Feb.  1,  189G.] 
iiupplpmmt  to  the  “ Tropical  Agricnlturist:’ 
581 
.Some  time  af»o  we  undertook,  at  tlio  instance  of 
the  then  iiayor  of  (Jolom))0  (Mr.  II.  II.  Cameron) 
to  carry  on  an  e.xperiment  in  the  li’ench  system 
of  dealing  with  night  soil.  The  result  of  this 
e.xperiment  was  so  satisfactory,  that  the  trench 
system  has  been  adopted  in  connection  with  the 
conservancy  of  the  School  of  Agriculture.  The 
deodorization  of  the  filth  was  so  complete,  that  a 
valuable  and  by  no  mean.s  objectionable  fertilizer 
is  now  utilized  as  manure.  It  has  of  course  to 
be  remembered  that  the  deodorizing  and  oxidising 
power  of  the  soil  is  not  unlimited,  and  that  the 
amount  of  tilth  disposed  of  must  be  regulated  by 
the  capacity  of  the  trenches,  while  a proper 
covering  of  earth  should  bo  carefully  laid  on. 
Careless  work  will  ot  course  result  in  objectionable 
odours  being  given  off  from  the  trenches.  If, 
however,  1 he  work  is  properly  suiier vised,  our 
e.xperience  of  the  “ trench  system  is  that  it  is 
an  admirable  method  of  disposing  of  night  soil. 
( To  be  continued. ) 
THE  riCRTIUTY  OF  SOILS. 
By  Profes.sor  Kinch. 
Another  plan  proposed  for  the  estimation  of 
the  available  plant  food  in  a soil  is  due  to  Dr. 
L.  Grandeau.  lie  had  been  led  to  the  conclusion 
that  the  effective  mineral  matter  in  a soil  is 
always  combined  with  organic  matter — -to  a certain 
extent  a return  to  the  old  humus  theory  of  Thaer, 
which  was  thought  to  have  been  effectually  buried 
by  Liebig — which  organic  matter  is  essential  to 
convey  the  food  to  the  plant.  The  mineral  matter 
in  fertile  soils  is,  he  considers,  in  much  the  same 
state  as  it  is  in  well-rotted  farmyard  manure. 
Gnindeau  therefore  treats  the  soil  with  very  dilute 
hydrocliloric  acid  to  remove  bases  and  carbonates, 
and  decompose  huraaces,  and  then  extracts  the 
residue  w'ith  ammonia;  this  solution,  he  con- 
siders, contains  the  available  plant  food  material  of 
the  soil.  Although  this  plan  seemed  to  answer 
with  certain  soils,  yet  it  is  not  altogether  satis- 
factory. It  is  probable  that  the  ammonium  humate 
formed  in  the  operation  is  the  active  solvent 
agent  on  the  soil  ingredients.  It  has  been  sug- 
gested that  perhaps  ammonium  citrate  in  solution 
would  answer,  or  a mixture  of  citric  acid  and  am- 
monium citrate  would  probably  still  more  closely 
represent  the  natural  processes  of  the  roots.  A 
greater  interest  has  been  awakened  in  such 
method  of  soil  analysis,  and  we  may  safely  leave 
methods  to  be  investigated  and  worked  out  by 
agricultural  chemists. 
The  fcotal  amount  of  combined  nitrogen  which 
is  found  in  soils  of  known  capabilities,  varies  in 
the  rather  poor  arable  soils  of  Rothamsted  from 
about  '1  to  -lo  per  Cent.  Generally,  in  the  arable 
lands  of  this  countrj'  it  is  between  T and  ’2  per 
cent,  in  the  surface  soil.  In  the  subsoil  roughly 
about  one-half  of  these  amounts  is  commonly 
found.  The  surface  .soil  of  a pasture  will  generally 
contain  more  than  this,froin  -ll  to  o or  ’4  ]>er  cent. 
There  are  many  cases,  however,  in  which  the 
percentage  of  nitrogen  in  the  surface  soil  is  much 
higher  than  this,  going  up  to  ‘6  or  ‘8  per  cent., 
and  then  a very  fertile  soil,  and  one  not  easily 
exhausted,  is  found  ; the  black  earth  of  Russia, 
someof  the  prairieland  of  Manitoba,  and,  in  this 
country,  some  of  the  Pen  lands  of  Lincolnshire  are 
example.s  of  the.se  fertile  alluvial  lands  full  of  the 
remains  of  previous  generations  of  jilants.  When 
we  remember  that  an  acre  of  soil  to  a depth  of  9 
inches  means  about  2k  million  pounds  of  line  dry 
earth,  we  see  that  the  stores  of  combined  nitrogen, 
even  in  a poor  .soil,  means  a large  ?uimber  of 
pounds ; T per  cent,  means  2,o00  lb.,  in  the  top  9 
inches;  ’4  per  cent,  is  equivalent  to  10,000  1b. 
