z, CIRCULAR 609, U. S. DEPARTMENT OF AGRICULTURE 
fresh manure to a satisfactory mushroom compost by means of fermen- 
tation in beds or trays under controlled conditions indoors. 
The results of these experiments indicate clearly that successful 
crops can be obtained consistently by following a composting pro- 
cedure that is essentially a prolonged sweating out. Composting 
indoors in this way has inherent advantages over outdoor compost 
heaps for experimental yield comparisons that will be explained in 
detail later. Furthermore, there are prospects of saving of labor and 
manure in commercial operations from the applications of principles 
learned from indoor composting. 
PREPARATION OF FRESH MANURE 
When manure is obtained fresh from the stables, as was the case 
in these experiments, it is usually too dry and of too open a texture 
to maintain a proper moisture content in the beds during prolonged 
indoor composting. This difficulty was overcome by chopping up- 
the fresh manure so that most of the straw was reduced to pieces 
about 2 inches long. Water was applied generously during the 
chopping process, and small amounts of superphosphate or gypsum 
mixed with soil were added. 
The manure was chopped with a silage cutter, and water was 
applied as it left the silage chopper until the water content was about 
250 percent of the dry weight. This was about all it could hold 
without water running out of the bottom of the heap. Various 
amounts of soil were added partly to make the manure more compact 
and partly to act as a carrier for the superphosphate or gypsum. In 
the first experiments 30 percent of soil, by weight, was added; later it 
was found that 10 percent was equally suitable. The preliminary 
experiments showed that the high water content necessary in the 
beginning of the process tended to make a wet soggy condition in the 
manure during composting in the absence of a flocculating agent, 
such as superphosphate or gypsum. Satisfactory results were ob- 
tained from the addition of either 2 percent of superphosphate or 
1 percent of gypsum. 
The manure was chopped, wet down, and mixed with the soil super- 
phosphate and gypsum in one operation (fig. 1). It was then imme- 
diately taken into the house and placed in the beds. If left in a pile 
after chopping and wetting, the bottom of the heap rapidly becomes 
sour. A day or two of souring in a large heap may produce sufficient 
acid in the manure to make it necessary to prolong the sweating out 
indoors for 2 or 3 days, and this should be avoided whenever possible. 
The beds were filled at the rate of 150 pounds for 10 square feet of bed 
space (fig. 2). Because of the increased weight of the manure due to 
the added soil and water and the comparatively small loss during 
indoor composting, the bed space filled from a ton of fresh manure 
was somewhat in excess of 200 square feet, which is about twice the 
usual coverage. 
TEMPERATURE CONTROL 
The desired temperature range for composting in the bed appears 
to be between 120° and 140° F. Decomposition is not so rapid below 
