About the review
An independent Science Advisory Panel was convened by MPI and MfE to conduct the review, in response to a Parliamentary Commissioner for the Environment’s recommendation. In their report, they find shortcomings in Overseer nutrient management tool.
The panel concluded it did not have confidence in Overseer’s ability to estimate total nitrogen loss from farms, which is a significant limitation in using the model to estimate N loss for regulatory purposes.
The review suggests Overseer can still be a valuable tool for other purposes, such as development of and setting the fertiliser strategy for a farm.
DairyNZ research shows nitrate leaching measurements from farm system experiments are generally well-aligned with Overseer predictions where actual climate data has been used on dairy land.
DairyNZ will continue to support farmers. Overseer is an important tool to help farmers understand the different options to reduce nutrient losses and provide resources to help manage their environmental impacts.
DairyNZ do not support Overseer as a regulatory tool in all situations. In combination with output modelling, Farm Environment Plans may be a better approach and factor in any risk posed by individual farms to the receiving environment.
DairyNZ endorses further redevelopment of Overseer to continue optimising farm systems to protect water quality, farm viability and economy, and supporting farmers to make management decisions.
The Government has also committed to examining a wider range of tools to support nutrient and sediment management at farm and catchment scale. DairyNZ's advice is that new modelling tools should be in addition to re-developing Overseer, not a replacement.
Input controls is not an adequate substitute for risk management approaches that consider the current state of catchment water quality, and the most appropriate mitigation options that take into account a farms inherent risk (soil type, rainfall, slope).
DairyNZ's view is that any tool used for regulatory purposes needs to be fit for purpose, accurate and reliable. We must have high confidence in Overseer and other tools.
Government and council actions
There is urgency to deliver the next generation Overseer tool, and any additional supporting tools, given the 2024 deadline for regional councils to develop RMA plans under the Essential Freshwater reform package. Overseer redevelopment and any new tools must be developed, tested and in-the-market well before then.
The implications of the Panel’s findings on consenting, farm plans and/or monitoring and enforcement processes that use Overseer are still to be determined. Councils are considering the review before making decisions.
Regional councils using Overseer to support their regional plans and/or consenting processes will continue to implement their plans but will be required to adjust their approach.
Government will be working with regional councils over the coming months to develop guidance to help with the transition. Government will also develop guidance for the use of models in environmental regulation.
Questions and answers
What do I do from here?
- Most regional councils have information on their websites. Take some time to assess what their steps are and what that means for you. Where Overseer has been used in regulation, your regional council will contact you.
- We’ll keep this webpage up-to-date as further information comes to hand.
- Further information is available via the MfE website (Responding to the Overseer review – advisory note | Ministry for the Environment)
What happens in regions where councils already use Overseer or were going to for regional plans?
- Councils will continue to implement their plans and the freshwater reforms.
- Government has committed to support work on a next generation Overseer so that future plan changes have a tool/s to estimate nitrogen loss.
- Environment Canterbury has applied for an extension to the timeframes to decide on the proposed plan change 7 and plan change 2.
What happens if I have a consent, farm plan, or monitoring and enforcement process that requires Overseer estimates of nutrient losses?
- Regional councils will continue to administer consents to manage freshwater at the farm level.
- MfE has suggested councils be alert to the review panel’s concerns and use Overseer plus additional information to increase their confidence level.
- The Government has committed to ensuring regional councils have fit-for-purpose tools available within 12 months.
- Developing tools suitable for every farm in this timeframe will be challenging due to the complex nature of farm systems, soils, and climate. Overseer has taken 30 years to get to where it is today.
- A council may choose to continue with Overseer until alternative tools are developed or develop their own tool/approach for compliance auditing.
What have regional councils said so far?
Regional councils will continue to provide information for those affected. DairyNZ will be working closely with regional councils.
- Horizons Regional Council will respond by the end of August with their approach (Overseer is used for N loss compliance in that region).
- Environment Canterbury are considering the review now to confirm the impact on consenting, compliance monitoring and enforcement, and Farm Environment Plan auditing processes.
- Environment Canterbury have temporarily paused Farm Environment Plan audits.
- For more information: Overseer review | Environment Canterbury (ecan.govt.nz)
- Waikato Regional Council: Government review of Overseer
Will existing mitigations promoted to reduce N loss be recognized and/or included in the development of new tools?
- We can expect the science that underpins the Overseer model to be considered and used in the development of new tools.
- Significant effort and investment has gone into testing mitigation efficacy and that work is likely to be recognized where there is a high degree of confidence.
My regional council specifies an Overseer year end nutrient budget. Will I have to do this and pay the subscription?
- Regional councils are working through this at the moment. We are unsure at this stage whether Government will provide assistance to those affected.
Given the 2024 deadline for all regional councils to develop RMA plans under Essential Freshwater, how will nutrient losses and catchment limits for nitrogen (and other contaminants) be assessed?
- Regional councils have been instructed to proceed with developing plans on the basis that nutrient loss estimation and risk assessment tools will be available for preparation of new plans by the end of 2024.
What were the limitations of Overseer identified by the panel?
The issues identified related to its ability to accurately predict N loss from a farm for a particular year.
Some of the key issues include:
- Overseer is a long-term model and does not accurately represent N loss for a particular year. It produces a long-term annual average.
- The model uses 30-year average climate data that does not account for climate variations and the implications of those variations on nutrient flows.
- Overseer assumes a homogenous soil profile. This does not capture variability in water and nutrient distribution through the soil as depth increases. On flat land this is less of an issue.
- Overseer does not account for ammoniacal N and soil organic matter dynamics and losses. This limits its focus to nitrate losses.
- Overseer does not consider surface water and nutrient transport, or account for the movement of nitrogen via overland flow and critical sources in the landscape.
- AgResearch and Overseer Ltd are confident the Overseer tool is underpinned by extensive scientific research. AgResearch do not agree with all of the content of the review but agree there are areas worthy of further investigation.
What wasn’t in scope for the review?
- The review only looked at nutrient modelling. It did not consider the user-interface, greenhouse gas modelling, or any other aspect of the suite of tools under the Overseer brand.
- Furthermore, the review did not examine whether Overseer could be used as a social tool to encourage farmers to adopt nutrient management strategies, nor whether it would improve the credibility of recommendations from rural advisors.