42 



jenny. ORIGIN OF SOILS 



[Ch. 2 



of soils are found in various regions. Thus the podsol profile (Fig. 1) 

 occurs in Sweden, in Russia, in Germany, in the Alps, in New England, 



in Canada, in California, in equa- 

 torial South America, and in many 

 other parts of the world. Second, dis- 

 similar soils may be grouped into 

 sequences such that the properties of 

 the soils within a sequence vary in a 

 systematic manner. 



The genetic and geographic rela- 

 tionships among soils may be con- 

 veniently expressed as 



s = f(cl, o, r, p, t) 



(1) 



10 20 30 40 



Depth of soil in inches 



Fig. 1. Variation of soil proper- 

 ties with depth of soil (podsol 

 profile). 



The letter s denotes any soil property 

 such as color, reaction (pH) , clay con- 

 tent, nitrogen content, or lime. The 

 symbol / designates "function of," or 

 "dependent on." The letters in paren- 

 theses represent the soil-forming fac- 

 tors. The specific symbols have the 

 following significance: 



cl = air climate (environmental climate) 



o = species of organisms, that is, flora and fauna 



r = topography, including certain hydrologic features 



p = parent material, defined as the state of the soil at 



the soil formation time zero 

 t = time of soil formation (age of soil) 



Equation (1) is employed in two ways. First, in a qualitative sense, 

 as a shorthand notation for stating that soils are affected by climate, 

 organisms, topography, parent material, and time. The second mode 

 of interpretation treats the soil-forming factors as independent vari- 

 ables, which define the state of the soil system. This approach permits 

 studying functions of individual soil-forming factors, as follows: 



Time functions or chronof unctions: 



® = J\P)cl,o,r,p 



Soil properties are related to time (age of soil) under conditions of 

 constancy of cl, o, r, p. 



