18 Mineral Nutrition of Plants 



portant in the aggregate, they are too small to be shown on a map of 

 this scale. 



Finally, we emphasize the vast areas of Latosols, especially in Africa 

 and South America. These are intensively used for crops in southeastern 

 Asia and in nearby islands, in Hawaii, in parts of northern Queensland, 

 and in many other small areas in Central America, South America, and 

 Africa. Nevertheless, great regions are little developed. Even if crop 

 production were increased on the Latosols only as much as it has on the 

 Gray-Brown Podzolic soils during the past 150 years, the results would 

 be enormous. The job is difficult; otherwise, it would not have waited 



so long. 



LAND AND FERTILIZER POTENTIALS 



It is obvious that any substantial increase in food production by boost- 

 ing yields on old land, and by bringing in new, will depend upon 

 vastly increased fertilizer use. What about potential fertilizer materials? 



Two years ago, Salter (6) made some estimates along this line. These 

 included not only 1,940,000,000 acres of existing crop land, but also the 

 suggested 1,300,000,000 acres of new land. 



Nitrogen can be obtained from the air wherever nitrogen-fixing 

 plants can be built. Thus, for nitrogen, industrial facilities, not raw ma- 

 terials, are limiting. Known reserves of mineral phosphate and potash 

 were estimated to be adequate for 2,000 and 500 years, respectively, 

 within an assumed rate of phosphate use eight times the present one, 

 and of potash use, eighteen times. These estimates, of course, take no 

 notice of probable deposits in the many inadequately explored parts of 

 the world. Nor do they allow for increasing efficiency in the use of 

 fertilizer, which also can be expected. Although fertilizers are in short 

 supply, the raw materials for them are abundant. 



CONCLUSIONS 



In our view, the soil problems, including the problems of fertility, 

 are manageable in the biological and physical sense. Through the ap- 

 plication of science and the expansion of research where needed, no 

 predictable limit of production can be foreseen. Of course, there must 

 be one, but it is very high. 



