On  the  Power  of  Soils  to  absorb  Manure. 
373 
phate  or  muriate  of  ammonia,  we  have  a new  and  at  present  un- 
known compound  of  that  base.  What  is  the  first  natural  and 
undeniable  inference  ? That  as  a source  of  supply  of  ammonia 
to  the  soil  it  is  indifferent  what  salt  we  employ — neither  the  sul- 
phate nor  the  muriate  is  direct  food  for  plants,  but  they  are  with 
equal  ease  converted  into  compounds  which  can  furnish  that  food. 
This  is  an  important  and  beautiful  truth,  and  is  well  worth  all 
the  labour  expended  on  the  investigation. 
Mr.  Solly  made  experiments  some  years  ago  at  the  Chiswick 
Gardens  upon  the  comparative  action  of  different  salts  of  am- 
monia on  wheat,  and  could  find  no  difference  in  their  effects. 
Mr.  Lawes  and  Dr.  Gilbert,  in  their  admirable  experiments  at 
Rothamsted,  have  observed  that  it  made  no  difference  what  salt 
of  ammonia  or  potash  was  employed.  At  first  they  used  the 
carbonates,  as  appearing  the  most  natural  form  in  which  to  present 
them,  but  they  now  employ  th e cheapest  salts  of  these  bases.  The 
explanation  of  these  interesting  observations  is  now  forthcoming, 
and  it  may  be  taken  as  a principle  that  in  artificial  manuring, 
where  any  particular  alkali  is  to  be  employed,  the  choice  should 
fall  on  the  salt  which  affords  the  cheapest  supply  of  that  alkali. 
Of  course  this  principle  must  be  applied  with  judgment,  and  it 
is  obviously  inapplicable  where  the  acid  of  the  salt  is  of  great 
agricultural  value.  Thus  the  carbonates,  sulphates,  and  muriates, 
must  be  put  in  a different  class  from  the  phosphates  and  nitrates. 
Further,  the  insolubility  of  the  alkaline  compounds  formed  in 
the  soil  has  a close  bearing  upon  the  method  of  applying  artificial, 
and  in  fact  all  kinds  of  manure.  It  has  been  shown  that  a 
moderately  fertile  soil  will  unite  with  3-10ths  per  cent,  of  ammo- 
nia ; in  other  words  1000  lbs.,  or  1000  tons,  will  combine  with 
3 lbs.,  or  3 tons,  of  ammonia. 
An  acre  of  soil  one  inch  in  depth,  weighs  about  100  tons — 
10  inches  deep,  therefore,  1000  tons.  Now  an  acre  of  soil  worked 
to  the  depth  of  10  inches,  wrould  upon  this  showing  take  up  3 
tons  of  ammonia,  a quantity  which  is  supplied  in  15  tons  of  sul- 
phate of  ammonia.  A large  dressing  of  this  salt  would  be  5cwt. 
to  the  acre,  consequently  we  have  60  times  the  power  in  the  soil 
that  is  actually  needed.  Now  comes  the  inference:  when  a salt 
of  ammonia  is  applied  to  the  soil  it  soon  becomes  combined  with 
it,  and  remains  fixed  and  insoluble.  When  once  this  combi- 
nation takes  place,  there  would  appear  to  be  no  power  in  water 
iurther  to  distribute  the  manure.  It  follows,  that  if  in  the  appli- 
cation of  manure  we  are  not  careful  to  ensure  an  equal  distribu- 
tion, we  entail  upon  the  roots  of  the  plants  the  necessity  of  seek- 
ing their  food  at  a distance,  and  thus  call  for  a greater  expenditure 
of  vital  force. 
Mr.  Lawes  tells  me,  that  although  he  has  taken  great  pains 
