INFLUENCE OF MAN ON SOIL FERTILITY — JACKS 327 



cannot be increased merely by getting the soil to take in its own 

 washing, that is, by self-contained or self-sufficient farming which, 

 at best, returns to the soil only a part of what is removed from it. 

 The fertility-producing farmer must be able to buy, or otherwise 

 procure, fertility from outside and he must have a continuing economic 

 incentive to do so. There are various ways in which farmers can 

 acquire money and various forms in which they can buy soil fertility 

 (by which I mean anything or any measure that will increase yields) ; 

 but, in general, farming Man can earn enough not only to pay for his 

 necessities and luxuries, but also to improve his land in the hope of 

 further gain, only by selling to a stable and wealthy market — a town 

 which produces many times more real wealth per acre than the best 

 soil can. In this industrial age enough wealth is being produced in 

 the towns and cities of the world to fertilize very large areas of food- 

 producing land. Most of the people in the cities have enough to eat ; 

 most of the 60 percent of the world's population that are underfed 

 are producers of food. 



I have so far distinguished three stages in the evolution of soil 

 under Man. First, there is the shifting-cultivation stage when human 

 activity has only an ephemeral effect on the soil. This stage is as- 

 sociated with a low density of population, and may not occur in 

 societies living in places, like Egypt, irrigated by fertility-producing 

 water. Secondly, as and when population increases, permanent settle- 

 ment occurs and soil-exhausting agriculture is practiced because society 

 has few other sources of wealth than the soil to draw on. Society tends 

 to develop a structure which prevents too rapid an exhaustion of the 

 soil. This we may call the soil-exhausting stage. Thirdly, as the 

 population increases further it congregates in towns, reducing the 

 pressure on overworked, unimproved land, but gradually increasing 

 the demand for its produce. Towns produce wealth from other sources 

 than the soil, which enables them to pay for their demands and makes 

 it profitable for farmers to satisfy them by investing money in soil 

 fertility. We may call this the soil-conserving or fertility-producing 

 stage. Society becomes urbanized and largely loses interest in agri- 

 culture, but wealth continues to flow from the towns into the soil. 

 A state of equilibrium may be reached when the input of soil fertility 

 by the towns is balanced by the output in rich harvests. 



What happens subsequently is not clear. We have examples of all 

 these three stages of social and soil evolution in the world at the 

 present time, and we may have examples of a later stage of soil evolu- 

 tion under Man in the overpopulated, because underurbanized, re- 

 gions of southeast Asia where nearly half the people in the world live. 

 We do not know whether yields in India and China were once higher 

 than they are today when they are much too low to support, except 



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