Kellogg and Orvedal 17 



Europe alone used 59 per cent of all nitrogen, 63 per cent of all phos- 

 phoric acid, and 78 per cent of all potash in the world's fertilizer. 

 Within Europe, these fertilizers were used largely in Germany, France, 

 Denmark, Britain, and the Low Countries (/). 



North of the Gray-Brown Podzolic soils is a great area of Podzols 

 and their associates in North America and Eurasia. Large percentages 

 of these are too stony, too sandy, too hilly, or too swampy for feasible 

 cultivation. A large part of the area has only a very short growing 

 season. However, some of the Podzols are under cultivation, and more 

 could be cleared and cultivated. The fertility problems are similar in 

 kind, but perhaps greater in intensity, to those of the Gray-Brown Pod- 

 zolic soils. At least, lime and fertilizers are usually needed almost at 

 once after clearing, for efficient production. 



Between the Gray-Brown Podzolic soils and the Chernozems are the 

 highly productive Prairie soils and Degraded Chernozems. They are less 

 leached than the Podzolic soils but have more moisture than the Cherno- 

 zems. The fertility problems are also intermediate. After some period 

 of cultivation, the length of which varies with the local soil type, lime 

 or fertilizers or both are required for efficient production on many of 

 the local soil types. Phosphates are of first importance, generally, in 

 mixed farming. Even then, supplemental nitrogen often gives responses 

 on corn. 



The Chernozem and Reddish Chestnut soils are found mainly in 

 Eurasia, North America, and South America, although there are im- 

 portant areas in Australia and elsewhere. These are the great wheat- 

 producing areas. 



Besides the Chernozems, there are Dark Gray and Brown soils in the 

 tropics. These are also fairly rich in mineral nutrients, more so than 

 the Latosols, but they are relatively low in organic matter and nitrogen 

 despite the dark color. 



On the dry side of the Chernozems are the Chestnut, Brown, and 

 Reddish-Brown soils. The fertility problems here are intermediate be- 

 tween those of Chernozems and those of Desert soils. 



Vast areas of soils in deserts and semideserts are found in Africa, 

 Asia, and Australia. Except for very extensive grazing, agricultural use 

 is limited largely to the irrigated places. Although these are very im- 



