Some  Secondary  Actions  of  Manures  upon  the  Soil.  29 
fx-om  waste.  Both  substances  act  alike  in  serving  as  bases 
for  such  processes  as  nitrification  ; the  carbonate  of  soda  is  a 
soluble  base  or  an  alkali. 
Though  the  selective  action  of  the  plant  ixpon  the  nitrate  of 
soda  is  the  main  agency  in  producing  carbonate  of  soda  in  the 
soil,  a similar  action  is  also  brought  about  by  bacteria,  particu- 
larly when  the  nitrate  of  soda  is  present  in  a water-logged  soil 
lacking  aeration.  The  process  of  denitrification  has  been 
discussed  in  some  detail  in  this  Journal  since  Warington 
originally  showed  that  a pot  full  of  a water-logged  soil  contain- 
ing nitrate  of  soda  lost  within  a week  as  much  as  80  per 
cent,  of  the  nitrate  applied,  the  nitrogen  being  evolved  in  the 
form  of  gas.  Though  no  such  destruction  occurs  under  field 
conditions,  even  when  nitrate  is  used  in  conjunction  with  an 
excess  of  farmyard  manure,  some  losses  of  the  soil  do 
undoubtedly  occur,  as  may  be  seen  from  the  fact  that  in  most 
experiments  the  whole  of  the  nitrogen  applied  as  nitrate  is 
not  recovered  in  the  crop  even  though  there  has  been  no 
washing  out  of  nitrates  by  drainage.  The  bearing  of  denitrifi- 
cation upon  our  problem  comes  from  the  fact  that  when  the 
nitrogen  of  the  nitrate  of  soda  is  thus  lost  the  soda  base  is  left 
behind  as  carbonate  of  soda,  hence  from  some  of  the  nitrate  of 
soda  that  is  not  taken  up  by  the  crop  there  will  be  carbonate  of 
soda  produced  by  the  organisms  of  denitrification.  Moreover 
there  are  other  bacteria  in  the  soil  which  will  take  the  nitrogen 
from  nitrate  of  soda ; they  do  not  waste  it  by  setting  it  free 
as  gas,  but  they  convert  it  into  proteins  and  similar  sub- 
stances out  of  which  their  own  bodies  are  constructed  ; in 
these  cases  also  the  soda  part  of  the  salt  is  left  behind  as 
carbonate.  This  process  is  strictly  comparable  with  the  pro- 
duction of  acid  by  the  action  of  micro-fungi  upon  sulphate  of 
ammonia ; in  each  case  the  living  organism  effects  a splitting 
of  the  salt  in  order  to  obtain  nitrogen,  and  it  rejects  and 
leaves  behind  in  the  soil  in  the  one  case  the  acid  part  of  the 
salt,  in  the  other  the  base. 
We  are  now  in  a position  to  sum  up  the  features  of  this 
secondary  action  of  nitrate  of  soda  applied  to  the  soil,  an  action 
which  causes  so  great  an  injury  to  its  texture  when  the  land 
is  at  all  heavy.  The  bad  texture  is  due  to  the  deflocculation  of 
the  clay  particles  which  is  brought  about  by  the  presence  in 
the  soil  of  a small  quantity  of  dissolved  carbonate  of  soda.  The 
carbonate  of  soda  is  formed  by  the  action  of  the  crop  plants 
and  of  certain  soil  bacteria  upon  the  nitrate  of  soda,  they  take 
up  the  nitrogen-containing  part  of  the  salt,  because  nitrogen 
is  an  element  indispensable  to  their  development,  and  leave 
behind  the  soda  base  combined  with  the  carbon  dioxide  which 
they  excrete. 
