412 VEGETABLE FORCING 
cial growers buy the usual supplies of city stable manure, 
which is often shipped in carlots. 
In many instances the manure is placed in large piles 
out of doors, as shown in Fig. 151, and allowed to fer- 
ment. There are advantages in keeping the manure 
under cover where there will be no loss from leaching 
and where it will not dry out rapidly, but the objections 
to open air composting are not serious. 
Certain essential chemical changes occur during the 
process of fermentation, which also materially alter the 
physical properties of the manure. Fire-fanging should 
be avoided as much as possible. To encourage the proper 
kind of fermentation it is necessary to keep the pile 
uniformly moist and fairly compact. The supply of 
moisture in the compost should be watched carefully 
Fig. 151.—Composting manure for the growing of mushrooms. 
from day to day. Copious applications of water or suff- 
cient amounts to soak the manure are necessary when it 
is placed in piles, and the latter should not be more than 
4 or 5 feet deep. It is generally customary to turn or 
fork over the piles from two to four times during the 
process of fermentation, which lasts about four weeks. 
This operation is essential in order to secure uniform 
fermentation throughout the compost and to make the 
manure shorter or finer in texture. Water should be 
added whenever necessary while the manure is being 
