ed and the
nature of the soil having an important influence.

_Tables of Value of Unexhausted Manures._

Numerous tables have been drawn up for the purpose of guiding farmers in
estimating this unexhausted value at different periods after
application, and in the case of different manures. Such tables, as a
rule, furnish only very rough approximations, and are little better than
mere guess-work. Still more complicated is the attempt to assess the
manurial value of foods consumed by the stock of the farm. Lawes and
Gilbert have devoted much attention to the elucidation of this difficult
question, and have drawn up most elaborate and valuable tables,
furnishing data for calculating unexhausted manure value in the case of
commonly used foods. These tables are given in the Appendix.[254] In
them will be found the manurial value of different cattle-foods,
calculated on the basis of numerous experiments carried out at
Rothamsted.

Thus these experiments have demonstrated that, on an average, probably
not more than _one-tenth_ of the nitrogen, phosphoric acid, and potash a
food contains is removed from the food in its passage through the animal
system. The exact amount will obviously depend on a variety of
conditions, referred to already in a previous chapter.[255]

In explanation of these tables, it may be pointed out that Table I.
gives the total quantities of the three fertilising ingredients in
various foods; while Table II. shows the proportion retained in the
animal body and the proportion voided in the manure, as well as the
manurial value of the food, assuming that it exercises its full
theoretical effect. As this, however, is never fully realised, it is
necessary to make some deduction. The deduction suggested by the
Rothamsted experimenters, on the basis of their wide experience, is 50
per cent for food consumed within the last year. That is to say, the
manurial value of food consumed during the last year is _only one-half
its theoretical value_. For food consumed within the last year but one,
they suggest a deduction of one-third of the allowance for last year;
while for food consumed three years back, a deduction of one-third from
this latter sum should be made; and so on for whatever number of years,
down to eight, may be taken.

FOOTNOTES:

[248] The term _insoluble phosphates_ is an unfortunate one, as the word
insoluble is purely relative in its significance. _Undissolved_
phosphates would be a bette