334 
matter, soil water solute content and soil 
water tension. Moreover, a natural soilsur- 
face consists of an amassment of particles 
and aggregates which can seldomly be grouped 
in a single particle size class. The optical 
properties of an aggregate of unsorted parti 
cles, however, closely ressemble those of the 
smallest particle size present (Adams and 
Filice, 1967, Stoner and Baumgardner, 1980). 
Thus, equation 6 could be tested on mineral 
mixtures of various particle sizes, using the 
smallest particle size significantly present 
as the input of particle diameter 0. 
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