Apr. 30, 1917 
Fixation of Ammonia in Soils 
155 
(12) When small amounts of ammonium salts are added, the per¬ 
centage of ammonia fixed remains constant. If increasing amounts of 
ammonia are added, a point is reached at which the percentage fixation 
becomes less, but the absolute fixation may continue to increase. 
(13) Aluminium, iron, and potassium salts added to soils prior to the 
addition of ammonia reduce the ammonia-fixing power of the soils very 
decidedly. 
Calcium, magnesium, and sodium salts added to the semiarid soils 
prior to the addition of the ammonia have little effect on the ammonia¬ 
fixing power of semiarid soils. 
(14) The anions of aluminium, iron, potassium, calcium, sodium, or 
magnesium salts apparently have no influence on the action of these salts 
in reducing the ammonia-fixing power of semiarid soils. 
(15) In semiarid soils the quantity of calcium brought into solution 
by ammonium chlorid increases with depth; when extracted with 
aluminium, sodium, or magnesium chlorid, the calcium brought into 
solution does not increase with the depth. 
