EFFECTS OF ALKALI ON CROPS 313 



175. Indirect effect. Indirectly alkali salts may in- 

 jure plants by their influence upon the soil tilth, soil 

 organisms, and fungous and bacterial diseases. 



176. Effect upon different crops. The factors that 

 determine the tolerance of plants to alkali are: (1) The 

 physiological constitution of the plant. (2) The rooting 

 habit. 



The first is not well understood, but resistance varies 

 with species, and even with individuals of the same 

 species. So far as the rooting habit influences tolerance 

 of alkali, the advantage is with the deep-rooted plants 

 like alfalfa and sugar-beets, probably because at least 

 a part of the root is in a less strongly impregnated portion 

 of the soil. 



Of the cereals, barley and oats are the most tolerant, 

 being able in some cases to produce a fair crop on soil 

 containing one-tenth per cent of white alkali. Of the 

 forage crops, a number of valuable grasses are able to 

 grow with somewhat more than one-tenth per cent of 

 alkali. Timothy, smooth brome and alfalfa are the cul- 

 tivated forage plants most tolerant of alkali, although 

 they do not equal the native grasses in this respect. 

 Cotton will also tolerate a considerable amount of alkali. 



177. Other conditions influencing the action of alkali. 

 The larger the water content of the soil, the less the 

 injury to plants from alkali; but, should the same soil 

 become dry, the previous large quantity of water would, 

 by bringing into solution a larger amount of alkali, 

 render the solution stronger than it would otherwise have 

 been, and thus cause more injury. 



The distribution of the alkali at different depths may 



