236 NITRIFICATION 



and drainage in 1879 and the winter rainfall in the following 

 year being both above the average. It will be seen that the 

 loss was greatest from Plot 9, receiving 550 Ib. of nitrate of soda, 

 and this excess of loss was chiefly in the summer drainage 

 water : the figures are, however, exaggerated by the fact that 

 half the nitrate plot received no mineral manures, and therefore 

 grew but a scanty crop. The losses during the winter months 

 are more nearly the same for all plots, and represent to a large 

 degree the nitrification of the organic residues in the soil. The 

 losses from the plots receiving minerals and varying amounts of 

 ammonium-salts (Plots 5, 6, and 7) increased with ^ach applica- 

 tion of nitrogen ; the losses from the plots receiving ammonia 

 and various mineral manures (Plots 10, 11, 12, 13, and 14) 

 diminished as the mineral manure became a more complete 

 plant food, because the greater growth of crop which resulted 

 removed more of the nitrates as they were formed, besides 

 hindering nitrification by drying the surface soil. 



Perhaps the most striking result that emerges from these 

 analyses of the drainage waters is the rapidity with which 

 nitrification takes place of such substances as the salts of 

 ammonia ; even in the colder autumnal and winter soils 

 nitrification is so active that great losses of nitrogen are sure to 

 occur if such manures are applied in the autumn, hence the 

 justification for using ammonium-salts only as a spring dressing. 

 It also serves to show that any differences in the effectiveness 

 of the nitrogen of nitrate of soda and of ammonium- salts is 

 most likely to be due to the differences in habit of growth 

 of the plant induced by the two manures, since the conversion 

 of the ammonium-salts into nitrate is so easily and completely 

 effected except in such soils as are short of the base necessary 

 for nitrification. Only in the wheat experiments is there 

 any indication that a wet and cold year may so check 

 nitrification as to make the ammonium-salts a less* valuable 

 source of nitrogen than usual. Again, we see how cereals, and 

 especially wbeat, are specially dependent on artificial supplies of 

 nitrogen, and have earned the character of being exhausting 



