Soil copper in relation to cereal crops
Mackenzie, E. Jean
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In field trials on soils of known copper status, plots of oats and "barley were given foliar and seedbed copper treatments, and in factorial pot experiments, oats under various conditions of water supply and illumination were also grown on deficient and treated soil. The following conclusions were made from the results of observations and experiments. In fields on a few farms in South East Scotland, copper deficiency is lowering cereal yields and sometimes causing withertip. The soils in these fields are in the Eckford or Hobkirk Series, and have an E.D.T.A. extractable copper level of about 0.5 p.p.m. ^Ithertip is seen most frequently when the preceding winter is dry, but there appears to be no correlation between its occurrence and weather conditions during the growing season. Oat plants, nevertheless, generally absorb less copper from sandy soil at about 80$ water capacity than from soil at 40$, and the uptake in young plants may be decreased when illumination is reduced. On deficient soils, similar increases in grain yield appear to be caused by foliar treatments of 5 and 10 lb. per acre copper oxychloride, although even 0.8 lb. is sufficient to cure withertip. Field seedbed oopper dressings are less effective at raising grain production than foliar treatments, and cause no response in straw yield. Under greenhouse conditions, on the other hand, copper treatment of deficient soil nay increase "both grain and straw yields, l?o evidence was found of copper toxicity in the field, "but a temporary reduction in the yield of young plants in pots occurred when sandy soil contained about 8 p.p.ra. applied copper The concentration of copper in "barley plants is generally higher than that in oats, although there are varietal differences in oats, "barley and wheat. The concentration is also higher in young plants than in those at maturity, and is influenced by moisture and light conditions. In the field, foliar treatments and moderate applications of copper to the seedbed have little effect on the copper level in mature plants, hut a heavy soil dressing in pots may raise the concentration in the "rain. Copper deficient oat plants contain a larger concentration of moisture than copper treated plants. Iron absorption may be reduced in young oat plants containing a high level of copper, and small copper dressings on a deficient soil may cause an increase in uptake of manganese. E.B.T.A. extraction of field soils gives a guide to the availability of copper near deficiency levels, and generally recovers 20 to 30$ of foliar applications and about 50$ of soil dressings for up to two years. The applied copper remains readily available to plants. The sampling date, however, influences the result of an E.D.T.A. extraction of a soil, particularly after copper treatment. The comparatively high concentration of copper in urban rain water makes copper deficiency unlikely in or near built up areas.