SOIL FORMATIONS AND CLASSIFICATIONS 57 



The soil strata are commonly classed as top soil and subsoil, and 

 in the name of a soil type the character of the top soil is indicated, 

 and also that of the subsoil if it is peculiar or markedly different 

 from the top soil. In the detail soil survey of Illinois conducted 

 by the State Experiment Station, which now covers about thirty 

 counties, or one third of the state, the preceding soil types have 

 been recognized and mapped, and records are kept under the 

 numbers and names given. 



The system of numbering (similar to the Dewey library system) 

 is flexible, and permits additions of main types or related types 

 (by decimals) , and the name is designed to carry with it a definite 

 suggestion of the character of the soil. 



NOTE TO CHAPTER VI. In considering the subject of sulfur, as discussed 

 in the following pages, the reader's attention is called to the fact that recent 

 investigations show soils and plants to contain considerably more sulfur than 

 was indicated by most of the analyses formerly reported, part of the sulfur hav- 

 ing been lost in the older methods of analysis (as suggested on page 64). On 

 the other hand, where this larger amount of sulfur is found in plants, it is not 

 known to be required, but more probably is merely tolerated by the plant. It 

 is safe to conclude that a plant requires all the sulfur it contains only when it 

 is grown on a soil in which sulfur is the element which limits the growth, so that 

 the addition of more sulfur would increase the yield. 



In the author's opinion, the fact that sodium nitrate is usually more valuable 

 than ammonium sulfate, and that bone meal in continued use gives as good or 

 better results than acid phosphate (containing calcium sulfate), justifies the con- 

 clusion that sulfur deserves no more consideration than is hereinafter given to 

 it. (Note the results from plots A i and N i in Table 66, plots 5 and 6 in Table 

 68, plots 5 and 17 in Table 70, and plots N i and A i, N 3 and A 3, and N 8 and 

 A 8, in Table 718. Also compare plots 6, 9, 10, 17, and 19 with plots 12 and 

 35, in Table 80.) 



It may be stated that, in addition to the sulfur contained in the soil and in 

 addition to the known amount brought to the soil in rain, there is an unknown 

 amount absorbed by the soil directly from the atmosphere, owing to the pres- 

 ence of sulfur oxids and sulfur acids in the air (as products of the combustion 

 of wood, grass, coal, etc.) and to the movement of the air into and out of the 

 pores of the soil with the changes in barometric pressure and wind velocity. 



