and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  347 
very  small  amount  of  nitric  acid,  amounting  in  the  mean  to 
barely  1*0  of  nitrogen  per  million.  The  water  from  Plot  6, 
manured  in  the  spring  with  200  lbs.  of  ammonium-salts  per 
acre,  contained  at  the  same  time  T9  of  nitrogen  per  million. 
The  waters  from  Plots  12,  13,  and  7,  receiving  400  lbs.  of  am- 
monium-salts, contained  respectively  2'3,  2-4,  and  4T  of  nitrogen 
per  million. 
With  the  evidence  already  before  us,  it  scarcely  admits  of 
doubt  that  nitrates  must  have  practically  disappeared  from  the 
upper  layers  of  the  soil  of  the  unmanured  plots  during  the 
preceding  summer  ; also  from  the  soil  of  Plot  6 ; and  probably, 
though  less  certainly,  from  Plots  13  and  7.  The  small  amounts 
of  nitrate  appearing  in  the  drainage-waters  from  these  plots  on 
Aug.  30,  are  therefore  in  all  probability  due  to  nitrification 
recommencing  in  the  soils  as  they  became  saturated  by  the 
heavy  rains  of  August.  Nor  is  the  fact  that  the  waters  from 
* Plots  6,  12,  13,  and  7,  contain  more  nitrate  than  those  of  the 
unmanured  plots,  conclusive  evidence  that  there  was  a residue  of 
nitrate  present  through  the  summer  in  these  cases  ; for  wherever 
nitrogenous  manure  is  applied,  and  larger  crops  are  annually 
produced,  there  the  soil  is  richer  in  nitrogenous  organic  matter 
(the  residues  of  previous  crops),  and  in  consequence  yields  a 
larger  quantity  of  nitric  acid  when  nitrification  sets  in.  That 
the  nitrates  in  the  waters  of  the  plots  already  named  were  not 
derived  from  the  washing  out  of  a residue  of  nitrates,  but  from 
fresh  nitrification,  is  further  shown  by  the  fact  that  the  pro- 
portion of  nitric  acid  rapidly  increases  with  each  running  of 
the  drains,  till  a maximum  is  reached  on  Oct,  23. 
W hen  we  turn  to  the  drainage  of  Plot  10,  which  had  received 
400  lbs.  of  ammonium-salts,  like  Plots  7, 11,12,13,14,15,  and  18, 
but  without  any  of  the  ash-constituents  required  for  the  crop,  a 
very  different  state  of  things  is  manifest.  Here  the  crop  has 
been  unable  to  assimilate  all  the  nitrates  at  its  disposal,  and  a 
considerable  residue  has  remained  in  the  soil  throughout  the 
summer.  The  first  drainage-water  from  this  plot  is  thus  rich 
in  nitrates,  containing  20’3  of  nitrogen  per  million,  and  the 
proportion  is  found  to  have  decreased  instead  of  increased  by 
October  23. 
The  soils  of  Plot  9 — on  which  nitrate  of  sodium,  half  with 
and  half  without  ash-constituents,  is  applied  ; Plot  8 — where  as 
much  as  600  lbs.  of  ammonium-salts  with  ash-constituents  are 
applied ; and,  to  a less  extent,  Plot  11 — wnere  potash  is 
omitted  in  the  manure — are  in  a condition  more  or  less  similar 
to  Plot  10.  In  all  these  cases  there  is  a considerable  residue  of 
nitrate  remaining  unassimilated  by  the  crop,  which  appears  in 
the  drainage-water  on  the  first  running  of  the  drains. 
2 A 2 
