The  amount  of  dried  blood,  steamed  bone,  and
potassium  sulfate  to  use  in  experimental  work
should  be  governed  by  the  requirements  of  the  crop
for  approximately  maximum  crop  yields.  Thus  a
crop  of  average  com,  yielding  100  bushels  of  grain
and  three  tons  of  stover  per  acre,  will  contain
about  148  pounds  of  nitrogen,  23  pounds  of  phos-
phorus, and  71  pounds  of  potassium ;  while  1,000
pounds  of  dried  blood,  200  pounds  of  steamed  bone-
meal,  and  200  pounds  of  potassium  sulfate,  should
supply  150  pounds  of  nitrogen,  25  pounds  of  phos-
phorus, and  80  pounds  of  potassium.  As  an  initial
application,  that  is  for  the  first  year,  it  is  well  to
apply  double  the  standard  amount  of  steamed  bone
because  it  is  less  readily  available  than  dried  blood
and  potassium  sulfate.  For  wheat  or  oats  the
nitrogen  may  be  reduced  to  one-half  and  the
phosphorus  and  potassium  to  two-thirds  of  these
amounts.  For  a  crop  of  a  different  class  of  plants,
as  sugar-beets,  quite  different  proportions  and
amounts  may  be  needed ;  while,  for  a  rotation  of
crops  including  a  liberal  use  of  legumes  and  some
farm  manure,  the  application  of  commercial  nitro-
gen should  be  entirely  omitted  and  the  amounts
of  mineral  elements  may  be  reduced ;  and,  with
liberal  quantities  of  farm  manure  containing  both
solid  and  liquid  excrement,  the  phosphorus  may  be
reduced  and  the  commercial  potassium  may  be
greatly  reduced  or  entirely  omitted.
Specific  examples  of  culture  experiments.
The  following  examples  will  illustrate  systems
of  pot  cultures  and  plot  experiments  and  at  the
same  time  show  the  actual  results  secured  on  dif-
ferent soil  types.
