﻿PLANT 
  INDUSTRIES 
  321 
  

  

  301. 
  Water 
  drainage. 
  The 
  amount 
  of 
  water 
  in 
  the 
  soil 
  va- 
  

   ries 
  and 
  depends 
  upon 
  many 
  factors. 
  The 
  coarse 
  soils 
  (gravel 
  

   and 
  coarse 
  sand) 
  soon 
  become 
  dry 
  when 
  there 
  is 
  little 
  rainfall 
  

   and 
  no 
  replenishment 
  of 
  water 
  from 
  below. 
  Fine-grained 
  soils 
  

   which 
  contain 
  a 
  good 
  supply 
  of 
  organic 
  matter 
  may 
  become 
  

   filled 
  with 
  water 
  and 
  may 
  retain 
  this 
  water 
  for 
  a 
  long 
  time. 
  

   They 
  may 
  become 
  so 
  filled 
  with 
  water 
  as 
  almost 
  entirely 
  to 
  

   exclude 
  the 
  air 
  of 
  the 
  soil, 
  thus 
  suffocating 
  the 
  roots 
  of 
  plants. 
  

   But 
  some 
  air 
  remains 
  in 
  all 
  soils, 
  even 
  below 
  ponds 
  and 
  

   streams, 
  and 
  some 
  water 
  plants 
  can 
  live 
  with 
  their 
  roots 
  in 
  

   such 
  water-logged 
  soils. 
  From 
  50 
  to 
  60 
  per 
  cent 
  of 
  the 
  total 
  

   water-holding 
  capacity 
  of 
  soil 
  is 
  found 
  to 
  be 
  best 
  for 
  the 
  growth 
  

   of 
  cereals. 
  Our 
  agricultural 
  plants, 
  except 
  rice, 
  cannot 
  endure 
  

   water-logged 
  soils, 
  and 
  drainage 
  has 
  often 
  been 
  necessary 
  to 
  

   bring 
  about 
  a 
  more 
  favorable 
  water-and-air 
  content 
  of 
  culti- 
  

   vable 
  lands. 
  

  

  Natural 
  drainage 
  may 
  be 
  either 
  on 
  the 
  surface 
  or 
  under- 
  

   ground. 
  It 
  is 
  evident 
  that 
  in 
  cultivated 
  soils 
  extensive 
  

   underground 
  drainage 
  will 
  in 
  times 
  of 
  heavy 
  rains 
  hasten 
  the 
  

   removal 
  of 
  surplus 
  water 
  and 
  at 
  all 
  times 
  will 
  facilitate 
  

   better 
  aeration 
  of 
  the 
  soil. 
  The 
  annual 
  rainfall 
  in 
  the 
  United 
  

   States 
  varies 
  from 
  ten 
  inches 
  or 
  less 
  to 
  more 
  than 
  sixty 
  

   inches 
  per 
  year, 
  and 
  when 
  any 
  considerable 
  part 
  of 
  this 
  rain- 
  

   fall 
  comes 
  in 
  a 
  short 
  period 
  of 
  time, 
  non-enduring 
  plants 
  will 
  

   suffer 
  and 
  sometimes 
  be 
  drowned 
  unless 
  adequate 
  drainage 
  is 
  

   supplied. 
  

  

  North 
  America 
  still 
  has 
  immense 
  tracts 
  of 
  waste 
  swampy 
  

   land 
  that 
  only 
  needs 
  drainage 
  and 
  tillage 
  to 
  make 
  it 
  highly 
  

   productive 
  soil. 
  It 
  is 
  estimated 
  that 
  the 
  United 
  States 
  has 
  

   nearly 
  100,000,000 
  acres 
  of 
  swamp 
  land, 
  much 
  of 
  which 
  is 
  

   drainable, 
  and 
  in 
  many 
  places 
  trained 
  engineers 
  are 
  devising 
  

   the 
  needed 
  drainage 
  systems, 
  and 
  the 
  land 
  is 
  being 
  reclaimed. 
  

  

  302. 
  Influence 
  of 
  cultivation 
  on 
  water 
  supply. 
  In 
  earlier 
  

   times 
  agriculturists 
  advised 
  against 
  cultivating 
  corn 
  and 
  other 
  

   crops 
  during 
  times 
  of 
  drought, 
  because 
  they 
  thought 
  that, 
  if 
  

   constantly 
  stirred, 
  the 
  soil 
  would 
  lose 
  its 
  moisture 
  more 
  rapidly, 
  

  

  