You can't manage what you don't measure.


The GroundTruth Lysimeter incorporates the best features from the design of the leading research lysimeters used by major NZ research institutions (column lysimeters and fluxmeters), but has a much greater area (equivalent to 15 column lysimeters or 95 fluxmeters). 

Statistically, one GroundTruth lysimeter is more accurate than a 12-fluxmeter site, and four have equivalent accuracy to the most advanced suction cup arrays used by New Zealand universities and crown research institutes.

Doesn't interfere with farming

Can be positioned almost anywhere in a paddock, completely below-ground and invisible, so it can be cultivated and grazed without harm. No need to remove equipment before cultivating - staff can just forget it exists. The only above-ground component is a suitcase-sized box at the fenceline (the autosampler), up to 150m from the lysimeter itself.


See what is happening today, so you can make decisions this season and actively manage your environmental losses. Don't just estimate what happened last year in an annual modelling exercise.


Automatically records drainage, day and night, and collects water for analysis. You just put the water sample in the mail.


Install the Lysimeter yourself for minimal capital investment. Autosampler available on a simple quarterly lease that includes all data management, repairs and nutrient analysis costs.

Frequently Asked Questions

What can it measure?

Almost anything. Total-N and Nitrate-N by default.

The GroundTruth Lysimeter collects physical water samples that are sent for laboratory analysis. By default, nitrogen (Total-N and Nitrate-N) analyses are included in the price of the system. However additional analyses such as other species of nitrogen, phosphorus, sulphur, potassium, calcium, magnesium, microbes and even chemical residues can be conducted. If a laboratory can detect it, GroundTruth can measure it.

How hard is it to use?

Very easy. Almost everything is completely automated.

You just need to send samples for analysis. When alerted that a sample needs to be posted, you : 
  1. Turn on a switch, and collect the water that is pumped out a tube in a pre-supplied sampling container.
  2. Send the container by courier for analysis.
Where can I use it?

Freely drained soils. Most intensively farmed land in NZ.

The GroundTruth Lysimeter is appropriate to use in all freely drained soils where the water table does not rise above 1m depth, on flat to gently sloping land. It can be installed in boulders of up to 30cm diameter. This means it is appropriate for most intensive land of concern for nutrient leaching losses.

It should not be used in soils with a dense, poorly draining subsoil, where digging up and repacking this subsoil would break it up and result in higher drainage volumes than would normally occur. If the water table rises to within 1m of the surface, the lysimeter may be flooded and overestimate drainage. Like any lysimeter, it is also likely to give misleading results on steep slopes where water is more likely to move sideways in the soil rather than vertically. Further tools are planned to address some of these situations.

How many do I need?

Rule of thumb: One per arable / horticultural crop. More under grazing.

The GroundTruth Lysimeter accurately measures leaching loss from a 10m long strip of a paddock. In ungrazed situations (arable / horticulture / industrial), if this strip is representative of the paddock as a whole, the result will reflect paddock-average leaching losses.

Grazing introduces more variation in nutrient leaching losses, due to animal urine patches. The number required will depend on the accuracy needed. For research-level accuracy, 3-4 lysimeters per plot should be sufficient. However the precise number required will depend on the situation. We strongly recommend seeking independent statistical advice.

We will soon be publishing a technical paper addressing this in more detail. Contact us if you have further questions.

When should it be installed?

Between crops, or whenever the soil is not saturated.

The lysimeter may be installed in 1 day (allow more time for your first installation), so can easily be installed between arable crops.
In pasture, it should be installed when the soil is dry enough to dig without making a mess of the paddock, and when pasture seed can be resown soon after installation. 
Summer installation allows measurement of leaching over the following winter.
Can I use it for regulatory compliance?

Not yet. But talk to your regional council.

The GroundTruth lysimeter has not yet been approved by any council for use for compliance measurements. However, it has a lot of potential for this use, particularly in horticulture, arable, free-range chickens, land-applied wastewater, and point-sources like composting systems and standoff pads. Any situation that is poorly supported by existing models can be measured directly using the GroundTruth System.

As it does not generate whole-farm loss it is not a direct drop-in replacement for models such as Overseer, so cannot completely replace modelling on pastoral and complex arable properties. However, it can be used in critical source areas to get more accurate data in those areas of highest concern.

