48 INVESTIGATIONS ON ROTHAMSTED SOILS. 
fifty years received ammonium salts containing the same quantity of 
nitrogen, viz, 86 pounds per acre, but their mineral treatment has 
varied. 
Table 25. — Broadbalk tcheat soils, 1893 — Plats 10a, 11, 13, and 7, all annually 
manured with ammonium salts containing 86 pounds nitrogen per acre. 
Mineral manure. 
Total 
annual 
weight 
of wheat 
and 
straw (42 
years 1 
aver- 
age). 
First 9 inches 
only. 
Annual 
excess of 
Excess of 
nitrogen 
per acre 
in first 9 
inches, 
as com- 
pared 
with plat 
10a. 
Excess of 
carbon 
per acre 
in first 9 
inches, 
as com- 
pared 
with plat 
10a. 
Nitro- 
gen. 
Car- 
bon. 
crop per 
acre, as 
com- 
pared 
with plat 
10a. 
Plat 10a . 
Plat 11 .. 
Plat 13 
Plat 7 ... 
None 
Pounds. 
3, 104 
3,988 
5,365 
5,629 
Per ct. 
0. 1069 
.1131 
. 1162 
.1222 
Per ct. 
1.049 
1.107 
1.165 
1.101 
Pounds. 
Pounds. 
Pounds. 
Superphosphate. 
Superphosphate and potassium 
salts. 
Superphosphate and potassium, 
sodium, and magnesium salts. 
884 
2,261 
2,525 
160 
241 
396 
1,503 
3,007 
1,348 
Here again we see that, as the crop has increased on the minerally 
manured plats, under the influence of more complete feeding, so has 
the excess of nitrogen in the surface soil increased again in proper 
sequence, though not in direct proportion. 
NITROGEN ACCUMULATIONS AS CROP RESIDUE. 
Now a study of the previous series (5, 6, 7, and 8) led clearly to the 
conclusion that the increase in soil nitrogen followed increased crop, 
increased crop following an increase of nitrogen applied as ammonium 
salts, provided that plenty of minerals were also applied. But from 
those plats alone — save perhaps from the carbon results — we could 
not draw any valid conclusion as to whether the excess was really 
rescued nitrogen existing as crop residue or whether it was actually 
an accumulation of manure: The series 10a, 11, 13, and 7, however, 
now considered, forms a complement to the other series, showing that 
even when the application of nitrogen is constant, the smaller the 
crop the less of it is retained in the soil. The more completely, by 
the supply of minerals, t he crops have been enabled to utilize the 
nitrogen supplied, the more have they accumulated in the soil; and 
conversely, the less that is utilized the less is retained. 
That whatever storage of manurial nitrogen from inorganic sources 
(such as ammonium salts or sodium nitrate) takes place in the soil, 
occurs in the form of crop residues — that is to say, as the remains of 
roots, Stubble, and the debris of weeds — broken down and modified 
by the influence of the worms, insects, fungi, and bacteria that feed 
upon them, is not a new conclusion. It was arrived at long since at 
Rothamsted, and has been largely supported by the study of the com- 
position of the drainage waters from the pipe drains of the wheat plats, 
as well as by 1 he results of earlier analyses of the soil; and the case 
