Results from a GRDC investment suggest that portable infrared technology could be used to determine the quality and neutralising value of lime.
With soil acidity on the increase across many parts of the southern region, significant effort is being made to find good-quality sources of lime to address acidity.
Agronomy Solutions director Dr Sean Mason is leading the investment, which aims to extend the use of infrared spectroscopy for measurement at a fine scale of selected surface soil properties that are important for farm management decisions.
Dr Mason says two factors determine the efficiency of a lime source for neutralising soil acidity: calcium carbonate content and particle size distribution.
These results are highly encouraging for the rapid and cheap analysis of lime sources to predict their effectiveness in ameliorating low soil pH.
"The higher the calcium carbonate content and the finer the material, the higher the effective neutralising value is," Dr Mason says.
"Lime recommendations are significantly affected by the quality of lime.
"Infrared spectroscopy has been shown to be able to accurately predict the amount of calcium carbonate in soils, in addition to soil texture and, therefore, offers the potential to quickly and cheaply assess the quality of a lime source.
"The current laboratory assessment of lime sources is time-consuming and costly."
In Western Australia, some growers are finding on-farm lime sources can be economic.
Comparative testing
To test the ability of portable infrared to predict the quality of lime sources, 31 samples submitted for lime analysis at Australian Precision Ag Laboratory in Adelaide were scanned in their natural state and compared to calcium carbonate level and effective neutralising value.
Dr Mason says highly accurate predictions were generated by portable infrared for measuring the calcium carbonate content of each lime source and, more importantly, the effective neutralising value.
Current efforts are trying to build on this calibration set. The true test of any calibration will be to test the prediction accuracy of a true unknown lime sample in a field setting, which will be done in later stages of the project.
"These results are highly encouraging for the rapid and cheap analysis of lime sources to predict their effectiveness in ameliorating low soil pH," Dr Mason says.
"This could save significant excavation costs for lime producers if it was deemed a source of lime was not economical as a soil neutralising product."
It could also lead to lime producers testing individual batches of lime to ensure growers are getting a product with consistent quality.
As part of this GRDC investment, Dr Mason's research is also focusing on the use of infrared for the prediction of a range of soil characteristics. such as organic carbon, soil moisture and soil pH, as well as pulse nitrogen content and fixation.
He says some exciting findings have come from the pulse nitrogen content and fixation research.
"Using infrared scans of the crop canopy, we were able to predict the biomass nitrogen content in lentils and chickpeas, which was related to the amount of nitrogen fixed by each crop," he said.
"This is an exciting result and suggests the infrared technology can not only predict wheat nitrogen content and, therefore, assist with in-season fertiliser decisions, but it can also assess the nitrogen fixation performance of a pulse crop and the amount of nitrogen that might be available for the following cereal or canola crop."
Project builds technology's potential
Dr Mason says the potential for the development of a commercial infrared spectroscopy service for lime quality has increased through outputs from this project.
"The range of important characteristics that can be predicted by infrared has already expanded (for example, lime quality and lime requirements) and is expected to increase even further," he says.
Increasing soil acidity levels is the subject of a separate new GRDC investment, 'New knowledge and practices to address topsoil and subsurface acidity under minimum tillage cropping systems of South Australia"'
The project will generate new information regarding lime movement and effectiveness when applied to the surface of different soils and environments in modern farming systems.
More information: Sean Mason, Agronomy Solutions, 0422 066 635, sean@agronomysolutions.com.au