5§0 
joTfRNAL  OF  BORTiaULTURB  ABI)  COTTAGE  GARDENER,  c^embcr  i7,  wsu. 
humas  increases  from  year  to  year,  while  the  coatiiiuous  culture 
of  grain,  Cotton,  or  Potatoes  gradually  reduces  the  original 
•tock  of  humus.  Grass  and  grain  crops  in  rotation  result  in 
alternately  increasing  and  decreasing  the  humus  of  the  soil  and 
keep  the  land  in  a  higher  state  of  productiveness,  although  more 
nitrogen,  phosphoric  acid,  and  potash  is  removed  from  the  soil 
than  when  grain.  Cotton,  or  corn  is  raised  continuously.  In  no  case, 
however,  do  those  systems  of  farming  which  return  humus-forming 
materials  to  the  soil  reduce  the  land  to  so  low  a  state  of  productive¬ 
ness  as  do  those  systems  in  which  there  is  a  continual  loss  of  humus 
from  the  soil. 
Agriculturally  considered,  the  two  most  important  points 
regarding  the  composition  of  humus  are  (1)  the  presence  of 
nitrogen  as  a  constant  constituent,  and  (2)  the  chemical 
union  of  the  humus  with  potash,  lime,  and  phosphoric  acid,  forming 
humates. 
Nitrogen  in  Humus. 
Humus,  as  ordinarily  obtained  from  the  soil,  contains  from  3  to 
12  per  cent,  of  nitrogen.  According  to  Professor  Hilgard,  the  soils 
from  arid  regions  are  poor  in  humus,  containing  from  1  to  2  per 
cent.,  but  this  humus  is  correspondingly  rich  in  nitrogen,  in  many 
cases  containing  14  per  cent.  In  many  of  the  prairie  regions  the 
soil  contains  about  5  per  cent,  of  humus,  and  this  humus  contains 
about  10  per  cent,  of  nitrogen.  Since,  therefore,  nitrogen  is  one  of 
the  prominent  constituents  of  humus,  it  is  easily  understood  how  a 
loss  of  humus  has  also  resulted  in  a  loss  of  nitrogen.  This  decline 
in  the  nitrogen  content  of  the  soil  is  one  of  the  most  serious  results 
of  the  loss  of  humus  from  the  soil.  A  virgin  soil  containing  4  per 
cent,  of  true  humus  and  0  35  per  cent,  of  nitrogen  will  after  twenty 
years  of  grain  cropping  show  about  2  5  per  cent,  of  humus  and 
0-2  per. cent,  of  nitrogen. 
In  the  twenty  years,  therefore,  there  has  been  a  loss  of  I'S  per 
cent,  of  humus,  equivalent  to  about  3500  lbs.  per  acre,  and  015  to 
0*2  per  cent,  of  nitrogen,  which  is  equivalent  to  3000  to  5000  lbs.  of 
nitrogen  per  acre.  Since  50  lbs.  per  year  of  nitrogen  is  a  large 
quantity  for  any  ordinary  grain  crop  to  remove,  the  twenty  crops 
have  at  the  most  removed  900  lbs.  of  nitrogen.  At  least 
2500  lbs,  have  therefore  been  lost  by  the  decomposition  of  the 
humus,  the  nitrogen  being  lost  either  in  the  free  state 
or  in  the  drainage  waters.  For  every  pound  of  nitrogen  removed 
in  the  crops  during  the  twenty  years  of  cultivation  there  has  been 
an  additional  loss  of  3  or  4  lb*,  of  nitrogen  from  the  soil  by  the 
decomposition  of  the  humus. 
We  know  that  most  if  not  all  of  the  changes  that  organic 
matter  undergoes  are  the  result  of  the  action  of  microscopic 
organisms.  Such  changes  as  nitrification,  or  the  transformation  of 
organic  nitrogen  into  nitrates  and  its  opposite  denitrification,  or 
the  reduction  of  nitrates  to  gaseous  nitrogen,  besides  many  others 
which  might  be  mentioned,  are  illustrations  of  the  work  of  these 
minute  organisms.  Humus  furniihes  a  medium  peculiarly  adapted 
to  the  activity  of  these  organisms.  The  decomposition  of  humus, 
by  which  it  loses  its  nitrogen,  U  due  chiefly  to  the  combined  action 
of  the  organisms  of  nitrification  and  denitrification.  The  nitri- 
lying  organism  feeds  upon  the  humus,  breaking  down  its  organic 
nitrogenous  constituents  and  producing  nitrates  which  may  be 
washed  out  in  the  drainage,  and  the  denitrifying  organism  com¬ 
pletes  the  work  by  feeding  upon  the  nitrates,  producing  free 
nitrogen  gas,  which  escapes  into  the  air. 
