Rothamsted Symposium on Trace Elements 76 



Dr. Hewitt:— 



It is particularly interesting to note that the symptoms of man- 

 ganese toxicity in beans just described by Dr. Lohnis are identical 

 with those produced with an excess of manganese in sand culture 

 experiments at Long Ashton. This independent confirmation 

 provides an interesting example of the reproducibility of visual 

 symptoms and gives further evidence of the value of visual 

 methods. 



Extensive experiments in sand cultures have shown that man- 

 ganese toxicity may produce a great variety of effects in different 

 plants but certain of these symptoms however appear to be common 

 in different groups of plants. Thus speckling of petioles is seen in 

 beans, mustard, potato and tomato; marginal cupping is common 

 in several brassicae; vascular necrosis may occur in tomato, potato, 

 clover and others, and stem lesions, particularly around nodes, oc- 

 cur in tomato and potato. The susceptibility of crop plants also 

 varies widely. Although beans are sensitive, red clover is much 

 less so. Most Brassicae are also relatively sensitive including mar- 

 row-stem kale, which differs markedly from the resistant hungry- 

 gap kale; potato, oat and sugar beet, in this order, are among the 

 more tolerant plants. 



The beneficial effect on manganese toxicity of liming the soil 

 noted by Dr. Lohnis raises the question of the effects of calcium 

 supply in sand culture. Increased calcium supply as calcium ni- 

 trate markedly reduces manganese toxicity effects and also the 

 accumulation of manganese, but when calcium is supplied as cal- 

 cium carbonate mixed in the sand the beneficial effect on man- 

 ganese toxicity may be little or nil in spite of an adequate supply 

 of available calcium, and this is in marked contrast with effects 

 produced in soil. 



