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Forest & Bird says the country needs strong rules on farming inputs, like fertiliser and stocking rates, after a report has shown problems with the widely used on-farm pollution modeling tool Overseer. 

Authors of an independent peer review of Overseer, initiated by Ministry for the Environment (MFE) and Ministry for Primary Industries, concluded they do not have confidence in the tool’s estimates of nitrogen pollution from farms.   

“Water quality in Aotearoa has been degraded by intensive farm systems, and we have known for a long time the limitations of Overseer for calculating the exact amount of nitrogen pollution entering waterways,” says Forest & Bird Freshwater Advocate Tom Kay.  

“We should put rules in place to restore our rivers that don’t rely on individual farms using an inaccurate model to work out their pollution,” says Mr Kay.  

“We need to stop pollution at its source with limits on polluting inputs going into our farming systems, like the limit recently introduced for synthetic fertiliser. This will also have benefits for reducing greenhouse gas emissions since fertilisers account for about 15 percent of the carbon footprint from dairy farms.”  

“We also need meaningful limits on pollution outcomes in our rivers, including a nitrate limit (DIN) of under one milligram per litre.”   

Overseer is jointly owned by Ministry for Primary Industries, AgResearch, and the New Zealand Phosphate Company/Fertiliser Association (an association funded by fertiliser companies Ballance Agri-Nutrients and Ravensdown).  

The internal workings behind the Overseer software, which guides farm management, have largely been a secret and was only shared for the purposes of this review.  

“The results of this review show how difficult it can be to quantify nutrient losses at a farm level and why peer review and transparency for software used for regulation is so important.” 

“The Government simply needs to get on with implementing strong rules that limit the pollution entering our rivers, and set pollution limits, like a DIN limit of under 1mg/L, that keep freshwater healthy for plants, animals, and humans,” says Mr Kay.  

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