**Copper in Horticulture**

Denis Rusjan

*Biotechnical Faculty, University of Ljubljana Slovenia* 

#### **1. Introduction**

Cu as a solid, conductive chemical (Cu) material has the ability to deform under tensile stress (ductile metal); its freshly exposed surface has a reddish-orange colour, it is easily recyclable and with an annual production of more than 5 million tons of copper nowadays, due to the increasingly vital part of the metal's use in many branches of modern technology, especially in architectural structures and electronic devices (Table 1), the material is gaining importance. Copper is an essential material of the future regarding solar heating, desalination of water, environmentally-sound cultivation practices in agriculture and its contribution to the production of linear motors. Its unique chemical characteristics provide for more than 200 year's use of Cu in phytochemistry especially in the role of fungicides.

Cu2+ and Cu+ ions are soluble in water and provide antifungal and antibacterial effects (biostatic elements) at low concentration levels, wherefore their contribution to the production of fungicides is, up to the present day, irreplaceable. On the other hand high concentrations of copper salts affect physiological and biochemical processes in higher organisms. Copper takes part in numerous physiological processes and is an essential cofactor for many metalloproteins. However, copper excess leads to problems in cell function and metabolism, as copper surplus inhibits plant growth and impairs important cellular processes (*i.e.,* photosynthetic electron transport).

Copper compounds are commonly encountered as salts of Cu2+, which often impart blue or green colors, in the past widely used as pigments, therefore. As a native metal it is one of the few metals to occur naturally as an un-compounded mineral and it seems to be the first metal used by man dating back at least 10,000 years in history. A wider usage of copper started in the Copper Age (5th millennium BC) and throughout the Antiquity and Middle Age to Nowadays being considered as one of the most important metals.

Copper plays an important function in human diet, because of shared similarities with iron it is crucial for the reddish coloration of hemoglobin in blood. It is essential and indispensable at all higher organisms (plants, animals) especially at cycles and functions of growth and reproduction. The average daily recommended uptake of Cu should be 0.9 mg, falling short of which frequently leads to an increase of cholesterol level and coronary diseases. Copper toxicity in terms of human health can be observed at concentrations higher than 11.0 mg kg-1, affecting functions of main vital organs. A protracted exposition to toxic concentration of Cu leads to irreparable damages of stomach, kidneys, liver and brain, therefore the daily food should be under permanent sanitary (chemical) control.

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system where they are ascribed many roles and have different functions, which is rendered

Limestone Sandstone Slate Average

possible with permanent transformation.

1994; Šajn et al., 1998)

Metal Sediment soils

Fig. 1. The mobility of metals according to pH of soil

Chrome (Cr) 10-11 35 90-100 70 Manganese (Mn) 620-1100 4-60 850 650 Cobalt (Co) 0.1-4 0.3 19-20 7 Nickel (Ni) 7-12 2-9 68-70 40 Copper (Cu) 5.5-15 30 39-50 30 Zinc (Zn) 20-25 16-30 100-120 50

Table 2. Average content of metals (mg kg-1) in different soil and stoneware types (Ross,

Copper as a microelement effects the characteristics of the soils, that are also its preliminary source, while its content depends on parental matter (Table 2). Copper reaches the soil almost exclusively in divalent form (Cu2+ ions) incorporated in minerals but also bound with soil organic matter. Reed & Martens (1996) reported the specifically adsorption of Cu to carbonates, soil organic matter, phyllosilicates, and hydrous oxides of Al, Fe, and Mn. Usually it is dissolved in soil solutions as Cu2+ or as an organic complex adsorbed to inorganic and organic negatively charged groups. The presence of Cu2+ ions in soil solutions decreases with increasing pH, whereas Cu complexes are less dependent on soil pH. Cu2+, compared to other divalent cations (Ni, Co, Zn, Mn, Mg), has a strong affinity to soil organic matter, its concentration in soil ranges from 1 x 10-5 to 6 x 10-4 mol m-3, what is controlled by Cu adsorption to organic and inorganic soil particles. Because of this the transition of Cu in deeper soil layers rarely occurs, however it can be promote by soil cultivation (deep ploughing) and by decreasing soil pH to 5.5-6.5, at which values the mobility of Cu increases (Fig. 1).


Table 1. Chemical and physical properties of copper (Cu)
