350 0. D. von Engeln — Factors influencing Percentages of 



Art. XXXVIII. — Some Factors Influencing the Percentages 

 of Mineral Plant Foods Contained in Soils /* by O. D. von 

 Engeln. 



The writer has attempted a correlation of selected soil anal- 

 yses with soil history in order to ascertain if any correspond- 

 ence exists between the present chemical composition of soils 

 and the formative processes involved in their production. The 

 comparisons presented are based on averages of analyses chosen 

 as typical ; and such tentative deductions as are made are 

 founded primarily on the results obtained from bulk analyses 

 of soils. The numerical insufficiency and incompleteness in 

 publication of such analyses, available for comparison, proved 

 to be the greatest difficulty in making the study. As it was 

 not intended to take account of the variations in chemical 

 composition of soils induced by climatic variation, the compari- 

 sons are confined to soils from the humid, temperate, eastern 

 portion of the United States, in order that this factor should 

 be, as near as possible, negligible 



A reiterated contention of the Bureau of Soils, United States 

 Department of Agriculture, is variously expressed in such 

 terms as : " Investigations have shown that there are sufficient 

 quantities of the mineral plant food constituents in the soil 

 moisture to produce good crops, and that the supply is main- 

 tained from the continuous solution of the minerals of all 

 ordinary soils throughout the growth of the crop ;"f and : 

 " The chemical composition of soils varies so greatly without 

 any obvious law of general relationship to crop production 

 that averages mean little or nothing, and figures are given 

 without any attempt at averaging.";]: These statements imply 

 that no direct relationship exists between either the origin 

 or fertility of soils and their chemical composition. 



The latter of the two statements quoted above prefaces a 

 compilation of " acid digestion " analyses of soils of the United 

 States, published in the same bulletin. An examination of 

 the sources from which the analyses were obtained made it 

 apparent that the data afforded no safe basis for so broad a 

 generalization. Aside from the fact that incomplete, i. e., acid 

 digestion, analyses are untrustworthy for purposes of compari- 

 son, it was also found that many of the analyses included in 

 the compilation were of extremely doubtful value from other 

 reasons. The exact origin and method of sampling is in many 



* The writer desires to express his obligation to Professor T. L. Lyon and 

 Dr. J. A. Bizzell of Cornell University for criticisms and suggestions in 

 connection with this paper. 



fBull. 55, Bureau of Soils, U. S. Dept. of Agri., 1909, p. 63. 



JBull. 57, Bureau of Soils, U. S. Dept. of Agri., 1909, p. 61. 



