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2023 - Overseer Redevelopment Programme Report

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  • Updated

A redevelopment programme for Overseer to address key concerns raised by the Science Advisory Panel review was established following advice from a technical advisory group in late 2021.

  • The development programme was delivered by Overseer in conjunction with researchers from NIWA, Plant & Food Research, Manaaki Whenua/Landcare Research, and AgResearch.
  • MPI reconvened the TAG in July 2022 and September 2022 to review the Overseer redevelopment work. The TAG noted that the redevelopment work was completed to a high standard. Further, the TAG agreed, in principle, that the redevelopment work improved the Overseer model and addressed the key technical concerns raised in the SAP review around Overseer’s ability to estimate nitrate loss. This increased their confidence in the use of Overseer for the proposed limited-use case of estimating nitrate leaching.
  • The TAG, however, suggested that validation work, comparing the Overseer modelled nitrate loss against observed nitrate loss, should be completed before they were comfortable endorsing Overseer’s use as an input into freshwater farm plans. The TAG noted that this validation work should be used to inform guidance material for regional councils.
  • Overseer completed validation work that compares Overseer modelled N-loss against N-loss observations. The work was peer-reviewed by AgResearch and shared with the TAG in mid-June 2023.
  • The validation used internationally accepted performance measures for nutrient models. These performance measures show that the Overseer model produces “very good” results in estimating nitrogen leaching from grazed pastures and “satisfactory” and “good” results for cropping data. This analysis further improves the confidence in the use of Overseer for estimating nitrate loss from grazing systems and, importantly, in cropping systems used for summer and winter feed on dairy and drystock platforms, a key source of nitrate loss in some dairy systems. 
  • The Overseer validation work is comparable with other work that shows a strong correlation between measured and modelled nitrate loss data. This provides further confidence for users of the Overseer model.
  • MfE has revised its guidance for how Overseer may be used to support regulation. The guidance has been revised considering the outputs from the Overseer redevelopment programme.

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