Leffinninous  Plants  as  collectors  of  y'ltroijen. 
Ill 
grass  l)ecame  comparatively  small,  averaging  36  cwt.  of  dry 
matter  per  acre  per  annum  over  the  nine  years  1890-1896, 
which  may  be  calculated  as  containing  in  all  about  720  lb.  of 
nitrogen. 
It  is,  however,  the  tank  containing  lucerne  which  shows 
the  greatest  accumulation  of  nitrogen. 
Tank  5. 
Crop 
Year 
Per  acre 
Dry  matter 
Nitrogen 
Cwt. 
Lb. 
Lucerne 
1890 
8 
24 
1891 
60 
188 
1892 
90 
280 
1898 
118 
366 
1894 
139 
433 
1895 
114 
352 
1896 
105 
325 
1897 
109 
338 
1898 
160 
480 
Total  2786 
This  represents  an  average  annual  }'ield  of  over  300  lb.  of 
nitrogen  per  acre,  all  drawn  from  the  atmosphere,  in  addition 
to  the  accumulation  in  the  root  residues  remaining  in  the  soil. 
In  1904  the  lucerne  was  still  vigorous  though  patchy,  and 
samples  of  soil  were  taken  both  from  this  and  from  the  tank  in 
permanent  mixed  grass.  Unfortunately  in  1896  the  lucerne 
tank  had  been  turned  out  to  secure  a soil  sample  at  a depth  of 
five  feet,  and  the  contents  were  somewhat  mixed  in  returning 
the  soil  to  the  tank.  Analyses  of  the  first  and  second  nine 
inches  showed  the  following  accumulation  of  nitrogen  : — 
Nitrogen 
Per  cent,  in 
dry  soil 
Per  acre 
lb. 
Lucerne,  1st  9 inches. 
0-0217 
651 
„ 2nd  „ . . . 
0-0143 
429 
Mixed  grasses,  1st  9 inches 
>1  ,,  2nd  ,, 
0-0290 
870 
0-0117 
351 
