886 
Sup2)lemeni  to  the  “ Tropical  Agi'iculturisL" 
[June  I,  1897. 
enormous.  In  1893,  the  estimated  losses  to  grain 
crops  in  the  Cape  caused  by  “ locusts  and  otlier 
plagues  ’’  were  nearly  twenty  per  cent,  of  the  har- 
vest for  mealies  (Iiulinu  corn),  about  fourteen  per 
cent,  for  wheat,  and,from  seven  to  twelve  per  cent, 
in  the  case  of  other  cereals.  Some  of  this  loss 
was  due  to  diseases,  but  probably  insects  were 
responsible  for  a loss  of  at  least  ten  per  cent, 
of  the  total  harvests,  and  for  very  much  more 
in  the  case  of  mealies. 
The  annual  loss  through  insect  ravages  in  the 
United  States  is  said  to  average  one-tenth  of  the 
crops.  Mr.  B.  D.  Walsh,  at  one  time  State 
Entomologist  of  Illinois,  thirty  years  ago  esti- 
mated that  insects  annually  inflicted  a lo.ss  of 
no  less  than  si.xty  million  pounds  sterling  in 
the  country,  and  subsequent  writers  think  his 
estimate  a moderate  one.  Most  certainly  these 
great  losses  to  the  agriculturist  cannot  be  entirely 
checked,  but  to  some  e.vtent  they  are  preventable, 
and  to  this  extent  they  should  be  prevented. 
POTASH  MANURES  AND  THE  NEED  FOR 
SPECIAL  POTASH  FERTILIZERS. 
Many  experiments  may  be  quoted  which  show 
that  active  potash  manures  produce  increase  of 
crop.s  on  soils  that  already  contain  potash  in 
plenty.  Hence,  though  n deficiency  in  a soil 
necessarily  points  to  its  requirement  in  the  manure, 
the  presence  of  abundant  potash  in  the  soil  by  no 
means  proves  that  potash  manuring  is  unneces- 
sary. Medium  soils  and  clay  soils  may,  in  many 
cases,  require  potash  manures,  just  as  surely  as 
light  soils  and  peaty  soils  ; and,  without  actual  e.x- 
periment,  the  assumption  that  potash  manures 
are  not  required  does  not  appear,  in  view  of  these 
experiments,  to  be  warranted  in  regard  to  any  soil. 
And  even  in  soils  where  farmyard  manure  has 
been  liberally  applied,  there  is  no  sufficient  ground 
for  assuming  that  artificial  potash  manures,  in 
readily  available  forms,  may  not  be  applied  with 
advantage. 
In  the  popular  assumption  that  potash  manures 
are  not  required  on  clay  soils,  the  fact  has  been 
overlooked  that  the  nature  of  the  manure  required 
is  determined  in  much  greater  degree  by  the  kind 
of  crop  grown  than  by  the  character  of  the  soil. 
All  kinds  of  ordinary  soils  possess,  in  greater  or 
less  measure,  the  chemical  constitution  and  physi- 
cal characters  that  are  required  for  the  growth  of 
any  crops  that  are  suitable  to  the  existing  condi- 
tions of  climate.  But  it  has  been  proved  by 
numerous  practical  e.xperimeuts  and  observations 
that  crops  differ  greatly  in  their  power  of  utilizing 
the  several  constituents  contained  in  the  soil. 
Some  crops  have  a difficulty,  in  most  soils,  in  pro- 
viding themselves  wdth  enough  nitrogen,  some  in 
providing  themselves  with  enough  phosphoric  acid ; 
others  are  unable  to  obtain  sufficient  potash.  It 
follows  that  the  substance  which  plants  take  up 
influence  and  produces  the  greatest  increase  of 
yield  when  applied  to  them  in  readily  available 
forms  in  manure. 
