Description:
Soil acidity impacts nutrient-use efficiency, and therefore agricultural productivity, through two main mechanisms.
In the topsoil (0-10 centimetres) low soil pH (high acidity) decreases the availability of key nutrients, whereas in the subsurface layer (deeper than 10 cm) toxic levels of aluminium at low soil pH reduce crop root growth and access to moisture and nutrients.
Applying agricultural lime is an effective method of managing soil acidity by increasing the soil pH.
Current lime use in WA agriculture is at 70 per cent of the estimated annual requirement to address current and ongoing soil acidification.
Better nutrient-use efficiency in the topsoil reduces runoff and potential contamination of waterways, while improved crop root growth in the subsoil increases the available area of crop roots to access water and nutrients.
Precision SoilTech samplet 152 farming businesses between 2019 to 2023.
Samples were taken to the Precision SoilTech lab for pH analysis in 0.01M calcium chloride solution (pHCa) and the results returned to growers in a spatial and PDF/excel format.
The spatial format retained the location information of the sample and allowed growers to view results in Google Earth, with the visual representation of colour coded soil pH results making it easy to interpretate the results to depth and at a whole farm level.
The PDF/excel document displayed results to depth with a corresponding 10-year lime recommendation attached to each site which have been calculated to provide the best return on investment for spreading.
Applying lime over a 10-year timeframe allows growers to budget for the application and understand the recovery and maintenance costs involved in managing soil acidity long-term.
DPIRD also collaborated with a leading agronomist to document growers long-term liming strategies and the resulting soil pH profile. Soil pH results from 30 growers were provided for this analysis. Using this historical dataset and iLime, we could understand how growers had effectively ameliorated soil acidity as well as model future scenarios, allowing growers to compare the return on investment for different rates of lime as well as the use of soil mixing.
Results:
In total 182 farming businesses (152 by Precision SoilTech and 30 by an agronomist), located in the Avon River Basin, were sampled for soil pH from 2019-2023 and in total, 40,470 soil samples were collected as part of this project.
The topsoil (0–10 cm) target pH is above 5.5 and critical pH is above 5, while for the subsoil depths (10–50 cm) the target pH is above 4.8 and critical pH is above 4.5.
In the topsoil, 56.5 per cent of samples were above target, 26.9 per cent between target and critical and 16.6 per centpc were below the critical level.
With 44 per cent of topsoil samples below the target pHCa of 5.5, there was an improvement on the results from a larger study conducted from 2005–2012 where 70 per cent of topsoils were below the target.
At subsoil depths of 10-20 cm, 72 per cent were above the 4.8 pHCa target, 16 per cent between target and critical and 12 per cent were less than critical.
For the 20-30 cm samples, 78 per cent were above target, 11 per cent were between target and critical and 11 per cent were below critical.
Subsoil pHCa also improved in comparison to the 2005-2012 study where 50 per cent of subsoils did not meet the target pH of 4.8.
At the deeper subsoil depth of 30-40 cm, 76 per cent of samples were above target, 7 per cent between target and critical and 17 per cent below critical, while for the 40-50 cm samples 84 per cent were above target, 6 per cent were between target and critical and 10 per cent were below critical.
These encouraging results show the positive efforts being made by growers to ameliorate acidity in the Avon River Basin, however it is also important to recognise that the growers involved in this study are proactive and already engaged with soil testing. Growers are encouraged to routinely soil sample to depth to ensure an above target soil pH profile is not only achieved but maintained long term.
Funding source:
DPIRD & DWER