Managing Soil Acidity by Targeting Lime to Low PH Zones

Precision Agriculture’s Andrew Whitlock speaks about the problem of soil acidity, and how to manage it.

Soil acidity is a problem with the large areas of Australian cropping country.

Most of the work we’ve been doing has been in South Australia and in Southern Victoria and Southern New South Wales.We’re down in the path of managing lime variably because it a critical factor of the crop nutrition. We know there’s a very good relationship between pH and nutrient availability.

Soil Acidity is Easy to Measure

We know that it’s an easy thing we can measure, so precision ag often starts with managing soil ameliorants like pH. soil acidity and salinity, so variable rate lime is a natural starting point The soil sampling we do is on a grid, so we do a one hectare grid across the paddock. And that’s on a planned grid through the program that we use and so we map that out before we get to the paddock and we’re going to take one pH sample at each of the one hectare grid points.

Satellite imagery linking in with other special data sets is really important, so we do a lot of work with understanding other data sets and looking for relationships between the NDVI or the biomass, maps we can produce through satellite imagery, and pH maps, and also yield maps. So we definitely want to look for relationships between when these constraints that we can identify and see if they are actually having an impact on plants.

Soil Biomass Relationship to PH

So, we know there might be poor biomass but we don’t understand why in some cases. So, we can use just a look for that relationship, maybe there’s low biomass, and there’s a relationship with pH. About twelve months ago we purchased the first vera-soil pH detector. and I was asked to rapidly test paddocks and produce zones of high and low ph.

And so then once we’ve got the zones we will then go and do some strategic soil samples in these areas 0-10 cm soil tests and send that away to a lab and then get the full soil test and convert that information in a prescription map. We would then get the farmer to work with their agronomist to look at their results from the to analyze the information and determine the final lime application rates.

Savings in Lime Due to Better Soil Measurements

It varies from paddock to paddock. Most paddocks are around 15 to 25 percent saving in lime, but we have had examples where we’ve had up to 85% saving in lime. Managing soil acidity through variable rate lime spreading is a fantastic starting point for precision ag. We know from the mapping we’ve been doing over the last 2 years, the return on investment is very high, and if we can achieve a 10% saving on the lime, we can pay for variable rate lime straight away.

There’s been very few cases where we haven’t been able to have immediate reductions of input costs and lime.