THE PROPERTIES OP SOIL 45 



solutions of chemical substances that serve 

 as plant food were subsequently poured on 

 the top of the soil in these tubes, it would 

 be found that in some cases the solutions 

 that drained away from the bottom of the 

 cylinders were weaker than the solutions that 

 had been poured in on the top. Clearly, 

 therefore, the soil had, in some way or 

 other, abstracted material from the solutions. 

 In other cases it would be found that the 

 solutions draining away from the foot of the 

 tubes were of as great strength as those which 

 were poured in above. It is evident that 

 substances which are absorbed by the soil 

 are in least danger of being lost in drainage 

 waters, while those that are not so absorbed 

 have more chance of escaping, and of being 

 lost so far as crops are concerned. The 

 three most important elements of plant food 

 that are supplied in artificial manures behave 

 somewhat differently as regards this property 

 of soil. Potash and phosphoric acid, even in 

 a soluble form, when applied in moderate 

 quantities, are not in danger of being lost to 

 any appreciable extent. The danger, there- 

 fore, of loss through heavy rainfall is not 

 great in the case of these substances. As 

 regards nitrogen, it is found that when this is 

 applied in the form of ammonia, e.g. sulphate 



