Jan.  1,  189G.]  Supplement  to  the  “ Tropical  Agriculturist.” 
503 
when  grown  in  the  field  ; possibly  they  had  less 
necessity  for  the  acid  when  in  the  probably  richer 
soil  of  the  pots.  However,  Dr.  Dyer  determined 
to  try  the  effect  of  a 1 per  cent,  citric  acid 
.solution  on  soils  ot  known  composition  and  history 
to  sec  if  this  would  really  act  in  the  same  way  as 
the  acid  gap  of  the  roots  on  tlie  phosphoric  acid 
and  potash  of  the  .soil,  and  S(^  he  in  .some  degree, 
at  all  events  a measurer  of  the  available  mineral 
plant  food  of  the  soil. 
Soils  suitable  for  testing  this  point  could  only 
be  obtained  from  one  place  in  the  world — viz., 
Rothamsted.  Here  alone  have  soihs  been  under 
exact  experiment  and  observation  for  a sullicient 
lengHi  of  time  for  their  agricultural  capabilities 
to  be  accurately  knoxMi.  From  Rothamsted  then, 
with  the  kind  assistance  of  Sir  John  Lawes,  were 
obtained  samples  of  soil  from  twentj’-two  ot  the 
barley  plots  in  Hoos  Field  which  have  grown 
barley  tor  forty  years  in  succession  under  various 
treatments  as  to  manure,  and  the  exact  amount  of 
the  produce  from  which  each  year  is  known,  as 
well  as  in  many  cases  the  chemical  composition  of 
the  produce.  The  weight  of  the  fine  soil  of  the 
plots,  calculated  to  a depth  of  9 inches  per  acre, 
varied  from  about  2 to  2^  million  lb.  In  these 
soil  samples  were  determined  the  amounts  of 
phosphoric  acid  and  of  potash  soluble  in  strong 
hydrochloride  acid,  much  as  in  an  ordinary  soil 
analysis,  and  also  the  amounts  of  phosphoric  acid 
and  of  potash  soluble  in  a 1 per  cent,  solution  of 
citric  acid,  which  solution  was  allowed  to  act  for 
seven  days  on  the  soil.  The  re.sults  obtained 
were  very  interesting  and  instruci  ive.  Calculating 
them  into  lbs.  per  acre  of  the  soil  to  the  depth  of 
9 inches,  they  showed  that  the  plots  which  were 
unmanured  or  received  no  phosphatic  manure 
contained  from  2,500  to  3,000  lb.  of  phosphoric  acid 
per  acre,  of  which  from  140  to  280  lb.  were  soluble 
in  the  dilute  solution  of  citric  acid.  The  soil  of 
plots  which  had  received  phosphates  in  manure 
contained  from  about  4,200  to  5,400  lb.  cf  jdio.s- 
phoric  acid,  of  which  generally  from  1,000  to  1,500 
11).  was  soluble  in  citric  acid  solution.  A plot 
w'hich  had  received  farmyard  manure  for  twenty 
years,  and  then  been  unmanured  for  eighleen 
years,  contained  5121b.  of  phosjdioric  acid  soluble 
in  citric  acid  per  acre  in  9 inches  of  soil  ; and  .a 
plot  receiving  farmyard  manure  for  the  whole 
thirty-eight  years  contained  932  lb.  of  such 
soluble  phosphoric  acid  per  acre.  The  amount  of 
potash  soluble  in  hyd.'ochloric  acid  in  the  soil  of 
unmanured  plots,  or  those  receiving  no  potash  in 
the  manure,  averaged  nearly  .3,000  lb.  per  acre  : 
where  potash  had  been  given  in  the  manure  ii 
averaged  about  0.750  lb.  per  acre  to  a depth  of  9 
inches.  But  with  citric  acid  solution  the  com- 
parative results  were  far  different,  the  potash 
soluble  in  a one  per  cent,  solution  of  citric  acid 
from  the  soil  of  plots  receiving  no  potash  was 
almost  always  under  100  lb.  per  acre,  whilst  from 
the  soil  of  plots  receiving  potash  in  the  manure  it 
averaged  over  800  lb.,  and  was  sometimes  over 
1 000  lb.  jier  acre.  The  citric  acid  soluble  potash 
in  the  farmyard  manure  plot  to  which  the  dung 
had  not  been  applied  for  eighteen  years  was  330 
