and  Subsoils  of  some  of  the  Fields  at  Rothamsted.  361 
farmyard-manure  is  applied  there  is  not  only  a nitrifiable  crop- 
residue  left  in  the  land,  but  also  a residue  of  nitrogenous 
organic  matter  from  the  manure,  which  still  further  adds  to  the 
I quantity  of  nitrate  produced. 
The  relation  between  the  previous  amount  of  crop  and  the 
quantity  of  nitrate  in  the  soil  is  far  less  marked  than  in  the 
wheat-field.  This  is  partly  owing  to  the  comparatively  washed- 
out  condition  of  the  barley  land,  but  mainly  to  the  much  smaller 
residue  left  in  the  soil  by  barley  than  by  wheat.  In  the  wheat- 
field  the  percentage  of  nitrogen  and  carbon  in  the  soil  of  each 
plot  is  plainly  related  to  the  quantity  of  crop  annually  pro- 
duced. In  the  barley-field  considerable  variations  in  crop  are 
attended  with  only  small  alterations  in  the  quantity  of  nitrogen 
and  carbon  in  the  soil.  The  recent  crop-residues  being  smaller 
in  the  barley-field,  a larger  proportion  of  the  nitrate  is  due 
to  the  old  nitrogenous  capital  of  the  soil,  or  in  some  cases  to 
residues  of  manure.  The  connection  between  the  amount  of 
crop  and  the  production  of  nitrates  is  best  seen  when  reference 
is  confined  to  the  last  two  crops  of  the  field.  The  relation 
between  the  results  of  different  plots  is  similar  to  that  shown 
in  the^wheat-field.  (Table  VII.) 
3.  Nitrates  in  Land  growing  Leguminous  Crops. 
Several  determinations  have  been  made  of  the  quantity  of 
nitrates  existing  in  soils  which  have  grown  leguminous  crops  ; 
to  these  we  must  now  call  attention. 
In  Table  III.  will  be  found  determinations  of  nitrates  in  two 
soils  in  Agdell  Field  which  had  grown  beans.  On  the  fully 
manured  rotation  the  bean-crop  yielded  26 J bushels  of  corn; 
the  total  crop  contained  about  66  lbs.  of  nitrogen.  The  soil 
gave  in  the  first  18  inches  2(V5  lbs.  of  nitrogen  as  nitrates ; 
the  other  half  of  the  land,  which  was  in  bare  fallow,  yielding 
at  the  same  time  48'8  lbs.  On  the  rotation  manured  with 
superphosphate  only,  the  produce  was  7f-  bushels  of  corn,  and 
the  total  crop  contained  about  26  lbs.  of  nitrogen.  The  soil 
yielded  10'6  lbs.  of  nitrogen  as  nitrates  in  18  inches,  the  cor- 
responding bare  fallow  containing  36‘3  lbs.  The  bean-crops 
were  cut  on  Aug.  24,  the  soils  were  sampled  on  Sept.  24-25, 
1878.  A part  of  the  nitrates  found  in  these  soils  would  pro- 
bably be  produced  in  the  month  of  August,  when  the  rainfall 
was  very  excessive  (nearly  5 inches),  or  in  September. 
In  Table  III.  will  also  be  found  a determination  of  nitrates  in 
the  same  field  after  a crop  of  clover  in  1882.  The  clover  was 
grown  on  part  of  the  fully-manured  rotation  plot.  The  crop,  in 
two  cuttings,  yielded  83§  cwts.  of  hay,  estimated  to  contain 
VOL.  XIX. — S.  S.  2 B 
