a crop of clover, which plant contains a large
percentage of the alkaline carbonates, which are entirely wanting in
Guano, furnish all the elements necessary to the entire wheat plant. In
this view of the subject, and for many other reasons that I cannot stop
to enumerate, there cannot be, when guano is extensively used, a more
judicious rotation than the Pamunky five field system, in which clover
occupies a prominent place. I have now enumerated some of the most
prominent means by which you may "keep your land rich." I would not
discourage the use of others. Science is daily making discoveries in the
art of enriching the earth, and we should discard nothing, without a
trial, which promises to be useful; always bearing in mind that the
wisest economy is entirely consistent with the most liberal expenditure,
in the purchase of manures, provided we take care, by judicious
experiments and observation, to ascertain their efficacy, and that we
get back our capital, with an actual _net_ profit _in cash_, on all our
investments. This latter caution is indispensable, in our country, where
new lands are so abundant and cheap, that highly improved farms can
never be rated in the market at their true value."

"The various manures compounded by chemists and manufacturers, should
also engage your careful attention. They should not be recklessly thrown
aside as humbugs, without trial or investigation, nor adopted and
extensively used with blind confidence in their efficacy. I have used
many of these manures by way of experiment, and the profit realized upon
them has not justified me in enlarging my operations. Poudrette,
manufactured in Baltimore; Bommers manure, Chappel's fertilizer and
Kentish & Co.'s prepared guano, (used, it is true, upon a small scale,)
have not realized the promises made in their behalf. Yet I would by no
means discourage the praiseworthy efforts of the manufacturers, and hope
they will persevere until, by lessening the bulk and increasing the
power of their compounds, they may be able to prepare an article that
for cheapness, convenience of application and efficacy, shall equal or
surpass the best Peruvian guano."

That desideratum, Professor Mapes believes he has already attained by
the addition of superphosphate of lime to the Guano, making a compound
of two-thirds of the latter to one of the former, more valuable by
weight than the pure article. That being the case will greatly increase
the consumption of