394 SOILS: PROPERTIES AND MANAGEMENT 



Black alkali is much more destructive to vegetation 

 than is white. A quantity of white alkali that would 

 not seriously interfere with the growth of most crops 

 might completely prevent the development of useful 

 plants if the alkali were black. 



305. Effect of alkali on crops. — The presence of 

 relatively large amounts of salts dissolved in water and 

 brought into contact with a plant cell has been shown to 

 cause a shrinkage of the protoplasmic lining of the cell, 

 the shrinking increasing with the concentration of the 

 solution. This causes the plant to wilt, to cease growth, 

 and finally to die. The nature of the salt, and the species 

 and even the individuality of the plant, determine the 

 point of concentration at which the plant succumbs. 



The directly injurious effect of the chlorides, sulfates, 

 nitrates, and other salts of the alkalies and alkali earths 

 is due to this action on the cell contents of the plants. 

 The carbonates of the alkalies have, in addition, a cor- 

 roding effect on the plant tissues, dissolving the parts 

 of the plant with which they come in contact. Indirectly 

 alkali salts may injure plants by their influence on the 

 soil tilth, soil organisms, and fungous and bacterial 

 diseases. 



306. Effect on different plants. — The factors that 

 determine the tolerance of plants toward 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 such as alfalfa and sugar beets, probably because 

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

 of the soil. 



