342 
Nitrogen  as  Nitric  Acid , in  the  Soils 
Samples  of  soil  taken  at  this  time  of  the  year,  after  the  autumn 
and  winter  rains,  seldom  contain  large  quantities  of  nitrates  near 
the  surface.  In  the  soils  of  Hoos  Barley-field,  sampled  in 
March  1882  (Table  VIII.),  the  nitrogen  as  nitrates  amounted 
on  the  permanently  unmanured  plot  to  15’7  lbs.  in  the  first 
27  inches;  in  the  plots  receiving  only  ash-constituents,  to 
183-23-5  lbs.  ; in  the  farmyard-manure  plot  to  44T  lbs.  ; and 
in  that  which  had  received  farmyard-manure  for  twenty  years,  but 
not  for  the  last  ten  years,  to  37  5 lbs.  per  acre.  Compared  with 
these  quantities,  the  143  lbs.  found  in  the  first  27  inches  of 
the  unmanured  land  in  Geescroft,  and  the  293  lbs.  in  the  plot 
formerly  receiving  farmyard-manure,  are  perhaps  what  we 
might  expect,  seeing  that  the  drainage  during  the  autumn  and 
winter  of  1882-3  was  considerably  greater  than  that  of  the  pre- 
vious year.*  What,  however,  has  become  of  the  very  con- 
siderable quantities  of  nitric  acid  which  must  have  been  pro- 
duced in  these  soils  during  the  last  four  years,  in  each  of  which 
the  land  was  without  a crop,  and  was  frequently  ploughed? 
How  is  it  that  larger  quantities  of  nitrates  are  not  found  in  the 
subsoil  ? 
It  is  in  the  soil  of  the  plot  which  was  formerly  heavily  dressed 
with  farmyard-manure  that  we  should  expect  to  find  the  largest 
accumulation  of  nitrate.  This  plot  lies,  however,  near  to  the 
hedge  green,  and  in  taking  the  samples  of  soil,  elm-roots  were 
found  down  to  the  fifth  nine  inches  from  the  surface:  it  is 
possible,  therefore,  that  in  this  case  the  nitrates  had  been  more 
or  less  removed  from  the  subsoil.  Omitting  this  plot  from  con- 
sideration, the  facts  furnished  by  the  remaining  plots  still  seem 
to  point  to  a disappearance  of  nitrates  in  the  subsoil.  With  the 
evidence  at  our  command  as  to  the  production  of  nitrates  in 
other  exhausted  soils  at  Rothamsted,  we  can  hardly  estimate 
the  annual  production  of  nitric  acid  in  the  soils  in  question 
as  equal  to  less  than  30  lbs.  of  nitrogen  per  acre.  Taking 
even  the  excessive  amounts  of  drainage  shown  during  the  last 
few  years  by  the  drain-gauges,  the  water  percolating  down- 
wards from  such  a soil  will  contain  an  average  of  at  least  7-5 
parts  of  nitrogen  as  nitric  acid  per  million  of  water.  The 
field  being  pipe-drained  at  a depth  of  3-4  feet,  the  quantity 
of  water  passing  downwards  will  be  diminished,  but  it  is  a 
question  whether  its  average  strength  can  be  reduced  thereby. 
Now  the  soil  and  subsoil  of  the  unmanured  plot  in  which 
nitrates  were  determined  contained  an  average  of  800,000  lbs. 
of  water  per  acre  in  each  nine  inches  of  depth.  We  should 
* The  drainage  shown  by  the  60-inch  drain-gauge  during  seven  months, 
August  to  February  1881-82,  amounted  to  12-515  inches ; and  in  eight  months, 
August  to  March  1882-83,  to  17  • 514  inches. 
