338 
Nitrogen  as  Nitric  Acid,  in  the  Soils 
from  the  removal  of  weeds  ; they  were  also  subjected  to  loss 
of  nitrogen  by  oxidation  and  drainage  for  seven  years  before  the 
systematic  examination  of  the  drainage-waters  commenced.  It 
is  thus  extremely  probable  that  the  annual  production  of  nitrates 
was  larger  in  the  earlier  history  of  the  soils  than  at  present,  and 
the  results  of  the  earlier  analyses  of  the  drainage-waters,  given 
in  the  previous  Report,  support  this  conclusion. 
One  fact  is  plainly  shown  by  the  monthly  analyses  of  the 
drainage-waters  from  the  soil-drain-gauges,  namely,  that  nitri- 
fication is  far  most  active  in  summer-time.  The  drainage- 
waters  are  at  their  minimum  strength  in  the  spring  months. 
It  is  generally  in  July  that  the  first  great  increase  in  the  pro- 
portion of  nitrates  is  observed.  As  the  process  of  nitrification 
has  been  shown  to  be  greatly  favoured  by  a rise  in  temperature 
up  to  98°  Fahr.  (37°  C.),  we  may  assume  that  it  is  most  active 
during  the  months  of  July  and  August,  if  the  rain  is  sufficient 
to  keep  the  soil  in  a moist  condition. 
In  Tables  III.,  IV.,  VI.,  and  VIII.  are  given  the  quantities  of 
nitrogen  as  nitrates  which  have  been  found  in  various  soils  and 
subsoils  on  the  Rothamsted  Farm.  The  previous  history  of 
these  soils  has  been  already  described.  We  will  first  consider 
the  results  yielded  by  uncropped  land. 
1.  Nitrates  in  Fallow  Land. 
In  Table  III.  (Nos.  1,  2,  7,  3),  we  have  determinations  of 
nitric  acid  in  four  soils  in  fair  agricultural  condition,  which 
had  been  cultivated  as  bare  fallow  during  the  summers  of  1878, 
1881,  and  1882.  The  samples  of  soil  were  taken  in  September 
or  October,  before  any  considerable  loss  of  nitrates  by  autumn 
drainage  had  taken  place.  In  these  four  soils  the  nitrogen  as 
nitrates  amounts  respectively  to  58'8  lbs.,  56-5  lbs.,  and  59’9  lbs. 
per  acre  in  the  first  27  inches,  and  to  48 ’8  lbs.  in  the  first 
18  inches  from  the  surface.  When  no  excess  of  rain  has 
fallen  during  the  summer  months,  the  nitrates  in  a fallow  soil 
are  chiefly  found  in  the  first  nine  inches,  where  nitrification 
principally  occurs  ; but  if  much  rain  has  fallen,  especially  in 
the  later  summer  months,  the  nitrates  are  found  at  a lower  level, 
and  a part  will  have  passed  below  the  depth  (27  inches)  to 
which  the  soils  were  sampled.  The  Agdell  fallow  in  1882 
is  an  example  of  the  former,  while  the  fallows  in  Clay  Croft  and 
Foster’s  Field  in  1881  are  examples  of  the  latter  conditions 
of  season.  In  1882  only  O'll  inch  of  water  passed  through 
the  20-inch  drain-gauge  in  the  two  months  preceding  soil- 
sampling ; but  in  1881,  3’58  inches  passed. 
