The influence of high concentrations of ammonium and sodium molybdates on flax, soybean and peas grown in nutrient solutions containing deficient or excess iron

Ammonium molybdate supplying 20 or 40 p. p. m. Mo prevented chlorosis caused by low iron supply in young flax plants, but sodium molybdate was effective only at the higher concentration. Temporary darkening of the green colour of the shoots was also produced by 40 p. p. m. Mo in iron-deficient soybean and pea plants, but was soon followed by more severe chlorosis. Symptoms of molybdenum toxicity always developed when 40 p. p. m. MO were given, whether or not the intensity of chlorosis was reduced. With an increase in iron supply, a reduction in molybdenum toxicity symptoms was confirmed in soybean and peas. In flax the higher level of iron eventually proved excessive unless it was combined with 40 p. p. m. Mo. High molybdenum thus seemed able to counteract both iron deficiency and toxicity in this plant. High iron reduced the molybdenum content (p.p.m./d.m.) of both shoot and root in soybean, peas and also in flax provided the iron was not excessive. High molybdenum usually reduced the iron content of the shoot, but markedly increased it in the root. Molybdenum-induced chlorosis could thus be partly attributed to inhibition in iron translocation, but the beneficial effect of high molybdenum or high iron on colour was not obviously correlated with the analytical data.