Zinc deficiency in wheat: symptoms, risky soils and fixes

What zinc deficiency looks like

DPIRD (WA) describes these signs, usually on young seedlings early in the season:

• Patchy growth of stunted plants with short, thin stems and pale green leaves.
• Yellow patches on young to middle leaves between the mid-vein and the leaf edge, running lengthways. The stripe may be on one side of the mid-vein only.
• Those areas die and turn pale grey or brown. Parallel dead lines ('tramlines') beside the midrib are a key sign.
• 'Diesel-soaked' leaves that die about halfway along, so the leaf bends and collapses in the middle.
• Delayed maturity.

It is often short-lived. DPIRD says deficiency in young wheat emerging into drying soil usually disappears once rain re-wets the topsoil.

Soils and conditions at risk

• Heavily limed soils, sands and gravels, and alkaline grey clays (DPIRD).
• High pH (alkaline) and clay soils. Incitec Pivot says availability falls about 100-fold for each one-unit rise in pH, so alkaline clays can hold plenty of zinc that plants cannot get.
• Acid sandy soils, where the problem is simply low total zinc, and soils low in organic matter (Incitec Pivot).
• Dry topsoil. Zinc barely moves in soil and becomes unavailable to roots when the topsoil is dry.
• Where soil zinc is marginal, liming, high nitrogen rates and copper fertiliser can tip a crop into deficiency (DPIRD).
• Root-pruning herbicides, particularly groups A and B (DPIRD), and long bare fallows that reduce root fungi that help zinc uptake (Incitec Pivot).

If you are planning lime, read how much lime per hectare and watch zinc on marginal paddocks.

How to confirm it

• Tissue test the youngest emerged blade (YEB). DPIRD says levels below 10 mg/kg indicate zinc deficiency.
• A whole-top plant test gives a rough guide if you take paired good and poor samples, but confirm with a YEB test.
• A soil test is at best a rough guide to zinc status (DPIRD). It is still worth having; see reading a soil test.

Soil, seed or foliar zinc

DPIRD lists two fixes: a foliar spray, which works only in the current season, or zinc fertiliser drilled into the soil.

Soil (drilled) zinc

• Topdressing (spreading on the surface) does not work well, because zinc only reaches the plant when the topsoil is wet.
• Mixing zinc through the topsoil spreads it more evenly. Drilling it deep helps roots find zinc when the topsoil is dry.
• Zinc in compound starter fertilisers often meets the crop's needs for that season (DPIRD).
• Incitec Pivot says that in narrow-row wheat and barley, zinc in every granule spreads it better along the row than blending in a concentrated zinc product. Granulock Z carries 1% Zn in every granule. Compare it with MAP & Zn or ZincStar.
• Concentrated products such as Zinc Sulphate Monohydrate (33% Zn) suit blends for wide-row and perennial crops, according to Incitec Pivot.
• Incitec Pivot adds that zinc worked into the soil before sowing can last several years.

Seed treatment

DPIRD says zinc seed treatment is used to promote early growth where root disease is a problem, but supplies less zinc than the crop needs that season. Yara lists a seed dressing rate of 4–6 L/t for YaraVita ZINTRAC.

Foliar spray

• Spray as soon as deficiency is detected to avoid damage that cannot be reversed (DPIRD).
• Incitec Pivot recommends 2 to 3 sprays of zinc sulphate heptahydrate at 1 kg/ha, at 3, 5 and 10 weeks after emergence, for grain crops.
• Yara's cereal rate for ZINTRAC is 0.3–1 L/ha from the two-leaf stage to first node (Z12–Z31), in 50–200 L/ha of water.
• Liquid options include EASY Liquids ZN-SUL. Follow the label for rates and mixing.

Browse all zinc fertilisers or phosphorus starters, and see MAP vs DAP for choosing the starter base. Always check with your agronomist before acting.