50 



Journal of Agricultural Research 



practical limit ranging from 0.4 per cent for Canada field peas up to 

 I per cent for barley. Sodium chlorid showed about the same toxicity 

 for all the crops except barley and oats, which were slightly more resist- 

 ant. The striking point about this diagram is the fact that the relative 

 toxicity of the different salts varies for each crop. 



SUMMARY 



(i) The effect of the various alkali salts in soils on plant growth and 

 the quantity of alkali that must be present to injure crops are of great 

 practical importance to farmers in arid regions, as well as of considerable 

 interest to the scientist. 



(2) A great amount of work has already been done on alkali, but this 

 does not give all the information that is needed. 



Fig. 47. — Diagram showing the percentage of alkali salt in coarse sand giving about half normal gennina- 

 tion and production of dry matter in wheat. 



(3) In this paper results of over 18,000 determinations of the effect 

 of alkali salts on plant growth are reported. 



(4) Only about half as much alkali is required to prohibit the growth 

 of crops in sand as in loam. 



(5) Crops vary greatly in their relative resistance to alkali salts, but 

 for the ordinary mixture of salts the following crops in the seedling stage 

 would probably come in the order given, barley being the most resistant: 

 Barley, oats, wheat, alfalfa, sugar beets, com, and Canada field peas. 



(6) Results obtained in solution cultures for the toxicity of alkali 

 salts do not always hold when these salts are applied to the soil. 



(7) The percentage of germination of seeds, the quantity of dry matter 

 produced, the height of plants, and the number of leaves per plant are 

 all affected by alkali salts in about the same ratio. 



(8) The period of germination of seeds is considerably lengthened by 

 the presence of soluble salts in the soil. 



