46 
INVESTIGATIONS ON ROTH AMSTED SOILS. 
removed in it from the soil, the greater is the quantity of nitrogen 
stored in the soil by accumulated crop residues, and so saved from loss 
in drainage. 
PLATS 5 TO 8 (ALL FULLY SUPPLIED WITH MINERAL MANURES, BUT 
RECEIVING DIFFERENT DRESSINGS OF AMMONIUM SALTS). 
This becomes still clearer if, instead of regarding the whole series 
of chemically manured plats, differing so much both in mineral and 
in nitrogenous treatment, we select for consideration certain of them 
which, owing to their comparative treatment, are very strictly com- 
parable. Let us, for instance, tabulate plats 5 to 8, all of which 
receive annually the same full dressing of minerals (superphosphate, 
with potassium, sodium, and magnesium salts), but are very differ- 
ently treated nitrogenously. 
Table 23. — Broadbalk wheat soils, 1SD3 — Plats 5, 6, 7, and S, all annually manured 
with a liberal supply of superphosphate and of potassiiun, sodium, and magne- 
sium salts. 
[First 9 inches only.] 
Nitrogen 
per acre 
added an- 
nually in 
ammoni- 
um salts. 
Annual to- 
tal weight 
of grain 
and straw 
(42 years' 
average). 
Nitro- 
gen. 
Carbon. 
Excess 
of crop 
per acre 
as com- 
pared 
with 
plat 5. 
Excess of 
nitrogen 
per acre in 
first 9 
inches as 
compared 
with plat 5. 
Excess of 
carbon 
per acre in 
first 9 
inches as 
compared 
with platS. 
Plat 5 
Pounds. 
Pounds. 
2,242 
3,842 
5,629 
6,613 
Per cent. 
0. 1013 
.1107 
.1222 
.1188 
Per cent. 
0. 931 
1.019 
1.101 
1.138 
Pounds. 
Pounds. 
Pounds. 
Plat 6 
43 
86 
129 
1,600 
3,387 
4.371 
244 
542 
454 
2.282 
4.408 
5,367 
Plat 7 
Plat 8 
In the presence of a full supply of minerals it will be seen that there 
was a progressive increase in crop with a gradual increase of the ammo- 
nium salts. The annual application of 86 pounds of nitrogen in the 
form of ammonium salts gives about double the increase obtained by 
the use of -43 pounds. A further increase of ammonium salts pro- 
duces a still greater crop, but the gain is no longer proportional. In 
fact, speaking generally, season by season it is noticed at Rothamsted 
thai in the presence of a full supply of minerals the first 43 pounds 
of nitrogen (as ammonium salts) produces 9 bushels of wheat; the 
second 43 pounds produces 9 bushels more, making 18 bushels of 
wheat for 86 pounds of nitrogen; but the third 43 pounds, making a 
supply of 129 pounds, produces a further increase of only 3 bushels of 
wheat , and the crop, it may be observed, is usually overgrown and 
"laid." 
It will be seen that the increase in accumulation of nitrogen in the 
surface soil in plats 6 and 7 (receiving respectively 43 pounds and 86 
pounds of nitrogen per acre per annum) as compared with plat 5 
(without nitrogen) is respectively 244 pounds and 542 pounds, corre- 
sponding very nearly to the doubling of the annual increase in the 
crop. 
