298 ACTIONS OF ARTIFICIAL MANURES 



different Rothamsted fields ; in each pair there was a plot 

 receiving nitrate of soda to compare with one receiving 

 ammonium-salts, while the other treatment was identical on 

 both plots. 



It will be seen that the percentage of clay is distinctly less 

 on the plots which had received nitrate of soda, and though 

 the difference may not appear to be great, it is without doubt a 

 real one, because it was found to exist in each pair of soils used 

 in the comparison (see Trans. Chem. Soc., 85, 1904, 964), and 

 it is contrary to what would have been expected from the 

 behaviour of the soils. Of the reality of the differences we 

 have, moreover, another indication in the fact that when the tile 

 drains, which are laid beneath the whole length of the narrow 

 strips constituting the plots on the Broadbalk wheat field, 

 begin to run, the water flowing from the drains beneath the 

 nitrate plots is always faintly turbid and carries a very light 

 cloud of fine mud, whereas the water from the plots receiving 

 ammonium-salts is always crystal-clear. Evidently the washing 

 out of the finest clay particles which we see going on in the 

 drainage water has been so continuous that the quantity 

 remaining in the soil has been definitely reduced by the 1 to 

 5 per cent, shown in the different analyses. It is also 

 evidence in the same direction to find that in the earlier years 

 of the experiment the drain beneath the unmanured plot ran 

 more frequently than that below the nitrate of soda plot, 

 whereas of late years, since so much of the finest stuff has been 

 washed out, the drains have been running more frequently 

 beneath the nitrate plots. 



The turbid aspect of the drainage water from the two sets 

 of plots suggested another experiment, which provided the 

 clue to the different texture of the two plots. Small equal 

 portions of soil from the plots were weighed out, and each was 

 shaken up with a large bulk of pure water; the resulting 

 muddy liquids were then put to stand separately in similar 

 tall jars. A certain time is occupied before the suspended soil 

 falls to the bottom of the jar and leaves the water clear above ; 



