On-the-go testing methods have developed rapidly in recent years and Bill Burgess, Technical Programs Manager for Society of Precision Agriculture Australia (SPAA) said there is no doubt that the technology works.
"It's not so much a question as to whether or not it works, because we know it does," Bill said.
"It's a question about the accuracy of the information we get from on-the-go testing and what we can surmise from that level of accuracy."
WHAT IS IT?
Proximal soil testing methods use sensors to either directly measure soil properties or to measure other parameters that can be related to soil properties. They differ from conventional laboratory soil analysis in that they do not require physical soil samples to be taken and analysed.
These sensors may be (and often are) mounted on a vehicle that enables soil testing to be done ‘on-the-go'. The on-the-go technology currently available does not take continuous readings, but rather takes measurements at specific, pre-determined places in a similar pattern to how traditional physical soil samples would be taken.
Different types of sensors and different approaches to proximal soil testing can detect different soil parameters, including chemical, physical or biological properties, or a combination of parameters.
"The best definition of on-the-go testing is the fact that someone can enter your gate and have some data collected by the time they leave the paddock," Bill said.
"That's becoming more and more common.
There's not quite as much accuracy with that as there is with lab testing but it can be surprisingly accurate, depending on how many samples are taken.
"My gut feel is that most soil types would need at least 2-3 samples per hectare if you are taking cores or looking at pH and variability mapping. Much less than that and you'll start to lose variation accuracy.
But you're likely to see decreasing ROI per data point if the number of samples is considerably higher. Ultimately it costs you more money the more work you get done, so there needs to be a practical upper limit.
"Most on-the-go systems still only test the top 5-10cm of the soil. There's a couple of different systems around and some do have the ability to go a bit deeper. To get subsoil, we still need cores and lab tests. But we can see some good results from some of the onthe-go systems that are around now.
"Phosphorus, nitrogen and pH are the three most significant on-the-go tests available that are relevant to the way we farm in Australia."
By way of a cost comparison, pH proximal sensing costs around $15/ha at around 8-10cm deep and according to Andrew Harding, Senior Consultant Soil and Land Management, PIRSA, over the past three years, around 120,000 hectares have been proximally sampled to date.
IS THE DATA USEFUL?
"I think if someone is ‘starting out' with a low database and there's not much history of testing on the property, then on-the-go is the way to start," Bill said.
But he advises caution before rushing out and booking someone to come and take measurements.
"You need a consultant that can get you data in a scientifically rigorous manner but also present that data in a way that can provide you with some actionable results, ideally a prescription map that you can put in and apply amendments from," Bill said.
WHAT WILL YOU DO WITH IT?
Bill said it was important to know how you are going to use the data before you collect it.
"You may not have the VRT to spread lime in response to your pH maps, but there may be a local contractor who can apply with variable rate. In that case, make sure the maps your consultant generates are compatible with what your contractor needs - get them talking to each other, rather than you interpreting results from one to the other.
"Even with VRT, some spreading equipment is not as accurate as the results that can be achieved with soil testing," Bill said.
That's an important point when you are considering whether something will be accurate enough for the job at hand.
Bill likens it to a high definition television screen - the image on the newest TV may be far superior to an older model, but if your eyes don't enable you to tell the difference, the extra definition is of little use. Similarly, if you have very accurate soil testing results but your spreading equipment is not so finely calibrated, the extra accuracy in the data is of little use.
"Data coming out of lab tests, is definitely more accurate that on-the-go systems at this stage," he said. "But if you are looking to save some money on inputs and improve yields then the on-the-go system is probably a good place to start.
"It's about being real about what you actually want. You want something that you can work with. It does not necessarily have to be to a research or university testing level."
Bill advises doing your research before you start, including what it will cost you and the results you will get. "Look into consultants and their reputations," he said.
"There is a lot of discussion about what is a fair price for soil sampling, but I would encourage people to think about what is a fair price for actionable results, versus a pretty map or even extreme accuracy you simply can't match.
"It's unfortunately new enough that it's hard to compare prices between consultants.
There are some very knowledgeable and reputable people in the industry who are still struggling to price on-the-go testing."
WHAT COMES NEXT?
"It's fair to assume that in the future, on-the-go soil testing will become cheaper and more accurate," Bill said.
"Inevitably, whether or not a manufacturer has thought about it yet or not, it will be cheap enough to read across the width of a machine - and test and treat in the same pass.
"It might be that it's reading pH and applying lime accordingly, or reading available N and applying in response.
"It could explode with a lot of weird and wonderful things in the next couple of years - more and more testing a wide range of parameters and broader applications."
For now, Bill's take home advice is to look for actionable results.
"If you are going to have a yield map use it for something," he said. "The data is only as valuable as the action you can make from it."
Bill Burgess, Society of Precision Agriculture Australia
0400 279 969
Andrew Harding, Senior Consultant: Sustainable Agriculture
Rural Solutions SA Primary Industries and Regions SA - PIRSA
08 8842 6231