THE HROADBALK WHEAT SOILS. 
41 
tain 900 pounds per acre of nitrogen more than the un manured plat 3, 
but it contains nearly 380 pounds more than the average surface soil 
of the seven plats cited. In the second !» inches, alt houirh plal 11* con- 
tains more than the unmanured plat, there is, however, practically no 
difference between it and the average second !» inches of the seven 
plats. In the third depth there is a very decided difference, the rape- 
cake plat containing more than the others. In both the second and 
third depths of plat L9 there is a much larger quantity of carbon than 
in the average corresponding depth of the seven plats, and One is 
inclined to draw t he conclusion that the organic mallei- of t lie rape 
Cake, including some of its nitrogenous compounds or organic bodies 
derived from them, has found its way more deeply down than has the 
organic matter of thednng. But not too much stress must be laid 
upon this, for averages are apt sometimes t<» lead to delusive conclu- 
sions, and a study of the subsoil resulls seems to show a gradation, 
i Ik mull not a unit' or m one, in the subsoils in the nature of an increase of 
nit rogen as we go across the field, the subsoils of plats 2a to 8 showing 
less nitrogen than those of plats 9a to 18; and the increase of nitrogen in 
the third depth of plat L9, as compared w i i h even its neighbor, plat 18, 
may possibly be at Least partly due to natural increase in this roughly 
graduated irregularity. This natural irregularity in the subsoils is no 
doubt mainly due i<» differences in the proportion of nitrogen-bearing 
clay and of fine gravel or sand with which it is mixed. 
THE CHEMICALLY MANURED PLATS. 
I'LAT -~> (MIXKKAL MANURES ONLY). 
We may now turn to the various chemically manured plats. One 
of them, plat 5, has received for fifty years a full supply of minerals 
without nitrogen in any form whatever. As compared with the unma- 
nured plat it has produced a uniformly larger crop of corn and 
straw, showfng an average increase over the unmanured plat, over 
forty-two years, of 2 bushels of wheat and 1 hundredweight of straw. 
We might expect it, therefore, to be poorer in nitrogen than the 
wholly unmanured plat, but this is not the case. Indeed, we find a 
Blight increase, and with it a distinct increase in organic carbon, as- 
shown in Table 21. 
Tarlk 21. — liroadhalk wheat soils, isn.i — Plat (unmanured) and plat ~> {mineral 
ma iik res only). 
Nitrogen. 
Carbon. 
Depth. 
Per cent. 
Pounds 
Per cent. 
Pounds 
per acre. 
per acre. 
Plat 8, unmanured: 
First 9 inches 
0.0992 
2,572 
0.888 
23,022 
Second 9 inches 
.0730 
1,950 
.565 
15.093 
Third !) inches 
.0651 
1,817 
.483 
13,483 
Plat 5, minerals only: 
First 9 inches 
.1013 
2.626 
.931 
24,137 
Second 9 inches 
.0739 
1 . 974 
.5S7 
15,681 
Third 9 inches 
.0645 
1,801 
.446 
12,450 
