ABSORPTION OF AMMONIA BY SOIL. 143 



lows, as a matter of course, that the ammonia is divided 

 between the water and the soil, and that from a soil 

 fully saturated with ammonia, pure water will extract 

 a certain quantity of it ; just as charcoal will complete- 

 ly withdraw the colouring matter from a slightly 

 coloured fluid, but from one more deeply coloured will 

 extract a much larger quantity ; a part of which, how- 

 ever, is but feebly combined and may be removed by 

 water. 



In Yolker's experiments, treatment with a copious 

 amount of water extracted one-half the ammonia from 

 a soil saturated therewith ; the other half was retained 

 by the earth. 



Soils which contain much decaying vegetable mat- 

 ter absorb more ammonia and retain it more firmly 

 than soils that are poorer in decaying organic substan- 

 ces. Even assuming that two cubic decimetres of 

 earth, instead of one, are required to retain completely 

 the amount of ammonia indicated by the absorption 

 number, it is clear that ordinary manuring with an 

 agent abounding in ammonia, such as guano or salts of 

 ammonia, can enrich the earth with this substance only 

 to a very inconsiderable depth. 



To saturate with ammonia, a hectare (2-J- acres) of 

 Bogenhausen loam, from the surface downwards to the 

 depth of one decimetre, fully, or to half-saturate it to 

 the depth of two decimetres (7*8 inches), would require 

 a supply of 2600 kilogrammes or 52 cwts. of pure am- 

 monia, or 200 cwts. of sulphate of ammonia. 



If 800 kilogrammes of guano, containing 10 per 

 cent, of ammonia, are applied to a hectare of Bogen- 

 hausen soil, the amount of ammonia added is 80 kilo- 

 grammes (= 176 Ibs.), which is a little more than the 

 thirtieth part of the quantity required to half-saturate 

 the soil to a depth of 20 centimetres. "Without the 

 plough and harrow, the quantity of ammonia contained 

 in the guano would not penetrate, at the furthest, 

 deeper than 7 millimetres (= 0*27 inch). But to thrive 

 well, plants do not require a soil saturated with nutri- 

 tive substances ; for, the absorption numbers we have 



