June 2,1923 
Effect of Manganese on Plant Growth 
785 
only and no manganese. Pot No. 3 received 5 parts per million of manga¬ 
nese in addition to the mineral nutrients. Pot No. 4 received 10 parts per 
million of manganese. Pot No. 5 received 50 parts per million of manga¬ 
nese. It is therefore readily apparent that 50 parts per million of 
manganese in the form of manganese sulphate are sufficient to produce 
toxicity in this soil. None of the seeds came up in the soil receiving this 
and greater concentrations of manganese sulphate. It is quite evident 
from Plate i, A, that the maximum tolerance for manganese sulphate 
in this soil and with this particular plant lies between 10 and 50 parts 
per million. 
Table II shows that the plants in the corresponding duplicate pots 
which are not shown made a similar growth. 
There is no noticeable difference in the growth of the plants receiving 
the 5 and 10 parts per million of manganese, as compared with those 
that received no additional manganese. It is apparent that the small 
amount of manganese contained in the soil was sufficient for the require¬ 
ments of the plants, under the conditions described. 
The growth attained by the plants in the neutralized Volusia soil is 
shown in Plate i, B, in which pot No. i is one of the control pots to which 
calcium carbonate was added. Comparison with the corresponding pot 
in Plate i, A, shows that the plants made a slightly better growth in the 
neutralized soil than in the acid soil. Pot No. 2 received mineral nutrients 
and calcium carbonate and the plants did not make as good growth as did 
those in the corresponding pots with the acid soil. Pot No. 4 is one of 
two to which 10 parts per million of manganese was added. Neither of 
the two pots of soil that received 5 parts per million of manganese is 
shown in the photograph, but it will be seen in Table II that the plants 
that received 5 parts per million of manganese in series No. 2 made a 
slightly better growth than did the plants in the corresponding pots of 
soil in series No. i. It will also be observed in Table II that the plants 
in the pots of soil that received 10 parts per million of manganese made a 
decidedly better growth in the neutralized soil than did the plants in the 
corresponding pots in the acid soil. Pot No. 5 shows the growth the 
plants attained in the neutralized soil to which 50 parts per million of 
manganese was added. It will be recalled that in the corresponding 
pots in the acid soil, the seeds did not germinate because of the toxic 
effect produced by an excess of manganese, while with the same con¬ 
centration of manganese in the neutral soil the plants made a fair growth, 
though apparently retarded by an excess of this element. This experi¬ 
ment illustrates in a very striking way the effect of calcium carbonate in 
reducing the toxicity produced by an excess of manganese sulphate. In 
pot No. 6, to which was added 100 parts per million of manganese, no 
plants grew. 
In Table II it will be observed that the applications of manganese 
to the acid soil reduced the yields, as shown by the green and dry weights 
of the plants, whereas with the same concentrations of manganese in the 
neutralized soil there was an appreciable gain. 
