Dec.  r,  1896.] 
THE  TROPICAL  AGRICULTURIST. 
419 
of  division  of  the  soil  particles  and  the  nature  of 
the  soil  itself.  Everyone  is  aware  how  parched 
sandy  soils  become  in  dry  weather,  and  how  well  clay 
soils  are  enabled  to  withstand  long  periods  of  drought. 
Among  the  inllaences  which  alfect  the  heat  aljsjrbbig 
power  of  a soil  colour  ma}'  be  said  to  bo  one  of  the 
most  important.  A dai'k  soil  absorbs  more  heat  than 
a light-coloured  soil.  What  gives  colour  to  a soil  is 
chiefly  the  amount  ol  organic  matter  it  contains.  Iron, 
again,  is  very  often  the  cause  of  the  colour  of  a soil' 
Even  a small  percentage  is  able  to  exert  an  important 
influence  in  this  respect.  Soils  containing  iron  gene- 
rally have  a very  red  colour.  Some  idea  of  the  influ- 
ence the  colour  of  a soil  has  on  its  po  ver  of  absorbing 
the  sun’s  rays  will  be  obtained  from  the  statement 
that  a difference  in  temperature  amounting  to 
thirteen  or  fourteen  degrees  Fahr.  has  been  found 
to  be  due  to  colour  alone  in  soils  adjoining  one 
another.  There  are  other  sources,  of  course,  from 
which  the  soil  may  derive  its  heat  in  addition  to  the 
sun’s  rays.  Thus  the  decay  of  organic  matter,  when 
taking  place  at  all  rapidly,  engenders  much  heat. 
But,  important  as  the  physical  properties  of  a 
soil  are,  they  only  partially  explain  its  fertility. 
The  soil  not  only  acts  as  a support  to  the  plant 
and  as  a medium  through  which  its  roots  may  drink 
in  air  and  moisture,  but  it  also  furnishes  the  plant 
with  certain  necessary  food  ingredients.  What,  then, 
are  these  food  ingredients,  and  to  what  extent  are 
they  present  in  most  soils?  The  composition  of  the 
soil,  as  we  should  naturally  expect,  includes  a largo 
number  of  different  substances,  but  the  greater 
part  of  it  is  made  up  of  only  a few  bodies.  Silica 
is  by  far  the  largest  constituent,  and  is  present  in 
an  almost  pure  form  as  sand,  or  in  combination  with 
alumina,  as  clay.  This  latter  substance  is  the  con- 
stituent which,  next  to  silica,  is  the  most  abundant 
constituent.  Together  they  may  be  said,  as  a rule, 
to  form  at  least  four-fifths  of  the'inorganic  portion  of 
soils.  Very  much  less  in  amount  is  lime.  Magnesia 
is  also  a constituentof  some  imxrortance.  It  may  be 
here  pointed  out  that  the  physical  properties  of  the 
soil  are  influenced  almost  entirely  by  the  proportion 
in  which  organic  matter  and  the  above-mentioned 
ingredients  are  present.  Very  striking,  more  especi- 
ally on  the  texture  of  the  soil,  is  the  effect  of  lime.  By 
its  addtion  the  stiffest  of  clays  may  be  made  friable. 
A very  strange  fact  with  regard  to  the  two  Ixrgest 
constituents  of  the  soil  is  that  neither  of  them  is 
a necessary  plant-food.  Silica,  it  is  true,  is  found 
almost  universally  present  in  plants;  but  the  most 
careful  research  has  failed  to  show  that  it  is  ab- 
selutely  necessary  for  plant  growth  ; while,  with  re- 
gard to  aluminia,  it  is  not  even  found  in  the  plant. 
Lime,  magnesia,  and  iron  are,  on  the  other  hand, 
necessary  foods;  but  the  fame  economic  importance 
does  not  attach  to  them  as  docs  to  two  other  plant- 
foods — viz.,  phosphoric  acid  and  potash,  and  this  is 
for  the  reason  that  the  three  first-named  sub.stanccs 
are  almost  invariably  present  in  amounts  which,  so 
far  as  the  needs  of  growing  plants  are  concerned, 
are  abundant ; whereas  the  last  named  are  by  no 
means  so  plentiful  and  hence,  along  with  nitrogen, 
do  much  to  limit  the  growth  of  the  plant.  It  has 
been  found  that  few  soils  contain  phosphoric  acid 
in  quantities  over  two-tenths  of  a per  cent ; while 
the  average  amount  in  most  fertile  soils  is  prob- 
ably not  more  than  half  this.  'There  are  a few 
soils,  it  is  true,  where  it  occurs  more  abnndantly. 
Thus  in  certain  very  rich  Eussian  soils  it  has  been 
tound  to  be  present  to  the  extent  of  more  than  one- 
half  per  cent. 
