The  Woburn  Pot-Culture  Experiments,  1908.  391 
however,  on  the  mustard  than  on  the  tare  soil.  Lastly,  mag- 
nesia had  a peculiar  effect ; on  the  tare  soil  it  produced  a 
slight  increase,  but  a diminution  with  the  mustard  soil.  The 
wheat  came  into  ear  on  June  9,  1908,  and  harvesting  was  done 
on  August  18.  The  following  table  gives  the  principal  results 
obtained,  the  untreated  tare  soil  being  taken  as  the  basis  of 
comparison  : — 
Tare  Soil 
Mustard  soil 
Corn 
Straw 
Com 
Straw 
Weight 
Percent- 
age of 
untreated 
Weight 
Percent- 
age of 
untreated 
Weight 
Percent- 
age of 
untreated 
Weight 
Percent- 
age of 
untreated 
G-rms. 
Per  cent. 
Gnus. 
Per  cent. 
Grms. 
Per  cent. 
Grms. 
Per  cent. 
No  treatment 
11-67 
100 
1811 
100 
11-85 
101 
18-27 
101 
Silicate  of  alumina  . 
4913 
421 
80-86 
446 
40-68 
348 
69-16 
382 
Kaolin  .... 
. 19-02 
103 
17-68 
97 
11-71 
100 
17-20 
95 
Silicate  of  soda  . 
22-03 
188 
41-45 
229 
21-61 
185 
31-37 
173 
Ground  lime  (caustic) 
24-94 
213 
46-32 
255 
31-58 
270 
53-06 
293 
Magnesia  (caustic)  . 
17-10 
146 
47-80 
264 
5-75 
49 
18-74 
11)3 
Taking  these  figures,  it  is  seen  that  the  result  of  adding 
to  the  soil  a colloidal  substance  like  silicate  of  alumina 
resulted  in  a very  large  gain,  and  that  this  was  more  marked 
with  the  tare  soil  than  the  mustard.  > Silicate  of  soda  also  gave 
an  increase,  though  not  so  large,  while  kaolin  had  no  effect. 
It  would  appear  from  this  that  the  altered  condition  of  the 
soil,  which  silicate  of  alumina  would  tend  to  produce, 
was  an  important  element  in  bringing  out  the  benefit  of  the 
previous  green-manuring,  as  well  as  the  superiority  of  the  tare- 
manuring.  This  would  show,  accordingly,  that  the  greater 
consolidation  of  the  tare  soil,  and  the  consequent  change  in  its 
physical  condition  (which,  further,  would  result  in  moisture 
being  retained  more  freely),  was  material  to  the  bringing  out 
of  the  value  of  the  ploughing-in  of  the  tare  crop. 
Passing  to  the  use  of  lime  and  magnesia,  it  would  appear 
that  lime  had  in  each  case  been  effectual  in  breaking-down  and 
rendering  the  organic  matter  available,  but  that  magnesia  had 
not  produced  a satisfactory  result. 
3.  Experiments  on  the  influence  of  Magnesia  in  Soils. 
Previous  experiments  having  shown  that  magnesia,  when 
applied  as  such  to  the  soil  of  Stackyard  Field,  produced 
very  marked  effects  on  the  wheat  crop  according  as  the  pro- 
portion of  magnesia  to  lime  in  the  soil  was  increased,  it  was 
determined  to  see  whether  this  held  good  with  regard  to  the 
insoluble  forms  only,  and  also  to  test  what  would  be  the  effect 
^ Subsequent  to  the  writing  of  the  above,  it  has  been  found  that  the 
silicate  of  alumina  used  was  not  pure,  and  this  may  possibly  necessitate  some 
modification  of  the  conclusions  come  to. 
