armed on
the four-course system. He assumes that half of the roots and 100 tons
of hay are consumed at the homestead; that the whole of the straw of the
corn crops is retained at home as food and litter; that twelve horses
have corn equal to 10 lb. of oats per head per day; and that about ten
shillings per acre are expended in the purchase of cake for feeding
stock. Under these conditions the amount of farmyard manure should be
855 tons (or an average of 8-1/2 tons for each of the 100 acres of
root-crop) of _fresh undecomposed dung_. (For composition, see Appendix,
Note XVII., p. 291.) Another method is by taking, as the data of
calculation, the number of cattle, horses, sheep, &c., producing the
manure. Lloyd considers that a fattening animal requires 3 tons of straw
in the year, and makes about 12 tons of manure. A farmer, therefore,
should make 8 tons of manure for every acre of that part of his land
which, in the four-course rotation, is put down to turnips.

The last method consists in taking as the data the amount of food
consumed and litter used in the production of the manure. Of these
methods Heiden considers the last as alone satisfactory and trustworthy.
Applying this method to the horse, he shows, from experiments, that a
little over 47 per cent of the dry matter of its food has been proved to
be voided in the solid and liquid excreta. Taking the average percentage
of water in the excreta as about 77.5, the percentage of dry matter in
the excreta will be 22.5. That is, every pound of dry matter in the food
eaten by the horse yields a little over 2 lb. of excrementitious matter.
To this of course must be added the amount of straw used as litter,
which may be taken at 6.5 lb.

From these data we may calculate the amount of manure produced in a year
by a horse, making certain assumptions as to the amount of work
performed. This Heiden does by assuming that a horse works 260 days, of
twelve hours each, in the course of a year, or 130 whole days, spending
235 days in the stall. Calculating from the above data, he estimates
that a well-fed working horse will produce about 50 lb. of manure in a
day, or 6.5 tons in a year. Of course this does not necessarily
represent all the manure actually produced by the horse, but how much of
the remaining portion of the manure actually finds its way to the farm
it is impossible to say. According to the 'Book of the Farm,' Division
III. p. 98, a farm-horse makes about 12 tons o