INFLUENCE OF MAN ON SOIL FERTILITY — JACKS 333 



soil exhaustion from going too fast. The soil-conservation district 

 aims not only to prevent soil erosion, but also to build up fertility — 

 which was impossible under the three-field system. The soil-con- 

 servation district may well turn out to be the characteristic not only 

 of the final stage of the soil-exhausting phase in these rapidly grow- 

 ing nations, but also of the emerging fertility-producing phase. It 

 was originally devised to check the precipitate exhaustion of the soil 

 that, in the previous absence of any social control, was getting out 

 of hand, but it is now being used everywhere to build up soil fertility. 

 The soil -exhausting phase is merging into the fertility -producing 

 phase. 



In South Africa, in particular, the soil-conservation-district move- 

 ment has swept through the country within the last few years only. 

 A sudden impetus has been given to soil conservation, the results of 

 which have not had time to appear, but there can be no doubt about 

 the impetus which, again, may not last. It does seem, however, 

 that the great progress and prosperity of South African industry are 

 convincing farmers that it will pay them to invest in soil fertility, 

 for example, by adoption of ley farming, by applying sulfate of 

 ammonia to grassland in order to build up the soil's humus content, 

 and other measures whose lasting efficacy cannot be known for many 

 years. The significant fact is that the spirit of soil conservation is 

 abroad, inspired by the money flowing from South Africa's young 

 industries. 



Australian pastoral and arable farming is also tending to become 

 fertility-producing, though, as in South Africa, the revolution, if it 

 is one, has scarcely begun. 



The creation of more fertility than was present originally in Aus- 

 tralia's soils has been made possible by using superphosphate to grow 

 wheat and clover. Australian soils are among the oldest in the world, 

 and were poor in the two essential plant nutrients, phosphorus and 

 nitrogen, even before soil-exhausting farming began with the arrival 

 of the white man. Wheat and wool have since removed much of the 

 remaining nutrients. Deficiency of phosphate is widespread in both 

 agricultural and pastoral land, and trace-element deficiencies are 

 common. A general advance in Australian soil fertility can only be 

 achieved by overcoming these deficiencies. There is also a deficiency 

 of water that is more difficult to overcome, but Australia has a long 

 way to go before water becomes the final limiting factor. 



By applying superphosphate to the — to European eyes — miserable 

 Australian pastures which, nevertheless, produce the finest wool in the 

 world, dense crops of subterranean clover can be grown that enrich 

 the soil with nitrogen, double or treble its carrying capacity, and pro- 

 vide humus for more intensive arable farming. By such simple 



