What is missing? Identifying and managing trace element deficiencies

Image of Nigel Wilhelm

SARDI scientist Dr Nigel Wilhelm believes early identification of trace element deficiencies is key to good paddock management.

PHOTO: Cox Inall Communications

It is a simple fact that micronutrients (or trace elements) are only needed by crops and pastures in small amounts, but they play a major part in maximising production.

So early identification of what is missing in the paddock is a key part of effective farm management, scientist Dr Nigel Wilhelm says.

New research into national micronutrient deficiencies, supported by the GRDC and overseen by Dr Wilhelm’s team from the South Australian Research and Development Institute (SARDI), has been examining tactics for detecting and managing trace-element deficiencies in crops.

“There is increasing concern thattrace-element deficiencies may become thenext nutritional barrier to lifting productivity,”he says.

“This is because our current cropping systems are exporting more nutrients to the grain terminal than ever before.

“There are a multitude of theories and ideas about how to identify these issues in the paddock, but the only foolproof way to find out what’s really going on is to do a plant tissue test.”

In southern New South Wales cropping zones he says the three most important trace-element deficiencies are zinc, copper and manganese.

“Of these three, zinc deficiency is probably the most important, because it occurs over the widest area and can severely limit annual pasture legume production and cereal grain yields by up to 30 per cent,” Dr Wilhelm says.

“Copper deficiency is also important because it is capable of causing total crop failure.

“If these three trace elements are not well managed further production can be lost through secondary effects, such as increased disease damage and susceptibility to frost.”

Zinc

Zinc deficiency has been identified on many soil types, from sandy to red-brown earths, mallee and calcareous grey and red heavy soils, and equally across both high and low-rainfall areas.

In pasture or grain legumes zinc deficiency causes shortening of stems and leaves fail to expand properly. So plants appear healthy but stunted, with small leaves.

In cereals, an early sign of zinc deficiency is a longitudinal pale-green stripe on one or both sides of the mid-vein of young leaves. The leaf tissue in this stripe soon dies and the necrotic area turns pale brown.

However, correction of zinc deficiency is possible via:

  • zinc-enriched fertilisers of the homogenous type, applied at two kilograms per hectare for severe problems for three to 10 years, depending on soil type; in addition, following the initial application repeat applications of 1kg/ha may be necessary (this can cost approximately $17/ha);
  • pre-sowing spray of zinc (incorporated with cultivation);
  • a foliar spray of 250 to 350 grams of zinc/ha can correct zinc, but will have no residual benefits and is not a long-term solution (cost is approximately $1/ha);
  • using a zinc-coated urea product, which is most useful when pre-drilling urea before the crop;
  • a new option with long-term benefits, which is the application of fluid zinc at seeding (ignoring the capital cost of the fluid delivery system, this application of 1kg/ha
  • can cost approximately $4/ha); and
  • seed dressings of zinc, but this will not completely overcome a severe deficiency or increase soil reserves (however, it can be used with soil applications and can cost approximately $3/ha).

Copper

Apart from shrunken heads in cereals, heads with gaps in them or ‘frosted’ heads, copper deficiency rarely produces symptoms in plants in the paddock.

“Leaf analysis to detect copper deficiency is critical, because it can produce devastating losses in grain yields and pastures with few symptoms,” Dr Wilhelm says.

“Traditionally copper deficiency has been corrected by applying copper-enriched fertilisers and incorporating them into the soil; most soils require 2kg/ha.”

Application of copper-enriched fertilisers can cost approximately $19/ha, while a fluid application at seeding can cost approximately $4.60/ha.

A foliar spray of copper, in the middle or late in the season, at a cost of about $4/ha, can also prevent a crop from suffering yield loss but has no residual benefits.

Manganese

The availability of manganese in the soil is strongly related to soil pH. Soils with a higher pH have lower manganese availability than soils with lower pH.

Manganese is also strongly affected by seasonal conditions and the availability is lowest during winter/early spring. It may also appear in cold, wet conditions.

“Symptoms of manganese deficiency first appear in young leaves, and results in plants that are weak, floppy and pale-green or yellow in appearance,” Dr Wilhelm says.

“Deficient crops can appear water-stressed, but the best way to diagnose the deficiency is a plant tissue test.”

The problem can be rectified by manganese-enriched fertilisers banded with the seed (3 to 5kg of manganese/ha), as well as one or two follow-up foliar sprays of 1.1kg/ha.

“Due to the high cost of manganese-enriched fertilisers, growers have tended to rely solely on foliar sprays, but getting the spray out early in the crop is key to a good result,” Dr Wilhelm says.

“Seed coatings with manganese used with foliar or enriched fertilisers are likely to be the most effective solution.”

Dr Wilhelm says growers and advisersshould keep in mind there are other trace-element deficiencies that occur inboth crops and pastures.

More information:

Dr Nigel Wilhelm,
0407 185 501,
nigel.wilhelm@sa.gov.au

Costs quoted in this article are offered as an approximate guide only. Product prices will vary from region to region, and season to season, and according to brand.

Useful resources:

Driving Agronomy podcast – Micronutrients
Micronutrients and trace elements fact sheet
MyCrop
International Plant Nutrition Institute

End of Ground Cover issue 123 (northern edition)
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