Copper in plants

Copper is an essential component of various enzymes involved in photosynthesis, respiration, protein synthesis and regulation of plant hormones. Owing to these diverse roles, deficiency of copper can lead to a variety of problems in plant growth some of which may display no visible symptoms apart from a loss of yield (Jewell et al. 1986, Tills and Alloway 1981, 1983)).

Copper is taken up by plants as the ion Cu²⁺. Offtake in arable crops is around 80 g Cu/ha. Soil type is an indicator of possible copper deficiency. Calcareous or organic soils, acidic sandy soils and peats are most likely to be deficient. In England and Wales for example, the Icknield chalks of the south and the breckland and peat soils in East Anglia are most prone to deficiency. Where there is doubt, soil analysis should be used to help formulate recommendations.

In grassland areas, copper deficiency may also occur in livestock. In animals as in plants, copper is essential for many metabolic processes including haemoglobin synthesis, pigmentation and hair texture, fertility and reproduction and bone development. There are differences among breeds as well as species of livestock in their efficiency of copper absorption from the rumen so copper content of the diet may not be adequate to define deficiency. A copper concentration in herbage that is adequate for plant growth may be inadequate for livestock unless supplemented.

Visible symptoms in plants generally are associated with severe copper deficiency. There is evidence that moderate deficiency does not result in symptoms other than yield reduction, particularly in cereals. Copper is relatively immobile in plant tissue (more mobile than calcium or boron but less than nitrogen, potassium or phosphorus). Deficiency symptoms therefore tend to appear initially in young tissues. Severely affected cereals show pale green young leaves which may become twisted and whitened. Ears may be malformed with full grains at the base, shrivelled grain in the middle and none at all towards the tip. In sugar beet, young leaves become darker, blue green while older leaves show white tips. Symptoms are rarely seen in grass but deficiency in livestock appears as browning of hair and growth retardation in cattle and swayback in sheep. Symptoms in livestock are not necessarily associated with low soil or herbage copper status and are usually dealt with by direct treatment of the animal.

Soil and plant tissue analysis may be used to predict or diagnose copper deficiency in plants. In soils, EDTA-extractable copper of less than 1 mg/kg indicates probable deficiency, 1 - 2 mg/kg possible deficiency and greater than 2 mg/kg adequacy. In a review for HGCA, a soil concentration for extractable copper of 1.6 mg/kg was proposed as an indication of probable deficiency (Sinclair and Withers 1995). A level of less than 4 mg Cu/kg dry-matter in plant tissue indicates possible deficiency for the plant though plant tissue testing may be less reliable than soil testing.

Copper Deficiency Examples

Barley Copper Deficiency in barley is demonstrated by senescence at the leaf tips. The ears of corn will contain blind grains which are often bleached-white.