The Influence of Man on Soil Fertility 1 



By G. V. Jacks 



Director, Commonwealth Bureau of Soils 



Rothamsted Experimental Station 



Harpenden, Herts., England 



By Man, spelled with a capital M, .1 mean human societies, includ- 

 ing men and women, cows, crops, microbes, cars, steelworks, and stock 

 exchanges. By soil fertility I mean the capacity of a soil to produce 

 living material, regardless of how the soil acquired that capacity. 

 If one man treats a spoil heap with fertilizers he may produce a fertile 

 soil within a year, but the fertility will be evanescent, and he will not 

 find it worth his while to maintain it. But Man — human society — 

 may judge it worth while to reclaim the spoil heap for permanent 

 agriculture, in which case he sets in motion some long-term processes 

 largely governed by such things as the output of cars, activity in the 

 steel industry, and level of the bank rate. These are among the 

 major factors which determine the influence of Man on the present-day 

 evolution of our soil. 



When a soil scientist studies the influence of a forest on soil forma- 

 tion he pays most attention to the influence of the tree canopy, which 

 is the dominant living influence on the soil because it conditions the 

 existence and activities of all the lesser living factors such as the 

 ground flora, the fauna, and the soil micro-organisms. But when a 

 soil scientist studies the influence of Man on the soil he gives all his 

 attention to the direct operations of the farmer and cultivator, the 

 downtrodden ground flora of the human forest, and ignores the domi- 

 nant influence exerted on the farmer's daily and secular activities by 

 social and economic emanations from the canopy of the towns. My 

 theme will be mainly the influence of towns on the secular evolution 

 of the soil. 



In embryonic societies, before towns exist, nearly everybody is en- 

 gaged in food production, agriculture is of the self -sufficient type, and 



1 Address delivered at the Sheffield Meeting of the British Association for the 

 Advancement of Science on Thursday, August 30, 1956. Reprinted by permission 

 from The Advancement of Science, No. 50, September 1956. 



325 



