214 Journal of A gricultural Research voi. xin. No. 4 



ammonifiers in very low concentration (78 X lo'^ mol. per 100 gm. of soil) 

 and all the other salts used, with the exception of calcium carbonate and 

 manganous carbonate, became toxic in some of the concentrations tested. 

 He states (p. 474) that — 



The increased osmotic pressure exerted by the salts added to a soil plays an impor- 

 tant part in the retarding of the bacterial activity, it is not the only nor probably the 

 main influence. The main influence is likely to be a physiological one due to the 

 action of the substance upon the living protoplasm of the cell, changing its chemical 

 and physical properties so that it cannot function properly. 



Osmotic pressure as the causal factor is also suggested by the work of 

 Harris,^ who found that the germination of different seeds was first 

 retarded by the salts studied when the soils contained a small amount 

 of moisture. With most of the salts the highest germination was in the 

 wettest sand, while with sodium chlorid the medium moisture gave the 

 highest germination. 



He also states that (p. 44) — 



In a general way salts with low molecular weights are more toxic than those having a 

 higher molecular weight, but there are so many exceptions that this can not be consid- 

 ered a general law holding for all salts. 



That the soil plays an important role in the toxic action of salts was 

 shown by Harris,* who points out (p. 26) that — 



Plants were able to endure much stronger chlorids and nitrates in solution culture 

 than in the soil, while the carbonates retarded growth more in the solution than in 

 the loam, but not as much as in the sand. 



The antagonism of salts was foimd to be less in soils than in solutions. 

 He also concludes that only about one-half as much alkali is required 

 to prohibit the growth of crops in sand as in loam soil. Sodium carbonate 

 was more toxic in sand than sodium chlorid, while with loam the reverse 

 was true. 



That soils of different chemical and physical properties influence 

 differently the effect of added substances on the lower organisms is 

 shown by the work of Lipman and Burgess ^ when they found that the 

 order of nitrifiability of various nitrogenous substances depends largely 

 on the soil used. 



Further evidence of the importance of the interaction of the soil with 

 the salts added is brought out by Headley, Curtis, and Scofield ^ in 

 determining the relative toxicity of sodium carbonate, sodium bicarbo- 

 nate, sodium chlorid, and sodium sulphate for wheat. They not only 



• Harris, F. S. effect o? alkali salts in soils on the germination and growth op crops. In 

 Jour. Agr. Research, v. 5, no. i, p. 1-53, 48 fig. 1915. Literature cited, p. 52-53. 



3 Lipman, C. B., and Burgess, P. S. the determination of availability of nitrogenous fer- 

 tilizers IN various CALIFORNIA SOIL TYPES BY THEIR NITRIFIABILITY. Cal. Agr. Exp. Sta. Bul. 260, p. 



103-127. 1915. 



«Headley, F. B., Curtis, E. W., and Scofield, C. S. effect on plant growth op sodium salts 

 m THE son,. In Jour. Agr. Research, v. 6, no. 22, p. 857-869, 8 fig. 1916. 