This  nitrogen  becomes  available  to  the  plant  by 
the  gradual  alteration  and  oxidation  of  the  organic 
matter  in  which  it  is  combined;  we  know  but 
little  of  the  rate  at  which  it  becomes  available, 
but  even  in  a very  poor  and  exhausted  soil 
nitrates  are  formed  annually,  and  at  a rate,  as  in  the 
Rothamsted  drain  guages,  equivalent  to  the  oxida- 
tion of  about  3o  pounds  of  nitrogen,  or  formation 
of  2 cwt.  of  nitrate  of  soda  per  acre  per  annum. 
In  a soil  in  high  condition,  certainly  twice  this 
amount  of  nitrogen  might  be  expected  to  be 
oxidised  per  annum,  equivalent  to  about  1 or  d 
cwt.  of  niti’ate  of  soda.  A factor  which  would  be 
of  use  in  estimating  the  fertilily  of  a soil  would 
be  the  knowdedgeof  the  rate  at  which  the  nitrogen 
became  oxidised,  and  nitrates  formed  from  the 
actual  nitrogenous  matter  in  the  soil;  this  yet 
remains  to  be  worked  out. 
The  amount  of  phosphonc  acid  soluble  in 
hydrochloric  acid,  as  in  an  Ordinary  analysis, 
in  a soil  should  never  fall  below  ’05  per  cent, 
and  in  really  first-class  soils  ic  will  much  e.xceed 
this  amount,  though,  excepting  in  some  clay  soils, 
it  rarely  exceeds  ’5  per  cent.  As  we  have  seen, 
the  amount  of  phosphoric  acid  soluble  in  a 1 
per  cent,  solution  of  citric  acid  shoud  not  fall 
below  'Ol  per  cent.  The  amount  of  potash  soluble 
in  hydrochloric  acid  in  a soil  varies  within  wide 
limits  ; in  a fairly  fertile  sandy  soil  it  may  be  less 
than  *1  per  cent.,  in  a clay  it  may  often  be  over  1 
per  cent.  The  amount  of  potash  soluble  in  a 1 
per  cent,  solution  of  citric  acid  should  not  be 
less  than  'OO-T  per  cent,  of  the  .soil.  Lime,  which 
is  for  the  most  part  present  in  the  form  of  calcium 
carbonate,  exerts  a considerable  influence  on  both 
the  physical  and  chemical  qualities  of  a soil.  In 
a very  sandy  soil  it  may  not  exceed  one-tenth  of 
a per  cent.,  but  in  most  good  soils  it  is  not  under 
three-tenths  of  a per  cent.,  and  it  may  with  great 
advantage  rise  to  2 per  cent,  of  calcium  carbonate. 
Lime  in  this  form  materially  assists  in  the  pro- 
cesses of  nitrification  and  absorption  going  on  in 
all  fertile  soils,  and  it  helps  to  keep  clay  in  a 
flocculated  and  more  workable  condition. 
The  effect  of  aspect,  elevation,  temperature, 
amount  of  rainfall,  and  other  climatic  conditions 
on  the  productiveness  of  a soil  are  matters  of  great 
practical  importance,  and  always  open  to  obser- 
vation. The  biological  factors,  especially  the  effect 
ol  minute  organisms,  are  most  intricate,  and  at 
jiresent  less  w'ell  known,  but  very  important.  A 
farmer  should  obtain  all  the  aid  he  can  from 
chemistry  and  physics  in  studying  the  composition 
and  properties  of  his  soil ; but  we  cannot  too 
st.rongly  advise  him  alway.s  to  take  in  addition 
tlie  “ opinion  of  the  plants”  by  making  for  him- 
sidf  on  his  own  farm  a few  simple  but  systematic 
m uuirial  experiments  with  two  or  three  different 
cl.isses  of  plants — et/.,  cereals,  roots,  leguminoste. 
lie  will  then  learn  much  more  thoroughly  and 
effectively  than  in  other  ways  whether  his  land 
requires  nitrogen,  phosphoric  acid,  potash,  or  lime, 
and  on  which  crops  these  may  be  most  beneficially 
employed. 
