system and it works well.

“But there are still a lot of unanswered questions, like how producers can maintain and achieve this on other farms.”

Dr Beechey-Gradwell said that conducting the trial on what were essentially working farms was different from most research projects where testing is done in isolation.

“There is also the aspect that farmlet four is run as close as we can to regenerative management in terms of the things we do and don’t put in as chemical inputs into the farm, that’s had additional interest from the regenerative crowd.”

In the final 12 months of the Dairy HIGH 2 program, researchers aimed to gain a deeper understanding of how to maintain a high clover level in pastures, obtain more precise estimates of the nitrogen cycle and gather information about changes in soil health.

Mr Raedts said one of the key learnings so far was the benefits of clover in the diet of a cow.

“They rely on a fermentation process in their stomachs to pre-digest what they eat – to make grass useful for them.

“And in that fermentation process, if you have clover in the diet, that happens a little bit more rapidly.

“That means the cow can eat a bit more every day and because of that, if she is willing to and wants to, she can use that extra intake to produce more milk.”

While there is a small risk of clover causing ruminal tympany, a life-threatening condition in cows where gas builds up in the rumen, Mr Raedts said the research team was able to mitigate it by adding a component to their diets.