wr 
and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  355 
same  plot.  The  figures  would  be  more  exact  if  we  knew  in 
every  case  the  quantity  of  nitric  acid  lost  by  drainage  before 
the  samples  of  soil  were  taken  for  analysis,  as  this  quantity  of 
nitric  acid  has  clearly  to  be  credited  to  the  soil  or  manure  of 
the  plots  in  question.  We  are,  however,  only  able  to  make 
this  correction  in  the  case  of  three-  of  the  plots  mentioned  in 
the  Table.  It  will  be  more  convenient,  therefore,  to  confine 
ourselves  to  the  figures  deduced  from  the  actual  determinations 
of  nitric  acid  in  the  soils.* 
On  the  permanently  unmanured  Plots  3&4,  1000  of  total 
soil  nitrogen  has  yielded  6’7  of  nitric  nitrogen ; and  on  the 
unmanured  Plot  16a  it  has  yielded  6‘6.  On  the  very  moderately 
manured  Plot  6a,  yielding  nearly  twice  the  produce  of  the  un- 
manured land,  the  product  in  the  same  time  has  been  102  of 
nitric  nitrogen  per  1000  of  soil  nitrogen.  This  increased  capa- 
city for  producing  nitrates  is  shown  by  every  plot  in  the  field 
yielding  an  increase  of  produce,  the  lowest  proportions  being 
8T  per  1000  in  the  case  of  Plot  13a,  and  7‘6  per  1000  in  the 
case  of  Plot  17a.  Plot  5a,  manured  with  ash-constituents 
alone,  shows  9'7  per  1000  ; the  amount  of  nitric  acid  found  in 
this  soil,  judged  by  the  evidence  of  the  drainage-water,  seems  to 
be  rather  high.  We  have,  further,  an  indication  that  with  a 
rise  in  productiveness  over  that  shown  by  Plot  6a  we  have  a 
further  rise  in  the  facility  with  which  soil  nitrogen  is  oxidised  ; 
the  product  of  1000  of  soil  nitrogen  on  Plots  2,  7a,  and  9a 
being  11*4,  12*9,  and  12'4.  The  high  figure  shown  by  Plot  8a, 
and  the  still  higher  figure  shown  by  9b,  are  of  course  due  to  a 
larger  residue  of  nitrates  in  the  soil. 
The  lact  indicated  by  the  above  calculations  is  one  of  great 
practical  importance.  Soil  contains  nitrogenous  matters  which 
nitrify  with  different  degrees  of  facility.  The  bulk  of  the 
nitrogenous  matter  of  soil  is  only  capable  of  very  slow  oxida- 
tion, but  a smaller  proportion  is  far  more  readily  converted 
into  nitric  acid.  In  thoroughly  exhausted  land  the  easily 
nitrifiable  matter  has  to  a large  extent  disappeared  ; in  soil 
in  good  agricultural  condition  it  is  being  continually  renewed 
by  fresh  crop-residues,  or  by  the  application  of  organic  manures. 
This  easily  nitrifiable  matter  constitutes  a chief  part  of  the 
floating  capital  of  the  soil,  on  which  its  immediate  productive- 
ness depends.  The  larger  quantity  of  more  inert  nitrogenous 
matter  constitutes  the  sunk  capital  which  only  very  slowly 
becomes  available. 
* In  the  case  of  Plots  3&4,  6a,  and  7a,  the  corrected  proportion  of  total 
soil  nitrogen  to  nitric  nitrogen  will  be  1000  to  7-3,  10  • 7 and  14*0;  and  the 
corrected  proportion  of  produce  (average  of  30  years)  to  nitric  nitrogen,  1000 
to  8-1,  7-6  and  7-5. 
