To explore variable responses to copper on wheat neutral to alkaline clay soils in Queensland.

• In glasshouse trials, which grew normally and produced grain when soil dressings of copper sulphate replied to surface soil from the field sites.
• There is therefore no inherent characteristics of the soils which makes fertiliser copper unavailable for plant uptake.
• The pattern of rainfall at each field site was compared with the rate of development of the wheat. When symptoms of coffered deficiency appeared in negligible grain yields occurred despite fertiliser application no effective rain fell in the 20 days before the plants reach the boot stage of growth.
• When soil dressings improved grain yield effective rainfall occurred within 14 days prior to booting.
• It is postulated that wheat cannot absorb sufficient copper for normal growth and development from a dry fertiliser zone.
• When the zone is dry just before booting wheat suffers an acute deficiency of copper during a critical phase of pollen formation resulting in infertile pollen.