30  So7ne  Secondary  Actions  of  Manures  upon  the  Soil. 
The  next  point  of  importance  is  to  find  both  a remedy 
for  the  injured  tilth  of  the  heavy  soil  where  nitrate  of 
soda  has  been  too  freely  applied,  and  a means  of  preventing 
such  action  in  the  future.  Lime  is  of  no  benefit  to  a soil 
which  has  been  deflocculated  by  an  alkali  like  carbonate  of 
soda  because  lime  is  an  alkali  itself  and  would  rather  tend  to 
make  matters  worse.  The  flocculating  action  of  lime  on 
ordinary  clay  soils  only  takes  place  when  the  lime  gets  washed 
into  the  soil  as  soluble  bicarbonate ; lime  itself  when  protected 
from  carbon  dioxide  has  curiously  enough  no  flocculating 
action  (see  Hall  and  Morison,  Jour.  Agric.  Sci.  1907.  2,  244). 
In  this  particular  case  the  flocculating  action  of  lime  would 
be  largely  masked  by  the  carbonate  of  soda  which  would  still 
remain  in  the  soil.  Gypsum  has  been  used  in  America  as  a 
means  of  getting  rid  of  carbonate  of  soda  in  those  unfertile  and 
unworkable  soils  known  as  “ black  alkali  ” ; the  two  substances 
interact  to  form  sulphate  of  soda  and  carbonate  of  lime.  It 
takes,  however,  a large  and  unprofitable  amount  of  gypsum  to 
effect  this  change,  and  a more  practical  plan  is  always  to  use 
superphosphate  as  the  phosphatic  manure  on  such  land.  The 
acid  of  the  superphosphate  will  go  to  neutralise  the  alkaline 
carbonate  of  soda,  and  the  gypsum  which  is  also  present  will 
aid  in  the  desired  flocculation  of  the  clay  particles.  However, 
the  best  remedial  measure  is  probably  a liberal  dressing  of  soot ; 
the  particles  of  carbon  have  a beneficial  mechanical  effect  in 
lightening  the  texture  of  the  soil,  and  at  the  same  time  the 
ammonia  salts  that  are  present  in  the  soot  are  helpful  in 
flocculating  the  clay.  As  a preventive  undoubtedly  the  simplest 
and  wisest  plan  to  follow  is  to  use  instead  of  nitrade  of  soda 
alone  a mixture  in  equal  proportions  of  nitrate  of  soda  and 
sulphate  of  ammonia  on  all  strong  soils,  especially  where 
considerable  quantities  of  concentrated  nitrogenous  manure 
are  required  for  market  gardening  purposes.  Since  one 
of  these  compounds  tends  to  produce  an  acid  and  the 
other  an  alkali  in  the  soil,  they  neutralise  the  effects  of 
each  other,  and  as  far  as  the  conditions  depend  upon  the 
manuring,  such  a mixture  will  not  disturb  the  reaction  of  the 
soil  in  one  direction  or  the  other.  Moreover  there  is  a good 
deal  to  be  said  for  the  use  of  such  a mixture  from  the  point  of 
view  of  the  nutrition  of  the  plant ; of  course  the  great  value  of 
nitrate  of  soda  lies  in  its  immediate  availability,  but  when 
too  much  is  put  on  it  may  easily  form  a solution  that  is 
injuriously  strong  in  certain  parts  of  the  soil.  Muntz  has 
recently  shown  in  an  interesting  paper  how  limited  is  the 
diffusion  of  even  so  soluble  a salt  as  nitrate  of  soda  in 
the  soil ; it  washes  down  with  the  rain,  but  it  spreads  very 
little  laterally,  and  Muntz’  conclusions  can  be  verified  by 
