46 AGRICULTURE 



of ammonia, it is fairly well fixed by the soil, 

 whereas when the nitrogen is in the form of 

 nitric acid, e.g. nitrate of soda, the soil has 

 practically no power to remove it from 

 solutions. Lime, magnesia, and soda are 

 also but little removed from solutions, and 

 therefore these substances, in common with 

 nitrates, bulk comparatively largely in the 

 drainage water of our fields. 



In connection with this subject it may be 

 mentioned that the soil absorbs relatively 

 most from weak solutions, while its power of 

 absorption is reduced almost in proportion 

 to the strength of the solution. If, for 

 instance, a solution containing one-twentieth 

 per cent, of sulphate of potash is poured 

 through soil, about one-half may be removed ; 

 but if the solution is twenty times as 

 strong, that is to say, if the solution is of the 

 strength of one per cent., the percentage of 

 potash absorbed will only be about one-third 

 of the relative quantity removed in the other 

 case. There is therefore greater danger of 

 loss by drainage where one applies a very 

 heavy manurial dressing than where one is 

 giving only moderate doses. 



The causes of such removal of substances 

 from solution are rather various, but in the 

 case of mineral substances the agents that 



