50 
INVESTIGATIONS ON ROTH AMSTED SOILS. 
nitrogen, but the drainpipes only discharge a fraction of the total 
drainage, and a large quantity of drainage must often find its way 
downward below the level of the drainpipes when the pipes are not 
running, and even when they are. 
Most, if not all, of the loss on the chemically manured plats may 
therefore be said to be in the form of nitrates. It is possible that 
under certain conditions of weather there may be slight loss by evo- 
lution of free nitrogen from the crop residues of the surface soil on 
these plats, but there is no evidence to show that any of the nitrogen 
added in the form of chemical manures is thus lost. But fermentative 
decomposition involving evolution of free nitrogen no doubt takes 
place on the heavily and continuously dunged plats, with their high 
quantity of organic matter, and in a less degree on the rape-cake plat. 
It is to be borne in mind, however, that the quantity of dung used in 
these continuous wheat-growing experiments is, on the yeaiTy average, 
far less than would be used in practical agriculture on any of the 
rotation systems. 
NITROGEN AND CARBON IN THE SUBSOILS. 
And now I would for a brief space divert your attention to the sub- 
soil nitrogen rather than to the surface nitrogen. 
We have seen that it is not clear that even the higher subsoil has 
either contributed nitrogen to the crops or has accumulated nitrogen 
from crop residues, i. e., from the indirect effects of manures; nor, 
indeed, is it clear how far the subsoil has contributed nitrogen to the 
nitrates found in or passing through the subsoils, though we have, as 
we shall see hereafter, some evidence that active nitrification, at any 
rate, does not occur in the lower subsoil. This statement as to the 
absence of evidence of accumulation from crop residues, however, 
must be restricted as referring to evidence of accumulation during 
the experimental period of fifty years during which the soil has been 
under continuous wheat cultivation. The diminution of nitrogen 
from the surface as we go downward into the subsoil is, however, for 
a certain range gradual and clearly points to accumulations in the 
pas1 . 
It is convenient to consult here a summary table that has been pre- 
pared from Table 11 so as to show the nitrogen, carbon, etc., in the 
average of all the Broadbalk soils at each depth. 
