Report of Experiments on the Growth of Wheat. 495 
But all practical men will admit that the amounts of produce 
here assumed to he exported from each acre, or equivalent 
amounts in other forms, could only he so under one of two con- 
ditions. Either the soil must be naturally a very fertile one, or 
the produce must be kept up by means of purchased cattle-iood 
or artificial manures. In the case of a soil so fertile as to have 
yielded for any considerable number of years the average produce 
supposed without assistance from import, it may well be ques- 
tioned whether it, with its workable subsoil, would not be com- 
petent to yield annually, by decomposition, the necessary amounts 
of the mineral constituents mentioned, and if of them of others 
also, for an all but indefinite period. In the other case — that in 
which the produce is kept up by means of the import of cattle- 
food or artificial manure, or of part one and part the other — the 
loss of the constituents in question derived from the soil itself 
will, of course, be by so much less than the amounts assumed 
above, and that of others will be also reduced. There can indeed 
be little doubt that, in actual practice, the loss to the soil itself, 
by the sale of corn and meat, is generally more nearly one-half, 
and frequently less than one-half, of the above assumed amounts 
of the constituents mentioned ; and that of others will be less 
accordingly. 
So far as the purchase of food for stock was relied upon, no 
selection could well be made from the current supplies in the 
market, that would not bring upon the farm more of the mineral 
constituents than the increase of produce due to the manure 
obtained from it would remove from the land in the form of corn 
and meat. In fact, to increase the sales of corn and meat by the 
import of cattle-food as generally practised, is to increase, and 
not to diminish, the amount of available mineral constituents 
within the soil. If, on the other hand, the produce were kept up 
by means of artificial manures, the rules of selection among intel- 
ligent practical men are such, that almost invariably much more 
of phosphoric acid at any rate, would be brought upon the land, 
than would be removed from it in the increase of corn and meat 
due to the use of the imported manures. 
In the case supposed without import, it is probable that, in the 
majority of instances, phosphoric acid would be the most liable to 
become deficient in relation to other constituents. The sources 
of phosphoric acid developed in recent years, promise, however, 
to answer to any demand that seems likely to be made upon them 
to remedy such exhaustion of it as the present agricultural prac- 
tices of the country induce. 
In the case of imports, on the other hand, especially where 
they consisted chiefly of the current artificial manures rather than 
2 M 2 
