182 THE SOIL: INORGANIC MATTER 



much of the soluble material is desposited. Aeration, for 

 example, frees carbon dioxide from the solution and pre- 

 cipitates calcium carbonate and magnesium carbonate. 

 Inter-reactions of bases and acids with new compounds 

 remove many substances. Dilution of water charged with 

 soluble material by fairly pure water reduces the con- 

 centration. 



Taking up drainage water alone, it is very noticeable 

 that potash is present in small quantities, whereas lime is 

 present in considerable amounts; and it will be remembered 

 (Section 138) that potassium is absorbed to a much greater 

 extent than calcium. Soda and magnesia are present in 

 nearly equal quantities. The acid radicles in the order of 

 increasing amounts are P2O5, Si0 2 , CI, S0 3 , and C0 2 , with 

 N 2 5 probably about equal to CI. Nitric acid, as nitrates, 

 of course, will be present in widely varying amounts, probably 

 more widely than any other radicle, acid or basic, and 

 hence an average figure does not mean much. This arrange- 

 ment indicates that most of the salts in solution are calcium 

 and magnesium bicarbonates and sulphates, sodium chloride, 

 some silicates of the alkalies, and nitrates of different bases. 



It may be said for nitrates that although the nitric acid 

 radicle is the least absorbed of all, there is not such a great 

 loss of it from ordinary soils as might be expected. Rapid 

 growth of crops at the time when nitrates are formed in 

 greatest amount, and lack of moisture for nitrification later 

 in the season when crop growth practically ceases, are two 

 factors which tend to prevent loss of nitrates. The practice 

 of fallowing, which fortunately is not very common nowa- 

 days, always results in a heavy loss of nitrates. Conditions 

 are ideal for nitrification and there are no crops to remove 

 the nitrates. 



Bicarbonates and sulphates of calcium and magnesium, 

 present in largest amounts in drainage water, are what 

 ordinarily make water "hard," although any soluble sub- 

 stance may be responsible for this condition. The hardness 

 of the water depends, of course, on the nature of the soil 

 drained. A limestone country yields a very hard water. 

 The bicarbonates of calcium and magnesium give a water 



