362 
Nitrogen  as  Nitric  Acid , in  the  Soils 
nearly  200  lbs.  of  nitrogen.  The  clover  land,  and  the  cor- 
responding bare  fallow,  were  sampled  on  September  8,  before 
the  clover  land  had  been  ploughed.  The  clover  land  con- 
tained in  27  inches  19'6  lbs.  of  nitrogen  as  nitrates,  while  in 
the  soil  of  the  corresponding  bare  fallow  59  9 lbs.  were  found. 
It  is  clear  that  in  each  of  these  comparative  determinations 
between  beans  and  fallow,  or  clover  and  fallow,  we  must  not 
assume  that  the  crop  had  at  command  the  whole  quantity  of 
nitrates  found  in  the  fallow  soil,  as  the  production  of  nitrates 
in  it  would  be  considerably  favoured  by  the  summer  tillage, 
a condition  which  was,  of  course,  wanting  in  the  case  of  the 
cropped  land.  Though,  however,  we  may  not  credit  the  crop 
with  having  assimilated  the  whole  difference  observed  between 
the  nitrates  of  the  cropped  and  uncropped  land,  there  can  be 
no  doubt  that  in  every  case  a considerable  quantity  of  nitrate 
has  been  taken  up  from  the  first  27  inches  of  soil,  the  depth  to 
which  the  sampling  was  confined.  Considerable  additional 
quantities  of  nitrate  would  probably  be  obtained  from  the  lower 
depths  of  the  subsoil,  especially  in  the  case  of  the  clover  crop. 
In  Table  IV.  determinations  of  nitrates  are  given  in  two  plots 
in  Hoos  Field,  which  had  frequently  grown  leguminous  crops, 
and  which  now  failed  to  grow  red  clover.  One  plot  had  just 
grown  a small  crop  of  white  clover,  amounting  to  24  cwts.  of 
hay  per  acre  ; the  other  had  just  produced  an  enormous  crop  of 
Bokhara  clover,  yielding  in  one  cutting  125£  cwts.  of  hay  per 
acre,  and  containing  about  144  lbs.  of  nitrogen.  The  samples 
of  soils  were  taken  on  July  26—31,  1882,  immediately  after  the 
removal  of  the  crops  ; the  sampling  was  carried  to  the  depth  of 
54  inches.  The  whole  amount  of  nitrogen  as  nitric  acid  found 
in  this  depth  was  26'3  lbs.  per  acre  in  the  case  of  the  short-rooted 
white  clover,  and  8‘5  lbs.  per  acre  in  the  case  of  the  deep-rooted 
Bokhara  clover.  In  the  first  27  inches  of  depth,  the  white- 
clover  soil  contained  13’5  lbs.,  and  the  Bokhara-clover  soil  only 
5 lbs.  In  the  second  27  inches,  the  white-clover  soil  contained 
12-8  lbs.,  or  nearly  as  much  as  the  first,  and  the  Bokhara-clover 
soil  only  3'5  lbs.  It  is  obvious  that  the  Bokhara  clover  had 
withdrawn  nitrates  to  the  full  depth  examined,  and  it  had 
doubtless  done  so  to  a lower  depth  still.  We  have  here  again 
evidence  that  a leguminous  crop,  and  especially  one  having 
a wide  distribution  of  roots,  assimilates  the  nitrates  of  the  soil  ; 
and  in  the  case  of  such  a plant  as  the  Bokhara  clover,  a great 
depth  of  the  subsoil  is  clearly  brought  under  contribution. 
We  have  one  experiment  yet  to  mention.  It  is  well  known 
that  a clover  lay  is  a good  preparation  for  wheat ; this  is 
doubtless  chiefly  due  to  the  gradual  nitrification  of  the  nitro- 
genous residue  left  behind  by  the  clover.  An  illustration  of 
