More Overseeing, Less Overseer? Changes to Nutrient Management on the Horizon

What does the future of nutrient management look like?

August 2021

The Ministry for the Environment (MfE) and the Ministry for Primary Industries (MPI) recently released two reports on OverseerFM:

  1. A peer review of Overseer by the Science Advisory Panel (Panel); and
  2. The Government’s response to the Panel’s findings.

In this update we summarise the main findings and what this might mean for nutrient management rules in future. Both reports can be accessed on MPI’s website here.

What is Overseer?

Most farmers in Canterbury will be familiar with Overseer, which originated in the 1980s as a fertiliser application tool and has been incrementally tweaked since then. Today it is used to estimate nutrient use and transfers and losses within a farm system and is currently relied on by various Regional Councils, including Environment Canterbury (ECan), to assist with measuring and controlling total nitrogen loss from farming activities.

Science Advisory Panel Findings

The Science Advisory Panel recognised that Overseer has migrated from its original intended use to now being used for a variety of regulatory decisions. The Panel said this was problematic because sometimes Overseer’s strengths (efficient use of available data, usability, reliance on user knowledge) become limitations.

Overall, the Panel’s core concerns are that Overseer:

  • Is a steady state model attempting to simulate a dynamic, continually varying system;.
  • Uses average climate data and therefore cannot model episodic events or capture responses to climate variation;
  • Does not account for difference in water and nutrient distribution through soils, which is influenced by various factors;
  • Is limited to measuring irrigation effects down to 1.5m below the surface. It does not adequately accommodate deep-rooting plants (for example, kiwifruit vines which can grow roots down to 9m);
  • Omits the contributions of ammoniacal nitrogen (for example, animal waste) and other organic matter on total nitrogen loss; and
  • Fails to consider surface water and nutrient transport, as well as critical landscape factors (for example, differences in topography and geology which can cause overland flow, a significant pathway for nitrogen loss).

The Panel concluded “…we do not have confidence that Overseer’s modelled outputs tell us whether changes in farm management reduce or increase the losses of nutrients, or what the magnitude or error of these losses might be. Although some of Overseer’s components […] appear sound, these coherences are outweighed by overarching structural problems. We, therefore, consider that Overseer’s structure is not adequate to provide more than a coarse understanding of a farm’s nutrient losses (except for surface flows since these are not included in the model). It cannot reliably estimate how changes in farm management would affect those losses.

It is important to note that the Panel did not assess Overseer’s modelling of greenhouse gases, nor some of the strengths of Overseer, such as its ease of use, its data files, nor its use as a social tool to encourage farmers to adopt farm management strategies that would successfully reduce a catchment’s nutrient load.

Government’s Response

The Government acknowledges that Overseer, in its current state, does not provide reliable results across the range of farming and growing situations it is currently used for.

The Government is therefore exploring, and intends to put in place one or more of the following options within the next 12 months:

1. Create a new risk index tool; and

2. Develop a next-generation of Overseer to address the Science Advisory Panel’s concerns; and/or

3. Using greater controls on practices and ‘inputs’ to manage nitrogen loss (including amendments to the National Environmental Standards for Freshwater); and/or

4. A completely new approach to understanding and managing diffuse nutrient loss risk (which might include, for example: real-time monitoring at a local scale; a tool that bases risk on characteristics of land; a new nutrient loss model).

In the meantime, the Government supports the continued use of Overseer until a better tool is available. But with an important proviso:

“Councils […] will need to be careful not to rely solely on Overseer modelling for their understanding of total nitrogen losses. This will be particularly important where nitrate-nitrogen is not the dominant form of nitrogen loss. Where existing plans provide for alternative modelling approaches or for control to be exercised using means not dependent on Overseer, those opportunities should be considered.”

Where to now?

Change is coming in the long term – whichever option(s) the Government ends up developing will be operational by at least 2024. This is so Regional Councils can include the new tool(s) and/or framework when they notify plan changes, which they are required to do in order to give effect to the National Policy Statement for Freshwater 2020. Ultimately, a new framework and/or new NES rules and/or calculations under any new or improved tool(s), may cause a shift in what can or cannot be done on farm. In other words, the intensity of farming activities undertaken, and/or amount of nutrients which can be discharged, on a farm may suddenly be more or less than currently calculated under Overseer.

Further changes in approach may be coming to cover the interim – the Panel’s findings pose a challenge for Regional Councils that have embedded Overseer into their Regional Plans and resource consents, particularly in light of the Government confirming a better approach is needed and that Overseer ought not be relied on as the sole assessment of nitrogen losses. MfE is currently working with Regional Councils to develop further guidance about the appropriate use of Overseer in its current form.

In Canterbury, ECan is also looking at the reports in light of its use of Overseer as part of its nutrient management controls. FEP Audits and decisions on Plan Changes 2 and 7 to the Land and Water Regional Plan, are temporarily on pause until then. Although ECan’s website currently indicates that consent applications will be processed as usual, we understand that some Farming Land Use consent applications are being placed ‘on hold’ for now.

How can we help?

While there will still be uncertainty for the time being, we can help you put your best foot forward. If you are wanting to acquire, divest, lease or re-finance farming property, talk to one of our specialist Agri or Resource Management lawyers. We can assist you in preparing to go to market, re-negotiating or tightening up your contracts, reviewing resource consents for compliance, and undertaking due diligence.

Johanna (JK) King
021 917 140

Sam Chidgey

021 221 1388

IMPORTANT: The information in this article is of a general nature only and does not constitute legal advice. Tavendale and Partners do not accept any liability for any reliance placed on the information contained in this article and shall not be liable to you or anyone else for doing something, or omitting to do something, on the information provided above.