Flooding halts northern Future Dairy Farm project

The Northland Agricultural Research Farm (NARF) at Dargaville took a serious hit in February, when heavy rain from Cyclone Gabrielle saw water surge down the Wairoa River breaching stop banks and flooding surrounding farmland.

The significant flooding, which saw evacuations around the Dargaville area, also saw about 90% of the research farm under water. The milking shed was out of action with the cows unable to be milked for two days.

With some donated paddocks from a neighbour and plenty of palm kernel and baleage on hand, the animals have been well fed and remain in good health. While the shed is now up and running, milking has dropped to once-a-day until the pasture has recovered.

The herds were expected back on their farmlets by May 1, to ensure the trial resumes by June 1, advises Northern Dairy Development Trust co-ordinator Kim Robertson. The research farm is run by the Northland Dairy Development Trust (NDDT).

About 60% of the pasture was seriously damaged after being under water for three days and was covered in fine silt.

“While the farm has flooded before, it is not a common occurrence,” says Kim. “The last time was eight years ago and it wasn’t as high. It also happened in spring so there wasn’t so much pasture death.”

Higher up the Wairoa River catchment farmland regularly floods on the Hikurangi Swamp. Farmers there have found through experience that summer floods are much harder on pasture. Higher temperatures see the shallow flood waters warm up – killing the plants. In colder winter conditions pasture can often survive for up to 10 days under water.

Several trials are underway on the farm and these were shelved for a few weeks, with efforts going into getting the pasture back up to scratch so research could continue into the next milking season.

As might be expected on a research farm the flooding event has become an opportunity to see how the different pastures perform under flooding conditions.

“So this is rather a silver lining in terms of research, but of course a big cost onfarm,” she says.

The main research project is comparing three pasture systems using kikuyu and ryegrass pasture on two of the 28 hectare farmlets with the other 28ha farmlet growing alternative pastures of tall fescue, cocksfoot, herbage and clover.

All the C3 plants – ryegrass, fescue and cocksfoot – died in the worst-affected areas. Kikuyu and white clover fared better and have started growing again.

The team mowed off the silted pasture as soon as the water went down with the dead vegetation removed from the farm.

One of the best ways to manage kikuyu pasture is to mulch it almost to ground level in late March and under-sow with ryegrass for winter and spring growth. The team decided to do this early in the worst-affected paddocks, hoping the kikuyu would be “shocked” by the flooding and won’t take off in the warm moist conditions. The badly affected alternative pastures of tall fescue and cocksfoot are also being under sown in an effort to get them up to scratch before weeds can take hold.

Where weeds have appeared they have been sprayed where needed, with slug bait applied in regrassed areas.

“We have also now had an outbreak of tropical armyworm which is common after an autumn flood,” Kim says.

“They will decimate any new seedlings so need to be monitored every two days and treated if needed.”

With three quarters of the season results already on record and growth rates still able to be taken from the unflooded pastures, the team is confident they will be able to model the rest of the season fairly accurately.

The Future Farm trial

Ironically the research was looking into which farming systems might cope better in relation to various ongoing climate change issues facing the dairy industry, including extreme weather events – although droughts were more anticipated than floods.

The farm is into the second year of a four-year trial comparing the performance of alternative pastures which may be better at handling warming northern conditions, reducing emissions on a traditional ryegrass-based farm, and using the kikuyu/ryegrass-based farming system highlighted in their previous trial as being the most profitable – as the control.

The research farm, run by the Northland Dairy Development Trust (NDDT), is split into three 28ha farmlets, with milk from the different farms collected separately.

Current/control farm – uses ryegrass and kikuyu pasture, with imported feed – palm kernel to fill feed deficits before milk fat evaluation index (FEI) limits are reached, with a stocking rate of 3.1 cows per hectare, and up to 190kg of applied nitrogen/ha.

Alternative pastures farm: Has at least 75% fescue, cocksfoot, legumes and herbs pasture, and also uses palm kernel to make up feed deficits. Stocking rates are at 3.1 cows/ha with up to 190kg applied nitrogen/ha. Fonterra is providing funding to monitor if there is a difference in milk quality and composition.

Low emissions farm: This system uses existing ryegrass and kikuyu farm pasture and targeted a 25% reduction in methane emissions and a 50% reduction in nitrous oxide emissions (compared to the current farm). The stocking rate was originally dropped to 2.1 cows/ha, but has since been increased to 2.2 cows/ha, with no nitrogen fertiliser applied.

Using the Overseer model, the low-emissions farm reduced methane compared to the current farm by 33% and nitrous oxide by 47%. There was also an 84% reduction in input CO2, and 9% CO2 reduction per kg/MS.

Swings in extremes in the last two years are showing farmers will need to be on their toes with management whatever their practices.

Last year was drier than usual through summer/autumn with lower growth than usual on all pastures. This season the very wet spring/summer saw more growth than usual on all pastures. No applied nitrogen saw the low-emissions farm producing 1376kg DM/ha less than the current farm the first year and 2297kg DM/ha this year, with the current and alternative pasture farms producing similar amounts.

When it came to pasture quality – ME (metabolisable energy) – the alternative pastures farm had higher ME through much of the first year especially through the dry summer/autumn. Current and low-emission farms produced similar quality pasture. Nitrogen fertiliser is clearly having a negative impact on clover in pasture as the low emissions farm, with no nitrogen application, has seen clover take off in the pasture and is now making up 26% of the pasture compared to 16% on the alternative farm and just 10% on the current farm. Given clover fixes nitrogen in the soil from out of the air, this is likely offsetting some of the effects of no fertiliser.

The lower stocking rate on the low-emissions farm is likely behind better pasture coverage during the warmer months than on the other two farms. It was also behind considerably more silage being able to be made on the low-emissions farm, which was mainly then fed out in late summer/autumn seeing little extra feed being bought in.

Because higher residuals are left in the paddock this was largely responsible for a lower pasture eaten rate of 10.4 compared to about 13 for the other farms.

Lower stocking rates were always going to affect milk production and can be seen in rates up to February 4 when the low-emissions farm was producing 681kg MS/ha, compared to 894 for the current and 953 for the alternative farm, with the cows on each farm producing about the same amount of milk – the alternative cows slightly more.

When looking at the finances there is little difference in profitability between a kikuyu and ryegrass farm and an alternative pastures farm.

In the first season with a $9.30/kg MS milk price the current farm had the highest operating profit of $5040/ha, the alternative farm close behind at $4786/ha and the low-emissions farm well behind at $3021/ha.

Milk price would need to reduce to about $5/kg MS before all the farms had a similar profit.

But this season, with higher onfarm costs including for nitrogen fertiliser and labour, along with increased milk production on the emissions farm, profit is likely to be closer across the three farms.

The report can be found on the NDDT website: nddt.nz

Funded by DairyNZ, MPI (Sustainable Farming Fund) and Hine Rangi Trust, the project will run until June 2025.