Nitrification  is  one  of  the  most  important  natural  provisions  for 
rendering  the  inert  fertility  of  the  soil  available  to  plants,  and  a 
certa,in  amount  of  it  is  necessary  to  plant  growth  ;  but  it  can  be 
readily  seen  that  under  injudicious  management  or  cultivation  of 
the  soil  it  may  work  a  positive  injury  by  causing  unnecessary 
waste  of  the  nitrogen,  or,  in  case  of  rich  soils,  it  may  supply  the 
growing  crop  with  too  much  nitrate  and  thus  produce  a  rank 
growth  of  straw  and  leaves. 
Summer  Fallomng  —Bare  si  mmer  fallowing  is  widely  practised, 
and  has  been  very  beneficial  to  the  succeeding  crop  by  increasing 
the  available  nitrogen  of  the  soil ;  but  frequently  more  nitrogen  is 
rendered  available  than  is  necessary  for  the  following  crop,  and 
whatever  the  crop  is  unable  to  utilise  is  lost  by  leaching  or  else 
escapes  into  the  air.  The  available  nitrogen  is  thus  increased, 
while  the  total  nitrogen  is  greatly  decreased. 
•  8,t  the  Minnesota  Agricultural  Experiment  Station 
indicated  that  one  year  of  fallowing  caused  a  gain  of  0  0022  per 
cent,  available  nitrogen  and loss  of  0  0114  per  cent,  of  total 
nitrogen  in  a  soil  containing  originally  0  1356  per  cent,  of  total 
nitrogen  and  0-0002  per  cent,  of  available  nitrogen.  For  every 
pound  of  nitrogen  rendered  available  by  the  fallow  treatment  there 
was  a  loss  of  over  5  lbs.  of  nitrogen  from  the  soil.  Bare  summer 
fallowing  1*,  therefore,  only  temporarily  beneficial  at  the  expense 
of  the  total  humus  and  nitrogen  of  the  soil.  When  a  soil  is  poor 
m  humus  and  nitrogen  the  loss  of  nitrogen  is  much  smaller  ;  but 
even  then  it  is  doubtful  whether  bare  summer  fallowing  is  a  wise 
practice.  In  no  case  should  summer  fallowing  be  practised  on  a 
new  soil , 
Fall  ploughing  keeps  the  humus  and  nitrogen  of  the  soil  in 
better  condition  than  late  spring  ploughing.  Nitrification  goes  on 
in  the  soil  until  quite  late  in  the  fall,  and  in  the  South  the  process 
goes  on  the  entire  year.  The  change  is  most  rapid  near  the  surface, 
where  there  is  plenty  of  oxygen  from  the  air.  In  early  fall 
ploughing  the  available  nitrogen  formed  from  the  humus  is  near 
the  surface,  where  it  does  the  sprouting  seeds  and  young  crops  the 
most  good.  With  late  spring  ploughing  this  available  nitrogen  is 
ploughed  under,  and  inert  organic  nitrogen  is  brought  to  the 
surface. 
In  old  soil*  the  process  of  nitrification  does  not  go  on  rapidly 
enough  to  furnish  available  nitrogen  to  the  crop.  In  a  new  soil 
the  process  of  nitrification  is  liable  to  go  on  too  rapidly.  Deep 
ploughing  and  thorough  cultivation  aid  in  nitrification  ;  hence  the 
longer  the  soil  is  cultivated,  the  deeper  and  more  thorough  must 
be  its  preparation.  Ploughing  mu*t  be  done  at  the  right  time, 
preferably  in  the  fall,  so  as  not  to  interfere  with  the  next  year’* 
water  supply. 
The  application  of  lime  and  wood  ashes  aids  in  the  reduction 
of  nitrogen  of  humus  to  available  forms,  and  prevents  the  forma¬ 
tion  of  sour  mould.  Good  drainage  is  also  necessary  to 
nitrification  in  the  soil.  In  waterlogged  soils  the  humus  does  not 
decompose  normally,  but  peat  is  produced  on  account  of  the  absence 
of  oxygen. 
