18 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT OH THE 
If then the surface soils have gained in nitrogen, it is obvious that they have not 
been the primary source of the nitrogen taken up by the plants. It must have come 
either from above or from below the surface soil—from the atmosphere or from the 
subsoil. The evidence does indeed point to the fact, that much nitric acid results 
from nitritication of nitrogen accumulated within the surface soil. But as this nitrogen 
either increases or does not diminish, much of the nitric acid produced must come 
from some other source than what may be called the original stock of nitrogen of the 
surface soil itself. Much doubtless comes from the nitrogen of crop-residue, itself 
derived from the atmosphere or from the subsoil. 
Before discussing this subject further it will be well to call attention to another 
remarkable experiment, showing the amount of nitrogen that may be taken up by one 
leguminous plant growing on land where another had to a great extent failed. 
4, Experiments on the growth of Red Clover on Bean-exhausted Land. 
Tire results in cpiestion were obtained in a field in which beans had been grown 
almost continuously for 32 years, but had considerably declined in yield, as the 
following Table will show ;— 
Table VII.—Quantities of Nitrogen removed per acre per annum, in lbs., in bean- 
crops, over four periods of 8 years each. Geescroft Field, Bothamsted. 
8 years, 
1847-1854. 
8 years, 
1855-1862. 
8 years, 
1863-1870. 
8 years, 
1871-1878. 
Average 
32 years, 
1847-1878. 
1. Without manure. 
2. With mineral manure containing potash 
3. With mineral manure and nitrogen . 
lbs. 
48-41 
60-19* 
68-94 
lbs. 
25-26 
34-25 
36-87 
lbs. 
9-12 
23-46 
35-05 
lbs. 
16-36 
26-66 
28-69 - 
lbs. 
24-79 
35-36t 
42-39 
The two upper lines show the amounts of nitrogen removed per acre per annum in 
the bean crops without any supply of nitrogen by manure. It will be seen that over 
each period of 8 years, the plot receiving a mineral manure containing potash yielded 
considerably more nitrogen than the one without any manure. In both cases, however, 
there was considerable decline from the first period to the last. Further, whilst over 
the 32 years the unmanured plot yielded an average of 24'8 lbs. of nitrogen per acre 
per annum, that with the potash manure yielded 35'4 lbs., or nearly one-half more, 
though without any supply of nitrogen from without. In the third experiment, where 
besides the potash manure some nitrogen was applied, in the early years as ammonium 
* Average of 7 years only, results not available for 1849. 
t Average 31 years only. 
