Micronutrients or trace elements are often suspected to be deficient in some Australian cropping regions. Some trace element applications are now routine. But recent trials in areas with reported deficiencies have shown little response to micronutrient applications.
In southeastern Australia, 23 trials were run on wheat, barley and canola crops. The trials tested response to zinc
(Zn), copper (Cu), manganese (Mn) and boron (B). Most sites did not respond to trace element applications. The exception was one site which had a spectacular yield response to Cu application.
The lack of response may be due to:
- growing varieties more tolerant to micronutrient deficiencies
- earlier sowing resulting in bigger root systems that are more efficient at taking up trace elements.
In 2015-16, a wet season, trials in Western Australia had similar results. Some crops responded to Mn in drier conditions. There was no response from Cu regardless of application method.
The trials suggest that soil testing and paddock history are not robust predictors of yield limiting micronutrient deficiencies. Tissue tests are more accurate in identifying micronutrient deficiencies.
What we should do differently
Where a micronutrient deficiency is suspected, use tissue testing to confirm the diagnosis. Visual observation of deficiency symptoms in plants is a valuable tool, when confirmed with tissue tests. If required, apply nutrients during the crop cycle, or at sowing for following crops.
Be aware that seasonal conditions exacerbate the expression of micronutrient deficiencies. Dry surface soils inhibit Cu uptake. High N applications can induce Cu deficiency because N limits the movement of Cu from old leaves to new growing tissue. Usually this only impacts on crop growth and yield where Cu supply is low in the surface soil.