Karen Trebilcock

Otago farming could be heading for a major shakeup when the council’s water plan kicks in on April 1 next year.

Unlike other regional councils, Otago has opted for an effects-only based
approach with nitrogen leaching limits set but no rules on how land must be managed.

All farms, including dairy, sheep and beef, lifestyle blocks and horticulture must be under 30kg N/ha/year with several sensitive catchments under 20kg N/ha/year and parts of the Southern Lakes
catchments under 15kg N/ha/year.

Nitrogen leaching is to be measured annually and calculated using the latest version of Overseer.

The water plan was announced in 2014 and since then all farmers have had to record data for Overseer and provide the information to council on request.

However, Otago Regional Council (ORC) land resource officer Bruce Monaghan said at a DairyNZ seminar on the water plan at the end of February at Invermay near Mosgiel that council had so far not requested this information from any farmers.

Monaghan said even when the plan became effective, council would still not be requesting the information from every farmer but instead would only concentrate on what it considered to be high risk areas.
Once a request was made, farmers would have up to a year to provide the information.

“We realise that Overseer needs robust data and it can take 12 months to collect that data,” Monaghan said.

While many dairy farms near Dunedin sat at around 10-15kg N/ha/ year due to the heavy soils in the lower Taieri catchment, some in South Otago were at about 40kg N/ha.

A farm consultant from Oamaru said most of her clients on the Waitaki Plains, which had free-draining soils, were above 100kg N/ha/year.

Although farmers could apply for consent to farm above the set levels,
Monaghan said it would only be granted if the farmer was actively reducing their N leaching.

When asked if farmers who knew they were above the limits should be applying for consent now he said they should instead be working towards lowering their Overseer figure.

Council would not be auditing Overseer calculations as only certified advisors were able to use the programme.

“If we see something that is suspicious we might have another look but the people using Overseer, it’s their reputation at stake.”

The Overseer figure was to be worked out on the total land holding, including support blocks which could be 100km apart or more, as long as they were in the same leaching zone.

The person actively farming would be responsible, whether they were the land owner, lessee or occupier.

For sharemilkers and contract milkers, the request would initially go to the land owner and if it was in contracts that the sharemilker or contract milker was responsible for Overseer then it was them who would be accountable.

Water testing was also part of the plan to ensure “good quality water” in the region’s rivers and lakes. This would only be done when the environment was in a “settled state” and not in times of high rainfall.

Monaghan said ORC would not be telling farmers how to farm.

“If your winter crop is on a certain slope, we are not going to be telling you how to feed it.”

He said ORC had done no economic modelling of the impact of the water plan on the region and he did not know of any plans to do it in the future.

Further information about the plan and how it would be implemented would be on the council’s website in April.

DairyNZ catchment engagement officer Katherine McCusker, a former farm consultant who used Overseer, said the model was an annual average model which was not designed to predict N leaching for a particular year as ORC wanted.

It also assumed farmers used “best practice” which in many cases ORC

was not requiring farmers to do in the region.

She said users of Overseer could “manipulate the figures entered to get what farmers wanted”.

With soil types a major influencer in the model, she said it was worrying ORC had done little to make sure soil maps in the region were correct.

“Both Environment Southland and Environment Canterbury have invested a lot in getting their soil mapping accurate,” McCusker said.

“In Otago there are large holes.”

Also worrying was as newer versions of Overseer were released, the figures changed and she gave one example of a farm at 12kg N/ha/year changing to 17kg N/ha/year to then over 20kg N/ha/year.

“This doesn’t help farmer confidence in what they are doing on farm is right.”

DairyNZ catchment engagement leader for the Lower North island Adam Duker showed examples of how Otago farms could reduce their Overseer figure by reducing nitrogen fertiliser applications, sending culls off earlier and extending the area used for effluent applications.

A North Otago border-dyke-irrigated farm milking 485 cows with a stocking rate of 3.7 cows/ha had an Overseer figure of 162.

It was reduced to 35 by spending $1.2 million on a centre pivot and sending 74% of culls away by the end of March instead of May which also reduced the need for palm kernel.

It was further reduced to 31 by reducing the stocking rate by 7%, using even less palm kernel and reducing the amount of nitrogen fertiliser.

The changes dropped the operating profit ($/ha) from $3871 to $2774 – a decrease of 28%.

However, Duker said more concerning was the example of a South Otago farm with no irrigation milking 785 cows at 2.7 cows/ha. It had a N leaching figure in Overseer of 41.

“There’s very little this farmer can do to reduce the figure, even though they only have to reduce it by just over 10.”

Sending culls away early, reducing the stocking rate by 10%, reducing the amount of winter crop, reducing the nitrogen fertiliser and supplements finally got the figure to the needed 30 but reduced operating profit by 26% from $1406/ha to $1047/ha.

He advised farmers to accurately model their farm in Overseer to find their current figure before making any changes to their farming system.

He said for North Otago farmers on free-draining soils, irrigation had a huge impact but capital upgrades came at a significant cost.

In South Otago, where farms did not use irrigation, whole-farm-system assessments would be required to try to lower N leaching figures.