Question: Target trace element soil concentrations
What target trace element (Zn and Cu) soil concentrations should a farmer be aiming for on duplex mallee soils? (Cascade, WA)
The value of soil tests in diagnosing micronutrient supply is limited. Soil test values give a general view of the potential response to added micronutrients such as zinc and copper but their reliability is not as good as tissue testing done at the correct time. Having said that, the general critical levels for soil zinc and copper – measured as DTPA extractable – are published. These are for soil samples taken from the 0-10 cm level.
For Copper, the critical DTPA soil test value for wheat are reported.
For wheat, the critical DTPA soil test values depend on soil organic carbon, soil pH and clay content. The general critical range reported for the sands of WA were 0.12 to 0.27 for DTPA zinc. The critical value for wheat on duplex soils from South Australia is given as 0.8 mg/kg. These values are taken from Soil Analysis: An interpretation manual.
I would also suggest you use an ASPAC and FertCare soil testing service. These two quality assurance systems check that the labs use calibrated and recognized soil tests and the laboratories that have been shown they can deliver reliable results. The regional soil testing services provided in Western Australia are reputable and reliable and have good research information that supports their interpretation systems.