366 
Nitrogen  as  Nitric  Acid , in  the  Soils 
5.  The  soils  of  the  various  plots  in  Broadbalk  Wheat-field 
were  sampled  in  October  1881  to  the  depth  of  27  inches.  There 
had  been  much  rain  after  harvest,  and  the  conditions  were 
very  favourable  to  nitrification.  The  nitrates  were  chiefly  near 
the  surface,  the  distribution  in  the  three  depths,  each  of  9 inches, 
being  on  an  average  as  100,  59,  and  31. 
6.  The  unmanured  plots  contained  lS'O-l?^  lbs.  of  nitrogen 
as  nitric  acid  per  acre  to  the  depth  of  27  inches.  Plots 
manured  with  ash-constituents  alone,  2T2-24-3  lbs.  Plots 
receiving  400  lbs.  of  ammonium-salts,  or  550  lbs.  of  nitrate  of 
sodium  per  acre,  with  ash-constituents,  24'6-39’8  lbs.  With 
the  same  nitrogenous  manuring,  without  ash-constituents, 
28-3-54T  lbs.  With  1700  lbs.  of  rape-cake  as  manure,  34‘2  lbs. 
With  14  tons  of  farmyard-manure,  52'2  lbs.  The  rape-cake  and 
farmyard-manure  were  applied  the  preceding  autumn ; the 
ammonium-salts  and  nitrate  of  sodium  in  March. 
7.  On  plots  receiving  no  nitrogenous  manure,  or  not  excessive 
quantities  of  ammonium-salts  or  nitrate  of  sodium,  the  nitrates 
found  were  doubtless  due  to  the  nitrification  of  nitrogenous 
matters  in  the  soil,  consisting  partly  of  the  original  stock  of 
humic  matter  of  the  soil,  but  mainly  of  more  recent  crop  and 
weed-residues.  The  quantity  of  nitrate  found,  generally  bore  a 
distinct  relation  to  the  quantity  of  the  preceding  crops.  Where 
an  excess  of  nitrate  of  sodium  had  been  applied  (Plot  9b),  a 
considerable  residue  of  unused  nitrate  was  found  in  the  subsoil. 
Where  rape-cake  or  farmyard-manure  had  beeen  applied,  the 
nitrates  present  were  partly  derived  from  the  nitrification  of 
residues  of  these  manures. 
8.  Comparing  the  quantity  of  total  nitrogen  in  the  first 
9 inches  of  the  Broadbalk  Wheat-field  soils  with  the  quantity  of 
nitric  acid  found  to  the  depth  of  27  inches,  it  appears  that  the 
nitrogen  of  permanently  unmanured  land  nitrifies  with  more 
difficulty  than  the  nitrogen  of  land  that  has  yielded  large  crops, 
or  has  received  rape-cake  or  farmyard-manure.  The  old 
nitrogenous  capital  of  the  soil  is  thus  more  slowly  oxidised  and 
converted  into  plant-food  than  the  more  recent  residues  of  crops 
or  of  organic  manure. 
9.  In  the  soils  of  Hoos  Barley-field,  sampled  in  March  1882 
to  the  depth  of  27  inches,  the  nitrates  had  been  distributed 
by  the  autumn  and  winter  rains  ; they  occurred  in  the  first, 
second,  and  third  9 inches  in  the  average  proportion  of  100, 
102,  and  88. 
10.  The  unmanured  plot  contained  15'7  lbs.  of  nitrogen  as 
nitrate  per  acre.  The  plots  receiving  ash-constituents  alone,  a 
mean  of  20T  lbs.  The  plots  receiving  200  lbs.  ammonium-salts, 
or  275  lbs.  nitrate  of  sodium  per  acre,  with  or  without  ash- 
