24.5
2400

23-9
2290

37-8
3753

3'-9
3205

38.0
3638

33-3
3280

CHAPTER  XX

PENNSYLVANIA    FIELD    EXPERIMENTS

IN  1882  the  Pennsylvania  Agricultural  Experiment  Station
began,  at  State  College,  the  oldest  extensive  field  experiments  now
in  progress  in  America.  They  include  four  separate  fields,  each
of  which  contains  36  eighth-acre  plots,  or  144  different  plots  in  all.
A  4-year  rotation  is  practiced,  consisting  of  corn,  oats,  wheat,
and  hay  (mixed  clover  and  timothy  seeded  on  the  wheat  land  in
the  early  spring) ,  every  crop  being  represented  every  year  (ex-
cepting the  hay  crop  in  1882).  The  land  is  quite  undulating,  but
the  individual  plots  are  separated  by  a  permanent  strip  of  grass
sod  or  turf  about  two  or  three  feet  wide,  which  practically  pre-
vents surface  washing  from  one  plot  to  another,  and  in  but  few
cases  is  there  evidence  of  soil  washing  on  the  fields.  The  plots
are  about  i^  rods  wide  by  16  rods  long.
The  soil  consists  largely  of  a  silty  clay  loam,  and  contains  perhaps
10  per  cent  of  small  angular  rock  fragments,  chiefly  of  chert.
While  this  field  had  been  treated  with  lime  some  years  before  the
beginning  of  these  experiments,  recent  examination  has  shown  that
the  soil  is  more  or  less  acid.  Even  where  sodium  nitrate  has  been
applied,  acidity  is  found  as  a  rule,  notwithstanding  the  tendency
of  sodium  nitrate  to  neutralize  soil  acidity,  much  of  the  sodium
being  left  in  the  soil  when  the  nitrogen  is  taken  up  by  plants.
