28 AEID AGEICULTUEE. 



clay, they are similar in several particulars. 

 They are rich in lime. They have all the min- 

 erals contained in the rocks from "\yhich they 

 came and sometimes more, because of accumula- 

 tion of soluble salts. They are poor in humus, 

 or vegetable mold. 



Doctor Hilgard states that the soils over a 

 larger part of the arid region have never been 

 wet to a depth of two feet. With light rainfall, 

 there is no percolation of water through the soil 

 to carry out soluble parts. When the compacted 

 surface soil is broken up, aerated and put in ab- 

 sorbing condition, it catches the rains and snows 

 and the lower soil which was before dry, becomes 

 saturated with the moisture which would other- 

 wise flow off the surface or be evaporated from 

 the upper layer. 



Soils in arid regions are much richer in solu- 

 ble alkalis, salts and mineral plant foods than 

 are the soils of himiid sections. Where the rain- 

 fall is heavy, these salts have been waslied into 

 the drainage. They have become a part of the 

 salt of the sea and are lost to agriculture. Some 

 of the minerals are essential plant foods, others, 

 soda and magnesia, seem to stimulate plant 

 growth. Still others, as lime, have a marked 

 effect on the character and condition of the soil. 



It has been shown that the humus in arid 

 regions contains an average of about three times 

 as much nitrogen as the humus of eastern soils. 

 Although our soils are poor in humus, they are 



