be used alone with very great advantage. In all cases
the rapidity of the action of guano makes it an important auxiliary of
farm-yard manure, and it is in this way that it may be most
advantageously employed. Experience has shewn that one-half the
farm-yard manure may be replaced by guano with the production of a
larger crop than by the former alone in its full quantity. The
proportion of guano usually employed is from three to five cwt., and it
is alleged that a much larger quantity produces prejudicial effects on
the subsequent crops, although it is not very easy to see on what this
depends.

The variety of guano to be selected must depend to a great extent on the
use to which it is to be put. Peruvian guano is most advantageously
applied as a top-dressing to young corn and particularly to oats. For
the turnip, the ammoniacal guanos were formerly preferred, and on strong
soils, under good cultivation, their effects are excellent, but on
light soils they are less applicable, their soluble salts being more
rapidly washed out, and their effects lost, and in these cases they are
surpassed by the phosphatic guanos.

No definite rules can be given for determining the soils on which these
different varieties are most applicable, but each individual must
determine by experiment that which best suits his own farm; and the
inquiry is of much importance to him, as, of course, if the phosphatic
guanos will answer as well as the ammoniacal, there is a large saving in
the cost of the manure. A very excellent practice is to employ a mixture
of equal parts of the two sorts of guano.

_Pigeons' Dung._--The dung of all birds, which more or less closely
resembles guano, may be employed with much advantage as a manure, but
that of the pigeon and the common fowl are the only ones which can be
got in quantity. Pigeons' dung, according to Boussingault, contains 8.3
per cent of nitrogen, equivalent to 10.0 of ammonia. Its value,
therefore, will be more than half that of guano, but it varies greatly,
and a sample imported from Egypt into this country, and analysed by
Professor Johnston, contained only 5.4 per cent of ammonia. Hens' dung
has not been accurately analysed, but its value must be about the same
as pigeons'.

_Urate and Sulphated Urine._--We have already discussed the urine of
animals, in reference to farm-yard manure. But human urine, the
composition of which was then stated, is of much higher value than that
of the lower a