Apr. 22, 1918 Biological A ctivities and Concentration of Soil Solution 223 



One point which, so far as the writer is informed, has been omitted 

 in toxicity work is the increase of osmotic pressure due to the addition 

 of dried blood. Table VII shows the increase in the osmotic pressure 

 of the soil solution of the soils used in the above experiments due to the 

 addition of various amounts of dried blood. 



It is very evident that the amount of blood used in ammonifying tests 

 has a great influence on the concentration of the soil solution and that 

 the increase in osmotic pressure is quite different with various classes 

 of soils. Just what effect the addition of varying amounts of such mate- 

 rial will have on the ammonifying power of the soil is yet to be deter- 

 mined. It seems improbable that results obtained under such abnormal 

 conditions will represent the power of soils to ammonify nitrogenous ma- 

 terials under field conditions where much lighter applications are made. 



CONCLUSIONS 



Since the osmotic pressure at which ammonification of dried blood is 

 depressed in sandy loam by the addition of various salts is different for 

 each salt tested, it seems improbable that osmotic pressure is the governing 

 factor. This conclusion is further strengthened by the observation that 

 ammonification proceeds unimpaired in sand where the osmotic pressure 

 of the soil solution is between 13 and 14 atmospheres, while in sandy 

 loam the process is depressed when the osmotic pressure reaches 4 to 6 

 atmospheres and in clay loam at a pressure of about 9 atmospheres. 



The effect of various salts on ammonification is apparently modified 

 very materially by the nature of the soil used. Thus, for the four salts 

 studied, each gave a definite point where the ammonification of dried 

 blood in sandy loam was depressed, while only one salt gave such a point 

 with clay loam. The cause of such variations is yet to be investigated, 

 but it seems possible that the chemical reaction between the salt added 

 and the soil constituents may play some part. 



The addition of the amount of dried blood usually used in ammonifi- 

 cation work has a very appreciable effect on the osmotic pressure of the 

 soil solution, the increase varying with the class of soil used. 



The effect of various salts on the ammonification of nitrogenous mate- 

 rials in soils offers the opportunity for much thorough investigation, one 

 of the chief needs being improved methods. 



