354 
Nitrogen  as  Nitric  Acid , in  the  Soils 
case  of  Plots  3 & 4, 16 A.  5 A,  17 A,  and  probably  of  several  others. 
Whether  any  of  the  nitrate  on  such  plots  as  7 A and  9a,  was 
due  to  a residue  of  nitrate  left  unused  by  the  crop,  must  remain 
doubtful,  but  the  amount  of  such  residues  can  hardly  be  very 
large.  Plot  9b  affords  a capital  example  of  a large  residue  of 
nitrate  left  unappropriated  by  the  crop.  In  Plots  2 and  19  we 
have  examples  of  the  influence  of  farmyard-manure  and  rape- 
cake  in  increasing  the  amount  of  nitrates  produced  in  the 
soil.  The  amount  of  nitrification  observed  was  probably  in  all 
cases  considerably  above  the  average,  being  largely  due  to  the 
early  saturation  of  the  soil  by  the  heavy  rains  of  August. 
As  the  nitrogenous  organic  matter  in  the  soil  was  clearly  the 
principal  source  of  the  nitric  acid  it  contained,  and  as  this 
nitrogenous  organic  matter  is  largely  derived  from  the  residues 
of  previous  vegetation,  it  will  be  of  interest  to  compare  the 
amount  of  nitric  acid  found  in  certain  typical  plots  with  the 
amount  of  nitrogen  found  by  analysis  in  the  first  9 inches  of 
soil,  and  with  the  average  amount  of  produce  which  the  soil  of 
each  plot  has  yielded.  This  comparison  will  be  found  in 
Table  VII.  The  nitrogen  contained  in  the  surface  soil  of  each 
Table  VII. — Nitrogen  as  Nitrates  in  Broadbalk  Soil,  October 
1881,  for  1000  of  Soil  Nitrogen,  and  of  Average  Produce. 
Plot. 
Manuring. 
Nitrogei 
For  1000 
of  Soil 
Nitrogen. 
a9  Nitrates  In  Soil. 
For  1000  Average 
Produoe. 
Average 
30  Years 
1852-81. 
Average 
2Years 
1880-1. 
3&4 
Unmanured 
6-7 
7-6 
8-6 
6 a 
200  lbs.  Ammonium-salts,  Mineral  Manure 
10-2 
7-3 
7-3 
7 a 
400  lbs.  „ „ „ „ 
12-9 
7-0 
7-8 
8 a 
000  lbs. 
13-3 
6-3 
6-7 
9a 
550  lbs.  Nitrate  of  Sodium,  Mineral  Manure 
12-4 
5*5 
6-1 
9b 
550  lbs.  Nitrate  of  Sodium 
19-9 
12-6 
20-4 
2 
14  tons  Farmyard  Manure 
11-4 
9-4 
10-1 
plot  was  ascertained  from  the  analysis  of  the  same  samples  in 
which  nitric  acid  was  determined.  The  produce  includes  corn 
and  straw.  The  nitrogen  as  nitric  acid  is  that  present  in 
27  inches  from  the  surface. 
In  the  above  Table  we  really  compare  the  quantity  of  nitric 
acid  produced  during  two  months  in  the  field  (plus  residues  of 
nitrates  in  certain  cases),  with  the  total  nitrogen  contained  in 
the  surface  soil,  and  with  the  amount  of  previous  produce  on  the 
