was the result. This will account
for the less yield on plot 8 than on plot 2. It would have been better
to have sown the ashes broadcast, but some previous experiments with
Peruvian guano on potatoes indicated that it was best to apply guano in
the hill, carefully covering it with soil to prevent it injuring the
seed, than to sow it broadcast. It was for this reason, and for the
greater convenience in sowing, that the manures were applied in the
hill.

The ash of potatoes consists of about 50 per cent of potash, and this
fact has induced many writers to recommend ashes as a manure for this
crop. It will be seen, however, that in this instance, at least, they
have very little effect, 400 lbs. giving an increase of only five
bushels per acre. One hundred pounds of plaster per acre gave an
increase of six bushels. Plaster and ashes combined, an increase per
acre of 15 bushels.

One fact is clearly brought out by these experiments: that this soil,
which has been under cultivation without manure for many years, is not,
relatively to other constituents of crops, deficient in potash. Had such
been the case, the sulphate of ammonia and superphosphate of
lime--manures which contain no potash--would not have give a an increase
of 84 bushels of potatoes per acre. There was sufficient potash in the
soil, in an available condition, for 179 bushels of potatoes per acre;
and the reason why the soil without manure produced only 95 bushels per
acre, was owing to a deficiency of ammonia and phosphates.

Since these experiments were made, Dr. Voelcker and others have made
similar ones in England. The results on the whole all point in one
direction. They show that the manures most valuable for potatoes are
those rich in nitrogen and phosphoric acid, and that occasionally potash
is also a useful addition.

"There is one thing I should like to know," said the Doctor. "Admitting
that nitrogen and phosphoric acid and potash are the most important
elements of plant-food, how many bushels of potatoes should we be likely
to get from a judicious application of these manures?"

"There is no way," said I, "of getting at this with any degree of
certainty. The numerous experiments that have been made in England seem
to show that a given quantity of manure will produce a larger _increase_
on poor land than on land in better condition."

In England potatoes are rarely if ever planted without manure, and the
land selected for this crop, even with