Copper (Cu)

The concentration of copper in the soil solution depends on the pH value and the available chelating agents, such as soil organic matter, manganese, and iron oxides. As a component of several enzymes, copper has a positive effect on the plant metabolism. For instance, it regulates the photosynthetic electron transportation. In case of copper deficiency, leaves roll together like a thread, wilt and eventually die. 

The copper content of unpolluted soils typically ranges between 2-40 mg Cu/kg soil. Copper has a tendency to bind to the soil organic matter of the soil. It is adsorbed by manganese and iron oxides or it can be bound to the lattice silicates. In addition, it can precipitate as the hydroxide, carbonate or phosphate form.

The concentration of copper in the soil solution depends on the pH value and the available chelating agents. The proportion of exchangeable copper generally increases with decreasing pH.

Copper deficiency occurs on recently cultivated moorland soils and due to Cu fixation also in podsol soils rich in organic matter.

Plants take up Cu²⁺-ions freely from the soil solution or as soluble copper complexes. As a component of several enzymes, copper has a positive effect on the plant metabolism.

Function of copper in the plant: 

• Regulates the photosynthetic electron transportation.
• Similar to manganese, copper assists in the binding of free oxygen radicals which renders them innocuous.
• Important for sub processes of lignification.
• Important for rhizobia production associated with legumes.

Copper excess in the plant

Plants exhibit different grades of copper tolerance. This is based on their ability to take up less copper from the soil solution or via a mechanism which excretes excessive copper or to transforms it into a harmless form. Copper excess only generally occurs at pH values of < 5. 

Consequences of copper excess:

• Causes yellowing of the youngest leaves.
• Can induce iron, zinc, and molybdenum deficiency in plants.
• Can accumulate in the plant roots and result in damage the root cell membranes.
• Greatly alters enzymic activity which inhibits root growth.
  
  

• In cereals, the youngest leaves turn white due to damaged chloroplasts.
• Leaves roll together like a thread, wilt, and eventually die.
• The internodes are shortened.
• Ears or panicles develop poorly with many blind grain sites.
• In fruit trees, growing points are stunted and both flowering as well as fruit set are hampered.
• Copper deficiency can be excaserbated by an increased nitrogen supply since copper forms strong bonds with the amino acids produced.
• Copper is often bound to the organic matter in newly cultivated fields and can also be locked up after heavy liming on reclaimed marshland or boggy areas.