An independent statistical analysis of data from the country’s most comprehensive farm management tool shows a downward trend in the amount of nitrogen loss per hectare from dairy farms in Canterbury.

OverseerFM is a decision support tool that assists farmers, growers, and their advisers to be environmentally and economically sustainable. It is used by farmers to understand the flow of nutrients on their farm from sources such as fertiliser and animal effluent.

The independent analysis of 1,269 farm records on OverseerFM shows a 27.5 per cent decrease in mean nitrogen loss per hectare over five years to 2021-22.

Jill Gower, chief executive of Overseer Ltd, says the analysis is a valuable contribution to the ongoing conversation about improving farming’s environmental footprint in Canterbury.

The analysis finds that across about 302,000 hectares of dairy production land, the mean nitrogen loss per hectare in 2016-17 was 63.8 kg per hectare. This had reduced to 46.2 kg per hectare in 2021-22.

The assessment provided estimates of trends in nitrogen loss after considering the size of dairy farms in terms of herd size and productive area. The analysis assesses within-year variability in nitrogen loss across farms and sub-regions and concludes that despite this variability, there is a statistically significant downward trend year-over-year.

For the entire Canterbury region, the OverseerFM data reported an average decrease in nitrogen loss of 5.7% per year for the six years from 2016–17 to 2021–22. The Waimakariri sub region had the smallest reduction of 3.6% per year, whereas the Ashburton sub region showed the largest reduction of 6.6% nitrogen loss per year.

“OverseerFM is a crucial decision support tool providing information and insights to individual farmers and growers,” says Ms Gower.

“The purpose of this analysis was to establish whether Overseer could also provide a reliable source of data at a regional or sub-regional level.

“In Canterbury, where the regional council and processors require dairy farmers to use OverseerFM, this analysis confirms that our picture of the number of farms and extent of dairy farming is consistent with other sources of information.

“Equally important, the data scientists found no evidence farmers were attempting to ‘game’ the model by manipulating their inputs. This helps give confidence in Overseer’s results.”

An independent science programme has recently reported back on a comprehensive evaluation of Overseer and found that Overseer’s estimates performed well against measured losses of nitrate (oxidised nitrogen), she says.

“This report, using OverseerFM data, shows nitrogen losses from Canterbury dairy farms are trending in the right direction. It’s important to keep in mind that this data measures nitrogen loss to soil on farms, not nitrogen levels in rivers– that is, the outcomes of farm system choices. OverseerFM also does not record other impacts on river water quality such as urban development and population growth in river catchments.

“With Environment Canterbury currently developing a new Regional Policy Statement, we hope that this is a useful contribution to that process.”

“Importantly, the report provides reason to be confident that OverseerFM information can shed light on how farmers are adapting their systems over time. It shows that when farmers have good information and support tools, they will make necessary changes to improve their environmental footprint.”

Please contact us for a copy of the report.