anure depends upon a number of more or less
complicated commercial considerations, such as the questions of supply
and demand, &c., which need not here be discussed, and which similarly
regulate the monetary value of any other article of commerce.

_"Unit" Value of Manurial Ingredients._

For the purpose of affording data for ascertaining the approximate value
of a manure, tables have been drawn up giving what is called the "unit"
value of the different manurial ingredients in various manures. This is
obtained by dividing the market value of a manure per ton by the
percentage of nitrogen, phosphoric acid, and potash it contains. Thus,
for example, sulphate of ammonia of 97 per cent purity contains 25 per
cent of ammonia, and at present (Dec. 1893) is valued at L13, 15s. per
ton. In order to obtain the unit value of ammonia in sulphate of
ammonia, we have only to divide L13, 15s. by 25, which gives us 11s. The
value of such tables depends on the competence of those drawing them up,
and they require to be subjected to constant revision. In the Appendix
will be found two of these tables, taken from the 'Transactions of the
Highland and Agricultural Society of Scotland.'[251]

_Intrinsic Value of Manures._

But there is another way of valuing manures, and that is by attempting
to ascertain what their intrinsic worth is in producing an increase in
the returns of the crops. Of course it may be said that the intrinsic
worth of manure affects directly its market value. This is doubtless
true, but it is not the only factor in determining the market value of a
manure.

Again, the intrinsic worth of a manure may be said to vary according to
the soil to which it is applied and the climatic conditions. This being
so, it is important for every farmer to try and ascertain for himself
what the intrinsic value of different manures is on the soil of his
farm; and this can only be done by carrying out manuring experiments for
himself. This leads us to say a word or two on the important subject of

_Field Experiments._

It is impossible that every farm should be able to support an experiment
station for the purpose of carrying out elaborate experiments on the
effect of different manures on different crops. Nevertheless it is
possible and highly desirable for _every_ farmer who is engaged in
arable farming on any scale to carry out simple experiments for the
purpose of ascertaining the characteristic manurial requirements of hi