We  thus  see  that  nitrification,  although  sometimes  a  serious 
source  of  loss,  may  be  largely  controlled  by  careful  management  of 
the  soil. 
Burning  Over  of  Soils. — Another  source  of  loss  of  humus  in  the 
prairie  and  forest  regions  is  the  frequent  burning  over  of  the  land. 
Soils  covered  with  Pine,  in  which  sand  largely  predominates, 
frequently  lose  half  or  three-'quarters  their  total  nitrogen  when 
visited  by  forest  fires.  The  sand,  being  of  an  open  and  porous 
nature,  aids  in  the  more  complete  combustion  of  the  humus.  In 
the  timbered  regions  of  the  North-West  the  great  forest  fires  of 
1894  resulted  in  the  average  destruction  of  over  1500  lb*,  of  humus 
nitrogen  per  acre,  to  say  nothing  of  the  nitrogen  lost  in  the  burning 
of  the  timber.  Analyses  of  soils,  before  and  after  the  fire,  made 
by  the  Minnesota  Agricultural  Experiment  Station  showed  a  loss  in 
some  cases  of  2500  lbs.  per  acre  of  nitrogen,  equivalent  to  a  loss 
of  75  per  cent,  of  the  total  amount  in  the  soil.  The  prairie  fires 
have  not  been  so  destructive  upon  the  humu*  as  the  forest  fires, 
because  the  burning,  has  been  confined  more  to  the  surface.  An 
average  prairie  fire,  however,  will  remove  more  nitrogen  from  the 
soil  than  five  ordinary  crops  of  Wheat. 
Mineral  Matter  in  Humus. 
Besides  being  a  great  reservoir  of  nitrogen,  humas  is  an 
indirect  means  of  supplying  the  plants  with  other  fertilising 
constituents.  Humus,  as  it  occurs  in  the  soil,  is  combined  with 
potash,  lime,  phosphoric  acid,  and  other  compounds  which  are 
essential  as  plant  food.  The  decaying  animal  and  vegetable 
matters  form  various  organic  acids,  which  combine  with  the  potash, 
lime,  iron,  and  alumina,  as  well  as  with  other  elements,  and  form 
a  series  of  compounds  known  as  humates,  of  which  but  little  is 
definitely  known. 
By  some,  the  potash,  lime,  and  other  mineral  constituents  of 
the  humus  are  regarded  as  simply  associated  with  the  humus  and 
not  organically  combined  with  it ;  but  there  are  a  number  of  facts 
which  indicate  that  the  union  is  chemical  and  not  simply  mechanical. 
The  mineral  matter  combined  with  the  humus  is  characteristically 
rich  in  phosphoric  acid  and  potash,  two  compounds  which  are  of 
great  value  agriculturally.  The  mineral  matter  combined  with 
the  humus  from  different  soil  types,  however,  is  not  always  of  the 
same  nature,  and  the  amount  of  plant  food  thus  combined  with 
humus  has  not  been  extensively  investigated.  In  the  case  of  rich 
prairie  soils  over  1500  lbs.  of  phosphoric  acid  and  1000  lbs.  of 
potash  per  acre  to  the  depth  of  1  foot  have  been  found  to  be  in 
combination  with  the  humus.  In  the  case  of  soils  poor  in  humus 
and  worn  by  croppibg,  the  amount  may  be  reduced  to  100  lbs,  per 
acre.  The  averages  of  analyses  of  the  mineral  matter  of  the 
humus  from  samples  of  productive  prairie  soils  yielding  25  per 
cent,  of  humates  showed  7-50  per  cent,  of  potash  and  12-37  per 
cent,  of  phosphoric  acid.  In  these  soils,  which  were  well  supplied 
with  humus,  1500  lbs.  of  phosphoric  acid  per  acre  out  of  a  total  of 
8750  was  combined  with  humus,  and  1000  lbs.  of  potash  out  of  a 
total  of  12,250  lbs.  According  to  Hilgard,  the  amount  of  phos¬ 
phoric  acid  usually  found  associated  with  humus  varies  from 
0-1  to  0'5  of  the  total  amount  in  the  soil,  indicating  in  many  cases 
the  amount  of  this  element  available  to  plants. 
(To  be  continued.) 
