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2021 Overseer Review and Response

An international science panel, convened by the government to assess whether the Overseer modelling approach is fit for use as a decision-making and regulatory tool, has released its report.

The Panel identified a number of concerns with Overseer, including that it:

  • is a steady state model attempting to simulate a dynamic, continually varying system
  • does not account for variation in water and nutrient distribution in the soil profile
  • does not adequately accommodate deep-rooting plants
  • focuses on nitrate and omits ammoniacal nitrogen and organic matter dynamics
  • lacks consideration of surface water and nutrient transport, as well as critical landscape factors.

    Based on these concerns, the Panel concluded that:

    • Overseer’s structure is not adequate to provide more than a coarse understanding of a farm’s nutrient losses. It also cannot reliably estimate how changes in farm management would affect those losses.
    • Used in isolation, Overseer is not an ideal tool for calculating nitrogen losses from pastoral, horticultural or arable farming systems.

    Government response to 2021 Overseer Review

    The government has responded to the Review Report with the following statements.

    • It will continue to support Overseer while issues regarding the Review Report are resolved.
    • It recognises that a wider suite of tools are likely necessary to adequately fulfil future needs,
    • It will evaluate other options to address the issues raised by the Review:
      • Creation of risk index tool
      • Development of improved Overseer Model
      • Greater uses of control on practices and inputs
      • New methods for measuring nutrient loss
    • That suitable tools will be available for use by the end of 2024 to give effect to the National Policy Statement – Freshwater.
    • With regard to resource consent applications:
      • “Where a plan requires that Overseer be used, this remains a legal requirement that applicants and consent holders must comply with.”
      • “Where operative plans use Overseer, considering other information in addition to Overseer, where possible, may give increased confidence in councils’ nutrient-management decisions.”

    For more information see:

    FAR response to the 2021 Overseer Review

    FAR welcomes this review. Its findings reflect and address many of the concerns FAR has raised in discussions with the Overseer owners over the last 10 years.

    We recognise that FAR levy payers, many of whom have been obliged to rely on Overseer to meet consent requirements, will be frustrated and concerned about how this review will affect them and their businesses.

    The Review document is long and complex, and we, along with other industry groups, councils and rural professionals will need some time to fully understand its implications. FAR will work with the Overseer owners and other stakeholders to ensure the best outcome for our growers.

    FAR urges all growers to continue with all their efforts to improve nitrogen use efficiency and reduce losses to the environment. In the meantime, here is some guidance on how we think this may affect you.

    Grower questions & answers

    Does this mean that the National Freshwater Plan process will be dropped?

    No, National Freshwater Plan goals will remain unchanged.

    Do I still need to do a Freshwater Farm Plan?

    Yes – eventually most farms will need a Freshwater Farm Plan. However, the regulation for these is still being worked out, so the best advice is to ensure you keep up with any regional requirements around such plans.

    Do I still have to use Overseer for regional compliance?

    “Regional councils are legally obliged to continue to implement their plans, administer existing consents and process new consents in a manner that promotes the objectives and policies of their plans. The Review Report does not change this. Where operative plans use Overseer, considering other information in addition to Overseer, where possible, may give increased confidence in councils’ nutrient-management decisions.”

    I have a farm consent and/or irrigation consent based on an Overseer nutrient budget and N loss number. Is my consent still valid?

    “Existing resource consents and permitted activity rules remain valid authorisations of resource use. Councils can continue to monitor these authorisations to establish the level of compliance that is occurring with the relevant national and regional policy, and their plans.”

    Is there any point in still using Overseer?

    The information you have entered into Overseer is still an important record of your farm management practices. Any decision to continue with it, or not, should be made based on how you use the model. It remains a valid tool to inform farm management and ‘direction of travel’ i.e. whether your losses are going up or down.

    I was going to use the greenhouse gas (GHG) emissions number that Overseer gives me for my emissions reporting. Is that number reliable?

    Yes. The GHG number calculated by Overseer can still be used and has been assessed by He Waka Eke Noa as an option for calculating arable emissions as part of the awareness milestones.

    For more information see: