The need for an improved in-paddock testing method to identify on-farm lime sources efficiently and accurately, and provide information about their quality and characteristics, was identified by growers specifically in the Kwinana East Port Zone of Western Australia.
GRDC engaged a team of researchers from GHD to explore technologies, new to agriculture, that could rapidly identify potential on-farm lime sources.
Status of acidic Western Australian soils
Seventy per cent of soils in south-west Western Australia have been shown through regular surveys to be acidic. Continued monitoring shows that this constraint, in the majority of the affected areas, is remaining static or deteriorating.
Lime is applied by growers to neutralise acidic soils and improve growing conditions for crop production. It is often sourced from coastal regions but transport costs can make this expensive. To reduce this cost, in some regions growers have identified soils on their properties that contain carbonates which are able to neutralise acidic soils.
To date, growers have been assessing the potential neutralising ability of these soils with a range of methods; variations of field based ‘fizz tests’, various kits or by sending samples to a laboratory for more comprehensive analysis.
Dr Clare Engelke, GHD’s project leader for the research says that an extensive desk-top review of technologies and economic analysis was undertaken and, at this point in time, none of the technologies were time-effective.
“This outcome prompted us to focus our effort on investigating the potential of improving and standardising the way growers do field-based ‘fizz tests’, in order to make the test more reliable and informative.”
Reducing costs through improved on-farm testing
Regardless of the future availability of rapid testing, laboratory tests will still be necessary to determine if there are any contaminants contained in the on-farm lime sources that could pose problems when broadly spread across paddocks.
It was identified that with improved on-farm sampling, farmers would be able to identify sources with high neutralising value more accurately. This would result in fewer samples requiring further testing, reducing costs for growers.
Review of new portable technologies
“We undertook a desk-top review of a range of portable technologies that are being used for elemental and mineralogical identification in other industries, particularly the mining industry, for their suitability for grain growers to identify on-farm lime sources.” Dr Engelke says.
These technologies included:
- Portable X-ray fluorescence
- Visible and near infrared spectroscopy
- Portable X-ray diffraction
- Short-wave infrared spectroscopy
- Laser induced spectroscopy
- Fourier transform infrared spectroscopy.
The review identified the two most promising portable technologies; portable X-ray fluorescence and visible and near infrared spectroscopy for field testing. These portable technologies can cost up to $40,000 per unit.
The two technologies were then further evaluated using 20 soil samples from the Kwinana East Port Zone.
Some locations were existing pits already in use as a lime source, while other locations were new and had not previously been investigated as on-farm lime sources.
It is important to note that effective neutralising value is affected by grain size and the carbonate content of the soil.
“We struck a complication here as technologies such as portable X-ray fluorescence do not determine grain size. Additionally, they analyse elements, and carbonates are compounds. So, the results must be processed in order to get a result that provides a carbonate content, and subsequent effective neutralising value,” Dr Engelke says.
“Although the technologies assessed have potential for use on-farm, they do not provide a rapid analysis, which was one of the drivers of the project. The cost of the technologies is not the limiting factor, but rather the length of time required to assess samples, and further work required to establish scientific confidence in the results.”
“As part of the evaluation we also reviewed the commonly used field-based ‘fizz test’ and found that this had a 98 per cent accuracy,” Dr Engelke says.
The ‘fizz test’ involves adding an acid to the soil sample and observing the level of fizz that results.
Growers are using different acids, if they use the same method with the same strength acid, they can potentially compare results in a shared database, thus improving the power and reliability of this method.
“Our findings suggest that growers can refine their technique used in the ‘fizz test’ as a tool to rapidly assess on-farm lime sources.”
GHD has recorded a demonstration video of the method used in laboratories, and produced a written method, adapted for use on-farm (see new resources).
A public review document comparing the portable tests is available from the GRDC.
Economics of on-farm extraction of lime
The research conducted by GHD included an economic comparison of using coastal lime against on-farm lime sources (without crushing and screening) to understand whether it is viable to incorporate the new technologies into growers’ systems.
Based on the deposits from the Kwinana East Port Zone that were tested and analysed, results suggest that on-farm lime can deliver marginally higher economic returns than commercial lime sand, depending on the quality of the lime deposits.
Figure 1: Comparative cost of on-farm versus commercial lime for 20 samples across the Kwinana East Port Zone (unincorporated and incorporated scenarios). Source: GHD Pty Ltd
The iLime app, developed by the Department of Primary Industries and Regional Development, with co-investment by the GRDC, was used to assess costs and outcomes and compare the long-term economic returns of these two liming strategies using a number of assumptions including the cost of using the best identified portable rapid lime test.
Sensitivity analysis was completed to compare the returns when lime is unincorporated versus incorporated into the topsoil and the results are shown in Figure 1.
As can be seen in Figure 1, performance of the 20 on-farm lime samples was highly variable according to the sample’s effective neutralising value, ie its ability to change the soil’s pH.
The results highlight the need for growers to understand the quality of the deposits before investing in extraction and spreading.
More information: Jo Wheeler, 0438 292167, Jo.Wheeler@grdc.com.au