Diagnosing zinc deficiency in narrow-leafed lupins
Lupins are less susceptible to zinc deficiency that wheat or barley
What to look for
Paddock
Plants with bunchy pale new leaves.
Deficiency will vary with soil type, with early deficiency possible in newly limed soils.
Plant
Markedly pale new leaves with shortened petioles, causing a bunchy appearance.
Leaflets of pale new leaves develop brown spots along their midribs.
Leaflets become bent and curled, often backwards towards the petiole.
Plants recover as they approach flowering.
Where does it occur?
Most sandy surfaced soils required copper and zinc when initially cleared for agriculture
Zinc is relatively immobile in soil and becomes unavailable to crops in dry soil.
Where soil levels are marginal, zinc deficiency may be induced by applications of lime
Management strategies
Spraying foliar
Foliar spray (effective only in current season) or soil fertiliser drilled with the following crop.
Zinc foliar sprays need to be applied as soon as deficiency is detected to avoid irreversible damage.
As zinc is immobile in the soil, topdressing is ineffective, as it would only be available to the plant when the topsoil is wet.
Zinc drilled deep increases the chances of roots being able to obtain enough in dry seasons.
Zinc has a 15 to 20 year residual life in soil.
Zinc present in compound fertilisers often meets the current requirements of the crop.
How can it be monitored?
Soil test
As zinc is immobile in the plant, young shoot or young leaf sampling is most accurate. The critical concentration for the youngest open leaflet before flowering is 12 to 14 mg/kg.
A DTPA zinc soil test provides at best a rough guide to soil zinc status for cereals. The critical concentration varies with soil type.
