x] FERTILISING CONSTITUENTS IN SOIL WATER 2S7 



of a fertiliser must be due to some other cause than the 

 direct supply of plant food, with which the soil water 

 must alwa)S be saturated to a degree which is quite 

 unaffected by the supply of fertiliser. 



This view of the interactions between the sparingly 

 soluble phosphates of the soil, the soil water, and the 

 added soluble fertiliser can hardly be regarded as valid 

 in theory, even if the conditions under which the 

 reagents exist in the soil were the same as those 

 which prevail in the laboratory when such states of 

 equilibrium between sparingly soluble solids and water 

 are worked out. It has no bearing whatever on the 

 amount of nitrates in the soil water, since they come 

 into a dissolved state as fast as the nitrifying bacteria 

 produce them and are not in equilibrium with any store 

 of undissolved nitrates in the background. As regards 

 phosphoric acid, the theory assumes such an excess of 

 bases that all soils behave alike in immediately pre- 

 cipitating the phosphoric acid in the same form ; 

 while as regards potash, the argument seems to 

 forget that though the addition of a soluble potassium 

 salt may throw some of the other sparingly soluble 

 potassium compounds out of solution, the total amount 

 of potassium remaining in solution will still be greatly 

 increased. The function of the carbonic acid in the soil 

 water is ignored, as also is the fact that the processes 

 of solution in the soil must be in a constant state of 

 change, so that it is the rate at which the constituents 

 go into solution rather than the actual amount dissolved 

 at any given moment which is of importance. The soil 

 is too complex a mixture to permit as yet of attaching 

 great weight to theoretical deductions as to the actions 

 taking place in it, and that the state of affairs postulated 

 by Whitney and Cameron does hold in the soil, has 

 not however been verified by experiment ; the analyses, 



