Effects of nitrogen, copper, and zinc fertilizers on the copper and zinc nutrition of wheat plants

Abstract

The effects of nitrogen, copper, and zinc fertilizers on dry matter yields and on copper and zinc absorption and distribution were studied in Gabo wheat plants grown in pots of an acid loamy sand from Badgingarra, Western Australia. Plants were harvested three times during vegetative growth and at maturity.

Copper and zinc fertilizers had no effect on vegetative or grain yields unless nitrogen fertilizer was also added. Nitrogen fertilizer overcame symptoms of severe nitrogen deficiency and increased growth five- to eightfold. Nitrogen induced slight symptoms of copper deficiency and of zinc deficiency after 80 days' growth and induced severe symptoms of copper deficiency at maturity. Nitrogen severely depressed the concentrations of copper and zinc in plant tops and roots by diluting the absorbed copper and zinc: two effects of nitrogen on growth contributed to dilution of copper and zinc - a large increase in total growth and a marked increase in top relative to root growth.

Deficiencies of copper and of zinc each depressed vegetative growth and delayed maturity: at maturity, each deficiency enhanced straw yields and depressed grain yields. Copper deficiency was aggravated by zinc sulphate, which depressed copper concentrations of tops and roots. Zinc depressed copper concentrations mainly by depressing copper absorption: it depressed the amount of copper absorbed, depressed the rate of copper absorption per gram root in early growth, and had no effect on the distribution of copper between roots and tops. The combined effects of zinc and nitrogen fertilizers induced such severe copper deficiency at maturity that they almost eliminated grain yield.

Zinc deficiency was aggravated by copper sulphate, which depressed zinc concentrations of tops and roots. Copper depressed zinc concentrations in plants partly by increasing growth but primarily by depressing zinc absorption: copper depressed the amount of zinc absorbed, depressed the rate of zinc absorption per gram root in early growth, and had no effect on the distribution of zinc between roots and tops.

It is suggested that nitrogen fertilizer could induce copper and zinc deficiencies in cereal crops growing on soils with marginal copper or zinc supplies. Zinc fertilizers would aggravate the effect of nitrogen on copper deficiency, and copper fertilizers would aggravate the effect of nitrogen on zinc deficiency.