Copper

Copper is a cofactor for enzymes involved in electron transport and in lignin synthesis, which strengthens cell walls and contributes to stem rigidity and disease resistance. It is also required for normal pollen formation and fertility.

Copper binds very strongly to soil organic matter, which reduces the fraction that is available to plants even when total soil copper is sufficient. Deficiency is historically most significant on reclaimed peat soils and on naturally sandy soils low in total copper.

• Organic (peat) soils commonly bind copper tightly, limiting availability
• Sandy soils can be naturally low in total copper
• Perennial crops such as grape and other orchard crops that receive repeated copper-based fungicide applications can, conversely, accumulate excess soil copper over time

Copper deficiency appears as wilting or chlorosis of young leaves and poor lignification, leading to weak stems. In cereals, it has been documented as reduced pollen fertility and poor grain set, historically a notable issue on reclaimed peat and sandy soils.

Copper toxicity restricts root growth and can arise from repeated copper-based fungicide applications, common in perennial crops such as grape and other orchard crops, or from copper-contaminated soils. Because organic matter binds copper strongly, toxicity risk is influenced by how much of the accumulated copper remains chemically available.

Copper competes with zinc and iron for uptake and for binding sites, so imbalances among these micronutrients can compound one another. Because copper availability is governed largely by soil organic matter, management of organic matter levels also influences copper nutrition.