and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  365 
summer-time  ? Or  are  the  nitrates  passing  below  a certain  level 
liable  to  be  destroyed  by  chemical  reduction,  of  which  action 
some  examples  were  given  in  the  previous  Report?  It  may 
well  be,  that  in  subsoils  of  different  character,  and  in  different 
conditions  of  saturation  with  water,  one  or  other  of  these  re- 
sults may  occur,  but  the  information  at  present  at  command 
on  the  subject  is  very  limited.  A further  examination  of  the 
composition  of  subsoils  at  low  depths  is  now  in  progress  at 
Rothamsted. 
Summary  op  Results. 
1.  The  soils  of  the  three  drain-gauges,  20,  40,  and  60  inches 
deep,  which  have  now  remained  without  manure  and  without 
crop  for  thirteen  years,  have,  during  the  last  six  years,  yielded 
nitric  acid  in  the  drainage-water,  equal  to  an  average  of  40-2  lbs. 
of  nitrogen  per  acre  per  annum.  The  production  of  nitrates  is 
greatest  during  summer.  The  minimum  amount  in  the  drainage- 
water  occurs  in  spring ; the  maximum  in  July,  or  in  the  first 
month  afterwards  in  which  considerable  drainage  occurs. 
2.  In  three  soils  at  Rothamsted,  in  fair  agricultural  condition, 
cultivated  as  bare  fallow  since  the  harvest  of  the  previous  year, 
56'5,  58-8,  and  59'9  lbs.  of  nitrogen  as  nitric  acid  per  acre  were 
found  in  September  or  October,  to  the  depth  of  27  inches.  If 
the  summer  has  been  dry,  the  nitrates  are  near  the  surface  ; after 
much  rain  they  are  at  a lower  level.  If  the  amount  of  nitrates 
which  it  is  estimated  have  passed  by  drainage  below  27  inches 
during  the  season  of  fallow  (15  months)  is  taken  into  account, 
the  total  production  of  nitrates  corresponds  to  about  80  lbs. 
of  nitrogen  per  acre.  When  the  soil  is  in  a poor  agricultural 
condition,  the  production  of  nitrates  during  fallow  is  much  less. 
3.  In  exhausted  land,  but  left  uncropped  four  years  (Geescroft 
Field),  only  very  small  quantities  of  nitrates  were  found  in  the 
subsoil  to  a depth  of  6 feet.  The  subsoil  was,  however,  saturated 
with  water,  and  it  seems  possible  that  a portion  of  the  nitrates 
had  been  destroyed  by  chemical  reduction. 
4.  The  results  relating  to  land  growing  cereal  crops,  receiving 
no  excess  of  nitrogenous  manure,  show  that  only  very  small 
quantities  of  nitrates  will  remain  in  the  uper  layers  of  the  soil 
through  the  summer,  the  crop  having  assimilated  the  nitrates 
formerly  present.  If  rain  follow  after  harvest,  and  especially  if 
the  land  be  ploughed,  a considerable  formation  of  nitrates  will 
occur.  Nitrates  will  continue  present  throughout  the  winter, 
notwithstanding  loss  by  drainage,  slow  production  being  always 
in  progress.  In  late  spring  or  early  summer,  the  nitrates  will 
again  disappear  if  the  land  is  once  more  under  crop. 
