the action of quicklime in liberating potash
from the clay; and then I considered it very important to
ascertain the proper quantity to be applied. The quantity required
to decompose the phosphate of iron was not great, and assuming
Liebig's theory of its action in liberating the potash to be true,
it seemed to me that an excess of lime would permanently
impoverish the land; for, supposing that the crop required 100
lbs. of potash, and as much lime was applied as liberated 500
lbs., what became of the 400 lbs. which did not enter into the
composition of the plant? was not a large portion of this 400 lbs.
washed down the drains by the rain, and so lost for ever? Perhaps
the absence of lime in this field accounts for its beneficial
action in the experiment just detailed; but if my supposition is
correct, that any excess of potash which may be liberated from the
clay by the use of quicklime (that is, any more than may be
required to perfect the crop), is washed down the drains, and thus
the land is permanently impoverished by the excessive use of lime,
it behoves landed proprietors to ascertain what is required, and
they should take care to apply no more than is necessary. This
caution is most particularly needed in this neighbourhood, where
lime is cheap, and where the opinion is prevalent that the more
there is applied the better it is for the land, and where it is
common to apply ten or twelve tons to the acre. I have stated
above that chemical manure was applied to a small portion of the
field after the setting-in of the drought in April. The action of
this manure showed that a good thing may be very injurious if
applied at an improper time; for, although it produced a
stimulating effect on the plant immediately after its application,
there was too little moisture in the land to dissolve it
thoroughly, and thus enable the plants to appropriate it, until
the rain came, about the end of June, when the wheat had been in
flower some time; but the stimulus was then so great that all the
plants threw up fresh stalks (from the roots), which were in
flower when the wheat was cut, and it was then found that they had
not only impoverished the plants, but had prevented the grain from
ripening. This was the case not only in the experimental field,
but in several others also, where the chemical manure was sowed
after the setting-in of the drought. When the field was sowed with
guano, it was thought desirable to cover one part of