Three farmers in Southland have teamed up with experts to see how they can mitigate nutrient loss to the environment on their farms beyond what regulations require.
The project was a collaboration between Thriving Southland and Land Water Science, funded by AgMardt.
It used LiDAR, drone-based photogrammetry and groundbased radiometric survey to create a high-resolution landscape model of the farms.
As understanding farm geography is key to understanding the effect of mitigations, the models were used to identify watersheds or basins, and identified location discharge points where water joins streams, or leaves a farm property.
At a recent field day held on one of the case study farms, experts discussed what modelling showed about the farms’ landscape, how that influenced mitigation options, and talked challenges and costs.
Arable farmers Blair and Jody Drysdale grow wheat, barley, oil seed rape, hemp, peas, lucerne and oats on their 321 hectare farm in Balfour, Southland.
Drysdale said he wants to stay viable while minimising the farm’s environmental footprint.
The farm property is mostly flat with elevation ranging between 152m above sea level in the southeast corner of the property and 160m above sea level along the northern boundary and centre of the property.
The farm also has a dairy grazing and sheep enterprise, with 21.7ha leased out for tulip production.
Drysdale applies on average 123kg N/ha/yr.
A report on the project by Thriving Southland, titled Understanding Your Landscape’s Resilience, Beyond Regulation, says the farm is in an alluvial terrace between the Waimea Stream and the Longridge Stream.
Both the streams flow in a southerly direction, and join into the Mataura River approximately 30km south-east of the property.
The property sits on the area known as Balfour Fan.
The fan is a well-known “nitrate hotspot”, with some of its groundwater zones exceeding New Zealand and World Health Organisation levels for safe nitrate concentration in drinking water, the report says.
Due to the nature of the aquifer – not being flushed by alpine or hill country water – the concentration of nitrate in some areas continues to build.
“Variability in climate, topography, geology and soils significantly influences the type of contaminant and severity of water quality outcomes,” the report says.
Clint Rissmann from Land and Water Science said a property should be thought about as a whole connected system. Groundwater has travelled kilometres down gradient and discharges far away from the source.
Land and Water Science used a high-resolution physiographic approach to map the inherent and varied susceptibility of the landscape to land use activities at property scales.
The 20mx20m resolution of the mapping provides a more resolved picture of contaminant susceptibility than current 1:50,000 physiographic environments maps, he said.
The report says the maps are of sufficient resolution to show paddock-scale variation in susceptibility.
“Radiometric surveys pick up radiation from the ground and is sensitive to soil texture, organic carbon and chemistry. We go out, dig holes and ground-truth it. We build a picture.”
Rissmann said understanding soil characteristics means they can understand if there will be leaching or recharge after a rain event, or what challenges a specific soil type holds.
For example, sector one on the Drysdales’ farm is “good arable soils, well drained, good at filtering pathogens, no issue with E coli, good at filtering organic carbon, good at retaining phosphorus, but has the Achilles heel of nitrate leaching”.
Drains and tiles also allow nitrate to move through to streams.
Where the soils on the farm are imperfectly to poorly drained or the water table is shallow, runoff does not continually happen, with one or two large rain events often responsible for most of a farm’s nutrient losses, he said.
“The property is variable. We used the combined survey datasets and ground truthing to split the farm into sectors that have different topography (slope), soil characteristics, hydrology and as a result different water quality outcomes.
“I’m interested in the landscape. Land use is the primary driver of outcomes, it doesn’t matter if you’re urban or rural. But it’s what’s under the hood that determines the type of outcome you get.
“If everyone looked at tributaries over their farm and across their catchment and talked to their neighbours about what they can do, then mitigations will be a huge service to the catchment.”
Rissmann said often the numbers that regulators will put out on, for example, nitrogen reduction targets seem exceedingly high and hard to comprehend.
However, the collective impact of multiple mitigations should not be underestimated.
For example, research shows that wetlands, sediment traps or woodchip bioreactors can make a big dent in contaminant losses to waterways, with some studies reporting reductions in sediment and phosphorus by 70-80%, and up to 90% removal of nitrates.
“That may be from a gold standard wetland or bioreactor, but at a paddock scale that is immense. Even a 30% reduction is huge. There’s value in small things targeted in the right place. Mitigation at catchment level accrues,” Rissmann said.
A high-resolution radiometric survey across the 1400ha of the Balfour Fan showed most of the farm is Benio soil.
Across the majority of the property soils are well to excessively well-drained, due to a high content of quartz sands coated with clay.
Due to their drainage characteristics and extreme weathering, the soils and aquifer materials of the Balfour Fan are less able to remove nitrate than younger soils and aquifer materials.
From west to east across the property various soil types have differences in draining ability and nitrate susceptibility and each covers an area as little as 23.8ha up to 64.8ha, meaning different mitigation options are viable depending on the site.
Farm systems and environmental consultant Miranda Hunter works with farmers to assess what environmental mitigations will cost and what they will mitigate, then uses modelling to give them options to choose from, depending on the goals for their business and their finances.
For the Beyond Regulation project, Hunter modelled mitigation options and their impacts on total GHG profile, nitrous oxide change, change in N loss, nitrogen surplus change and P loss, and the costs and impact on the farm system.
“This gives a sense of how big a lever we can pull with mitigation.”
On the Drysdales’ farm, options included targeting nutrients to meet plant requirements, crop rotations, selling crop residues, developing wetlands and alternative land use by establishing 2ha of chestnuts.
Farmers can mitigate both what goes into a landscape and what comes from it and in essence have an ambulance at both the top and bottom of the cliff, she said.
Hunter said in some cases farmers consider large scale land use change as a mitigation option.
However, large scale change needs investors with deep pockets, a market and often involves skills that farmers do not have on farm.
Large scale change should not be undertaken primarily for environmental reasons but rather as a consideration for succession or changing farm goals.
Most want to make incremental changes and to learn in the process, an approach Hunter said is safer.
Project lead at Thriving Southland Richard Kyte said the long-term result from the project is to build farmer and catchment group confidence in their ability to deliver their own solutions, on their farms, using the right data and information.
Drysdale said he will now do measurements around water flow and laser tile levels, which will help to determine if a wetland or a bioreactor is most viable as a mitigation option.
In Focus Podcast | A local approach to rural mental health
Bryan talks with Minister for Mental Health Matt Doocey about how the Government plans to tackle the mental health crisis in rural communities. Doocey says local organisations are best placed to meet the needs of their communities and he outlines a new decentralised approach.
