Key points
- WA growers are proving it is economic to use on-farm sources of lime to ameliorate soil acidity
- Native vegetation can be good indicators of on-farm lime
- On-farm lime sources need to be tested for efficacy
- Application rates are higher than most other products and lime dumps in paddocks should be considered to reduce handling time
Soil acidity is commonly treated using a source of carbonate - traditionally lime - transported on to a farm. Usually sourced from the coast, the cost of this lime, together with freight and spreading costs, makes it an expensive, sometimes uneconomical, option for dealing with soil acidity.
Central and eastern wheatbelt growers in Western Australia have been locating sources of naturally occurring soil carbonate on their own farms and assessing whether these 'stack up' against coastal lime in terms of more cheaply increasing soil pH and removing acidity as a constraint.
Finding lime on-farm
Deposits of on-farm lime have been found on silty clay loam soil types, which are light pink to brown in colour and have a very fine-textured topsoil.
White carbonate nodules are found on, or near, the soil surface and generally contain a fine, white, powder-like substance when crushed.
On-farm lime deposits are almost always found on areas that have well-below-average crop yields in all years, except those with well-above-average rainfall.
These soils typically have soil pH values greater than 7.0, are affected by transient salinity (indicated by high electrical conductivity values) and have soil potassium (Colwell) values above 500 to 1500 milligrams/kilogram in the zero to 10-centimetre layer.
Adapted native tree species are good indicators of carbonate in the soil - specifically black morrel (Eucalyptus melanoxylon), red morrel (Eucalyptus longicornis) or salmon gum (Eucalyptus salmonophloia) and the understorey species Melaleuca.
Western Australian growers are economically using on-farm lime sources to more productively farm acid soils.
Testing the value
The carbonate within an on-farm lime deposit will fizz when an acid such as vinegar is applied to the sample. This provides a very quick and cheap method to assess whether the soil contains carbonate and how reactive it may be.
The samples that show the most potential in the fizz test should be further examined through laboratory analysis.
A bulk neutralising value (NV) test provides a carbonate content percentage for the entire sample and does not take into account the particle size of the carbonate.
Dry and wet sieve NV analysis, which involves first filtering the lime samples through different-sized sieves and measuring the NV of each portion of the sample, can then be carried out.
Detailed information is available from the 'Locating and assessing on-farm lime sources' booklet.
Extracting and spreading
Extracting on-farm lime with a bulldozer or excavator is possible if the operator works in shallow runs, scraping off five to 10cm of product in one pass as this avoids large clods.
On-farm lime sources that do not have large blocks of lime, rock or tree roots may not need to be screened, which will reduce the time and cost of the operation.
If screening is needed, it can take place before the product is stockpiled, before it is taken to the paddock or as it is spread.
Morrel soil with carbonate nodules near the surface. This source has a neutralising value near 50 per cent. Photo: The Liebe Group
Application rates can be determined by using the iLime app and are usually much higher than most other products, which can cause logistical issues.
The distance travelled while spreading may require lime dumps to be strategically placed in each paddock to reduce the time spent travelling empty and loading.
Economics
On-farm lime needs to cost significantly less than using other sources of lime, such as the equivalent amount of coastal lime, or it will not be worth the extra effort.
Some growers who are using on-farm lime have found it to be $30 to $40/hectare cheaper than lime from the coast when large tonnages are processed.
Typical costs are $3 to $4/tonne to dig up and screen, $3 to $5/t for transport to the paddock and $6 to $7/t for spreading. This works out to be about $60 to $80/ha at an application rate of 5t/ha.
More information: Joel Andrew, Map IQ, joel@mapiq.com.au, 0429 917 743; Liebe Group, eo@liebegroup.org.au, 08 9661 1907; locating and assessing on-farm lime sources.