360 
Nitrogen  as  Nitric  Acid,  in  the  Soils 
theless  show  rather  more  nitrates  than  Plots  2 and  4 ; which 
would  seem  to  be  due  to  a greater  residue  of  manure  in  the 
former  plot. 
The  plots  receiving  farmyard-manure  give  the  largest  amounts 
of  nitrates.  On  Plot  72,  where  14  tons  of  farmyard-manure  have 
been  applied  annually  for  30  years,  the  nitrogen  in  the  form  of 
nitric  acid  amounts  to  44T  lbs.  per  acre  to  the  depth  of  27 
inches.  Of  great  interest,  too,  is  the  result  presented  by  Plot  71. 
Here  14  tons  of  farmyard-manure  were  applied  for  20  years, 
but  the  land  during  the  next  10  years  was  unmanured,  and 
continually  cropped  with  barley.  The  effect  of  the  previous 
manuring  is  still  abundantly  shown  in  the  barley-crop  (see 
Table  I.),  and  the  land  is  found  to  contain  37’5  lbs.  of  nitrogen 
as  nitrates,  a quantity  larger  than  on  any  other  plot,  excepting 
that  still  receiving  an  annual  dressing  of  farmyard -manure. 
The  relation  between  the  quantity  of  nitrogen  as  nitrates 
found  in  27  inches  of  the  barley  soils,  and  the  total  quantity  of 
nitrogen  present  in  the  surface-soils  of  the  same  plots,  is  shown 
in  Table  IX.  The  relation  of  the  nitrates  to  the  average  total 
produce  of  the  land  is  also  shown. 
Table  IX. — Nitrogen  as  Nitrates  in  Hoos  Field  Soils,  March  1882, 
for  1000  of  Soil  Nitrogen,  and  of  Average  Produce. 
Plots. 
Manuring. 
Nitrogen  as  Nitrates  in  Soil. 
For  1000 
of  Soil 
Nitrogen. 
For  1000  Average 
Produce. 
Average 
Fourteen 
Years 
1868-81. 
Average 
Two  Years 
1880-1. 
lo 
Unmanured  
0-7 
9-4 
8-4 
1—4  A 
Ammonium-salts,  -with  and  without  Minerals 
8-8 
5-5 
5-1 
1-4  A A 
Nitrate  of  Sodium  „ „ „ 
8-7 
5-3 
4-9 
1-4  c 
Rape  Cake  „ „ „ 
10-0 
6-2 
5-5 
7* 
Farmyard-manure 
9-9 
7-2 
6-7 
The  comparison  between  the  quantity  of  total  nitrogen  in  the 
surface-soil,  and  the  quantity  of  nitrates  existing  in  the  land,  is 
not  so  striking  as  in  the  case  of  the  wheat-field,  partly  because 
in  the  present  case  the  nitrates  were  to  a considerable  extent 
removed  by  drainage  before  the  samples  of  soil  were  taken.  The 
results,  however,  are  in  the  same  direction  as  before.  Any  in- 
crease in  the  produce  of  the  land  is  attended  with  an  increase  in 
the  amount  of  nitrates  produced  within  the  soil,  due  therefore 
to  an  increased  amount  of  crop-residue.  Where  rape-cake  or 
