66 DRY FARMING 



People have become accustomed to thinking of the 

 bacteria and fungi wholly as enemies; we think only of 

 the ravages of disease. The science of bacteriology has 

 developed more along this line. In our farm practices 

 i.e. plowing, cultivation, manuring, etc., we give little 

 heed to the consideration of the effects of these opera- 

 tions on the bacterial activities of the soil. It is fortun- 

 ate indeed that the practices which favor the production 

 of crops from the plant standpoint are also favorable to 

 the activity of the beneficial bacteria. 



45. The Soil a Living Mass. The soil is inhabited by 

 five kinds of microorganisms, bacteria, fungi, algae, 

 yeasts and protozoa. The first four are vegetable or 

 plant forms of life, the last, protozoa, are miscroscopic 

 animals. Of the five groups the bacteria and fungi are 

 most important. It is with the bacteria that we are 

 mainly concerned, though the fungi take part in many of 

 the useful activities in the soil. 



The numbers of the bacteria in soils vary with the 

 type of soil, season of the year, moisture present, etc. 

 The number may vary from several million per gram in 

 a thin, poor soil, to a thousand million per gram in sew- 

 age farmed land. If, on ordinary soil, we assume a con- 

 tent of 60,000,000 per gram, 27,216,000,000 per pound of 

 soil, not at all an unreasonable or unusual number, we 

 find that the surface 6 2/3 inches of soil over an acre 

 (2,000,000 pounds) would contain a live weight of 

 bacteria equal to 250 pounds. This would represent a 

 volume of about 3.8 cubic feet. These figures bring out 

 the very great numbers of the bacteria and their ex- 

 tremely small size. Due to the very great numbers ever 

 present, the soil has frequently been spoken of as a 

 "living mass". 



