Project Status: Complete
Project Participants: Alcoa, Department of Agriculture and Food WA
Project Leader: Evan Jamieson (Alcoa)
Since being cleared for agricultural use, many of the Western Australian soils have acidified. Surface applications of lime and other neutralising amendments are the most common way to correct acidity. The use of alumina production by-products as "liming" ameliorants for agricultural soils affected by soil acidity presents an opportunity to alleviate the stress currently being placed on traditional lime sources
and their reserves.
These trials investigated the effectiveness of two new agricultural lime materials in high rainfall pasture and medium rainfall cropping farming systems. The key performance indicators were the soil pH at surface and through the soil profile; soil exchangeable cation and sodium and aluminium levels; soil nutrient levels and Phosphate Retention Index; plant productivity; and plant tissue analyses.
The lime sources were compared with standard lime sand and crushed limestone at three locations in Western Australia – one located on a property near Busselton (used for beef grazing of clover/ryegrass pastures), and two in medium rainfall inland areas on the Merredin and Newdegate Research Stations (in a barley cropping system). Each site was assessed for a range of soil parameters before the application of the lime treatments. Lime treatments were applied before the expected onset of consistent winter rainfall. Drought severely impacted upon results and so potted plant trials were added to the project scope.
At the highest rate of application, fine bauxite residue (Alkaloam®) and bauxite lime residue both worked as well or better than crushed limestone and lime sand in raising soil pH – which answered the key question being asked. Alkaloam and lime residue at most sites worked to a depth of 10 centimetres.
While the soil pH did increase, there were no significant increases in pasture productivity or wheat yield for any ameliorant during the trial period. This was attributed to the initial soils not being limited by exchangeable aluminium, hence plant growth was not limited by existing pH.
Metal analysis of potted trial plant tissue samples indicated that there were no deleterious effects on the plants from using lime residue or Alkaloam. As with previous trials undertaken using Alkaloam, there was an increase in total aluminium in the soil but no associated increase in exchangeable aluminium.
Lime residue and Alkaloam® should both be seriously considered as alternatives for Western Australia's declining agricultural lime reserves. The use of nitrogenous fertilisers and leguminous pastures in Western Australian agricultural systems is likely to continue into the foreseeable future and this is likely to result in continued acidification of the soil resource base.
Given these trials were affected by drought conditions, it may be worthwhile establishing a field and glasshouse trial which is more directly designed to assess plant response to the ameliorants under controlled conditions. It is recommended that further, more detailed cost-benefit analyses of the use of these materials be undertaken in order to develop a realistic plan for their utilisation in the lime marketplace.