198 CROPS FOR ALKALI LAND 



unhealthy. It is a very sensitive plant to black alkali 

 when in the seedling stage. 



The limits for an old stand of alfalfa range between 

 2000 and 7100 parts per million of total salts, according to 

 the various authors. The lower of these limits was for a 

 sandy soil, and Sanchez (25) states that on a loam soil a 

 higher concentration may successfully be withstood. That 

 the crop should produce a heavy mature crop on soil 

 containing 7100 parts per million, most of which was 

 sodium chloride, might have been due to the fact that there 

 was standing water at a depth of four feet and that the 

 salt was considerably diluted by the moisture. Most 

 estimates place the limits between 3000 and 4000 parts 

 per million of white alkali. 



With black alkali, or sodium carbonate, the observa- 

 tions on old alfalfa land vary between 300 and about 900. 

 These differences are partly due to the differences in the 

 nature of the soil and to the different methods of determin- 

 ing and expressing the results of the analyses. As this 

 salt is generally found in connection with other alkali 

 salts the limit can hardly be expected to be a definite 

 quantity even in soils of like character. Likewise, the 

 quantity of sodium chloride and sodium sulphate endured 

 successfully vary through a wide range modified by the 

 presence of other salts. Where the salt was mostly sodium 

 chloride, the variation assigned by the authorities ranges 

 from 2000 parts per million on a sandy soil to 7100 parts 

 per million on a loam soil well supplied with moisture. It 

 is probable that on a loam soil handled so as to protect it 

 from accumulation of alkali when the crop is not shading 

 the ground and kept well irrigated will support a satis- 

 factory growth of alfalfa when it contains as much as 4000 

 parts per million of sodium chloride. On a sandy loam 



