Some  Secondary  Actions  of  Manures  upon  the  Soil.  35 
upon  which  he  founded  his  general  statements  into  regions 
where  they  will  no  longer  fit  the  facts,  and  it  is  by  picking  up 
the  hints  of  such  discrepancies  as  the  practical  man  can 
often  supply,  that  the  theory  may  be  founded  on  a more 
accurate  basis.  And  lastly,  if  one  more  general  reflection  may 
be  permitted,  the  various  investigations  which  have  been 
described  above  afford  an  illustration  of  the  necessity  of 
continued  research  even  about  matters  which  may  have  become 
common  knowledge  ; all  our  conclusions  are  approximate  only, 
and  every  advance  of  knowledge  calls  for  their  re-examination 
in  the  new  light ; in  this  very  question  under  discussion  there 
remain  one  or  two  doubtful  points  which  might  have  applica- 
tions in  practice,  but  which  cannot  as  yet  be  investigated  until 
the  mathematicians  and  the  physicists  have  settled  some 
fundamental  points  on  the  interactions  between  liquids  and 
solid  particles. 
Summary. 
1.  The  long-continued  use  of  sulphate  of  ammonia  on  soils 
poor  in  lime  results  in  the  soils  becoming  acid. 
2.  The  acidity  is  caused  by  certain  micro-fungi  in  the  soil 
which  split  up  the  sulphate  of  ammonia  in  order  to  obtain  the 
ammonia,  and  thereby  set  free  sulphuric  acid. 
3.  The  infertility  of  such  soils  is  due  to  the  way  all  the 
regular  bacterial  changes  in  the  soil  are  suspended  by  the 
acidity ; instead  fungi  permeate  the  soil  and  seize  upon  the 
manure. 
4.  The  remedy,  as  may  be  seen  upon  the  Woburn  plots,  is 
the  use  of  sufficient  lime  to  keep  the  soil  neutral. 
5.  From  the  Rothamsted  soils  carbonate  of  lime  is  being 
washed  out  at  the  rate  of  800  to  1,000  lb.  per  acre  per  annum, 
the  losses  being  increased  by  the  use  of  sulphate  of  ammonia, 
but  lessened  by  dung  or  nitrate  of  soda. 
6.  Nitrate  of  soda,  when  applied  to  heavy  soils  in  large 
quantities,  destroys  their  texture. 
7.  Some  of  the  nitrate  of  soda  gets  converted  into  carbonate 
of  soda  by  the  action  of  plants  and  bacteria,  and  carbonate  of 
soda,  by  deflocculating  the  clay  particles,  destroys  the  tilth. 
8.  The  best  remedies  are  the  use  of  soot  or  superphosphate  ; 
the  best  preventive  is  the  use  of  a mixture  of  nitrate  of  soda 
and  sulphate  of  ammonia  instead  of  either  separately. 
9.  Soluble  potash  manures  and  common  salt  may  also  injure 
the  tilth  of  heavy  soils  through  the  production  of  a little 
soluble  alkali  by  interaction  with  carbonate  of  lime  in  the  soil. 
The  remedy  is  to  apply  such  manures  in  the  winter  or  in 
conjunction  with  superphosphate. 
A.  D.  Hall. 
Rothamsted  Experimental  Station, 
Harpenden,  Herts. 
