114 



L. T. SHARP 



The thickness of the film of hygroscopic moisture, calculated by 

 A. D. Halp2 as 0.00001 of an inch, may in itself offer sufficient 

 moisture for the maintenance of a portion of the soil flora. The 

 very minute size of the organisms may even permit of their 

 complete protection in soils of high hygroscopic power. This 

 suggests the necessity of increasing the water holding power and 

 hygroscopicity of soils in the arid regions by introducing organic 

 matter through green manuring. Certain extremely hygroscopic 

 salts, as salts of magnesia or the alkali nitrates, may gather 

 sufficient moisture to offer protection to bacteria, pro\aded the 

 solutions formed are not toxic, or do not bring about destructive 

 plasmolysis. 



Hygroscopic moisture is a protective factor, gravitational and 

 capillary water are rejuvenating forces. The reclamation of the 

 desert by irrigation must produce striking effects in the bacterial 

 flora of the soil. The results in this paper indicate that the 

 bacterial activity may be renewed by addition of sufficient mois- 

 ture to dry soils. Thus in ammonification and nitrogen fixation, 

 though the original number of organisms is limited, they become 

 physiologically active when placed in solutions. Nitrification 

 does not proceed, — except in two cases — because the extreme 

 drying period to which the soils had been subjected had entirely 

 destroyed the nitrification flora. Irrigation, suppl3dng the much 

 needed capillary moisture, must bring about rapid bacterial 

 development in the desert soils. 



SUMMARY 



1. Soils free from excessive alkali salts retained from 75,000 to 

 570,000 organisms per gram after thirty years drying under room 

 conditions. Alkali soils contained under similar conditions 5000 

 to 60,000 organisms per gram. 



2. The ammonification flora is most resistant, being especially 

 strong in the alkali soils. 



3. Nitrification occurs feebly in two soils and is permanently 

 destroyed in the other seven soils. 



" The Soil, p. 82. Button and Company, 1910. 



