Variable-Rate Liming Pays on Acidic Soils
Originally published by GRDC.
Adopting variable-rate lime application has shaved 40 per cent off one Victorian family’s lime bill. Nick Paterson farms with his partner Neka and parents Rowly and Judy at Mininera in the Western Districts, where soil pH levels can vary from 4.3 on paddocks with a long pasture history up to 6 on long-term cropping paddocks, with “everything in between”.
The more-acidic patches of the farm can have a considerable yield penalty, which Nick estimates to be between 15 and 20 per cent in canola crops on problem areas.
“We have previously just applied a blanket rate of lime based on the average pH of a paddock, but that wasn’t giving us the results we were after, particularly in areas that were more acidic than others,” Nick says.
To help better target problem areas, the Patersons had their paddocks’ pH mapped by Ballarat-based company Precision Agriculture four years ago and adopted a variable-rate system through their spreader to apply more lime where it was needed on acidic patches.
They lime paddocks once every three years and will have the property remapped after six years to see what the improvement has been.
“Since we have had the paddocks mapped for pH, we have noticed that those maps line up with the yield maps from the headers in that the yield drops on the more acidic patches. The rates we put out across one paddock might range from nothing to four tonnes per hectare,” he says.
“In the years since we started variable-rate liming we have noticed crops are more consistent across the paddock and less patchy.”
An added benefit of applying lime where it is most needed has been crops’ ability to handle waterlogging – a common constraint for growers in the Western Districts.
“A lot of the time the more acidic areas are also wet areas, so applying more lime in those patches has seen that soil become more alkaline and the crops in those areas develop better root systems to help them better handle waterlogging,” Nick says.
The savings from variable-rate lime applications have been significant, with Nick estimating every $1 invested on mapping and variable-rate technology has saved $5.
“We also had phosphorus mapped at the same time as we were getting pH mapping. That has allowed us to variable-rate phosphorus at seeding, which has saved some money off our fertiliser bill as well,” Nick says.
The Patersons have also had some pH testing done down to 15 centimetres, which has uncovered a problem with subsoil acidity on some of their paddocks.
Nick says the layer from 7.5 to 15cm below the soil surface is half a point lower in pH than the zero to 7.5cm layer.
They recently invested in a disc seeder and noticed that lime applications were not as effective as they had previously been, so have set about incorporating lime on some paddocks. “If the pH is below 5 then we will incorporate lime using a deep-ripper or chisel plough,” Nick says.
“The soil testing indicated that subsoil acidity is definitely an issue, so it is important we incorporate lime in some areas.”
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