Tissue testing a health check-up for micronutrients
Author: Rebecca Barr | Date: 11 Jun 2015
Growers are urged to consider tissue testing to diagnose micronutrient deficiencies.
Trace elements can be depleted by high yielding cropping, resulting in the potential for deficiencies to become more common.
Incitec Pivot technical and development manager Charlie Walker, who is a member of the GRDC trace elements project advisory committee, says tissue testing can be compared to blood testing in humans.
“When someone isn’t feeling 100 per cent they may get a blood test so their doctor can assess if there’s anything going on. In a similar fashion, growers who are seeing something that doesn’t look right in their crop can use tissue testing to diagnose micronutrient deficiencies,” he said.
Unlike macronutrients such as nitrogen and phosphorus, micronutrients, or trace elements, cannot be reliably assessed using soil tests alone due to their low concentration in the soil. Because of this, tissue testing is the best way to confirm a suspected micronutrient deficiency.
The micronutrients most likely to limit production in Australian soils are zinc (Zn), copper (Cu), manganese (Mn), molybdenum (Mo) and boron (B).
The four-year GRDC project is aiming to test and update the rules and advice given to growers on micronutrient management.
“The current rules were set around 30 to 40 years ago, and in the meantime a lot of things have changed, including a move to more intensive cropping, no-till and stubble retention and significant improvements in yield. This has potentially changed the situation enough that the old rules need to be updated,” Mr Walker said.
One example of how practice change has altered the presentation of deficiencies is controlled traffic farming, where deficiency symptoms sometimes appear in bands between windrows.
“In this example, a grower may see stunted or off-colour growth in bands. They could then perform a tissue test from where the crop looks good and one where it doesn’t look so good, and the comparison may diagnose a deficiency. Depending on the nutrient, they may be able to correct the deficiency in the same season, such as copper, but even if it can’t be treated in that year, they will be ready to take action in the following season,” he said.
When performing tissue testing, it is important to sample at the right crop development stage, the correct plant part and sample size. Hygiene is also important in sampling as contamination with soil or sweat may give misleading results. An example of one laboratory’s instructions for tissue testing are shown in Table 1.
Table 1: Example tissue testing sampling instructions*
|Crop Type||Growth Stage||Plant part||Number|
|Cereals||Early to late tillering||Youngest expanded leaf blade||100 leaves
|Lupins||Early vegetative stage and before flowering||Youngest open leaves||100 leaves|
|Faba Beans||Early vegetative stage and before flowering||Youngest open leaves||50-100 leaves|
|Field Peas||Early vegetative stage and before flowering||Youngest open leaves||100 leaves|
|Oilseeds||Early vegetative stage and before flowering||Youngest open leaves||100 leaves|
*Source: Nutrient Advantage Lab Services (http://www.nutrientadvantage.com.au/)
“Growers should remember that soil conditions can affect chemistry and micronutrient availability. Just because certain soils have never had deficiencies in the past doesn’t mean it won’t happen now. In some cases growers have been improving acid soils with liming. But with this comes decreased availability of zinc at the higher pH,” he said.
While zinc deficiencies have historically been a challenge with alkaline soils, Mr Walker says he has seen isolated pockets of deficiencies in the slopes of New South Wales, where increased yields and liming practices have reduced zinc availability.
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