WW CIRCULAR 609, U. S. DEPARTMENT OF AGRICULTURE 
The coefficient of variability of a single plot averages between 10 
and 15. When it is remembered that mushrooms are picked from each 
plot for a 3-month period this amount of variability cannot be con- 
sidered excessively high. Less variability would be distinctly desir- 
able, but this figure compares favorably with that from plots of sim- 
ilar size representing variability within single outdoor compost heaps 
of either stable manure or synthetic compost.* As the yield from each 
plot with the indoor system was the end product of an entire com- 
posting process, the variability between replicates of these plots is more 
strictly analogous to the variability in the yield of plots representing 
differences both within and between replicate outdoor compost heaps. 
In the writer’s experience the variance between heaps usually has 
been considerably higher than that within the heaps. 
Brief analyses of variance and the arrangement of treatment com- 
binations are given in tables 1, 2, and 3. These data will serve to illus- 
trate the degree of precision that can be expected in making compara- 
tive yield tests with the indoor-composting system. The experiments 
were laid out in factorial design. It is evident from these tables that 
yield differences may be tested by the indoor composting method with 
sufficient precision to enable a critical analysis of treatment effects. 
SUGGESTIONS FOR COMMERCIAL GROWERS 
The manure received by commercial growers is usually somewhat 
more decomposed and easier to wet than the manure used in the 
Arlington Farm experiments, which came fresh from the cavalry 
stables at Fort Myer, Va. Because of this the commercial growers 
who have tried indoor composting have experienced less difficulty with 
breaking up and moistening the manure and with temperature and 
moisture control in the bed than would have been encountered with 
manure fresh from stables. 
Whether shortening outdoor composting and prolonging indoor 
composting will be found feasible by commercial growers depends in 
the last analysis on whether a saving of labor and manure can be made 
sufficient to warrant the change in procedure. It is possible that many 
erowers will find the method presents more difficulties than advan- 
tages. On the other hand, growers who already have turning ma- 
chines to break up the manure will want to give controlled composting 
serious consideration. For growers interested in filling an experi- 
mental house, the following procedure is suggested: 
1. Wet the manure while forking it from the car and at every 
opportunity until sufficient water has been applied, usually somewhat 
more than would be desirable for composted manure at filling time. 
2. Add to each ton of manure, either on the cars or when piled up in 
the composting yard, a mixture of 20 pounds of superphosphate and 
20 pounds of gypsum, using about 150 pounds of soil as a carrier to 
facilitate the distribution of the fertilizers. 
3. Break up the manure with from 1 to 3 turnings in a manure- 
turning machine. The number of turnings necessary will depend on 
the efficiency of the machine in breaking up the manure and the 
facilities for wetting the manure sufficiently and uniformly. If the 
manure is received fresh from the stables the process of breaking it up 
and wetting it should be prolonged over a period of 2 or 3 days in 
4 See footnote 3 and SINDEN, J. W. SYNTHETIC COMPOST FOR MUSHROOM CULTURE. PA. Agr. Expt. 
Sta. Bul. 365, illus. 1938. 
