70 



of the occurrence of soluble aluminum and iron under 

 such conditions has not been disregarded, since it has 

 been shown that under certain conditions quite appre- 

 ciable amounts of aluminum, with usually less amounts 

 of iron occur in the water extracts of acid soils. Con- 

 nor et al (3) have shown that acid soils of the Kankakee 

 region of Indiana contained relatively large amounts 

 of water soluble aluminum, and small amounts of iron. 

 The soils studied appeared to support a vigorous nitri- 

 fication , with aluminum as the base, in part at least, 

 uniting wdth the nitric acid formed. The aluminum ni- 

 trate thus produced was thought to account for the bar- 

 renness of the soils in question. A water extract of 

 these soils was found to be about as toxic as a solution 

 carrying aluminum nitrate and nutrient salts to ap- 

 proximate the composition of the soil extract. The ad- 

 dition of various chemicals which would precipitate 

 the aluminum, removed the toxicity of such extracts. 



Ruprecht and Morse (15) found considerable 

 amounts of water soluble iron and aluminum in soil 

 that had been continuously fertilized w4th ammonium 

 sulphate; further, treatment of the soil with ammonium 

 sulphate increased the solubility of these compounds, 

 showing that use of this nitrogenous fertilizer on acid 

 soils may cause injury to crops through the solution 

 of such elements even though no nitrification takes 

 place. 



In the writer's work on the soils from the Alabama 

 Experiment Station Farm, not more than traces of 

 iron was found; and in many instances, only traces of 

 aluminum were present. One of the very concentrated 

 extracts used early in the work had less than one-tenth 

 as much soluble aluminum as manganese; while a re- 

 cent extract contained 15.8 p. p. m. of aluminum and 80 

 p. p. m. of manganese. The extracts from plot 32 of 

 the Pennsylvania Ex])eriment Station contaned mere 

 traces of icon, and but little more than traces of alumi- 

 num. On the other hand, under various treatments 

 this soil has been found to contain from 75 to more 

 than 100 p. p. m. water soluble manganese. Since nor- 

 mal soils have been shown by Robinson (14) to contain 

 very much more aluminum than manganese, it would 

 appear that the manganese compounds found in soils 

 are more readily soluble than aluminum. It is con- 

 ceivable, however, that in time the small amounts of 



