282 



SOIL PHYSICS AND MANAGEMENT 



face foot of soil. This is spoken of as the " rise of alkali " and the 

 effect is to ruin the land for ordinary crops. The result is well 

 shown in the table on page 281, where the surface foot contained 

 19,7(>0 pounds, while the same depth under natural conditions con- 

 tained 860 pounds. 



Amount and Composition of Salts in Alkali Spot from Center tb Circumference, 

 4 Feet Apart and 1 Foot Deep 3 



The irrigation canals and ditches sometimes pass through a 

 rather open soil that permits considerable seepage. It is estimated 

 that 30 per cent of the water taken in at the headgates is lost by 

 seepage from the canals themselves and another third is gone before 

 it is used for irrigation. 



This seepage water passes through the soil, dissolving the alkali, 

 and finally both water and alkali come to the surface in some slightly 

 lower place in the field. This alkaline water gives rise to alkali 

 marshes which, although very small at first, gradually increase in 

 size until much of the land is affected. The " rise of alkali " has 

 ruined large amounts of land because of the excessive use of irriga- 

 tion water. The desire of farmers to get their " money's worth " of 

 water has hastened their ruin. 



Effect of Alkali on Plants. A few plants have become adapted 

 to growing where large amounts of alkali are present and are in- 

 jured only when the soil becomes very strongly alkaline. There are 

 small local areas where the alkali is sufficient to kill all vegetation. 

 As a general rule, the^e alkali-resistant plants are not of much eco- 

 nomic importance. 



As a result of this poisoning, cultivated plants are injured to 

 varying degrees (Fig. 129). Where the alkali is very strong the 

 plants show a sickly growth and finally die without fruiting. If 

 less in amount they may become dwarfed and produce rather 

 scantily. Affected trees show a scanty leafage with small fruiting. 



The external injury done to plants is confined to a narrow zone 



