16 On the Valuation of Unexhausted Manures. 
5. Nitrate of Soda. 
From what has been already said of the loss of the nitrogen 
of manure by drainage, and especially of the very great loss that 
may arise when such soluble and rapidly active nitrogenous 
manures as nitrate of soda or ammonia-salts are used, it will be 
readily understood that, when they are employed, we have not 
to look forward very far to reach the limit of their action, and 
consequently the period at which any claim for compensation 
for their unexhausted residue should cease. This point is in 
fact sooner reached in their case than in that of any other nitro- 
genous manures. Next in order in lasting character, so far as 
the nitrogen is concerned, comes guano, then perhaps, folding, 
then rape-cake, and then bones ; whilst farmyard-manure is the 
most lasting of all. 
Notwithstanding the very great solubility of nitrate of soda, 
and its greater liability to loss by drainage than any other nitro- 
genous manure, some experiments at Rothamsted have shown 
that after it had been used in large quantities, and for many 
years in succession, considerable benefit accrued to future crops. 
To what extent this result was due to the disintegration of the 
subsoil, by which it became more porous, more capable of re- 
taining water in a condition favourable for the growing crop, 
and more permeable to its roots, and how much to the retention 
of nitric acid by virtue of the increased porosity, and therefore 
increased surface for absorption, of the subsoil, there is not 
sufficient evidence to show. It would, indeed, be quite unsafe 
to assume that any conclusions applicable to ordinary practice 
can be drawn from these results, obtained under such excep- 
tional circumstances. 
It must in fact, for practical purposes, be assumed that nitrate 
of soda, used only occasionally, and only in the moderate 
quantities usually applied, leaves no beneficial residue after the 
removal of the first crop. Whatever is not taken up by'the crop 
itself, or washed out during its growth, will probably be in 
great part drained away in the winter following, leaving at any 
rate but a small, an uncertain, and a doubtfully effective residue. 
If nitrate of soda have been used for roots consumed upon the 
farm, and the manure so produced have not yielded a crop, 15.s-. 
for 20.y. original value of the manure may be allowed if the roots 
have been consumed on the land, or 14s. if in the yards. If the 
manure produced from the consumption of the roots have yielded 
a corn-crop, the corn sold and the straw left, 4.s-. for 20.9.; or if a 
second corn-crop have been taken, l.v.; or if instead of a second 
corn-crop, grass or hay be grown and consumed, 25. may be 
allowed. 
