MPI review of Overseer

11 August 2021

Delivering a nutrient management tool that works for farmers

Creating tools to assist farmers to make the right choice on nutrient management is a long and sometimes expensive process. The Fertiliser Association is committed to a journey of enabling New Zealand farmers to meet their goals for profitability and heightened environmental responsibility.

Overseer is the most widely used decision support tool used in New Zealand farming. Over 12,000 farms have used the tool to make real decisions about nutrient management on-farm, so that they can have confidence in balancing production goals with their environmental responsibilities.

The Fertiliser Association partnered with MPI and AgResearch to develop Overseer as a trusted on-farm strategic management tool, using the best of New Zealand science to give farmers confidence in making good decisions on nutrient management.

Having the regulator, the national science organisation and industry in the partnership brings robustness and credibility to Overseer. It means that the three parties are committed to working together to deliver a tool that works for farmers.

MPI Review

MPI has just published a review of Overseer, that highlights some concerns they have over the use of Overseer for regulatory use.

“No model can fully reflect what is happening in a real-world situation, but they can still be extremely useful,” said Dr Vera Power, Chief Executive of the Fertiliser Association of New Zealand.

“Our view is that continuing to evolve and develop the model is the answer for New Zealand farmers.”

“There are recommendations in the report that could be valuable in terms of ongoing development and improvement of the current Overseer model. The reviewers did not fully consider the regulatory environment in which the model is applied, or the practicality of its application as a tool that supports farmer decision making.”

“The New Zealand public is clear on their environmental aspirations and supportive of a farming sector that is moving forward, so using tools like Overseer to support the journey ahead is critical,” added Dr Power.

Millions of dollars have been spent by the partners—including the Crown—to improve the model and there will always be more to do.

That development has been guided by an independent science oversight group panel and supported by over one hundred peer-reviewed papers and tested through the Environment Court.

As farmers work hard to both understand and meet objectives for water quality and greenhouse gas emissions, they need to have confidence in the tools they use to make their decisions.

“Overseer needs to evolve as further mitigation technologies are developed,” says Dr Power.

How the model is used by farmers

As compliance with regional councils’ regulations becomes more challenging, farmers and their advisers and consultants use Overseer to assist with nutrient budgets, nutrient management and scenario planning. It assists farmers to manage nutrients well by understanding the likely impact of proposed farm system changes on nutrient cycling. This includes understanding of potential nutrient loss.

This has been core to managing the potential impacts of agriculture in New Zealand’s effects-based regulatory regime, which focusses on the impacts of the proposed operation of a farm system.

How the model works

Overseer is made up of a set of science models and components that work together to model nutrient flows including greenhouse gas emissions for a farm system. It focuses on the aspects of management that are under a farmer’s control and has been designed so that it uses information that is directly available to farm managers, supported by default information from national databases.

“A model is necessary because monitoring actual nutrient loss on each and every farm is impractical, guessing is unacceptable and blanket rules on inputs are undesirable,” said Dr Power.

Complex simulation models used by researchers will be more accurate in describing what is happening on a single paddock.

Unfortunately, such models do not translate to the reality of a farm system where they can be used by the farmers and their advisers who have both the data and the need to use the data to make real decisions.

Models such as Overseer are useful in helping to think about the farm system, what can be done to improve and which innovations support improved management.

“This is the basis of the journey we all need to make so that New Zealand farms can meet their goals for profitability and heightened environmental responsibility,” says Dr Power.

For further information on Overseer, including FAQs and a link to the Overseer website, see here.



About the Fertiliser Association of New Zealand (FANZ)

The Fertiliser Association of New Zealand promotes and encourages responsible and scientifically-based nutrient management. Managing nutrients well is in all New Zealanders’ interests, both for economic benefit and environmental management.

To promote good management practices, we develop training programmes, fund research, participate in government and local body working groups, and work closely with other organisations in the agricultural sector.

Founded over 70 years ago, the Association is funded by member companies to address issues of common public good. Members include Ballance Agri-Nutrients Limited and Ravensdown Limited who manufacture, distribute and market fertilisers sold in New Zealand.

For more information, please contact Dr Vera Power, Chief Executive of the Fertiliser Association of New Zealand at or phone 027 244 3739.