38

8

68

AVAILABLE   PLANT   FOOD


in


TABLE  21.   ANNUALLY  AVAILABLE  FERTILITY  IN  ILLINOIS  SOILS,  ROUGHLY
ESTIMATED  —  Continued


SOIL

AVAIL-

AVAIL-

AVAIL-

TYPE
No.
Son,  AREA  OR  GLACIATION

Son.  TYPE

ABLE
NITRO-

ABLE
PHOS-

ABLE
POTAS-

GEN

PHORUS

SIUM

SAND,  SWAMP,  AND  BOTTOM  LANDS


1331

Old  bottom  lands  ..
Deep  gray  silt  loam  ..
72

14

91

1451

Late  bottom  lands

Brown  loam    ....
94

16

100

1481

Sand  plains  and  dunes

Sand  soil    ....
2Q

8

77

1401

Late  swamp

Deep  peat.
(?)  »

20

7

1415

Late  swamp       .     ..
Drab  clay

US

iQ

1  2O

1  The  nitrogen  in  peat  is  so  very  slowly  available  that  not  even  a  rough  estimate
can  be  made  here.
they  first  dissolve  in  the  soil  water  and  spread  over  the  surface  of
the  soil  particles  before  becoming  insoluble,  and  thus  they  offer
a  much  more  extensive  surface  for  contact  with  plant  roots  than
would  plant-food  particles  applied  in  insoluble  form,  unless  very
finely  ground.
Third,  we  may  apply  different  elements  of  plant  food  to  the  soil
and  note  the  effect,  if  any,  in  increasing  the  yield  of  crops,  and  thus
sometimes  discover  what  element  is  most  deficient  in  the  soil.
