FACTORS AFFECTING RESISTANCE 193 



and most cultivated grasses, may fail to give a satisfactory 

 crop because the alkali tends to concentrate near the 

 surface if evaporation is active. This accumulation makes 

 the salts very strong throughout the feeding zone of the 

 plant and, therefore, toxic even when the total quantity 

 of salts in the upper three or four feet 'is rather small. 

 Deep-rooted plants, like alfalfa and trees, may penetrate 

 the alkali strata by growing in the upper soil while the 

 alkali is beneath and gradually feeding lower as the alkali 

 accumulates at the surface. In this way some plants not 

 exceptionally tolerant may withstand what seem to be 

 excessive quantities when the whole feeding zone is not 

 considered. Where alfalfa, cotton, and other deep-rooted 

 plants get a good start but encounter a strong alkali 

 stratum at a short distance below, these plants may prove 

 less resistant than the cereals which may feed in the upper 

 less alkaline soil. The latter condition is especially marked 

 when alkali is accompanied by a hardpan or heavy clay 

 subsoil. The same may also be said of soils that are under- 

 lain by a shallow water-table, pasture or meadow grasses 

 and grains making much better crops than the deeper, more 

 resistant crops. 



Another important factor is the resistance of the plants 

 to reclamation methods. A few crops, among which are 

 alfalfa after once well started, sorgo, rice and berseem 

 clover, can endure the frequent heavy irrigations that may 

 accompany reclamation. The best crop of course depends 

 on the particular conditions, alfalfa doing well with good 

 drainage but not in a soil containing excessive quantities 

 of water, whereas some of the other crops like sorgo may 

 do best where drainage is not so good. During the re- 

 clamation process it is a great aid to have the land shaded 

 or cultivated in order to prevent alkali from rising. Alfalfa 