lb.  per  acre,  that  in  the  continuously  dunged  plot 
was  009  lb.  per  acre.  Now  there  is  nearly  six 
times  as  much  pliosphoric  acid  dissolved  by  dilute 
citric  acid  solution  from  the  soil  of  the  plots 
receiving  phosjjhates  as  from  those  not  receiving 
phosphates,  and  nearly  nine  times  as  much  potash 
from  the  potash  receiving  plots  ns  from  those 
wliich  had  received  no  potash  for  forty  years.  If 
these  results  of  soil  analyses  are  compared  w'ith 
the  actual  cro])s  of  grain  and  straw  obtained 
during  thirty-eight  years,  it  i.s  most  clearly 
brought  out  tliat  those  soils  in  which  citric  acid 
soluble  phos^jlioric  acid  is  low  are  those  suffering 
from  deficiency  of  available  phosphoric  acid,  and 
likewise  w’heii  the  potadi  soluble  in  citric  acid 
solution  falls  below  a certain  limit  that  the  soil 
and  the  crop.s  upon  it  are  suffering  from  deficiency 
of  ])otnsh.  Thus  a plot  not  receiving  phosphates 
and  with  152  lb.  of  phosphoric  acid  soluble  in  one 
percent,  citric  gave  a yield  in  1889  of  224  bushels 
of  barley,  a ])lot  treated  in  the  same  way  except 
that  it  had  3^  cwt.  superhosphate  per  acre 
annually  in  addition,  yielded  1,073  lb.  of 
phosphoric  acid  to  the  citric  acid  solution,  and 
gave  35^  bushels  of  grain  in  1889.  Such  cases 
might  be  repeated  many  times.  In  the  case  of  the 
j)hos])horic  acid  it  is  found  that  the  amount 
dissolved  of  citric  acid  is  roughlj’^  proportional  to, 
and  approximately  one  half,  the  amount  calculated 
to  be  left  in  the  soil  from  applications  of 
phosjihates  and  not  recorded  in  increase  of  crop. 
From  a careful  consideration  of  the  whole 
results.  Dr.  Dyer  concludes  “ that  it  would  not  be 
unreasonable  to  suggest  that  wlien  a soil  is  found 
to  contain  as  little  as  '01  per  cent,  of  phosphoric 
acid,  soluble  in  a 1 per  cent,  solution  of  citric 
acid,  it  would  be  justifiable  to  a.ssume  that  it 
stands  in  need  of  jdiosiihatic  manure.”  This 
amount  would  be  ecpuil  to  about  250  lb.  per  acre  to 
a de[)tli  of  9 inches.  Again,  as  regards  potash,  it  is 
“ more  difficult  than  in  the  ca.se  of  phosphoric 
acid  to  draw  from  the  figures  any  fairly  plausible 
suggestion  as  to  wliat  percentage  limit  of  citric 
acid  soluble  potash  should  be  regarded  as  marking 
tlie  non-nece.ssity  of  special  potash  applications. 
Prohabhj  this  limit  lies  below  '005  per  cent.  ” That 
is  about  125  11).  jier  acre  to  a depth  of  9 inches. 
Tills  plan  of  treatment  of  soils  with  dilute 
solution  of  citric  acid  does  undoubtedly  give 
valuable  indications  as  to  the  condition  of  some  of 
the  im])ortant  mineral  plant  foods  in  the  soil,  and 
is  a decided  stei)  in  advance  in  the  macter  of  soil 
analysi.s.  We  are  very  glad  to  know  that  Dr. 
Dyer  is  extending  his  observations  to  the  soils  of 
the  celebrated  wdieat  field  (Broadhalt)  of  Rotham- 
sted, where  wluat  has  now  grown  continuously  for 
more  than  half  a century. 
(To  be  continued.) 
(.'Hi  LON  WOODS. 
r Continued.) 
Ill  Myristicacem. 
109  Myristica  laurifolia.  Malaboda. 
170  ,,  irya.  Ireya. 
113  Lanraceie. 
171  (7ry])tocarya  Wightiana.  Galmora. 
172  i’ersea  semecarpifolia.  Wewarani. 
173  Litsea  sebifera  Hd-mi. 
174  ,,  zeylanica.  Dawal-kuruudu  t Ivudu- 
dawulii. 
175  ,,  ovalifolia. 
115  Thymeheacea’. 
17(5  Gyrinops  walla.  Walla ; Patta-walla. 
118  Santalaeea'. 
177  Seleropyrun  Walliehianum.  Katu-pamburu. 
110  Euphorbiacea). 
178  Bridelia  retusa.  Keta-kala. 
