Mineral Plant Foods contained in Soils. 357 



his compilation of published HC1 analyses of soils of the United 

 States were consulted in the sources for the states of Alabama, 

 Florida, Kentucky, Maryland, "West Virginia, Tennessee, and 

 North Carolina for residual, alluvial soils ; and for Indiana, 

 Maine, Michigan, Minnesota, North Dakota, New York, New 

 Hampshire, Ohio, .Rhode Island, and Wisconsin for glacial, 

 alluvial soils, with the result that while for certain sections, 

 e. g., Tennessee, a representative number of such analyses were 

 found available, in other states there are none, or the analyses 

 are of samples individually unrepresentative, their exact origin 

 and manner of sampling being obscure, and their total number 

 inconsiderable. The only HCl analyses data at all permissible 

 of comparison on this basis are some fourteen alluvial soil anal- 

 yses from Tennessee, and an average of some 72 surface soils, 

 not all alluvia], from Minnesota. As the samples from the 

 latter state are from the different parts of its area, it may, how- 

 ever, be assumed that their average represents a commingling 

 comparable with that in the Tennessee alluvial soils. Analyses 

 showing extreme percentages were omitted in both cases. 



HCl Analyses 



$P 2 6 



#CaO 



$K 2 



* Tennessee Residual, Alluvial 



•108 



•376 



•376 



f Minnesota Glacial, General . 



•20 



1-29 



•43 



The reputed worth of partial HCl digestion analyses is in the 

 vaguely probable relation their figures bear to the amount of 

 ' available' plant food in the soils analyzed. If the percentage 

 of acid soluble, mineral plant food constituents has any such 

 relation to the proportions of these materials available to crops, 

 then the ratio of acid soluble substance to total amount present 

 is an index as to the relative fertility of the lands, provided other 

 fertility factors are equal. Data are available in the bulletins 

 cited above for an application of this idea to the Illinois glacial 

 soils and the Maryland residual soils. In the Illinois glacial 

 soils the total content and the acid soluble figures for the ele- 

 ment of potassium vary so widely for different samples from 

 the same glaciation that the ratio of their averages would have 

 little or no significance. The acid soluble percentage of the 

 element phosphorus, however, shows a much greater constancy 

 for different samples from the same glaciation. A comparison 

 of averages shows the following : The acid soluble portion of 

 the phosphorus content of the gray silt loam subsoil, 20-40" 

 deep, on undulating prairie lands, of the oldest or Lower Illi- 

 noian glaciation comprises 81*2 per cent of the total amount 



*Mooers, Charles A., The Soils of Tennessee. Bull. 78, Agri. Expt. Station 

 of the University of Tenn., 1906, pp. 74 and 83. 



f Snyder, H., Soil Investigations, Bull. 65, University of Minnesota Agri. 

 Expt. Station, 1899, p. 69. 



