DairyNZ says it will continue to update its Dairy Effluent Storage Calculator (Desc) to keep it fit for purpose after it was labelled “a dog” that had never been ground truthed.
DairyNZ general manager of farm systems and policy David Burger.
The dairy-farmer levy funded organisation, based in Hamilton, issued a statement from DairyNZ general manager of farm systems and policy David Burger after Agricultural Business Associates natural resource engineer Fred Phillips questioned the effectiveness of the tool at a meeting of the Waikato Federated Farmers executive.
Phillips claimed the Desc model, which had never been ground-truthed on low-risk soils, significantly over predicted storage requirements on free draining soils.
He estimated 120,000 hectares, or about 17 per cent of the 685,542ha dairy land in the Waikato, was incorrectly designated as High Risk including about 60 per cent or more of the region’s peat based agricultural soils.
Agricultural Business Associates natural resource engineer Fred Phillips
“At best this is just irresponsible,” Phillips said. “The excessive storage being recommended as a result of this misinformation has a cost of about $400 per hectare or $48 million and it has zero environmental benefit.”
Burger said until there was new research or advice supporting the assumption that high infiltration rates on low-risk soils was not an environmental issue, it was reluctant to update the tool, and the good practice advice it provided, based on advice from experts and independent scientists.
“DairyNZ will continue to update the Desc to keep it fit for purpose and welcome all engagement on this,” Burger added.
DairyNZ provides Desc to dairy farmers to demonstrate their system can comply with regional council rules, while maximizing their use of a key farm resource.
It provides the farmer with the required storage volume assuming irrigation occurs on every possible day at the chosen irrigation rate and pumping volume.
More storage provides the ability to differ irrigation during busy times of the year and more strategic use of a valuable farm nutrient.
“We’ve worked directly with Fred and others over the past few years to keep modifying the calculator including updating general useability, the platform format and its performance on free draining soils, and we have also undertaken a review of the tool with scientists from Massey University and AgResearch,” Burger said.
“Following this review, we made changes to how irrigation is scheduled on low-risk soils. Specifically, the tool now allows for more irrigation days than the old version, as application depths below 10mm reduce due to the Desc combining rain drainage and farm dairy effluent (FDE) irrigation drainage caping at 10mm. The old version did not allow for irrigation on a drainage day.”
DairyNZ recommended dairy farmers engage with an Irrigation New Zealand accredited system designer when installing a new effluent pond to identify regional council requirements.
“The advice from AgResearch specialists at the time was that higher rates of infiltration on free draining/low ponding risk soils remains an environmental risk, not only for nitrogen but also for the fate and transport of pathogens and phosphorus.
“The risk to try and avoid is farmers putting in a system with very low storage now, who may then need to invest in a new system in future. Having enough storage provides flexibly in management during unusual wet seasons and better use of the nutrients captured. “
Waikato Regional Council’s Strategy and Policy Committee voted in November for the council to undertake desktop-based geospatial work to update the existing map of soil risk for farm dairy effluent.
It also voted to approach DairyNZ to discuss the potential revision and update of the Desc user guidance regarding the sources and use of soil information for establishing soil risk as input data for the calculator.
An effluent irrigation system helps the grass grow on a Waikato farm.