But  it  must  not  be  imagined  that  the  whole  of 
this  amount,  trifling  though  it  may  appear,  is  in  a 
form  in  which  the  plant  can  at  once  make  use  of 
it.  ’This  is  not  the  caS'C.  Only  a very  small  trace 
is  present  in  a condition  available  for  the  needs  of 
the  plants.  How  much  this  is  it  is  very  difficult  to 
say,  as  we  do  not  know  any  e.xact  method  for  esti- 
mating it.  It  must  be  pointed  out  that  is  not  merely 
that  which  is  soluble  in  water  which  is  in  a condi- 
tion available  for  the  plant.  'There  is  a certain 
amount  of  plant  food  in  the  soil  which,  although 
not  soluble  in  water,  is  yet  available  for  the  plant’s  im- 
mediate requirements,  since  it  is  capable  of  being 
dissolved  by  the  acid  sap  of  the  plant ; and  lately  an 
ingenious  method  has  been  devised  which  aims  at 
estimating  what  this  amount  of  available  mineral 
food  really  is  in  the  case  of  phosphoric  acid  and 
potash  in  soils.  For  this  purpose  a weak  solution  of 
citric  acid,  1 per  cent,  strong,  is  used'  The  results 
a.s  yet  obtained  by  this  method  show  that  while 
the  total  amount  of  phosphoric  acid  in  a fairly 
fertile  soil  may  be  as  much  as  between  three  and 
four  thousand  pounds  per  acre  in  the  surface  foot  of 
soil,  the  amount  irmnediately  availabh\  for  the  plant’s 
needs  may  be  considerably  less  than  a tenth  of  this 
amount.  Similarly  with  potash,  which  may  be  taken 
in  most  soils  to  run  as  high  as  1 per  cent,  very  few 
soils  probably  would  contain  anything  like  a hundredth 
of  a per  cent  in  the  soluble  condition.  The  constant 
removal,  due  to  drainage  and  the  growth  of  crops,  of 
phosphoric  acid  and  potash,  as  well  as  of  that  other 
important  plant- food,  nitrogen,  which  is  being  effected 
on  our  cultivated  fields,  calls  for  the  application  of 
fertiliser's  if  the  fertility  of  our  soil  is  to  be  maintained. 
Uence  it  is  that  much  of  our  cultivated  land  is  con- 
stantly being  reinforced  in  its  fertilising  constituents 
by  the  addition  of  costly  manures.  But  with  the  ad- 
vance of  recent  science  we  are  beginning  to  recognise 
that  what  is  probably  the  most  important  condition  of 
fertility  of  the  soil  i'r  the  presence  of  countless  myriads 
of  microbic  life,  with  which  we  know  every  ounce  is 
teeming. — Scotsman. 
COFFEE-PLANTING  IN  BRITISH  CENTRAL 
AFRICA. 
(From  Chambers’s  Journal  for  October.) 
BY  MR.  II.  D.  HERD. 
Although  by  the  latest  arrangement  between  the 
British  South  Africa  Company  and  the  Foreign 
Office  with  regard  to  these  territories  in  1894  the  area 
over  which  the  British  protectorate  immediately  ex- 
tends has  been  considerably  lessened,  there  still  re- 
mains under  the  direct  administration  of  Her 
Majesty’s  Commissioner  a country  equal  in  extent 
to  the  area  of  Great  Britain. 
This  countr-y  extends  from  Lake  Nyassa  on  the 
north  to  a point  on  the  Shire  Kiver  near  its  confluence 
with  the  Zambesi  on  the  south  ; but  the  district  to 
which  our  attention  is  more  particularly  directed  is 
that  tableland  lying  between  the  Shire  on  the  west 
and  the  borders  of  the  protectorate  on  the  east,  and 
perhaps  best  known  as  the  Shire  Highlands. 
Here  is  the  latest  h.ome  of  coffee  ; and  seeing  that 
the  country  has  now  passed  through  its  little  fever 
of  war.s  with  the  Arab  slave-traders  on  its  borders, 
and  peace  seems  to  have  come  to  stay,  we  think  that 
the  present  position  of  its  staple  industry  and  its 
future  prospects  merit  a wider  publicity  in  the  in- 
terests of  those  to  whose  enterprise  and  hardihood 
the  country  owes  what  prosperity  it  has. 
The  history  of  coffee  in  Nyasaland  dates  back 
only  to  the  year  1878,  when  three  small  coffee 
plants  from  the  Edinburgh  Botanical  Gardens 
were  taken  out  by  Mr.  Duncan,  then  gardener  to 
the  Church  of  Scotland  Mission  at  Blantyre,  and 
planted  in  the  mission  garden  there.  This  was  done 
at  the  energetic  representatioirs  of  Mr.  .John  Buchanan. 
In  the  5-ear  1880  the  sole  survivor  of  the  three  plants 
brought  out  by  Mr.  Duncan  bore  a crop  of  about 
one  thousand  beaus.  From  the  distribution  of  the 
seed,  three  years  later,  may  be  dated  the  beginning 
of  coffee-  .hinting  on  an  extensive  scale  ; but  in  1881 
the  first  serious  attempt  to  put  coffee  on  the  home 
market,  and  to  gau;;e  its  value  as  a commercial  pro- 
duct in  competition  with  other  coffees,  was  made  by 
the  late  Mr.  .John  Buchanan,  of  the  firm  of  Buchanan 
Brothers,  who.se  name  is  so  honourably  connected  not 
only  with  the  commercial  but  the  political  develop- 
ment of  the  Shire  Highlands. 
A sample  of  the  tirst  crop  was  sent  home  for  valua- 
tion, and  was  quoted  in  the  London  market  at  eighty- 
five  shillings  per  hundredweight. 
