Sick Soils not Influenced by Parasites 35 



latter does not act so much on the soil as on the or- 

 ganic matter, turning it black. This black material 

 is always found on the surface with the salts. The 

 blackening of the soil, however, is not always an 

 indication of black alkali. Many dark spots are 

 found to contain the white alkali. Moreover, soils 

 which contain little or no organic matter may con- 

 tain large quantities of sodium carbonate and never 

 turn black. The white alkali in reality is not a true 

 alkali. The salts found in it are sodium chloride or 

 table salt, calcium sulphate or gypsum, sodium sul- 

 phate, magnesium sulphate or Epsom salt. In 

 addition to these may be found salts of potassium. 

 Table 7, taken from Harris, x shows a comparative 

 study of the total soluble salts which are found to be 

 injurious to plants. 



TABLE 7 



Summary of Total Soluble Salts, Chlorides, Carbonates, 



and Sulphates in Alkali Soils. Average to a Depth 



of Four Feet, Parts per Million of Dry Soil. 



Parts of field producing best crop 



x Harris, F. S., Utah Agr. Expt. Sta. Bui., 145 13-21, 1916. 



