BACTERIA IN THE INDUSTRIES 167 



In soils, the maximum bacterial activity dependent upon temperature, 

 is due to the warmth created by the sunUght. At the optimum soil 

 temperature, such plant foods as ammonia, nitrates, phosphates and sul- 

 phates, are rapidly formed. It is perhaps self-evident that soils in warm 

 countries furnish more available plant foods than the soils in cold or 

 temperate countries. The production of more plant food due to increased 

 bacterial activity results in the more vigorous growth of higher plants and 

 this in turn means the more rapid depletion of soil moisture. In warm 

 countries having rich soils, but with comparatively low annual rainfall, 

 the conservation of soil moisture is of the greatest importance. 



To sum up very brieiiy, soil bacteria are of the greatest importance in 

 agriculture. The farm cultural operations are for the purpose of 

 encouraging the growth and development of the beneficent soil and plant 

 bacteria to a maximum degree. The top soil must be kept fine for the 

 purpose of checking the evaporation of the capillary moisture. The 

 soil layers holding the capillary moisture must not be too fine nor yet 

 too coarse and must be frequently aerated by means of the cultivator. 

 Wet soil must be properly drained so as not to allow the development of 

 soil souring and otherwise objectionable algae, molds, protozoa and bac- 

 teria. If the soil is too dry, there is a paucity of desirable soil bacteria 

 and the other two groups of plant bacteria already mentioned. If the 

 •soil is inadequately aerated, bacterial development is greatly reduced. 



Soil Fertility and Bacterial Activity. — Soil fertility is directly depend- 

 €nt upon the available plant food which is present and the fertility is main- 

 tained in two ways. By the setting free (by chemical methods) of the 

 as yet unavailable plant foods which exist in the soil, and through the 

 addition to the soil of plant foods in the form of fertihzers. Of the latter, 

 only certain chemical fertihzers are directly available to the crop plants, 

 others must first be rendered available through bacterial activity. It is 

 true, all manures contain some available plant food but this also has been 

 the result of bacterial activity. If follows as a natural consequence that 

 the need for adding fertihzers to soils is reduced in the direct proportion 

 to the increase in the development of the normal and beneficent soil and 

 plant bacteria. How long the fertility or productiveness of a field may be 

 maintained by proper tillage, suitable crop rotation, intelligent summer 

 fallowing, green manuring, including the rational use of microbial crop 

 inoculation, has not yet been determined. It is known that soil has 

 yielded good crops for over one hundred years, without the addition of 

 chemical fertilizers or of manure. There can be no objection raised to 

 the intelligent use of fertihzers, excepting the cost and the labor of apply- 

 ing them. The time honored practice of spreading a top dressing of 

 rich soil, from a fertile field, upon virgin soil (virgin to the crop under 



