318 EXPEBIMENT STATION BECOED. [Vol. 37 



Recent studies on nitrification in soils, J. U. Sabachaga {BoI. Min. Agr. 

 lArgentina'^, 20 (1916), No. 9-12, pp. 719-728).— This is a raview of recent work 

 by the author and others bearing ou the subject, in which several different types 

 of organisms were studied. 



It is concluded that nitrites are not normally found in a fertile soil, that the 

 reduction of nitrates is always brought about by a certain class of bacteria, 

 and that there are certain conditions of soil favorable to the reduction of 

 nitrates. It was found that none of the organisms examined possesses a 

 nitrifying power comparable to that of the organisms in soil. The total studies 

 appeared to demonstrate that with isolated species only a small amount of 

 nitric or nitrous acid was obtained in .solutions. 



Fixation of ammonia in soils, I. G. McBeth (U. S. Dept. Agr., Jour. Agr. 

 Research, 9 (1917), No. 5, pp. 141-155, fig. 1). — Experiments on the fixation of 

 ammonia by soils, conducted in cooperation with the California Citrus substa- 

 tion at Riverside, are reported. 



It was found that " many semiarid subsoils have the property of fixing large 

 quantities of ammonia. Much of the ammonia fixed can not be removed by the 

 ordinary methods for determining the ammonia content of the soils. Extract- 

 ing the soil with 10 per cent hydrochloric acid gives approximately the same 

 quantity of ammonia as distilling the soils with magnesium oxid. Anions 

 apparently have little or no influence on the fixation of ammonia by .soils. The 

 ammonlaeal 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 witli magnesium oxid frequently fail to 

 give a satisfactory agreement. A large percentage of the ammonia added to 

 semiarid soils and subsoils can not be recovered by boiling the soil with exces- 

 sive amounts of caustic solutions. Boiling soils with 10 per cent hydrochloric 

 acid removes practically all of the ammonlaeal nitrogen from one soil studied, 

 but less than 75 per cent was recovered from another .soil. 



" The fixation of ammonia by semiarid soils increases with depth. In this 

 regard semiarid soils appear to differ from humid soils. The addition of 

 ammonum salts in a concentrated solution results in greater fixation than 

 when the same amount is added in a dilute solution. The fixation of ammonia 

 by soils increases with the temperature. The fixation of anmionia by a soil is 

 most rapid during the first few minutes, but tiie fixation process appears to 

 continue for several days. Heating a soil for six hours at temperatures of 

 200° C. or above reduces its power of fixing ammonia. 



" When small amounts of ammonium salts are added, the percentage 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 abso- 

 lute fixation may continue to increase. 



"Aluminum, iron, and potassium salts added to soils prior to the addition 

 of ammonia reduce the ammonia-fixing power of the .soils very decidedly. Cal- 

 cium, 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 

 semi-arid soils. The anions of aluminum, iron, potassium, calcium, sodium, or 

 magnesium salts apparently have no influence on the action of these salts in 

 reducing the ammonia-fixing power of semi-arid soils. 



" In semiarid soils the quantity of calcium brought into solution by ammo- 

 nium chlorid increases with depth ; when extracted with aluminum, sodium, or 

 magnesium chlorid, the calcium brought into solution does not increase with the 

 depth." 



Relation of the transformation and distribution of soil nitrogen to the 

 nutrition of citrus plants, I. G. McBeth (f7. S. Dept. Agr., Jour. Agr. Rescnrch, 



