and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  343 
I expect,  therefore,  on  the  above  suppositions,  to  find  about  6-0  lbs. 
of  nitrogen  as  nitrate  in  each  depth  of  the  soil,  or  48  lbs.  in  all. 
A glance  at  the  figures  shows  at  once  that  a considerably  smaller 
quantity  is  actually  present  in  each  of  the  three  plots,  and  that 
the  deficiency  is  most  marked  in  the  lower  layers  of  the  subsoil. 
It  is  a question,  therefore,  whether  the  nitrates  produced  in  the 
surface  soil  have  not  suffered  partial  reduction  in  the  lower  layers 
of  the  clay  subsoil ; but  the  evidence  on  the  point  is  confessedly 
very  incomplete. 
2.  Nitrates  in  Land  growing  Cereal  Crops. 
In  the  previous  Report  it  was  shown  that  nitrates  are  always 
found  in  the  drainage- waters  of  Broadbalk  Wheat-field  during  the 
winter  months.  It  was  also  shown  that  a large  proportion  of 
the  ammonium-salts  applied  as  manure  is  speedily  nitrified 
, after  their  application  to  the  land.  A good  example  of  the  latter 
fact  is  afforded  by  the  analyses  of  the  drainage-waters  of  Plot  15 
(see  Table  V.,  p.  346),  to  which  400  lbs.  of  ammonium-salts  per 
acre  were  applied  on  October  27. 
It  was  further  stated  in  the  previous  Report,  that  as  the 
development  of  the  wheat-crop  proceeds,  the  assimilation  of 
nitrates  by  the  growing  plant  becomes  so  active,  that  in  summer 
nitrates  are  not  found  in  the  drainage-waters  of  many  of  the 
plots  in  the  Experimental  Wheat-field.  The  plots  which  exhibit 
for  a time  a drainage  free  from  nitrates  are  those  which  receive 
no  nitrogenous  manure,  or  which  receive  200-400  lbs.  of  am- 
monium-salts with  all  the  ash-constituents  required  by  the 
crop.  In  a season  very  favourable  to  early  growth,  as  1882, 
the  nitrates  may  disappear  from  the  drainage-waters  of  the  un- 
manured plots  by  the  end  of  April ; while  in  a very  unfavour- 
able season,  as  1879,  the  disappearance  may  not  occur  till  the 
beginning  of  June.  The  nitrates  disappear  from  the  drainage 
of  Plot  6,  receiving  200  lbs.  of  ammonium-salts  with  ash-con- 
stituents, soon  after  their  disappearance  from  the  drainage  of  the 
unmanured  plots.  On  Plots  7 and  13,  with  400  lbs.  of  ammo- 
nium-salts and  the  necessary  ash-constituents,  the  disappearance 
of  the  nitrates  from  the  drainage-waters  is  later,  and  small 
quantities  may  continue  to  be  found  for  some  time. 
The  quantity  of  nitrates  which  disappears  from  the  soil  in 
early  summer  is  in  some  cases  truly  astonishing.  In  the  case  of 
the  plots  receiving  a spring-dressing  of  ammonium-salts  it  may 
apparently  amount  to  more  than  the  quantity  of  nitrogen 
found  in  the  crop  at  harvest.  It  must  be  recollected,  how- 
ever, that  the  crop  as  harvested  does  not  represent  the  whole 
plant — the  roots,  stubble,  some  of  the  lower  leaves,  and  shed 
