210 MOVEMENTS OF SALTS IN THE SOIL 



The next running occurred on May 29. The second and 

 third collections are in this case the strongest. The principal 

 band of salts is now no longer at the surface, but it is still 

 distinctly above the level of the drain-pipes. The nitrates 

 are now diminishing in quantity, owing to their consumption 

 by the growing wheat crop. 



At the next running on June 2 (see Table XXXIV) the 

 previous order has become reversed ; the last running from 

 the pipes is now the strongest both in chlorides and nitrates, 

 the soil surrounding the pipes being now richer in these 

 salts than the upper layers. The same order is from this 

 date maintained throughout the rest of the season. 



It is of course quite possible that the various salts present 

 in a soil may be distributed in a different manner, and that 

 the chief band of one may occupy a different position from 

 the chief band of another. We have already pointed out 

 that the wide differences which exist in the rates of diffusion 

 must tend in some cases to separate the various salts within 

 a soil. The nitrates will be found very commonly to hold 

 an independent position, as a continual production of these 

 salts near the surface of the soil takes place, especially in 

 showery summer weather. 



A marked instance of the different position of the chlorides 

 and nitrates in a soil is supplied by the analyses of the 

 drainage waters from Plot 15 in Broadbalk field collected 

 on November 15 and 16, 1880. The plot had received 

 400 Ib. of ammonium salts (mixed chloride and sulphate) on 

 October 25 ; heavy rain followed from the 26th to the 

 29th. The chlorides had thus been washed into the lower 

 layers of the soil before any considerable amount of nitrifica- 

 tion had taken place. The drain-pipe next ran on November 15. 



