32  Some  Secondary  Actions  of  Manures  upon  the  Soil. 
from  any  absolute  poverty.  For  the  same  kind  of  reason  then, 
nitrate  of  soda  gets  described  as  an  exhausting  manure,  not 
because  it  robs  the  land  in  any  special  way,  but  simply  because 
it  sets  up  a bad  texture  of  the  soil  which  so  easily  leads  to  an 
inferior  yield  in  the  following  crop. 
The  list  indeed  of  these  secondary  interactions  between 
fertiliser  and  soil  which  may  have  a potent  influence  on  the 
value  of  the  fertiliser  in  practice  is  not  ended  with  the  changes 
set  up  by  nitrate  of  soda  and  sulphate  of  ammonia  ; there  is 
plenty  of  pi’actical  evidence  that  the  effect  of  applying  potash 
salts  such  as  kainit,  muriate  or  sulphate  of  potash,  is  not 
wholly  comprised  in  the  provision  of  a certain  amount  of 
potash  for  the  nutriment  of  the  crop.  In  the  fii’st  place  it  has 
often  been  remarked  by  those  concerned  with  field  experi- 
ments that  cases  occur  when  the  addition  of  potash  salts  to  a 
mixture  so  far  from  increasing  the  return  actually  reduces  it. 
As  a rule  these  results  have  been  set  down  to  the  lai’ge  experi- 
mental error  which  is  inevitable  in  all  field  trials,  but  so  con- 
vinced have  been  some  experimenters  of  the  reality  of  the 
effect  that  they  have  begun  to  speak  of  the  “ depressing  effect 
of  potash”  upon  the  crop.  Now  from  the  point  of  view  of 
nutrition  alone  such  a depressing  effect  is  impossible,  in  some 
way  the  effect  must  be  special  to  the  soil  and  due  to  an 
unsuspected  interaction  between  soil  and  potash  fertiliser.  A 
clue  to  the  sort  of  action  to  be  looked  for  may  be  found  in  the 
observations  which  have  been  recorded  in  some  of  the  cases 
where  the  use  of  potash  had  resulted  in  a lowered  yield,  that 
the  ground  remains  a little  wetter  after  the  application  of  kainit 
or  other  potash  salts.  As  in  the  case  of  nitrate  of  soda  this 
apparent  wetness  has  been  set  down  to  the  water-absorbing 
properties  of  potash  salts,  which  are  chiefly  due  to  the 
magnesium  chloride  which  is  always  present  in  them,  but  as 
we  have  already  indicated  the  small  amount  of  water  which  is 
absorbable  by  an  ordinary  dressing  of  potash  salts  would  be 
inappreciable  when  diffused  through  the  soil.  The  wetness 
suggests  deflocculation,  and  the  appearance  of  many  of  the 
plots  receiving  potash  at  Rothamsted  would  bear  out  this  view. 
On  the  mangold  field  in  particular  the  characteristic  defloccu- 
lation features  shown  by  the  plots  receiving  nitrate  of  soda, 
especially  their  way  of  drying  with  a tough  glazed  crust  on  top, 
are  reproduced  on  the  plpts  receiving  sulphate  of  potash,  and 
the  worst  plot  of  all  is  that  which  receives  both  of  these 
fertilisers.  Tested  by  the  suspension  of  a small  quantity  of  soil 
in  a large  bulk  of  pure  water  the  opinion  is  confirmed  that  the 
soil  of  these  potash  plots  is  completely  deflocculated.  Another 
practical  case  has  fallen  under  the  observation  of  the  writer 
where  the  application  of  8 cwt.  per  acre  of  kainit  to  a piece  of 
