Pasture failures a big cost

YIELDING RESULTS: New Lincoln research could reduce the high costs of replacing pastures.
YIELDING RESULTS: New Lincoln research could reduce the high costs of replacing pastures.

Pasture failures cost farmers heavily after the 2008 drought and a big gap in the dairy industry's knowledge of why ryegrass pastures misfire is being closed by a Lincoln researcher and his team.

DairyNZ's David Chapman is leading a government and industry funded $5 million project, Transforming the Dairy Value Chain, as part of the Primary Growth Partnership programme to get to the bottom of poor pasture persistence.

Obvious failures come from ryegrass-clover pastures providing less feed after a major pest strike or a serious drought. Gradual yield leakage can also be from sown species being replaced by poorer-yielding species or changing so they produce less nutrition for cows.

Chapman said there was not enough evidence to show which factor was contributing mostly to their decline and this highlighted a big gap in the dairy industry's knowledge.

"Farmers should be able to expect to get 10 to 12 years from a new pasture, but some dairy farmers believe they're getting two or three years."

DairyNZ productivity strategy and investment leader Bruce Thorrold said pasture failures could be a heavy expense for farmers.

"It depends very much on the individual situation, but after the 2008 drought we saw some poor persistency of pastures. The cost of renewing pastures would be $1000 to $1500 a hectare and some farmers might have had to renew 10 per cent to 20 per cent of their pastures after that drought and then there is the cost of production."

He said the loss of production from drought-hit pastures after 2008 was likely to be another $600/ha.

The $5m project investment was "small beer" compared with potential savings and the development of persistency as a trait in a pasture index  would be valuable for farmers, he said.

Thorrold said the research team was looking closely at the causes and speed of gradual declines in yield.

The slower rate of decline compared with a drought or pest attack might be from plants dying out and being replaced with brown top or summer grasses, and researchers want to know if this was because of their age or because they were less vigorous.

Chapman's team started a survey of perennial ryegrass in 72 paddocks in 2011 on dairy farms around the country.

Samples taken from them have formed a collection of more than 15,000 plants at AgResearch's Ruakura Research Centre and researchers are comparing the surviving plants with others from the same seed lines.

Northern farmers appear most vulnerable as perennial ryegrass  dislikes warmer night-time temperatures, gets stressed by more summer dry spells and is prone to pests such as black beetle and weeds such as paspalum.

Some farmers believe older cultivars persist better, so the research team is including nui ryegrass in the project and taking into account the effect of stocking rates on pasture.

About 40 perennial ryegrass types are on the market and to help farmers choose the most resilient ryegrass, researchers want to understand what happens to them when they suffer stress.

Chapman said the genetic expression of plants had possibly changed and they might still be in the ground, but could have lost the traits that gave the yield advantage in the first year.

As part of the project, researchers are tracking the yield, survival and population densities of several 2011-planted ryegrass cultivars  in controlled trial conditions at Northland, Hamilton and Lincoln sites. They are looking at their structure, growth above and below ground, and how they respond to competition from other plants.

Chapman said they were also testing the DNA of individual plants to see if their genetic composition had changed. 

The results will be used to develop a breeding-worth scale for persistence. This will be used as one of three rankings in the DairyNZ Forage Value Index, which will also assess ryegrass types on their major traits, yield and digestibility.

This will help plant breeders identify more persistent ryegrass types.

Thorrold said New Zealand's long-term competitive advantage in dairy and meat production rested on genetics gains in pastures as it could not compete with the ''cropping and confinement'' systems of the United States.

Fairfax Media