150 
DRY  FARMING . 
A great  deal  of  attention  has  been  given  of  recent  years  to  a 
system  of  cultivation  upon  lands  which  have  a scanty  rainfall  and 
no  available  irrigation  supply.  At  a time  when  the  general  watch- 
word of  the  country  is  “Conservation”  it  may  be  worth  while  to 
call  attention  to  this  comparatively  new  method  of  crop  manage- 
ment termed  “Dry  Farming,”  which  has  for  its  object  the  con- 
servation of  the  natural  rainfall.  As  the  system  has  many  en- 
thusiastic advocates  and  has  proved  undoubtedly  valuable  on 
semi-arid  tracts  on  the  mainland,  it  would  be  well  at  this  time 
to  ascertain  by  suitable  experiment  whether  its  adoption  in  cer- 
tain localities  of  the  islands  would  not  result  in  bringing  into  agri- 
cultural use  land  which  hitherto  has  been  not  profitable  to  cul- 
tivate. 
The  term  “dry  farming”  is  of  itself  to  an  extent  misleading,  as 
it  is  self  evident  that  no  crop  can  he  produced  without  a certain 
supply  of  moisture — for  all  plant  food  must  be  presented  in  solu- 
ble form  to  the  root  system  before  absorption  into  the  plant.  The 
object  of  dry-farming,  however,  is  to  produce  crops  without  arti- 
ficial water  supply.  This  is  accomplished  bv  a series  of  operations 
which  look  to  the  most  economical  use  of  the  available  rainfall. 
Speaking  generally  it  is  found  that  an  annual  rainfall  of  twelve 
inches  if  properly  conserved,  is  sufficient  for  the  production  of 
crops  when  “dry  farming”  methods  are  practiced.  The  loss  of 
moisture  from  land  may  be  said  to  be  due  to  three  main  causes, 
“run-off,”  seepage  and  evaporation.  Of  these  the  first  mav  be 
prevented  largely  by  contour  furrows  and  the  construction  of  the 
usual  barriers  and  reservoirs.  Loss  from  seepage  is  largely  pre- 
vented by  deep  plowing  and  by  compacting  the  lower  laver  of  soil. 
It  is  not,  however,  to  these,  the  most  obvious  sources  of  loss,  that 
depletion  of  soil  moisture  is  mainly  due,  but  to  the  less  suspected 
cause  of  evaporation. 
After  a heavy  rainfall  the  surface  of  the  soil  presents  a caked 
and  dry  appearance  forming  a crust,  which  may  be  thought  to  act 
as  a preventative  against  loss  of  moisture.  Such,  however,  is  not 
the  case,  for  this  cracked  and  flaked  crust  acts  as  the  most  perfect 
medium,  for  the  diffusion  of  moisture  from  the  soil  to  the  air. 
This  is  brought  about  bv  the  force  known  as  “capillary  attraction” 
which  permits  evaporation  as  rapidly  as  water  can  be  brought  to 
the  surface  of  the  ground  and  continues  it  until  all  moisture  with- 
in reach  of  the  root  system  of  crop-plants  is  exhausted. 
The  principal  of  moisture  being  conducted  between  the  in- 
terstices of  contiguous  surfaces  is  familiar  to  all.  Its  most  useful 
application  is  perhaps  made  in  the  ordinary  lamp  wick,  between 
whose  filaments  the  oil  is  rapidly  sucked  up  for  combustion.  Such 
a process  is  at  work  when  the  medium  of  the  cellular  flake  of  dried 
earth  connects  the  moist  substratum  of  earth  with  the  warm  over- 
