HARMFUL SOIL CONSTITUENTS 165 



plants in the no phosphate cultures containing mannite wefe 

 healthy and clean and fully as good as the control cultures, 

 while the root growth in the mannite solutions which contain 

 phosphate, were unhealthy and short and made a poor growth. 



When the solutions had grown plants for three days they were 

 replaced by new solutions and the old solutions analyzed. More 

 nitrates had disappeared in the set of solutions containing man- 

 nite than in the control set of solutions. In the mannite cul- 

 tures nitrite and ammonia were detected in solutions Nos. 1 to 

 46. The amount of nitrite varied from 6 to 10 parts per mil- 

 lion, and each culture gave a good test for ammonia. There 

 was no nitrite or ammonia in the mannite solutions Nos. 56 to 

 66 which contained no phosphate. The set of nutrient solu- 

 tions containing no mannite, and used as a control, contained no 

 nitrites or ammonia, nor have they ever been observed in these 

 control sets. 3 



These data show that the mannite in the nutrient solutions 

 containing all three of the nutrient elements, underwent decom- 

 position, there was a formation of nitrites and ammonia, and 

 that consequently the decomposition caused poor plant growth. 

 The solutions in which there was no phosphate was not a good 

 medium for the development of bacteria, consequently there was 

 no decomposition of the mannite. Mannite as such does not 

 seem to be harmful to wheat seedlings, and when decomposi- 

 tion does not take place the material would seem to be used by 

 the plants and an increased growth results. 



In view of the fact that the Mount Vernon soil was found to 

 contain both salicylic aldehyde and mannite, an experiment in 

 nutrient solutions was planned and conducted in which both 

 these substances were added to the culture solution. 



In this experiment the nutrient solution contained calcium 

 acid phosphate, sodium nitrate and potassium sulphate in 

 amounts of 16-32-32 p. p.m. of the fertilizer constituents P 2 5 .NH 3 

 and K 2 0. Mannite was added in amounts of 100 p. p.m. and the 

 salicylic aldehyde added, varied in the different solutions, from 



3 Schreiner, O. and Skinner, J. J., Nitrogenous soil constituents and their 

 bearing on soil fertility. Bull. 87, Bureau of Soils, U. S. Dept. Agric. (1912). 



