Burrumbuttock farmer Joe Corrigan says soil testing based on electromagnetic (EM) surveys and yield maps allows him to save costs, as he can split his paddocks into zones and apply fertiliser at variable rates.
"It's just about minimising your cost and maximising your production by putting out the right amount of fertiliser," Mr Corrigan said.
"We don't have any control over the weather and little over prices at the end of the year, but what we can control is our costs."
Mr Corrigan, who farms 1200 hectares, including 900ha of cereal and oilseed crops, said he had employed an agronomist to do an EM survey of his property.
"My average paddock size is 40ha, within the 40ha each paddock is split into three zones based on the EM survey.
"The soil testing of the three zones is done at the same GPS position every two to three years so the trends can be graphed, that informs the variable amounts of lime and nitrogen we put on.
"Nitrogen behaves differently depending on the soil type, while we're using lime to slowly raise our pH levels to around 5.5."
He said he also used yield maps from as many as three previous harvests to create zones for phosphorus replacement.
Mr Corrigan said the EM mapping cost around $10 per hectare, but it was well worth it when you looked at how variable your inputs could be.
"For example, we averaged 90kg of urea per hectare for canola last year but the variance was between 60 and 120kg," Mr Corrigan said.
Senior Research Fellow (Soils) at the Graham Centre for Agricultural Innovation, Dr Jason Condon, recently spoke to growers about getting more from soil testing at a webinar organised by Holbrook Landcare Network.
He said soil testing was crucial for informing growers as to whether their soil fertility was limiting yield and for enabling them to monitor the results of their management over time.
"If you're not soil testing you don't know what impact you're having long term on the land you're responsible for," Dr Condon said.
Cheap methods for adding precision
He had several suggestions for reducing the cost of soil testing, including using free or low cost software for mapping and data storage.
"You are able to get quite a lot of information about soil variability through free imagery, like Google Earth Pro, Sentinel-2 or yield maps," Dr Condon said.
"They're able to be used to identify areas of different plant growth or soils, then you can use that information to choose the areas that you sample in instead of randomly going out into the paddock.
"That allows you to create zones of management and that's a really cheap way of getting some precision into your program."
Dr Condon said his co-presenter at the webinar, Sue Briggs from CSBP Soil and Plant Analysis Labs, Victoria, spoke about the web-based platform called DecipherAg, which allowed growers to log their sampling points, select analyses and record their test results.
"Rather than sticking a soil report in a drawer, it's logged online and is easy to access," Dr Condon said.
He said farmers could also reduce costs by reducing the number of components tested for.
"You can make savings by just getting an analysis of the values you actually use, like soil pH and plant available phosphorus," Dr Condon said.
"They're quite cheap to monitor so they could be monitored every year and then something like soil carbon could be measured every five years."