A new review out today of farm nutrient management system Overseer seriously damns the tool, and shows the model is leading to continued contamination of water and pollution of climate, says Greenpeace. 

Overseer is a software program designed by fertiliser companies and widely used by farmers. It is touted by the dairy industry and relied upon by regional councils as the number one tool for tracking nutrients – such as synthetic nitrogen fertiliser – applied to and leached from farms.  Expert reviewers of Overseer concluded that they ‘don’t have confidence in the ability of the model to predict nitrogen loss.’

The report notes ‘serious’ and ‘significant’ concerns with the model. Greenpeace lead agriculture campaigner Christine Rose says that undermines confidence in the system that has supported dairy conversions and intensification.

“Because Overseer has been used to defend the overapplication of synthetic nitrogen fertiliser and has been embedded in resource consents, the whole dairy model and its environmental impacts are a house of cards,” says Rose.

“Instead of relying on an industry tool that does a bad job of measuring nitrate pollution as it seeps into rivers or contaminates people’s drinking water, the Government must deal to the problem at source by phasing out polluting synthetic nitrogen fertiliser altogether.”

Over three hundred and fifty thousand tonnes of synthetic nitrogen fertiliser are used every year in New Zealand. 98% of this fertiliser is sold by two companies, Ravensdown and Ballance. When applied to land, synthetic nitrogen fertiliser converts to nitrate, which seeps off land into waterways and groundwater.

Rose says that given evidence of how devastating nitrate contamination is for freshwater and human health, the Government cannot rely on a model that fails to accurately predict and track how much nitrate is entering waterways and groundwater.

“From the start, Overseer has been peddled by fertiliser companies as a means to sell more fertiliser – the very thing that is wrecking rivers and driving intensive dairying,” says Rose. 

“Overseer has been used for years as an excuse for allowing too much synthetic nitrogen fertiliser and too many cows to be crammed onto the land, despite worsening freshwater quality and drinking water contamination that threatens people’s health.

“That’s no surprise given that Overseer is managed by the fertiliser companies that make a killing off farmers dumping synthetic nitrogen fertiliser onto the land. Ballance boasted strong financial returns for the past year, at the expense of human and environmental health.”

The peer review found fundamental flaws that undermined confidence in the model, including the use of historic weather averages instead of daily data. It fails to account for ‘potentially significant nutrient losses’, especially from heavy rainfall events. Given nitrogen leaching is hugely impacted by rainfall, the reviewers found this to be an issue. 

Overseer also fails to account for droughts, variation in water and nutrients in soil, surface water, nutrient flow and critical landscape factors. The reviewers found the model applies ‘a steady state model for a dynamic, varied system’.

“The fact the experts appointed by the Government have given Overseer a thumbs down exposes the lies on which intensification is founded, and which has allowed the application of massive amounts of fertiliser and cows crammed into paddocks without properly regulating harm to rivers and drinking water,” says Rose. 

“If New Zealand is to continue using Overseer for regulatory purposes, it must be publicly owned and all the underlying assumptions in the model published publicly. 

“The peer review recommendations include options to improve Overseer while more robust solutions are developed. But that’s like fiddling while Rome burns. What we need are input controls, lower cow stocking rates, and a phase out of synthetic nitrogen fertiliser, starting now.”


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