Actual year-to-year losses can vary greatly, while regulations and models are written assuming long-term-average leaching losses. For regulatory use, losses need to be monitored for a number of years to allow rolling-average losses to be compared with regulatory limits.
Does this replace Overseer?

No. It complements Overseer, by working where Overseer does not. And it can be used to check and improve Overseer estimates.

Overseer is a whole-farm model. It estimates the nutrient loss from an entire farm system, taking account of many different factors. Overseer also estimates P loss via runoff, which the GroundTruth system does not do.

However, Overseer can only estimate losses when the crop, livestock, soil, fertiliser etc have been researched in enough detail to accurately represent them in the model. There are many situations that cannot be modelled in Overseer at all (e.g. many key arable and horticultural crops, free-range chickens, composting), and many more situations where Overseer will give a number but the accuracy of that number is questionable as it is based on minimal research.

For more information on what Overseer can and cannot do, see page 47 of the Parliamentary Commissioner for the Environment's report on Overseer.

The GroundTruth system measures actual leaching losses - at one location on a property (or a small number of locations if several lysimeters are installed). It can measure leaching losses in any situation, under any crop or even industrial sites, whether or not that situation has been researched before. Small seed crops, vegetables, industrial hemp, "biological" management, free-range chickens, industrial wastewater, composting windrows, standoff pads, silage heaps - if you can install the lysimeter under it, you can measure it.

However, the result will only tell you what the leaching loss is in the paddock that you installed the lysimeter. It cannot tell you whole-farm losses, unless the farm is simple enough that the entire farm can be monitored by installing a number of lysimeters in representative areas.

Overseer and GroundTruth therefore do two completely different things. They complement each other, and can even be used together.

  • GroundTruth can determine the actual leaching loss from key areas of concern, while Overseer can estimate losses from the remainder of the property.
  • GroundTruth can be used for model development, to measure leaching losses from situations not yet accounted for in Overseer, to provide the data necessary to include that situation in a future update of the model.
  • GroundTruth can be used to validate Overseer results, to check that its estimates are accurate and improve future estimates.
  • GroundTruth can be used alone to determine losses from systems that are not yet supported in Overseer.

The biggest limitation of Overseer is that the results of the model have not been actually checked against real on-farm data for most situations (see Table 3.1 in the PCE report) , so on many pastoral farms and all arable, horticultural and forestry properties the accuracy is largely unknown. This is not the fault of the model developers, it is simply because little data has been available to check the model against - and there is little data because, to date, it has been too difficult and/or expensive to collect that data. There is an urgent need for a large number of measurements of actual on-farm leaching losses in order to verify and improve Overseer. The GroundTruth system provides a cost-effective way to collect this crucial data.

It is vital to have access to both models and real measurements. To date, the industry has generally been limited to models alone. GroundTruth adds a vital tool to the toolbox that was always needed. It is not a replacement for models, rather it is the complementary tool that should have always been used alongside them.
What does "real-time" mean?

Every 10 minutes (electronic data), within 2 weeks (chemical analysis)

During rainfall and drainage events, rainfall mm, drainage mm and drainage water electrical conductivity are delivered every 10 minutes.

Within around 2 weeks of sample delivery, actual drainage water nutrient concentration and total annual leaching loss to date will be available.

How long will it last for?

At least 10 years.

The Lysimeter is designed to last indefinitely. It is not yet known how long it will last in actual usage, but should be in excess of 10 years.

The Autosampler is offered on a lease basis, and will be repaired and/or replaced whenever required to also operate indefinitely.

When the system is no longer required, the Autosampler is returned to Grounded and the Lysimeter remains in the ground (not affecting farm operations as it is buried deeply). If desired, a new Autosampler can be connected at a later date and measurements can be resumed.

How does the lysimeter compare to other methods?

Similar principles to leading research methods, but far larger.

