114 THE ROYAL SOCIETY OF CANADA 



Does tillage bring about an upward movement of moisture through the 

 subsoil by osmotic pressure? 



The operations of tillage: plowing, harrowing, &c., open up the 

 soil and thus increase aeration. This makes the conditions more 

 favorable for the growth of bacteria. The bacteria thus produce more 

 plant food, that is, more salts soluble in water. If these salts make 

 the concentration of the soil solutions in the surface soil greater than 

 that of the solutions in the lower soil, they make the osmotic pressure 

 of the former solutions greater than that of the latter. This should 

 cause an upward movement of the moisture through the subsoil to- 

 wards the surface soil by osmotic pressure. 



Does the application of manure to the surface soil cause an upward 

 movement of moisture by osmotic pressure? 



Experiments made by King* show that manure applied to the 

 surface soil increases the amount of moisture in the upper 2 or 3 feet 

 of soil at the expense of the lower 2 or 3 feet of soil. This cannot be 

 due to a greater capillary rise of moisture because manure added to 

 water decreases the surface tension of water. 



Our theory offers an explanation. The manure added to the land 

 increases the amount of food available for bacteria and also increases 

 the number of bacteria. The bacteria thus produce a larger supply of 

 plant food in the form of salts soluble in water. If these salts make 

 the concentration of the surface soil solutions greater than that of 

 the solutions in the lower soil, they make the osmotic pressure of the 

 former solutions greater than that of the latter. This should bring about 

 an upward movement of moisture through the subsoil by osmotic pressure. 



Do mineral fertilizers when added to the surface soil cause an upward 

 movement of moisture by osmotic pressure? 



If mineral fertilizers increase the concentration of the soil sol 

 utions in the surface soil, either directly or indirectly through chemical 

 or bacterial action, they increase the osmotic pressure of these sol- 

 utions. This should cause an upward rise of moisture by osmotic 

 pressure, as noted above. 



In this connection it should be noted that certain fertilizers tend 

 to fioculate the subsoil and thus make it more open. This may tend 

 to make the soil less efficient as a semi-permeable membrane. On 

 the other hand, certain fertilizers tend to defloculate the subsoil and 

 thus may make the subsoil more efficient as a semi-permeable membrane. 



*King, F. H. Wisconsin Station Report, 1893, pp. 167-200. 



