Copper plant micronutrient deficiencies, soils

The total content of the major elements in soil is of little practical significance since only a tiny, soluble fraction is available for absorption by plant roots (West, 1981 Tinker, 1986). To some extent this is less true for trace elements and micronutrients where for example, analyses of total copper or zinc can be used to assess the likelihood of plant deficiencies or toxicities. Nonetheless, for an element to be bioavailable it has to be relatively soluble. 

Fertile soils supply plants with all of the trace elements essential for growth, believed at the present time to be Fe, Mn, Zn, B, Cu, Mo, and CL These seven elements are called the micronutrients, a term that indicates the small quantities needed by plants but not necessarily the concentrations found in soils. Deficiencies can occur in soils either because they contain extremely low concentrations of these elements or because the elements are present in very unavailable (insoluble) forms. Conversely, many trace elements, including ail of the micronutrients, can reach concentrations in soils that are toxic to plants and microoiganisms. Some of the most toxic are mercury (Hg), lead (Pb), cadmium (Cd), copper (Cu), nickel (Ni), and cobalt (Co). The first three are particularly toxic to higher animals. The last three are more toxic to plants than animals and are termed phytotoxic. From the standpoint of potential hazard to human health, an extended Ust of priority metals has been established. This list presently consists of ... 

Micronutrients are elements such as Boron, Zinc, Copper, Cobalt, Iron, Magnesium etc. which are required in trace amounts. The addition of extra trace elements has no effect on plant growth but a deficiency of any or all of these can cause serious disturbance of plant growth, leading to a loss of active chemical. Since plants can be cultivated in areas with different soils of varying fertility, it follows that the site of cultivation could influence quality, indicating again the need for assays for chemical content. 

The micronutrients of major interest to soil chemistry because of plant deficiencies are boron, manganese, iron, cobalt, copper, zinc, and molybdenum. Other ions— chromium, nickel, cadmium, mercury, and lead—behave similarly in soils but the problems are usually plant toxicity. The availability of most of the micronutrient and toxic ions increases with increasing soil acidity. Those present as anions—-molybdenum, chromium, and boron—differ in that their availability generally decreases with increasing acidity. 

One of the important benefits of chelates, other than supplying metals, is realized as a result of their improvement of the micronutrient balance of plants. For example. Holmes and Brown (1955), in studies with calcareous soils, observed that certain effective chelates increased the concentration of iron in soybeans, and at the same time decreased the concentration of manganese and copper. This suggests that the cause of iron-deficiency chlorosis in this case may have been improper microelement balance in these calcareous soils. These workers also observed that when chelate was applied to several soils, it alleviated iron chlorosis completely in some soils, partly in others, and caused toxicity in yet others. From the work of others we know that under other conditions chelates may also eliminate or greatly decrease toxic effects where heavy metals are present in excessive amounts. Numerous soil factors influence these varying responses. 

These Fe deficiency-induced processes are likely to operate ubiquitously in soils because of limited bioavailability of Fe, especially in neutral to alkaline soils. Iron deficiency in crops may thus affect metal speciation in soil, and ultimately enhance the uptake of metals by plants. In the present study, we examined this hypothesis in the case of copper (Cu) and zinc (Zn), which are micronutrients and also potential metal contaminants. 

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