154 
Journal of Agricultural Research 
Vol. IX, No. s 
Of the five salts used, aluminium chlorid gave the maximum effect, 
while the minimum effect was found with the sodium chlorid. The 
addition of an ammonium salt to a nonammoniacal salt gave a greater 
effect than when either of the salts was used alone. It is also observed 
that the increase in the solubility of calcium due to the addition of 
aluminium, sodium, or magnesium chlorid is fairly constant for the 
different depths, while the amount of calcium dissolved by the ammonium 
salts when used alone or in combination with other salts increases with 
the depth in the semiarid but not in the humid soils. This would seem 
to indicate a possible relation between the removal of calcium and the 
fixation of ammonia; but the data collected are too limited to warrant 
any definite conclusion at this time. 
SUMMARY 
(1) Many semiarid subsoils have the property of fixing large quanti¬ 
ties of ammonia. Much of the ammonia fixed can not be removed by 
the ordinary methods for determining the ammonia content of the soils. 
(2) Extracting the soil with 10 per cent hydrochloric acid gives 
approximately the same quantity of ammonia as distilling the soils with 
magnesium oxid. 
(3) Anions apparently have little or no influence on the fixation of 
ammonia by soils. 
(4) The ammoniacal nitrogen removed from duplicate samples of 
soil extracted with 10 per cent acid gives remarkably consistent results, 
while duplicate samples of soil distilled at atmospheric pressure with 
magnesium oxid frequently fail to give a satisfactory agreement. 
(5) A large percentage of the ammonia added to semiarid soils and 
subsoils can not be recovered by boiling the soil with excessive amounts 
of caustic solutions. 
(6) Boiling soils with 10 per cent hydrochloric acid removes practi¬ 
cally all of the ammofiiacal nitrogen from one soil studied, but less than 
75 per cent was recovered from another soil. 
(7) The fixation of ammonia by semiarid soils increases with depth. In 
this regard semiarid soils appear to differ from humid soils. 
(8) The addition of ammonium salts in a concentrated solution results 
in greater fixation than when the same amount is added in a dilute 
solution. 
(9) The fixation of ammonia by soils increases with the temperature. 
(10) The fixation of ammonia by a soil is most rapid during the first 
few minutes, but the fixation process appears to continue for several 
days. 
(11) Heating a soil for six hours at temperatures of 200° C. or above 
reduces its power of fixing ammonia. 
