28 ARID AGRICULTURE. 



J 



clay, they are similar in several particular?. 

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

 erals contained in the rocks from which they 

 came and sometimes more, because of accumula- 

 tion of soluble salts. They are poor in humus, 

 or vegetable mold. 



Doctor ITilgard states that the soils over a 

 larger part of the arid region have never been 

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

 there is no percolation of Avnter through the soil' 

 to carry out soluble p.irt^. When the compacted 

 surface soil is broken up, aerate;! and put in ab- 

 sorbing condition, it catches the rains and SUOAVS 

 and the loAver soil which Avas before dry, becomes 

 saturated with the moisture 1 Avhich would -other- 

 Aviso 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 humid sections. Where the rain- 

 fall is heaA T y ? these salts have bc'en washed into 

 the drainage. They haA T e 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 shoAvn 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 



