51 



cultures, it would appear that the amount of soluble 

 manganese in soil relative to the amount of other solu- 

 ble bases, is more important than the actual amount 

 of soluble manganese. The work further indicates that 

 precipitated manganese com])ounds are not toxic to pea 

 roots, since many of the roots w^ere buried in the pre- 

 cipitate in the container, at the time the experiment 

 was discontinued; and there was no injuiy to these, 

 so far as could be judged by external appearances. 

 The writer believes that the evidence given is suf- 

 ficient to justify the conclusion that the toxicity of the 

 soils and soil extracts studied Avas due chiefly to inor- 

 ganic compounds and that manganese is the element 7'e- 

 sponsible for the toxicity observed. And since but 

 small amounts of sulphates and chlorides w^re usually 

 found, manganese nitrate is believed to be the specific 

 form in which the soluble manganese occurs. 



Does Nitrification Develop Soluble Manganese? 

 Studies on Alabama Soils 



In order to throw light on this question the follow- 

 ing experiments were performed, using two different 

 soils. One of the soils was taken from a plot on the 

 Experiment Station Farm which had received annual 

 application of sulphate of ammonia, and is very sour. 

 It is designated "soil from plot 4" in the table. The 

 other soil w^as taken from the plots described earlier 

 in this paper and is designated "soil from nitrification 

 plots"; this soil is but moderately sour. From each 

 of these soils, three sets of pots were prepared, each 

 treatment being made in duplicate on each soil. One 

 set of pots was planted to sorghum on the day that the 

 treatments were applied; the second set of pots was 

 l)lanted about seven weeks later; and the third set was 

 left unplanted. The pots of this last set were leached 

 after 95 days, the leaching fdtered through a Pasteur- 

 Chamberland filter, and analyzed. The treatment giv- 

 en, the crop yields, and the analyses of the extracts, 

 are given in Table VII. Photographs of the pots are 

 shown on Plate V, figs. 1 and 2. 



