BACTERIA IN THE INDUSTRIES 165 



As is known certain plants survive in air dry soils because they them- 

 selves carry a surplus water supply upon which they draw during the rainless 

 season. To this group of plants belong the cacti, the palms, the cycads 

 and others. The plants with succulent or fleshy roots, as the radish, 

 beet and turnip, store water for use during seasonal dry spells. In these 

 cases the bacteria living upon the root surfaces, or in the root tissues, 

 continue to multiply. 



The essentials of field cultural operations, as far as bacterial develop- 

 ment and soil moisture are concerned, may be stated as follows. No 

 farm implement should ever be allowed to operate in the soil layers con- 

 taining hydrostatic water. All farm implements may work freely in 

 soils with capillary moisture, especially during the early growing season. 

 During the actively growing season the cultivator should keep the soil 

 layers containing the hygroscopic moisture, fine to very fine and should 

 penetrate through the air dry layers into the soil containing capillary 

 moisture, to a depth of several inches. Keeping the top layer of the soil 

 fine reduces the loss of moisture by evaporation. 



Numerous scientific tests have been made (Russell. Rothamsted 

 Exp. Station, England, and others) which prove that soils which are par- 

 tially sterilized by exposing them to a temperature of 60 C. improves the 

 productiveness, due to the fact that the harmful protozoa (harmful 

 because they feed upon the soil bacteria) present are largely killed at 

 that temperature whereas trie more resistent soil bacteria survive and 

 continue their beneficent work unhindered by the protozoa. Similar 

 results follow when soils are exposed to certain antiseptic vapors, as of 

 toluene, benzine, benzol, etc., which also destroy the objectionable pro- 

 tozoa without killing the soil bacteria. These undoubtedly beneficial 

 methods of partial sterilization of soils are not practicable on a large 

 agricultural scale. The farmer must therefore employ those methods 

 of cultural operation which will encourage to a maximum, the destruction 

 as well as inhibition of the agriculturally objectionable protozoa (including 

 also other objectionable organisms), and at the same time encourage to 

 the optimum degree the growth and multiplication of the desirable soil 

 bacteria (including also some other organisms). This, as has already 

 been suggested, is accomplished through tillage, drainage, cultivation, 

 etc. Soils which are excessively wet, though otherwise satisfactory, will 

 encourage the water loving protozoa; and moist soils very rich in humus 

 are apt to encourage the development of the soil souring molds. Proper 

 drainage and tillage prevents these troubles. 



2. Soil Aeration and Bacterial Development. The beneficent soil bac- 

 teria are essentially aerobes (requiring free or uncombined atmospheric 

 oxygen) as already stated, and in order that they may develop to a 



