**3.3 Copper**

Copper is a relatively abundant metal in the earth's crust. Its presence in the soil is therefore natural but can be enhanced by anthropogenic activities. The concentration of copper in the earth's crust is between 10 and 100 mg.kg−1 [24]. In soil, the availability of copper to plants depends mainly on pH, cation exchange capacity (CEC), organic matter content, the presence of iron, manganese and aluminium oxides and redox potential [1]. Thus, in neutral or basic soil with a high CEC, copper will be adsorbed to the solid phase of the soil and therefore less available to the plant.

### **3.4 Manganese**

The origin of manganese in soils and plants is mainly from rock decomposition and to a lesser extent from anthropogenic activities. Natural levels of manganese in soils are between 400 and 1500 ppm. In the soil, manganese is moderately mobile, compared to highly fixed elements such as cesium or lead. Its mobility depends on soil characteristics such as pH, cation exchange capacity, organic matter, and especially clay content.
