Copper deficiency made worse by
- Organic soils
 - Calcareous soils
 - Sandy soils
 - Reclaimed heathland
 - High nitrogen applications
 
Copper is important for
- Component of enzymes
 - Important role in photosythesis and phenol metabolism of plants
 - Regulation of destructive superoxide radicals inside cells
 - Bulb quality
 - Skin finish and colour
 
Yara recommended fertilizers for Copper
YaraVita® MANCOZIN™
Onion: 1½ quarts/acre when there is sufficient leaf area to obtain coverage (4 to 6 leaf). Repeat during bulking if necessary. Water rate: 3 to 20 gallons/acre.
Read more about YaraVita® MANCOZIN™