Verifying the forage value of perennial ryegrass shows the value in sowing five-star seed. By Karen Trebilcock.

Work on verifying the perennial ryegrass Forage Value Index (FVI) is continuing with one research study finished in Southland but DairyNZ’s Waikato trial producing some unexpected results.

DairyNZ senior research technician Nicole Hammond’s Lincoln University masters thesis looked at the grasses sown at the Southern Dairy Hub when it was converted from a sheep farm in 2016/2017. Sixteen paddocks were planted in FVI five-star grasses and another 16 in one-star grasses, including Nui. The well-known ryegrass is this year celebrating its half century since its release by the Grasslands Division of DSIR.

Nicole, using a plate meter, measured the grass in all 32 paddocks before grazing and post grazing to calculate drymatter (DM) grown and eaten from the start of October 2020 to the end of May 2021 with the DairyNZ technical team continuing to measure the grasses during the winter.

The five-star paddocks grew, on average, 900kg DM/hectare/annum more than Nui and the other one-star grasses.

“You couldn’t pick the difference between the paddocks when looking at them, it was quite subtle, but the proof was there that the higher FVI grasses were growing more,” she said.

“It shows that in a Southland farm system, the high FVI grasses are outgrowing the low FVI grasses but the model appears to overestimate the dollar amount.”

FVI ranks grasses according to region as a $/ha figure which is the expected return for growing that cultivar compared with Nui which is ranked at zero.

Nicole’s research showed the overall economic advantage of the five-star grasses was $109.30/ha/ year return, not the predicted difference of $503/ ha/year.

“It still showed a good return for buying more expensive grass seed, if you consider it over a typical Southland 200ha dairy farm and the nine years which is the expected life of the pasture.”

The hub is split into low and standard nitrogen input farmlets and Nicole’s research also showed five-star grasses grew more drymatter under 190kg N/ha than five-star grasses under 50kg N/ha inputs. The one-star grasses grew about the same yield under both levels of nitrogen inputs.

“The five-star grasses whipped the lower FVI grasses in the high nitrogen input farmlets.”

Good grass growing weather also contributed to higher grass growth in the five-star grasses.

“If you give these grasses what they need to perform they will outshine the others,” she said.

However, further north at DairyNZ’s Scott Farm in the Waikato, a four-year trial which ended in May last year, has not given such clear-cut results.

It went a further step than the Southern Dairy Hub’s trial by calculating whole-season milk production from cows grazing low or high FVI grasses.

“We didn’t get the results we expected,” DairyNZ strategy and investment leader Bruce Thorrold said.

“We expected the cows which were grazing the high FVI grasses would produce more milk than those of the low FVI grasses but it didn’t happen. They both produced about the same.

“We’re digging deep into the data to figure it out and we want the right explanation, not the quick one.

“We had very dry summers in the Waikato during the four years of the study and it’s in summer when the highly ranked grasses should really perform but they didn’t, perhaps because it was so dry.

“Or it could have been management or something else going on. We don’t have the answers but we’re trying to figure it out.”

An explanation would hopefully be found in the next few months and plant breeders, just as much as farmers, wanted transparency on what grasses were the best to grow.

“We have to have confidence in the rankings. We want to drive genetic gain in grasses so we need to know they are performing as they should on farms, not just in trial plots.”

Farmers should in the meantime follow the key principles when selecting cultivars – the right endophyte, a diploid or tetraploid and the right heading date for the farm.

“Using a high-FVI grass will give you a good result, we’re confident in that, we’re just not sure by how much.”