The  Wohurn  Field  Experiments,  1909.  387 
being  drawn,  it  is  clear  from  the  other  two  sets  that  there  is 
little  to  choose  between  the  four  materials — sulphate  of 
ammonia,  nitrate  of  soda,  calcium  nitrate,  and  calcium  cyana- 
mide — so  far  as  the  efficacy  of  the  nitrogen  contained  in  them 
respectively  is  concerned.  Certainly  the  differences  are  not 
always  tending  in  the  same  direction,  nor  so  regular  as  to 
warrant  a distinct  preference  for  one  manure  over  the  other, 
provided  that  the  nitrogen  is-  obtainable  in  each  at  approxi- 
mately the  same  price  per  unit.  On  this — that  is,  their 
respective  selling  prices — the  preference  for  one  or  the  other 
will  depend,  and  it  remains  to  be  seen  what  these  prices  will 
in  the  future  be.  An  objection  to  calcium  nitrate  is  its 
tendency  to  take  up  moisture  and  the  consequent  difficulty 
of  keeping ; on  the  other  hand,  because  of  the  lime  it 
contains,  it  will  be  specially  useful  on  land  poor  in  lime.  As 
regards  calcium  cyanamide,  it  is  the  most  troublesome  of  the 
four  materials  to  handle,  and  will  not  mix  well  with  other 
manures.  It  has  a pungent  smell,  and  the  fine  dust  is 
objectionable  if  it  blows  about.  It  remains  to  be  seen  whether 
the  new  materials  leave  any  residue  in  the  land  for  a subsequent 
crop,  and  this  is  being  tried  with  the  foregoing  plots  in  1910. 
Experiments  with  Magnesia  on  Potatoes. 
( Warren  Field),  1909. 
Table  XIII.,  page  385,  besides  giving  the  results  of  the 
application  of  nitrogenous  top-dressings  to  the  potato  crop, 
puts  out  also  the  results  obtained  from  using  magnesia  in 
different  forms  on  potatoes.  The  different  forms  used  were  : 
(1)  Magnesia  itself  (MgO)  at  the  rates  of  3 cwt.  and  6 cwt.  per 
acre  ; (2)  carbonate  of  magnesia,  3 cwt.  and  6 cwt.  per  acre  ; 
(3)  magnesian  lime,  6 cwt.  per  acre  ; (4)  magnesian  limestone, 
finely  ground,  10  cwt.  per  acre.  Magnesian  limestone,  it  may 
be  said,  is  carbonate  of  lime  and  carbonate  of  magnesia,  and 
the  magnesian  lime  used  was  the  same  material  after  burning. 
The  applications  were  given  early  in  May,  just  before  the 
“ sets  ” were  planted.  The  “ standard  ” manurial  dressing 
(dung,  superphosphate,  and  sulphate  of  potash)  was  given  in 
all  cases  alike. 
During  the  period  of  growth  it  Avas  noticed  that  plot  7 
(magnesia  6 cwt.  per  acre)  looked  decidedly  inferior  to  plot  6 
(magnesia  3 cwt.  per  acre).  An  examination  of  the  weights 
given  in  Table  XIII.  shows  that  in  every  case  the  produce  of 
plots  to  which  magnesia  in  any  form  had  been  given  fell  below 
that  of  the  “ standard  ” dressing  only.  The  decrease  was  most 
marked  in  plot  7 (magnesia  6 cwt.  per  acre),  and,  speaking 
generally,  the  plot  to  which  the  higher  quantity  of  magnesia, 
in  one  form  or  another,  had  been  given,  fell  below  the 
0 c 2 
