THE BROADBALK WHEAT BOILS. 
53 
enced by past surface accumulations or crop residues, and get only, 
or mainly, the nitrogen and carbon naturally indigenous to the clay 
itself. 
NITROGEN CONTENTS OF VARIOUS OTHER ROTHAMSTED 
SUBSOILS. 
With regard to the question of subsoil as compared with surface 
nitrogen, it is here relevant to ask how the Broadbalk wheat field 
compares with other fields and clays from other sources. By the 
kindness of Sir Henry (Gilbert, who has spent much time in their con- 
sideration and tabulation, I am able to present here the averages of 
a very large number of nitrogen determinations in different depths of 
different fields at Kothamsted. Indeed, the results represent 1,810 
different samples taken in various places from the different plats, the 
nitrogen determinations being for t he most part made on a mixture 
of the samples represent ing each plat sampled at each depth and at 
each date of collection. The results, however, are derived from 1,8-40 
separate nitrogen determinations. As the results on all the earlier 
samples were obtained by the soda-lime method, the soda-lime results 
for the 189.'} wheat soils are in this case taken for comparison. 
We have results for the following series of samples: 
Broadbalk wheat field. — Samples collected in is»;r>, issi, iss?, and 
1893. 
HoOS fit U /. -Samples collected in 1881 from wheat and clover land; 
in 1S8-, ISS.'J, and 1SS.5 from leguminous land and wheat fallow, and 
in 1SC>S and 1SK:2 from the barley plats. 
AgdeU field. — Samples collected from rotation plats in L867, 1874, 
and 1883-84. 
Bam field. -Various samples collected in 1870 from root land. 
In a great number of cases the sampling has been carried down 
to twelve depths or !) feet. Tables 28 and '2U show not only the per- 
centages of nitrogen in the line dry soil, but also the (plant it ies of 
tine dry soil and stones per acre. The various series of samples are 
recorded separately in the large tabic (Table 28), while in the smaller 
table (Table 29) they are condensed so as to give only the averages 
of the various series for each of the four fields, but showing also the 
mean results for the whole 17 sets of samples. 
