Copper in Plant, Animal and Human Nutrition-Foreword
It has become increasingly apparent over the past 40 years, that copper plays a major role not only in the physiology and metabolism of crops but also in animals and man himself.
This review of the current state of knowledge regarding copper in soils, plants and animals and the use of copper compounds in combating deficiencies is intended to set the scene against which the rapidly accumulating data can be placed.
It is not the intention of this review to try to encompass the whole of the literature relating to copper in agriculture and biological systems - this is manifestly impossible. The aim is to bring copper to the attention of agricultural scientists, veterinarians, medical practitioners as well as those concerned with research, extension, education and administration in agriculture and medicine who may not have the opportunity to consider the relevance of copper in their work and lives.
Information is given on the occurrence of copper deficiency in both animals and crops. Details of the symptoms caused in crops and livestock by copper deficiency are given to assist in the recognition of deficiencies and information is provided on diagnostic procedures which should be used where problems are suspected.
It is strongly recommended that local specialist advice is obtained regarding the treatment of copper deficiency.
Copper is absolutely essential for the normal healthy growth and reproduction of all higher plants and animals. The crop and animal losses caused by shortages of copper can, at one extreme, be total, for example lambs can die of swayback and crops on newly reclaimed peats or sandy heathlands can fail completely; but fortunately, such occurrences are fairly rare. Far less dramatic, but economically very important, are the yield reductions of up to around 20% which can result from hidden (subclinical) copper deficiency in many crops without the appearance of any obvious symptoms. Even Iarger effects on live weight gain can occur in subclinically copper deficient livestock, especially cattle. In addition to its essential role, copper has also been shown to have a very beneficial effect on the food conversion efficiency of pigs. Average daily live weight gains of up to 9.1% have been obtained by adding copper sulphate to the diet of fattening pigs.
Copper deficiency has been found throughout the world in all climatic zones where crops are grown or animals kept on farms. Its incidence varies according to soil, crop, livestock and management factors. In particular it can occur in crops growing on soils with a sandy texture, on those rich in organic matter and on calcareous soils, but other soil factors can also cause a deficiency. In the case of grazing livestock, copper deficiency can also be caused on pastures with elevated concentrations of antagonists of copper, such as molybdenum and sulphur, in addition to herbages with low copper contents on deficient soils. Soil ingestion while grazing in muddy or dusty conditions can also cause copper deficiency. Intensive management with highly productive crop cultivars and animal breeds can often exacerbate copper deficiencies, especially where much nitrogen and phosphorus fertilizer is used.
Biological systems have made good use of the properties of copper, especially its ability to accept and donate electrons and thus participate in oxidation/reduction reactions, and also its capacity to form complexes with organic compounds. Copper normally occurs as a constituent of proteins, mostly enzymes, and these "copper proteins/enzymes" are involved in vital metabolic functions. If the metabolic pathways concerned are disrupted as a consequence of a shortage or sometimes an excess of copper, then the growth, yield and quality of the organism will be impaired as shown in the typical response curve in Figure 1.
Figure 1.1 A Typical Dose-Response Curve for Micronutrients such as Copper.
In Figure 1.1 the deficiency side of the curve can be divided into severe effects, which are manifested by distinct stress symptoms, such as reduced growth, chlorosis of the leaves in plants and coat discolouration in livestock, and into moderate and mild deficiencies with increasing copper concentrations. The mild forms are often referred to as 'subclinical', 'latent' or 'symptomless' deficiencies and also 'hidden hunger'. This is where the growth or performance of plants and animals is reduced by the slightly deficient supply of micronutrient without the manifestation of obvious symptoms.
Likewise at the toxicity end of the graph, subclinical toxic effects may also occur at the beginning of the downward slope. The relative sensitivity of fungal spores to copper toxicity has been exploited since 1885 in the widespread use of copper compounds as foliar fungicides on crops such as potato, grape vine and coffee.
All of the micronutrients are present in plant and animal tissues in very low concentrations (parts per million, mg/kg) and the elements: copper, iron, zinc, and manganese can interact sometimes at the sites of absorption or utilization and, possibly, during transport and storage. As a result, a relative excess of any one can induce metabolic disorders that are often apparent as a deficiency of other metal cations. One should not, therefore, consider copper (or any other micronutrient) in isolation, because other trace and macroelements can have marked effects on its uptake/absorption and utilization in plants and animals.
At a time when surplus agricultural production is causing concern in some countries (while famine is a major problem in others), yield losses due to trace element deficiencies are still important because they cause expensive inputs, such as fertilizers and pesticides, to be used inefficiently. Other considerations, such as the quality of food products and the composition of the human diet, are also relevant even where there is a requirement to temporarily reduce agricultural output in some western countries.
Further Reading
Bowen, H.J.M. Environmental Chemistry of the Elements. 1979, Academic Press, London.
Loneragan, J.F.; Robson, A.D. and Graham, R.D. Eds. Copper in Soils and Plants. 1981, Academic Press, Sydney.
Underwood, E.J. Trace Elements in Human and Animal Nutrition. 4th edn. 1977, Academic Press, New York.
WHEAT. Irregular maturation in Japan - often seen in copper deficient fields; the green parts are the most severely copper deficient areas where most plants are sterile.Acknowledgement: N.Mizuno, Hokkaido Agricultural Experiment Station, Japan
WHEAT. Effect of copper application during early stages of growth in trial in France; treated crop on right.Acknowledgement: I.M. Deterre, G.R.C.E.T.A. - Aube, Troyes, France
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WHEAT. Extreme copper deficiency results in sterile ears.Acknowledgement: J.F.Loneragan, Murdoch University, Western Australia
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CARROTS. Crop failure in control plot in trial on peat soil in Ireland; carrots on left were treated with 10 kg/ha copper sulphate.Acknowledgement: F.MacNaeidhe. An Foras Taluntais, Johnstown Castle Research Centre, Ireland.
