364 
Nitrogen  as  Nitric  Acid , in  the  Soils 
An  attempt  was  there  made  to  correlate  the  amount  of  nitro- 
gen applied  in  the  manure,  recovered  in  the  crop,  and  passing 
away  as  nitrates  in  the  drainage-water,  in  the  case  of  many  of 
the  experimental  plots  in  Broadbalk  Wheat-field.  The  cal- 
culations showed  that  wherever  a large  quantity  of  ammonium- 
salt  was  applied,  a considerable  part  of  the  nitrogen  of  the 
manure  was  unaccounted  for  in  the  crop,  and  in  the  drainage 
from  the  plot,  and  the  amount  unaccounted  for  was  the  larger  in 
proportion  to  the  quantity  of  ammonium-salt  applied.  A similar 
calculation  made  regarding  the  chlorine  supplied  by  the  manure 
showed  that  it  also  was  only  partially  accounted  for  in  crop 
and  drainage.  It  was  assumed  that  the  composition  of  the  pipe- 
drainage  did  not  afford  full  information  as  to  the  amount  of 
nitric  acid  and  chlorine  that  was  passing  downwards,  and  that 
if  this  amount  were  fully  known,  the  unaccounted-for  loss  of 
nitrogen  and  chlorine  would,  more  or  less,  entirely  disappear. 
Some  of  the  new  results  described  in  the  preceding  pages 
support  the  explanation  thus  offered.  Where  large  amounts  of 
nitrates  are  present  in  a soil,  the  composition  of  the  pipe- 
drainage  doubtless  fails  to  represent  the  whole  amount  of  nitrate 
which  passes  downwards  into  the  subsoil. 
The  evidence  is  by  no  means  so  clear  as  to  what  proportion 
of  a dressing  of  nitrate  of  sodium  or  ammonium-salts  remains 
in  the  soil  unused  by  the  crop.  The  nitrates  found  in  the  soil 
after  harvest  are,  in  fact,  largely  due  to  the  nitrification  of 
nitrogenous  organic  matter  in  the  soil,  and  it  is  impossible  to 
discriminate  between  the  nitrate  so  produced,  and  that  remain- 
ing in  the  soil  as  a residue  of  manure. 
Much  has  been  said  in  these  pages  of  the  passage  of  nitrates 
into  the  subsoil  ; and  in  wet  seasons,  such  as  we  have  lately 
suffered,  the  quantity  of  nitrates  passing  downwards  from  arable 
soils  in  good  agricultural  condition  must  generally  have  been 
very  large.  Indeed,  it  would  appear  that  under  certain  circum- 
stances the  quantity  of  nitrates  in  the  subsoil  may  considerably 
exceed  the  quantity  near  the  surface.  As,  however,  our  ex- 
amination of  soils  has  in  most  cases  been  confined  to  the  depth 
of  27  inches,  we  have  as  yet  very  imperfect  information  as  to 
the  quantity  of  nitrates  which  may  exist  in  the  lower  layers  of 
the  subsoil  under  varying  conditions  of  cropping,  manuring,  and 
season.  The  agricultural  importance  of  these  subsoil-nitrates  is 
also  at  present  not  clearly  determined.  Are  we  to  regard  the 
nitrates  in  the  lower  layers  of  the  subsoil  as  preserved  intact, 
subject  only  to  further  removal  by  drainage,  as  available  for 
the  nourishment  of  deeply-rooted  crops,  and  capable  of  being 
brought  again  near  the  surface  when  the  evaporation  of  water 
becomes  considerable  during  the  growth  of  a vigorous  crop  in 
