No. 6. DEPARTMENT OF AGRICULTURE. 306 



bacte:ria of the: soil in thkir relation 



to agriculture. 



By Frederick D. Chester, Bacteriologist, Delaware AgriciMural Experiintnt Station 



The bacteria of tlie soil bear a most important relation to the nu- 

 trition of plants. If a soil be heated to a temperature sufficient to 

 destroy its bacterial life, the growth of plants will be maintained 

 therein only up to the point of the exhaustion of its easily soluble 

 and assimilable plant food, at the end of which time they will die 

 of starvation. The reason for this is that new plant food can no 

 longer be elaborated since the agents concerned in the latter process 

 are wanting. Should this condition of sterility of the soil continue 

 it can no longer produce crops, and were this condition universal the 

 world would become a barren waste. 



In every soil a series of complete chemical changes are taking 

 place, due to the activities of soil organisms. These changes involve 

 the digestion of crude plant food whereby an otherwise useless con- 

 stituent of the soil is put into such a state that it can be absorbed 

 by the plant. Digestion, therefore, implies the rendering soluble of 

 an otherwise insoluble substance. 



Nutrition whether applied to animals or plants implies three dis- 

 tinct processes; digestion, absorption and assimilation. Digestion 

 is the rendering soluble; absorption is the taking up of the soluble 

 products, while assimilation is the elaboration of new tissues from 

 the absorbed products. 



Substances to be absorbed must be so changed that they will dis- 

 solve in the fluids of the organisms, which in the case of an animal, 

 is the blood or lymph, and of the plant, its juices. 



Starch taken as food is insoluble in the fluids of the body; it 

 therefore cannot be absorbed until it is converted into a soluble 

 sugar A morsel of lean meat is insoluble, however fine its state of 

 division, hence before it can be absorbed it must be converted during 

 digestion into a soluble pepton. 



What is true of the crude elements of animal food is equally true 



of the crude plant food of the soil. Thus the granule of mineral 



matter, the bit of bone in a fertilizer, the shred of dried blood or 



other animal matter, the top and root of the clover turned under — 



20—6-1902 



