NUTRIENT SOLUTIONS 43 



approaches. Since the conditions under which plants 

 grow at different times is modified by rainfall, movement 

 of ground^ water, evaporation, and other factors, an analysis 

 of the soils at a particular period of growth is not so definite 

 for indicating toxicity as might be wished*. Because of 

 the difficulty in fixing definite toxic limits under field 

 conditions, these observations will not be considered in 

 the present discussion but will be reserved for Chapter XIV 

 dealing with crops for alkali land. 



Toxicity in Solution. Some of the first attempts to 

 establish the toxic limits of alkali were made in solution 

 cultures because the solution was easy to make up, easy 

 to analyze subsequently where it was desired to learn the 

 final concentration of the water, and because such com- 

 plicating factors as absorption of the salts, moisture con- 

 tent of the soil, and nature of the soil were eliminated. 

 Some of the experiments were carried on in cultural media, 

 such as Knop's solution, in an attempt to duplicate soil 

 conditions as nearly as possible, whereas others were made 

 in water containing only alkali salts. 



Nutrient Solutions. Some of the nutrient-solution 

 cultures were carried to later stages of growth than those 

 with the toxic salts alone. Since, however, the strength 

 of the nutrient solution, its composition, and other factors 

 modify the results almost as much in some cases as the 

 alkali salts the advantages of the culture media over the 

 simple solutions are not so apparent. Plants are usually 

 at their most critical life period in the seedling stages 

 where they are still depending on the seed for their nu- 

 trition. The results of LeClerc and Breazeale (17) show 

 the tolerance of wheat seedlings for sodium chloride in 

 culture solutions to be about 3000 parts per million, 

 which is not essentially different from certain other results 



