Trials measure mapping profitability

Image of people in a paddock of stubble

Frank D'Emden (left) and Dowerin grower Andrew Todd are assisting the GRDC RCSN with trials investigating various mapping layers for variable-rate technology.

PHOTO: Cox Inall Communications


Owners: Andrew Todd, wife Jacinta and parents Geoff and Tricia

Location: 'Laharna Farms', Dowerin

Farm size: 4000 hectares

Enterprises: 100 per cent continuous cropping

Average annual rainfall: 310 millimetres

Soil types: highly variable, from predominantly duplex sandy loam over clay and sand over gravel to areas of white sand and yellow sand clay loams

2014 cropping program: 45 per cent wheat, 25 per cent canola, 20 per cent barley, 5 per cent lupins and 5 per cent field peas

The trial is looking at the use of PA tools with mapping layers, such as electromagnetic induction (commonly EM38), gamma radiometrics and normalised difference vegetation indices (NDVIs), to develop more ‘high-tech’ VRT zone application maps.

A trial on the Todd family’s Dowerin property, initiated by the GRDC Regional Cropping Solutions Network (RCSN) this year, is assessing the benefits, economics and pitfalls of different precision agriculture (PA) mapping layers for use with variable-rate technology (VRT).

Trial coordinator Ben White, from the Kondinin Group, says the high cost of some map layers has resulted in some reluctance by central and northern wheatbelt growers to invest in this technology, which may – or may not – be able to generate returns when used to create input application maps.

Related video

Preview screenshot of video - activate link to watch video

Follow the link in the image above to hear more about the GRDC RCSN-funded VRT trials at the Todds’ Dowerin farm and sites at Mingenew and Carnamah or visit to watch this video on YouTube.

Mr White has worked with specialist PA advisers Precision Agronomics Australia (PAA) and consultants from Agrarian Management and Planfarm to set up the RCSN Kwinana West and Geraldton-funded VRT focus paddock trials at the Todds’ property and two other sites at Carnamah.

These trials were established on soil types common to those regions. Some of the sites also have RCSN-funded soil water probes (installed for other projects) that are being used for further data integration.

“We are looking at which map layers are the most valuable and worth the investment for input subscription map development,” Mr White says.

For each focus paddock site, input zone maps using EM38, gamma radiometrics, retrospective yield, NDVI-biomass, soil sampling and analysis, topographic maps, in-crop imagery, satellite imagery and paddock history have been developed – for lime and phosphorus prior to seeding, nitrogen during the growing season and potassium where potential benefit was identified.

After harvest there will be a comparison analysis of the economics, benefits and constraints of zone variance management for each type of map layer/technology.

For the Todd family it is the ‘edges’ of low and high-production zones in paddocks that they want to better define and manage with VRT.

Andrew, his wife Jacinta and parents Geoff and Tricia are self-described early adopters of PA tools, such as VRT, in their continuous-cropping operation.

They have used autosteer and GPS guidance at seeding since the early 2000s and, in recent years, started zoning paddocks into areas of good and poor productivity based on long-term cereal yield map data.

This year for the first time the family used VRT on seeding equipment for site-specific phosphorus replacement based on paddock zones.

“We got someone to help us load mapping data into the controller, but then we were pretty much on our own during seeding and it was easier than we thought,” Andrew says.

He says the main benefit of using this technology is better redistribution of inputs across paddocks, rather than fertiliser cost savings.

“We built a phosphorus-replacement strategy around trying to average the base rate we would have used if we had done our usual blanket application of 40 kilograms per hectare MAPSZC® as a starter fertiliser,” he says.

“We just distributed it differently and we expect VRT will allow us to do the same with lime and other inputs in future.”

Andrew says further investment into VRT and PA tools is inevitable as the family focuses on trying to lift production from the highly variable soil types across their property.

“For example, last year we had barley crops that yielded 4 tonnes/ha and 0.5t/ha in the same paddock,” he says.

“I have seen CSIRO data that indicates VRT can pay if you have more than 1t/ha variability in yield across a paddock.”

Andrew says he was not confident during this year’s seeding that the family’s paddock zones were defined enough, but wanted to try VRT to get used to the technology.

He says the next step is to better define these zones to ensure the system is not costing them money.

“The crop production we have seen visually in our paddocks over time is pretty much the same as what our yield maps are telling us,” he says.

“We have a good idea where our poorest and best areas are, but we are now trying to hone in on where these areas switch from one to the other and the underlying causes of variability.

“There could be 50 to 100-metre inaccuracies in the edges of zones and we want to make sure we close these gaps and change the rate of inputs in the right areas.” 

Precision agriculture

Some precision agriculture (PA) tools being used in Western Australia include:

  • global positioning system (GPS): provides location and time information in all weather conditions and is freely accessible to anyone with a GPS receiver;
  • soil testing: used in PA to determine the average nutrient status, some measure of nutrient variability and trends of fertiliser levels in paddock ‘zones’;
  • electromagnetic induction (EM or EMI): measures bulk electrical conductivity in the plant root zone;
  • gamma radiometrics: useful to help define soil type and characterisation and map the landscape by measuring natural gamma ray emissions of radioactivity;
  • normalised difference vegetation index (NDVI): the reflection of the crop canopy in red and near-infrared zones to help determine biomass; and
  • yield maps: provide data that can be used to estimate nutrient removal, gross margin, water use efficiency and delineation of PA management zones.

More information:

Andrew Todd,
0428 323 027,;

Ben White,
0407 941 923,

Applying PA – a reference guide for the modern practitioner is available at:

A Precision agriculture made easy GRDC Radio podcast is available at:


Pasture cropping with perennials


Ground Cover Direct

GRDC Project Code KDI00026

Region West