OVER-IRRIGATION AND ALKALI 395 



For fruit trees, the tolerance of Glauber salts varies 

 from 0.25 to 0.025 of 1 per cent; of common salt from 

 0.062 to 0.005 of 1 per cent; of sal-soda from 0.005 to 

 0.0001 of 1 per cent. For the small cultures, tolerance of 

 Glauber's salt, as of salt and sal-soda, is increased con- 

 siderably. However, the variation for various crops in 

 the table is so great as to make it practically impossible 

 to lay down any definite rules that may be generally used 

 in agriculture. Loughridge concludes that, in general, for 

 fruit trees, the maximum tolerance of alkali in the soil 

 ranges from 0.28 per cent to 0.04 per cent; for small 

 cultures, excluding the salt bushes, from 1.0 per cent to 

 0.06 per cent. 



The experience of the Bureau of Soils is perhaps the 

 best for formulating limits of the tolerance of plants for 

 alkali. The staff of the Bureau of Soils has investigated 

 practically every important alkali area of the United States. 

 They have had ample opportunity to correlate the 

 growth on the soil with the alkali content. It has been 

 found that on land containing, to a depth of 6 feet, 

 up to 0.2 per cent of total alkali, none of the common 

 crops are injured, unless carbonates greatly predominate, 

 or unless most of the salt is concentrated in the upper 

 part of the first foot. On land containing from 0.2 per 

 cent to 0.4 of total alkali, or from 0.05 to 0.1 per cent of 

 black alkali, or 0.5 per cent of sodium chloride, or 1 per 

 cent of sodium sulfate, all but the most sensitive crops 

 will grow. Near the higher limits, all but the most resis- 

 tant crops show signs of distress. A grade of land contain- 

 ing from .4 to .6 per cent of total alkali and from .1 to .2 

 of black alkali contains a little too much for common 

 crops. Pastures usually grow on such land. Where the 

 land contains from .6 to 1 per cent of total alkali it is 



