Tissue test the best way with micronutrients

Tissue test the best way with micronutrients


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Farmers are being advised to conduct tissue tests to check for micronutrient deficiencies rather than rely on visual assessments.

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Ross Brennan says tissue testing for micronutrient deficiencies is the most accurate and timely way of identifying any potential issues.

Ross Brennan says tissue testing for micronutrient deficiencies is the most accurate and timely way of identifying any potential issues.

A LEADING authority on crop micronutrients has warned growers not to rely on picking up visual clues of micronutrient deficiencies.

Ross Brennan, recently retired from the WA Department of Primary Industries, said by the time crops were visually showing signs of a lack of micronutrients it was too late fix.

Speaking at Incitec Pivot Fertilisers’ Agronomy Community forums Dr Brennan said it was a better idea if farmers got plant tissue samples tested.

“This is the most reliable method because it tells you what the plant is getting from the soil,” he said.

He said soil tests could be of benefit, but overall were less reliable than tissue tests.

“Soil testing has some value for zinc and to a lesser extent copper, in that it can tell you if you’re well and truly above critical soil concentrations, but when you get towards the responsive range, it’s less precise.

He said visual crop monitoring left farmers behind the eightball, with yield losses of up to 20 per cent possible with copper deficiency before it could be visually picked out.

“If you rely on seeing deficiency symptoms, it’s often too late to recover from the yield setback, so a better approach is to review fertiliser history and tissue test regularly,” he said.

In terms of managing micronutrients, Dr Brennan said putting out some copper and zinc upfront was a safe strategy.

“Applying a bit of copper or zinc with your starter fertilisers is one way, and a quite cheap way, to avoid these hidden losses,” he said.

“If you do find a severe deficiency, which is pretty rare these days, arrange a foliar application without delay.

“You can expect good responses to foliar sprays if they’re made early, with chelate forms of zinc and copper tending to be more effective.”

While widespread severe deficiencies have largely been addressed in Australia’s cropping country, Dr Brennan said there were still deficiencies occurring in individual cases and opportunities for growers to improve yields by supplying optimum levels of micronutrients.

Some of his recent research has focused on the residual value of copper and zinc applications in cropping country and their reapplication in minimum tillage situations, which can be difficult, given copper, in particular, is best incorporated through cultivation.

 “The greater the number of cultivations mixing the copper through the soil, the better it is for plant availability,” he said.

“Smaller granules increase the number of particles in the soil, increasing the chance of root interception.”

However, with minimum tillage used extensively in modern cropping systems and growers preferring easy to handle granulated fertilisers, not powder, these options are unlikely to be widely adopted.

“One option is to band between the rows on a different inter-row line each year for several years, to improve spatial availability through the soil,” he said.

“Another option might be to apply micronutrient fertilisers on diagonal rows.”

He said some growers might consider a strategic cultivation of the top 10 cm of soil every five to seven years following an application of micronutrients.

“We know that copper and zinc will last a long time and continue to be effective in crop for many, many years,” he said.

Dr Brennan advised against copper seed coatings, because they could negatively affect seed germination.

Spraying liquid copper on the soil surface was also shown to be ineffective unless followed by cultivation.

“As agronomists, we just need to keep in mind the principles of what works with micronutrients,” he said.

“They’re not mobile so they need to be in the soil where the roots can intercept them and if you can increase the number of particles through the soil, that can help.”

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