40 



seem all the more probable that in certain cases the 

 effect of soil acidity may be partly due to the manga- 

 nese in solution." 



Experimental 



Soil and Solution Cultures. 



All the pot culture work here reported was done in 

 2-gallon pots, in the green house. The pots were filled 

 to within about one inch of the top with the soil to 

 be used, after the soil had been thoroughly composit- 

 ed. No attempt was made to maintain a given water 

 content in the pots, but tap water was added from 

 time to time as the need was indicated. A part of 

 the solution cultures was grown in pint jars, and a 

 part in ordinary tumblers. The manner of setting up 

 the tumbler cultures was essentially that of McCool 

 (12). 



Manganese Determinations. 



The manganese determinations were made by the 

 ammonium persulphate method, as described by Hille- 

 brandc (7). The standard used contained one p. p. m. 

 of Mn. The comparisons were made in tall form 

 Nessler cylinders. 



Preparation of Soil Extracts 

 Bulk soil extracts were obtained by leaching approx- 

 imately 20 pounds of soil until about 2 liters of perco- 

 late were obtained. However, these ratios were not 

 exactly maintained. In some cases where a very con- 

 centrated solution was obtained, more than 2 liters 

 were passed through the pot of soil. The leaching was 

 usually done in a 2-gallon pot provided with a covered 

 opening in the bottom; or in an inverted aspirator 

 bottle, the bottom of which had been broken out. In 

 either case, little difficulty was experienced in securing 

 clear extracts. 



Preliminary Pot Experiments on Soil with a High 



Nitrate Content 

 As stated in the introduction, preliminary work with 

 the sandy soil from the Alabama Experiment Station 

 Farm carrying a very high nitrate content gave disap- 

 pointing yields of corn in pots in the green house, 

 while sorghum made little or no growth under tlie 

 same conditions. From a bulk supply of the soil with 

 a high nitrate content, duplicate pots were prepared 

 and treated as follows: 



