402 SOILS: PROPERTIES AND MANAGEMENT 



316. Control of alkali. — Where excessive amounts of 

 soluble salts do not exist in a soil, the control of the alkali 

 with a view of keeping it well distributed in the soil 

 column is the best practice. The retardation of evapora- 

 tion is, of course, the main object in this procedure. The 

 intensive use of the soil mulch is therefore to be advocated, 

 especially in all irrigation operations where alkali concen- 

 trations are likely to occur. Such a method of soil 

 management not only saves moisture, but also prevents 

 the excessive translocation of soluble salts into the root 

 zone. This method of control is the most economical, 

 the cheapest, and the one to be advocated on all occasions, 

 no matter what may have been the previous means of 

 dealing with the alkali situation. 



317. Cropping with tolerant plants. — Certain soils 

 that are strongly impregnated with alkali may be grad- 

 ually improved by cropping with sugar beets and other 

 crops that are tolerant of alkali and that remove large 

 quantities of salts. This is more likely to be efBcacious 

 where irrigation is not practiced. Certain crops, more- 

 over, while somewhat seriously injured while young, are 

 very resistant once their root systems are developed. 

 A good example is alfalfa, the young plants being very 

 tender while the more mature ones are extremely resistant. 

 Temporary eradication of alkali may allow such a crop to 

 be established. It will then maintain itself in spite of the 

 concentrations that may later occur. 



318. Alkali spots. — In semiarid regions small areas of 

 alkali are often found, varying from a few square yards 

 to several acres in size. The quantities of alkali in these 

 are usually not sufficient to prevent the growth of plants 

 in years of good rainfall, but in periods of drought the 

 concentration of the salts and the compact condition that 