The lysimeter has been designed to combine the best features of leading research techniques, and even improve upon them, to achieve very high accuracy. The diagram compares an average end-on cross-section of the below-ground construction of the GroundTruth lysimeter with the leading alternatives used in New Zealand. Column lysimeters (50cm diameter) are usually unsuitable for widespread use in the field (due to high cost and sidewalls that prevent cultivation), but are the 'gold standard' technique for research in controlled laboratory conditions. Fluxmeters (20cm diameter) are being used in a national trial investigating leaching losses under arable and horticultural crops. Suction cups are used in a range of field trials. 60cm is the depth that Overseer claims to estimate leaching losses at. 1m is the depth preferred by arable researchers for leaching measurements.
Lysimeter comparison

The GroundTruth lysimeter combines the best features of Column Lysimeters and Fluxmeters, in order to achieve maximum accuracy while still allowing cultivation. 

  • To accurately capture drainage, column lysimeters use side walls to trap water, while fluxmeters use a hanging wick to create a suction to pull water into the lysimeter. The GroundTruth lysimeter uses both.
  • Like fluxmeters, the GroundTruth lysimeter uses repacked soil to minimise costs. However the GroundTruth lysimeter can be installed in boulders of up to 30cm diameter, while for practical reasons the Fluxmeter can only be installed in soils that are able to be augered to 2m depth.
  • The depth of soil solution samplers varies, but is often quite shallow as depicted here as they cannot be used in gravelly subsoils. Solution samplers are tiny, drainage water can miss them entirely, and they have many other disadvantages also.
  • The GroundTruth lysimeter is many times larger than any other option (hence more accurate as it takes a more representative sample of drainage).
A technical paper will be published here soon explaining the differences between these options in more detail. However the advantages of the GroundTruth system are so clear that several leading research organisations are currently in discussions with Grounded about using the GroundTruth system for their own research. This is a robust, scientifically sound system.
What are the implications of repacked soil?

Reduced accuracy in year 1, and only suitable for freely drained soils

With repacked soils:
Year 1: The results may not reflect the paddock average leaching, but comparisons between treatments are still valid.
Year 2 and on: The results should be close to the paddock average. Some residual effects of disturbance may still remain, diminishing over time, but the results will still be considerably more accurate than models.

To install the GroundTruth Lysimeter (or a fluxmeter), the soil is removed, with the topsoil placed to one side and the subsoil to the other, and then repacked. This changes the soil in a number of ways. However, in a freely draining soil with a sand or gravel subsoil, these changes are acceptable. The subsoil disturbance does not severely alter soil structure, as there was little structure to begin with. And the topsoil disturbance is similar to a deep cultivation event, so is not completely unusual - it may cause a pulse of additonal leaching in year 1, but should have minimal long-term effect. 

A soil with a dense clay subsoil would however be substantially changed by repacking. This is why the GroundTruth Lysimeter is only suitable for freely drained soils.

A future technical paper will discuss this issue in more depth. Repacked soils have been used for leaching loss research internationally for over a century, and are used today in New Zealand for fluxmeters. All methods have drawbacks, but repacking is a reasonable compromise to obtain cost-effective leaching loss measurements from freely drained soils.
How much does it cost?

Contact us for a quote

The GroundTruth System is priced to minimise capital investment, shifting most of the expense into a quarterly lease fee that includes all data management, nutrient leaching analysis and equipment repairs. This allows the majority of the cost to be considered "operating expenditure", allowing it to be requested from most research funding agencies. 
As a general rule, expect GroundTruth to cost more than modelling, but substantially less than any other research tool.
The actual cost will depend on the situation. Contact us today to discuss your requirements.
When will it be available?

Right now

Equipment is manufactured on demand and will have a lead time of several weeks or up to 2 months depending on the volume of the order, so please contact us for a quote ASAP if you are interested.



A 2-page printable brochure explaining the GroundTruth system, with photographs.

Technical: Lysimeter

A technical report explaining the lysimeter itself and the advantages / disadvantages when compared to other leaching measurement systems.

Coming soon.

Technical: Site design

A technical report explaining the number of lysimeters required to accurately measure leaching loss in a range of situations.

Coming soon.



The initial development of the lysimeter was part-funded by a generous AgMardt grant, which was immensely beneficial in kick-starting lysimeter development.


The Foundation for Arable Research funded the installation of an initial prototype lysimeter + autosampler.

Callaghan Innovation

Financial support from Callaghan Innovation for business development advice is greatly appreciated.


The vast majority of the system development cost has been self-funded by Grounded.