Copper fertilization: function, application, and advice

Deficiencies caused by limited availability

Copper deficiency is usually the result of limited availability of copper reserves in the soil. This availability is strongly influenced by several field characteristics:

• Organic matter: copper binds more strongly to organic matter than almost any other nutrient. Copper deficiencies are therefore often found in crops growing on peat soils or other soil types containing more than 8% organic matter.
• Soil pH: the solubility of copper decreases at a pH above 7.0. At higher pH levels, the clay-humus complex retains copper more strongly, making less copper available to the crop. This is commonly seen in calcareous soils.
• High nitrogen availability: crops growing on soils with high nitrogen levels (due to high fertilizer applications) are less able to absorb copper efficiently.
• Nutrient balance: high concentrations of zinc, phosphorus, aluminum, and/or iron in the soil reduce the plant’s uptake of copper.

Sensitive to copper deficiency

Copper deficiencies in potatoes and sugar beet are often difficult to detect visually. Wheat and oats, however, show deficiency symptoms much more clearly. Symptoms include curling leaves and the appearance of white leaf tips that later die off. In severe deficiency cases, the crop may fail to head properly or the ear may develop poorly (see image below).

Because copper is an immobile element, meaning it cannot be redistributed within the plant, deficiency symptoms are mainly visible in the young, newly formed leaves.

Copper excess

In some cases, copper availability in the soil is too high. This is often the result of excessive use of copper-containing fungicides or excessive application of pig or poultry manure. Copper excess first manifests itself through reduced root growth and later through yellow discoloration of the leaves (chlorosis). A soil analysis can determine the level of plant-available copper (Cu) in the soil.

Copper foliar fertilization

On soils where copper availability is problematic, or where copper deficiency occurs, it is advisable to carry out one or more foliar applications with a copper fertilizer. Soiltech offers Optima Leaf-Cu+, a foliar fertilizer containing organically complexed copper.

Thanks to the organic complexation, the crop can absorb copper more quickly and efficiently. In addition, the organic complexation prevents the copper cations in the product from reacting with other elements in the spray solution, ensuring that the plant receives the copper in the correct form. This also makes the product highly compatible with most fertilizers and crop protection products.