IN LOAM SOIL 53 



while sodium sulphate is considerably less harmful than 

 the former two salts. 



In Loam Soil. From a practical point of view loam 

 soil is a much more desirable medium for studying the 

 effect of alkali on plants than is either sand or a solution. 

 Absorption, antagonism, and physical conditions must 

 all eventually be taken into consideration before the real 

 toxic effect of the salts under normal conditions can be 

 arrived at correctly. 



The use of loam, or other soil containing organic matter 

 and having high absorptive properties, complicates the 

 determination of the toxicity of salts. Harris and Pitt- 

 man (n) found that of two soils containing equal quantities 

 of alkali and equivalent moisture contents, wheat on the 

 soil with highest organic matter was injured less than 

 where the organic matter was about as it is in ordinary 

 loam. The organic matter appeared to remove sodium 

 carbonate from the soil solution so that this salt appeared 

 less toxic than has usually been ascribed to it from solu- 

 tion or sand cultures or field extraction experiments. 

 Wheat plants tolerated more alkali in a loam than in either 

 a sand or clay and more in a coarse loam than a finer one 

 with the same percentage of moisture, although with 

 equivalent moisture contents the coarser loam was less 

 tolerant than the finer. The toxicity of the salts de- 

 creased with increasing percentages of soil moisture up 

 to the maximum moisture content producing good crops. 

 Changing the moisture relationship of the soil influenced 

 the toxicity of sodium chloride and sodium sulphate more 

 than did changing the organic matter, but the organic 

 matter had the greater influence for sodium carbonate. 

 High organic matter and moisture content offered the 

 most favorable conditions for alkali toleration. 



