Three projects completed for OverseerFM last year have underlined the software as a fit-for-purpose tool for farmers.
The science projects were part of the work that came out of the 2020 government review of Overseer. They assessed the tool’s reliability and whether any updates or improvements to the Overseer science model were necessary.
The projects investigated the impact of using different climate datasets, incorporating deeper-rooting plants and model sensitivity and uncertainty analysis for N-leaching estimates.
The investigation into the OverseerFM model’s use of long-term average monthly climate data, including a comparison with daily climate inputs, concluded that the current long-term climate dataset remains fit for purpose, Overseer Limited chief executive Jill Gower said.
It showed there was no real difference between the two datasets, OverseerFM business development manager Alastair Taylor added.
“What we have got is perfectly fine.”
Analysis of the impact of deeper-rooting plants such as lucerne and maize and some pasture species on N uptake below 600mm found that the uptake will generally occur only when there is insufficient N available above 600mm.
Gower said the sensitivity and uncertainty analyses confirmed that the Overseer science model is most sensitive to climate and soil inputs and that these factors contribute the most to the uncertainty of N-leaching estimates.
“Overall, the uncertainties for the OverseerFM estimates were in the range of other environmental models and the results were comparable for dairy, beef and sheep and cropping farms.
“The model sensitivity and uncertainty work really emphasised the importance of a farm’s geophysical characteristics – where it is, what climate it is farmed in, things which our farmers consider each and every day.”
Taylor said it showed that OverseerFM was useful for comparing a farm system with itself and others similar to it, but it was not useful to compare it with a table.
“You shouldn’t be trying to regulate in that manner. If you look at proposals like Healthy Rivers in Waikato – that’s a reasonable use of Overseer.
“In that case, you’re comparing farms with like farms in a similar area. It’s a reasonable use of the software.”
This was in contrast to other plans that were more arbitrary, he said.
Two science model research projects are still to be completed.
These projects are improving and simplifying the crop model and incorporating the transportation of water and nutrients through different soil layers down to 600mm into the current drainage model. This project is currently going through validation work, which will inform decisions on any drainage model change.
Those crops included grains, vegetables and forage crops.
The two science research projects are on track for completion early this year and once complete will conclude the science programme of work started in late 2021.
“We know some farmers and growers have had some questions about OverseerFM following the technical review of the Overseer model released in 2021,” Gower said.
“This research increases confidence in the fitness for purpose of OverseerFM. It shows that OverseerFM remains a useful decision support tool that allows farmers and growers to make informed decisions about their farm management practices, improve their productivity and profitability, and improve their environmental impact.
“Overseer Limited is working hard to improve the understanding of OverseerFM and the way it should be used,” Gower said.
“One way to think about OverseerFM results is to view them more like a weather forecast than a measure you might obtain from a rain gauge or thermometer. Weather forecasts provide valuable insights and are continually improving, but nobody expects them to be 100% right 100% of the time.”
