456 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



they are back in the soil ready to nourish a new generation and start 

 the cycle again. The population on the surface of the soil, including 

 ourselves, is thus entirely dependent on the population, mostly in- 

 visible to our eyes, living within it. 



Much of our agricultural effort is really an attempt to help the soil 

 population prepare the food for the next generation of plants. Plant 

 residues — grass and clover leys, straw mixed with animal manure — 

 are ploughed into the soil so that the soil population can get at it 

 more easily. E. W. Russell * compared the number of calories of 

 human food produced with the number in the organic matter supplied 

 per acre to the soil population : 13 million calories had been given, 

 which would have sufficed for 12 persons for a year, but the calories 

 in the human food produced numbered 2 million, sufficient for the 

 needs of two persons only. More economical procedures are now 

 known, but even the best are extravagant, and much research is needed 

 to insure a more equitable distribution. 



It will ultimately be necessary to obtain control of the soil popula- 

 tion so as to insure more efficient working in our interests. For this 

 purpose the soil population must be studied as a whole and not in 

 isolated groups. Fortunately the subject is attracting increasing at- 

 tention and much good work is now being done. Considerable prog- 

 ress may be expected in the near future. 



* Russell, E. W., Soil conditions and plant growth, 9tli ed., Longmans, 1961. 



