Tissue test early for miconutrient deficiencies

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Fast fact

For the most accurate diagnosis of micronutrient deficiency use a tissue test of the plant’s youngest fully expanded leaf.

Photo of crop: on the left, the green wheat had two foliar sprays of copper, unlike the deficient wheat on the right, which was more vulnerable to hot winds at Edililie on the Eyre Peninula, SA< in 2015

The green wheat on the left had two foliar sprays of copper, unlike the deficient wheat on the right, which was more vulnerable to damage by hot winds at Edillilie on the Eyre Peninsula, SA, in 2015.

PHOTO: Nigel Wilhelm

While tissue testing is the most effective way to identify micronutrient deficiencies, it is best done before visual symptoms are observed to ensure there is time for foliar sprays to be effective

In recent years there has been renewed interest in micronutrients to maximise crop production in more intensive cropping systems. Many growers are concerned that crop root systems will need to work harder in minimum-tillage systems than in traditional cultivated paddocks to seek out micronutrients such as copper and zinc, which are immobile in the soil.

Anecdotally, growers have observed poor performance early in the season under drought conditions and suspected micronutrient deficiency could be a contributing factor. This has led to a perception of widespread deficiency of micronutrients. However, under dry conditions the availability of all nutrients, including micronutrients, is limited and, in many cases, crops can recover as conditions improve.

Given the speculation, the Western Australian Department of Primary Industries and Regional Development (DPIRD) and the South Australian Research and Development Institute (SARDI) compared the effectiveness of different micronutrient application methods as part of the GRDC’s More Profit from Crop Nutrition initiative. The micronutrients investigated were copper, zinc, manganese and molybdenum.

Tissue testing of crop leaves is the most effective way to test for micronutrients when a deficiency is suspected and is more accurate than soil testing. Sample only the youngest fully expanded leaf of the plant for the most accurate result.

If a deficiency is identified, treatment with a foliar spray can be effective. For manganese and zinc, tissue testing needs to happen early enough to leave adequate time to correct any deficiency, especially when you are on track for a high-yielding crop.

Researchers found foliar sprays of manganese and zinc applied at early tillering, rather than when the crop was running up, produced the maximum yield response in our trials, despite most of the spray ending up on the soil surface. As manganese is readily fixed in the soil, foliar applications are less expensive and more effective than application at seeding.

In contrast, the timing is different for copper, which can be treated by foliar sprays as late as booting for cereals. However, copper foliar applications have little or no residual effect so follow-up treatment will be required at the next seeding.

For growers who suspect a zinc or copper deficiency, the most effective long-term strategy is application at seeding rather than waiting for visual symptoms to appear because once symptoms appear it can be too late for foliar sprays to make a big difference. In the WA DPIRD/SA trials, there were few visual symptoms of deficiencies, yet micronutrient applications occasionally resulted in yield increases of 25 to 30 per cent in WA and up to 70 per cent in SA.

Micronutrients can be applied at seeding as seed dressings, banded fluids or compounded onto fertiliser granules. However, seed dressings are not suitable for copper as they can decrease crop emergence. Where there is marginal supply of copper an application of nitrogen will exacerbate copper deficiency in wheat and barley.

Researchers found copper deficiencies in high-yielding crops on soils where this had not been seen before. But, in contrast, found no evidence of zinc deficiencies in trial work in WA and SA, despite zinc historically being the most widespread micronutrient deficiency.

Molybdenum may be required at seeding or as a foliar spray where soil pH is less than 4.8 because, unlike other micronutrients, its availability decreases with decreasing pH.

GRDC Research Codes DAW00239, DAS00146

More information:

Dr Ross Brennan
08 9892 8474

Dr Nigel Wilhelm
0407 185 501