There  are  various  sources  from  which  the  soil 
may  be  replenished  and  the  crops  provided  with 
potash.  In  the  first  place  there  is  farmyard 
manure  produced  by  the  consumption  of  cakes  and 
Other  foods  rich  in  potash.  Were  the  supply  of 
potash  from  this  source  abundant  enough  and 
cheap  enough,  none  other  would  be  required.  But 
great  as  is  the  total  quantity  of  farmyard  manure 
that  is  available,  it  is  not  adequate  for  the  pur- 
pose. The  straw  or  litter  which  is  generally  asso- 
ciated with  cattle  manure  contains  a considerable 
percentage  of  mineral  food.  The  ash  ingredients 
in  straw  amount  to  about  5 per  cent  or  about  112 
lbs.  per  ton,  of  which  15  to  30  per  cent  is  potash. 
Taking  the  mean  of  a very  large  number  of 
analyses  of  farmyard  manure,  it  may  be  said  that 
in  the  ash  of  well-rotted  dung,  the  amount  of 
potash  is  from  5 to  7 per  cent,  that  is,  one  ton  of 
manure  contains  only  from  9 to  15  lbs.  of  pota->lr 
Heiden  calculates  that  25  tons  of  farmyard  raannro 
would  not  suffice  to  restore  the  potash  removed 
by  an  ordinary  rotation  of  crops  sold  off  the  land, 
even  if  every  ounce  of  potash  in  the  manure  were 
to  find  its  way  into  the  roots  of  the  crops,  which 
is  not  possible.  More  probably  nearly  double  that 
quantity  would  be  required  to  make  good  the  loss. 
It  is  hardly  necessary  to  .say  that  so  large  an  appli- 
cation of  manure  is  very  rarely  customary,  and 
that  in  general  farming  practice  there  is  a large 
deficit  to  be  made  good  by  the  application  of  arti- 
ficial ma-iure.«.  This  is  especially  the  case  in 
this  country  where  litter,  which  supplies  the  bulk 
of  the  potash  of  farmyard  manure,  is  practically 
entirely  absent,  and  where  the  manure  generally 
purchased  has,  ns  a rule,  suffered  much  from  ex- 
posure to  sun  and  rain. 
Moreover,  on  many  soils  and  especially  on  light 
sandy  and  on  peaty  soils,  the  policy  of  an  enlight- 
ened management  would  aim  beyond  the  mere 
restoration  to  the  soil  of  the  potash  removed  by 
the  produce  of  the  land  carried  off  it.  As  they 
are  always  deficient  in  potash,  it  is  a necessary 
condition  of  good  cultivation,  if  any  steps  towards 
their  improvement  are  to  be  taken,  to  endeavour 
to  enrich  them  by  adding  to  their  deficient  stock 
of  phosphoric  acid  and  potash.  For  such  a pur- 
pose applications  of  farmyard  manure  alone  are 
insufficient. 
The  chief  commercial  manures  which  are  sources 
of  potash  are  kainit,  chloride  of  potash,  and  sul- 
phate of  potash.  AVe  shall  refer  to  these  and  give 
full  details  regarding  composition,  price,  &c.,  in 
our  next,  but  in  the  meantime  would  wish  to  refer 
to  the  use  of  potash  manures  as  a means  of 
enriching  cultivated  soils  in  another  sense. 
A very  important  aspect  of  potash  manuring 
is  that  connected  with  the  growth  of  certain 
leguminou.o  crops,  and  their  method  of  obtaining 
nitrogen.  It  is  only  within  the  last  few  years 
that  the  very  important  discovery  has  been  made 
that  certain  kinds  of  plants  are  able  to  draw 
upon  the  air  for  their  stock  of  nitrogen.  Hence, 
a very  cheap  way  of  manuring,  land  with  nitrogen 
is  to  grow  such  crops,  and  then  plough  them 
in,  so  that  the  nitrogen  they  obtain  from  the 
air  in  the  course  of  their  growth  may  be  added 
to  tlie  soil,  and  thus  furnish  a store  of  nitrogen 
for  other  plants  which  do  not  possess  this  property. 
.Such  plants,  however,  in  order  to  grow  luxuriantly, 
require  to  be  well  supplied  with  the  two  mineral 
ingredionts,  potash  and  phosphoric  acid.  To 
manure  such  crops  with  costly  nitrogenous 
manures  is  simply  to  waste  money,  and  to 
neglect  one  of  the  best  means  at  our  command 
of  enriching  the  soil  in  nitrogen.  The  growth 
of  leguminous  crops,  therefore,  is  a valuable 
