62 DRY LAND FARMING 



elements of plant food, especially those that are mineral 

 in character, than the soils of humid areas, and in many 

 instances it is easier to maintain them in proper condition 

 as to tilth after they have been broken. The sparse char- 

 acter of the vegetation that frequently grows on them in 

 a state of nature still further enhances the contempt 

 which many persons from humid regions cherish for the 

 soils of the semi-arid country when they first see them. 

 Soils in dry areas are much richer in soluble salts, 

 alkalies and mineral plant food than the soils of humid 

 areas. They have all the minerals contained in the rocks 

 from which they come, and of soluble salts there may 

 be even an accumulation. They have not been washed 

 out as in humid areas. The soluble silica and alumina 

 which indicate the availability of these soils are about 

 2J^ times greater in the former and about 4 times greater 

 in the latter than in the soils of humid climates. Soda 

 and magnesia, which up to a certain limit stimulate plant 

 growth, are also plentiful. Where the accumulation of 

 these is excessive, vegetation partly or wholly disappears. 

 Phosphate, potash and lime are also more abundant in 

 dry than in humid soils. It has been claimed that the 

 phosphate is from 1 to 2 times greater on the average, 

 that potash is more than 3 times greater, and that lime 

 is frequently from 10 to 12 times greater. It is fortunate 

 that so much lime is present in semi-arid soils. Among 

 the benefits resulting from its presence are the follow- 

 ing: (1) It aids in the quick conversion of organic matter 

 into humus, and this in many instances represents the 

 main portion of the nitrogen content of the soil. (2) In 

 so doing it encourages the presence and action of bac- 

 terial life, which is an important factor in maintaining 

 and developing soil fertility. (3) It aids in liberating 

 and rendering more available the phosphoric acid and 

 potash in the soil through the chemical changes which it 

 brings about. (4) It tends to prevent acidity in soils 



