Independent statistical analysis of data has revealed an encouraging downward trend in nitrogen loss from Canterbury dairy farms.
The data from farm management tool Overseer FM shows the amount of nitrogen loss per hectare from dairy farms in Canterbury has decreased almost 30% in the past five years.
OverseerFM 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 1269 farm records on OverseerFM shows a 27.5% decrease in mean nitrogen loss per hectare over the five years 2016-2017 to 2021-22.
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 kilogram a hectare. This had reduced to 46.2 kg/ha 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 on year.
Overseer chief executive Jill Gower said the analysis is a valuable contribution to the ongoing conversation about improving farming’s environmental footprint in Canterbury.
For the entire Canterbury region, the OverseerFM data reported an average decrease in nitrogen loss of 5.7% a year for the six years from 2016–17 to 2021–22.
The Waimakariri subregion had the smallest reduction of 3.6% a year, with the Ashburton subregion showing the largest reduction of 6.6% nitrogen loss a year.
“OverseerFM … provides information and insights to individual farmers and growers. 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,” Gower said.
In Canterbury, where the regional council and processors require dairy farmers to use OverseerFM, this analysis confirms that the picture of the number of farms and extent of dairy farming is consistent with other sources of information.
Equally important, Gower said, the data scientists found no evidence farmers are 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).
“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 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,” Gower said.
“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.”