176 SYSTEMS OF PERMANENT AGRICULTURE 



In all humid regions where water passes through the soil, there 

 is loss of calcium carbonate, leached out in the form of soluble 

 bicarbonate. The " lime " carried in solution in " hard " waters 

 from surface wells appears as a crust or scale in the teakettle, the 

 soluble bicarbonate being decomposed by heat and the insoluble 

 normal carbonate thus precipitated. Even virgin soils in old soil 

 formations are often not only deficient in limestone, but they are 

 sometimes found to be exceedingly acid, and thus require heavy 

 applications of limestone to correct or neutralize the acids in the 

 soil. 



Usually these soil acids exist in part, at least, as organic acids 

 (humic acid etc.), but it is very evident that they are not always 

 entirely organic, because the acidity often markedly increases while 

 the organic matter decreases, with depth of soil, as will be seen 

 from Tables 15, 16, and 17 (see soil types 330, 135, and 335), in 

 which the measure of acidity is shown by the " limestone required," 

 and the organic matter is indicated roughly by the nitrogen. 

 Thus, in the Lower Illinoisan yellow silt loam, limestone required 

 to correct the acidity increases from 310 pounds in the surface to 

 3315 pounds in the subsurface, and to 7200 pounds in the sub- 

 soil, considering 2 million pounds of each; while the nitrogen de- 

 creases from 2150 pounds in the surface to 1085 pounds in the 

 subsurface, and to 827 pounds in the subsoil; and, as a matter of 

 fact, the organic carbon decreases from 23,400 pounds in the sur- 

 face, to 9710 pounds in the subsurface, and to 6190 pounds in the 

 subsoil, 2 million pounds of each being considered. 



Detmer assigns to humic and ulmic acids the molecular formula 

 C 60 H 54 O 27 , and to their salts such formulas as Ag 8 C 60 H 46 27 , and 

 Ca 3 (NH 4 ) 2 C 60 H 46 O 27 . These would correspond to Ca 4 C 60 H 46 O 27 . 

 On this basis, if all of the organic carbon in the subsoil were in the 

 form of humic acid, it would be equal to less than one half of the 

 acidity found. These computations are based upon the average of 

 many analyses of soil samples from this type. Individual samples 

 show as high as six times as much acidity as could be accounted 

 for from the total organic carbon if in the form of humic acid. 



Acid silicates (see acid salts), formed from polysilicates (see 

 under silicon), from which some basic elements may have been 

 removed and replaced with acid hydrogen, by reaction with soluble 



