Farming’s engine room gets an improvement through better science

By Gerald Piddock, 11 December 2015, www.stuff.co.nz

Rye grass and white clover, the cornerstone of New Zealand’s pastoral farming system, are being reinvented by AgResearch scientists.

The work could lead to a new generation of grasses and a reduction of the environmental footprint of Kiwi farmers.

As world leaders gathered in Paris to discuss climate change solutions, Dr Jim Crush believes the scientists’ work could help farmers adapt to a hotter climate while reducing their fertiliser inputs.

A test plot of rye grass at Ruakura, which has been developed to better mitigate nitrate leaching.”I think that this approach has got way more potential than anything we have tried before,” Crush said.

Crush and colleague Shirley Nichols are part of AgResearch’s germ plasm development team at Ruakura.

The historical focus of forage plant breeding had been on above-ground traits in pastures, but Crush and Nichols want to improve traits below the ground.

Their work involves developing cultivars to help farmers to withstand drought and grow livestock under looming environmental regulations while retaining the core requirements of any pasture plant – palatability, persistence and resilience to disease and pests.

It is funded through the Pastoral Genomics Consortium and the P21 Consortium.

Grass and clover seeds are collected from around the world and examined for traits that could be incorporated into future hybrid cultivars by using introgression breeding. It’s a technique that gave commercial breeders access to more variations that existed within a pasture species.

“This is not genetic engineering. It’s taking two clovers, it’s taking pollen from one, transferring it to another using a little brush. It’s an entirely natural process.”

Nichols said they discovered a trait in the Mediterranean clover trifolium uniflorum that grew in a hot, dry environment that could improve white clover’s tolerance to drought.

A hybrid was created and tested in a drought experiment at Lincoln that compared the plant’s shoot and root dry weight, leaf size and senescence (dead leaf material) under water stress to a typical white clover species.

“That showed that some of these hybrids are less affected by drought stress than white clover,” Nichols said.

In a separate experiment, Nichols also compared the root depth between the hybrid and white clover. Having deeper roots would allow the plant to access greater amounts of moisture in the soil, which would be advantageous in a drought, she said.

Nichols also tested the hybrid’s phosphate use efficiency.

Grass roots were better at acquiring phosphorus than clover roots because of the plant’s root structure. Currently, farmers had to apply more superphosphate on a paddock when rye grass and clover are grown together in order to satisfy the requirements of clover.

This was a key issue in New Zealand agriculture, Crush said.

“It’s been calculated that the actual increase in rate for growing a mixed sward of growing ryegrass and clover, you have to put on superphosphate at three times the rate than if you grew the components separately.”

It was a huge inefficiency and created big economic and environmental costs.

“We’re farming soils with an elevated phosphate status to look after clovers,” he said.

Developing a clover with higher phosphate use efficiency could solve this issue.

So far, their work has shown that the plant’s root to shoot ratio was higher in the hybrid clovers when P levels were low. This is due to the plant putting more of its mass into its roots to find that nutrient. As P levels increased, that ratio decreased as more of its mass was shifted into its shoots.

This was potentially an extremely valuable trait for clover growing on hill country farms where fertiliser application was intermittent.

The hybrids also had a greater root length and higher rate of root branching, she said.

A further study involved searching for solutions around mitigating nitrate leaching in rye grass by improving its root depth. In Waikato, 70 per cent of a rye grass plant’s root mass occurred in the top 7cm of soil.

“They are very shallow rooted systems,” Crush said.

This experiment involved growing different rye grasses in metre-deep tubes of sandy soil. The plants were then taken out and the root length weighed. Crush said they found it was possible to select rye grass based on deeper roots.

Hybrids of these plants are currently out in small plots on a nearby paddock for testing. A synthetic urine patch is applied to simulate livestock urinating on the pasture.

Crush was also trying to develop a plant with a root system shaped like the letter T. This would allow the plant to capture urine from cattle more readily and capture the nutrients that were washed further down.

He said it would take his team several cycles and selections to develop a hybrid that had these characteristics.

It was an ongoing process and the future of forage plant breeding was in hybrid clovers and grasses. These were non-GE, meaning there were no regulatory constraints and gave scientists more abilities to explore, he said.

Crush estimated the timeline between now and when a seed could potentially be available for farmers was 15 years away.

“At that stage you can have something that’s thoroughly tested, it’s robust and reliable and you can have confidence in its performance. It’s an ongoing process.”

The research started five to eight years ago, and was all at different stages. Studies of moisture stress tolerance were currently in field trials on research farms and the scientists planned to shift some of that work onto small scale testing on hill pastures on commercial farms in the next 12 months.

If successful, the best of the hybrids would then be tested on larger paddocks on hill country farms in the next five years and then the seed companies would produce a commercial cultivar.