22  Some  Secondary  Actions  of  Manures  upon  the  Soil. 
The  action  of  ammonium  salts  upon  the  soil,  the  investiga- 
tion of  which  was  originally  started  by  Way  and  continued  by 
Voelcker,  has  thus  continued  to  afford  material  for  research 
right  up  to  the  present  day,  and  has  developed  in  an  entirely 
unexpected  direction  now  that  it  has  become  necessary  to 
regard  the  soil  as  the  seat  of  a number  of  active  living  organ- 
isms, a point  of  view  which  had  not  become  possible  to  the 
earlier  chemists  of  the  Society  who  took  up  the  problem.  The 
history  of  the  investigation  affords  an  interesting  illustration  of 
the  fact  that  old  questions  have  to  be  reconsidered  with  each 
large  advance  of  knowledge  ; it  also  affords  a notable  instance 
of  the  secondary  effect  of  a fertiliser,  in  this  case  its  acid- 
making power,  which  is  lost  sight  of  under  ordinary  conditions 
but  becomes  the  dominant  feature  when  the  experiment  is 
pushed  long  enough. 
Another  example  of  these  secondary  actions  between 
fertilisers  and  the  soil  which  are  not  immediately  apparent, 
is  afforded  by  nitrate  of  soda.  The  relation  of  nitrate  of  soda 
to  the  plant  may  be  regarded  as  the  simplest  possible  ; we 
know  that  the  compound  need  undergo  no  change  in  order  to 
feed  the  plant,  it  can  be  taken  up  directly  and  has  a very 
immediate  nutritive  effect.  Similarly  it  has  but  the  slightest 
action  upon  the  soil  ; nitrate  of  soda  is  not  only  readily  soluble 
in  water,  but  it  does  not  enter  into  combination  with  any  of 
the  soil  constituents,  and  is  therefore  not  retained,  but  is 
washed  out  at  once  when  there  is  any  drainage  through  the 
soil.  There  is  without  doubt  some  interchange  of  bases 
between  the  soda  of  the  manure  and  the  other  bases  in  the  soil 
zeolites,  because  a dressing  of  nitrate  of  soda  always  assists  the 
plant  to  obtain  potash  from  the  soil ; but  the  nitrate  part  of  the 
salt  enters  into  no  change  whatever,  except  its  absorption  by 
plants  and  other  organisms.  Yet  it  is  very  clear  that  nitrate  of 
soda  has  some  action  upon  heavy  soils,  for  all  farmers  upon 
clay  recognise  that  the  use  of  nitrate  of  soda  leaves  the  land 
very  wet  and  sticky.  This  is  perhaps  most  apparent  in 
districts  where  early  vegetables  are  grown,  as  in  the  Evesham 
country  and  in  Cornwall,  for  there  the  market  gardeners,  who 
are  trying  to  push  on  early  cabbages  and  broccoli  to  secure  the 
earliest  possible  market,  use  quantities  of  nitrate  of  soda  which 
seem  incredible  to  the  ordinary  farmer,  as  much  as  10  and 
15  cwt.  per  aci-e.  Such  a dressing  is  apt  to  leave  the  land 
in  a terrible  state  of  bad  tilth,  from  which  it  takes  some 
time  to  recover.  Some  of  the  Rothamsted  plots  show  exactly 
the  same  result  ; the  bad  texture  of  the  soil,  where  nitrate  of 
soda  has  been  applied  regularly  in  large  quantities,  is  not 
perhaps  so  marked  on  the  wheat  field  as  it  is  on  the  mangold 
field,-  but  there  the  nitrate  plots  are  excessively  wet  and  sticky 
