42 
INVESTIGATIONS ON ROTHAMSTED SOILS. 
Notwithstanding the annual removal in crops of something like 3 
pounds more of nitrogen per acre per annum for the last forty years 
(or probably nearly 5 pounds per annum, if we include in the average 
the earlier years of the experiments), the surface soil of plat 5 now 
contains distinctly more nitrogen, and no diminution is indicated in 
the second and third depths. The organic carbon is also greater in 
the surface soil of plat 5 to the extent of over 1,100 pounds per acre, 
and in the second depth to the extent of nearly GOO pounds per acre. 
The difference is clearly to be attributed to crop residue, and the fact 
that plat 5 is now richer in nitrogen than plat 3 is due to the storing 
up in stubble and root residue of a portion of the natural soil nitro- 
gen that without mineral manure to aid in its assimilation would have 
been lost, as on plat 3, in drainage. 
It must not, even for a moment, however, be supposed that plat 5 
has gained nitrogen. We shall see hereafter, on comparison of the 
nitrogen results obtained by the examination of samples collected in 
1865 and 1881, that the soils of both plats are steadily losing nitrogen; 
but the loss on plat 5, owing to the influence of the mineral manure, 
has been less than on the wholly unmanured plat. 
GENERAL COMPARISON OP ALL CHEMICALLY MANURED PLATS. 
We may next pass to the perhaps more practically interesting series 
of plats which, although they receive no dung or other form of organic 
nitrogen, have nevertheless received nitrogen in the form of ammo- 
nium salts or, in some cases, of sodium nitrate, with and without vari- 
ous additions of minerals. 
It will be most instructive to concentrate our attention on the sur- 
face soil; that is to say, on the first 9 inches. The results of the sub- 
soil analyses are all to be found in the collective tables, where they 
can at leisure be consulted in detail; but the natural irregularities 
already several times referred to must be taken into account, and this 
renders a detailed examination of the subsoil results for each of the 
many plats, as regards organic nitrogen and carbon, too large a task 
1o be entered upon now. 
It will be convenient to give here, for the plats now under consid- 
eration, an abstract showing briefly the mode of manuring, the aver- 
age yield of crops for forty-two years, and the quantities of nitrogen 
and carbon in the surface soil depths. 
The average annual crops arc expressed in pounds and are the sum 
of the average annual weight of grain and straw, the weight of grain 
being calculated with reference to the average weight per bushel for 
each separate plat, as recorded in the official "Memoranda." 
Fora reason that will presently be seen, the plats are here arranged 
in the order of the annual total yield of grain and straw, plats 3 and 
l (unmanured) and plal 5, already referred to, being included for pur- 
poses of comparison. 
