The  Production  of  Plant  Food  in  the  Soil. 
21 
India  ; Mr.  Francis  renders  a passage  in  the  Stories  of  Buddha's 
former  births,  as  follows  : — 
“ Like  to  a tender  plant  whose  roots  are  fed 
On  soil  o’er  which  devouring  flames  have  spread.” 
A similar  practice  prevails  in  other  parts  of  India,  in  Ceylon, 
and  Malaya.1 *  It  is  also  known  in  the  West  Indies  ; in 
Trinidad  a small  cultivator  will  rent  a piece  of  derelict  land, 
burn  the  bush  in  the  dry  season,  and  plant  with  maize  followed 
by  cassava,  yams,  &c.’  The  soil  is  not  enriched  with  organic 
matter  during  this  period  and  consequently  is  soon  exhausted 
and  is  then  allowed  to  run  to  waste.  It  speedily  becomes 
covered  with  bush,  and,  as  nothing  is  removed,  organic  matter 
accumulates,  so  that  after  a time  it  can  once  more  be  burnt 
clear  and  cultivated.  On  the  mainland  also  the  practice  is 
known  ; in  the  grazing  districts  of  Colombia  the  bush  is 
periodically  burnt,  and  the  new  crop  of  grass  that  comes  on, 
although  weak  at  first,  as  might  be  expected,  becomes  after  a 
time  very  heavy,  dark,  and  succulent,  and  will  carry  more 
cattle  than  before,3  besides  being  free  from  ticks,  snakes,  &c. 
Turning  to  another  continent,  the  beneficial  effect  of  burning 
the  scrub  or  the  stubbles  is  well  recognised  in  South  Australia, 
and  has  been  shown  not  to  be  due  to  the  ashes.4  In  our  own 
country  it  is  commonly  observed  that  crops  are  darker  and 
better  on  places  where  heaps  of  stubble  or  weeds  have  been 
burned  than  on  the  surrounding  ground.  Paring  and  burning 
was,  until  comparatively  recent  times,  a regular  part  of  the 
husbandry  of  certain  districts  of  the  British  Islands. 
Wherever  these  practices  have  come  under  the  notice  of 
chemists  they  have  been  condemned  because  of  the  waste  of 
organic  matter  and  of  nitrogen  involved,  but  it  is  now  clear 
that  there  is  another  side  to  the  question.  Heating  kills  the 
harmful  factor  and  gives  the  useful  bacteria  full  scope  for 
their  activity  ; further,  it  effects  a certain  amount  of 
decomposition  and  thus  leaves  less  work  for  the  bacteria  to 
do.  What  the  practical  man  has  to  decide  is  whether  this 
gain  is  worth  the  cost  of  the  fuel — the  fuel  often  being  valuable 
soil  organic  matter. 
The  economic  problem  is  more  straightforward  in  another 
case.  Large  growers  under  glass  are  greatly  troubled  by  the 
accumulation  of  insect  pests  in  their  soils,  and  by  the  soils 
“ wearing  out  ” after  two  or  three  years  and  no  longer 
responding  sufficiently  to  manure.  The  latter  phenomenon 
1 J.  C.  Willis  : Agriculture  in  the  Tropics. 
3 C.  H.  Wright  : Nature , October,  1910,  page  630. 
1 I am  indebted  to  Mr.  J.  M.  Vaughan  for  these  facts. 
4 Herbert:  Journal  of  Agriculture  of  South.  Australia,  1910;  April, 
page  791,  and  June,  page  967,  also  Grasby,  West  Australian , Nov.  3,  1910. 
