Rothamsted Symposium on Trace Elements 74 



CaCOs (0.8 g) and half of this number, in addition, MnS04 

 (250 mg). In the untreated soil, young bean plants showed the 

 same symptoms as the plants grown in the plot from which the 

 soil came. In the soil, with CaCOa added, healthy, normal 

 plants developed. When MnS04 had been added plants devel- 

 oped typical symptoms (Plate 9). Acidity, as such, cannot be 

 the causal agent. The addition of 250 mg MnS04 has been 

 large enough, it appears, to keep part of the manganese in an 

 unoxidized soluble condition. In fact, at the end of such an 

 experiment 86 p.p.m. Mn was still found in the soil. 



In the summer of 1947 we found in vetch (Vicia sativa) a 

 plant even more susceptible to excess manganese. This plant 

 was used in our test because, being known to be highly non-sus- 

 ceptible to manganese deficiency, it might well take up manganese 

 easily. In all experimental plots half a row was now planted 

 with vetch. It proved, to such a degree, susceptible to excess of 

 manganese that in the more acid plots I hardly succeeded in 

 gathering samples for chemical analysis as it died off too quickly. 

 On the more heavily limed plots, however, large and healthy 

 plants developed. The content of manganese in these samples 

 has not been estimated as yet. 



Affected plants show a purplish discolouration of the margins 

 of the leaflets, chlorosis of the young leaves, and stunted growth 

 (Plate 10). In the dry summer of 1947 the affected plants died 

 before well developed. 



Solution cultures furnished proof that the injury was actually 

 due to excess of manganese. When the nutrient solution had 

 been supplied with 25 or 37.5 mg MnS04, the field symptoms 

 could be reproduced exactly. 



In this case, soil cultures in Neubauer dishes, similar to those 

 carried out with beans, were also very conclusive. 



As the analysis of exchangeable manganese in the soil will 

 furnish widely divergating results depending on the time of sam- 

 pling, it can hardly serve as a sound method of testing soils sus- 

 pected of excess of manganese. It seems to me that culture 

 experiments with beans ("Prinsesseboon") or vetch, in Neubauer 

 dishes, may give more reliable results. 



My investigations have not been concluded, as yet, and could 

 only be presented to you in this preliminary form. 



