THE NITROGEN CYCLE 467 



it has been found that the mere drying of soils effects 

 important changes in their solubility and in the bacterial 

 processes that occur in them. As the result of the in- 

 vestigations, certain well-established facts have been 

 worked out in connection with certain treatments when 

 applied to most soils. 



385. Effects of carbon bisulfide and heat on properties 

 of soils. — Volatile antiseptics usually increase the pro- 

 ductiveness of soils, although there may be at first a slight 

 temporary retardation of plant growth. It is of course 

 customary to permit the antiseptic to volatilize from 

 the soil before seed is planted. For this purpose the soil 

 is spread out in a thin layer, in which condition it is al- 

 lowed to remain until the odor of the antiseptic has dis- 

 appeared. The soil is then placed in vessels and moistened 

 and the seeds are planted in it. 



Other characteristic effects of treatment with volatile 

 antiseptics reported by different investigators are : (1) 

 an initial decrease in the numbers of bacteria, followed by 

 a long-continued increase ; (2) a disturbance of the equi- 

 librium of the flora, by which certain bacteria multiply 

 more rapidly than others; (3) a slight initial increase 

 in ammonia content, followed by a considerable increase 

 in the rate of production of ammonia; (4) depression of 

 the process by which ammonia is converted into nitric 

 acid, and a very slow recovery in the activity of the bac- 

 teria concerned, as a result of which ammonia accumulates 

 in the soil ; (5) an increase in the rate at which oxidation 

 takes place in soils ; (6) destruction of protozoa. 



386. Hypotheses to account for effects of carbon 

 bisulfide and of heat. — A number of hypotheses have 

 been formulated by which to account for the increased 

 plant growth and for changes induced in soils by treat- 



