The influence of iron supply on toxic effects of manganese, molybdenum and vanadium on soybean, peas and flax

The investigations were carried out in nutrient solution with iron as ferric citrate and nitrogen in the form of nitrate. Addition of 2.5 p.p.m. vanadium to plants in which iron chlorosis was already-established, either by a lack of iron or by excess manganese, failed to counteract the condition, and caused toxic symptoms. Reduction of the standard iron supply to ½ or ? accentuated the toxicity of 2?5 or 5 p.p.m. V to soybean and flax, but a similar reduction in phosphorus had no influence. Toxicity to peas, however, was increased when the phosphorus was reduced to 1/10, provided the iron level was high (20 p.p.m. Fe). Raising the iron supply to 20 or 30 p.p.m. Fe counteracted the toxicity of manganese (10 p.p.m.), molybdenum (40 p.p.m.) and vanadium (2.5 p.p.m.), but the result was less marked when these three elements were combined. Iron supplied in successive, small doses proved less efficient in overcoming molybdenum or vanadium, but not manganese excess, than the same amount of iron supplied in fewer and larger quantities. Varying the iron supply had little effect when the concentration of the three elements was low. When increased iron supply had reduced the chlorosis caused by high manganese or vanadium, it also reduced the manganese and vanadium contents of the shoot (p.p.m./d.m.), but the molybdenum content was only lowered by high iron when given in non-toxic concentration (0.1 p.p.m. Mo) combined with excess manganese. The iron content of the shoot (%/d.m.) was scarcely affected by the amount of iron supplied, but was generally reduced by high concentrations of manganese, molybdenum or vanadium. Results regarding the effect of vanadium on the phosphorus content of the shoot were conflicting, and differences occurred only when the iron supply was low. Here the phosphorus content of soybean and peas was generally reduced, while that of flax was increased. Yield data for soybean and flax indicated an interaction between manganese with both molybdenum and vanadium if the iron supply was low, but none between molybdenum and vanadium. The effect of all three metals was additive in respect to iron.