INDOOR COMPOSTING FOR MUSHROOM CULTURE 9 
replicated three or four times, the effect of different treatments is 
usually susceptible of critical analysis. This method of comparing 
materials has distinct advantages over pure culture tests in that the 
results may be directly applicable to the planning of yield compari- 
sons in the beds, whereas the results of pure culture tests are only 
suggestive when applied to the mixed-culture conditions of mushroom 
compost. 
The advantage of making yield comparisons with materials com- 
posted in trays or in small sections of a bed imstead of m outdoor 
compost heaps lies in the fact that the replication of plots in the bed 
receiving different treatments insures the replication of the entire 
composting and cultural procedure. With the outdoor heaps com- 
parable results can be obtained only through the replication of whole 
experimental compost heaps to measure the uncontrolled variability 
of composting conditions between heaps and by following this with 
replicate test beds from each heap to sample variability within the 
heaps. In most cases the cost of doing this would be prohibitive except 
for a very limited number of tests. 
The experiments summarized in tables 1, 2, and 3 illustrate the 
type of experimental data that may be obtained with the indoor com- 
posting method. It will be noted that in.each of the experiments 12 
treatments have been compared and that each treatment has been 
replicated 4 times. To obtain comparable data with outdoor heaps 
at least 48 compost heaps would be necessary to sample variability 
between heaps, and if variability within the heaps were measured the 
number of plots on the bed would need to be increased 4 times, or a 
total of 192 plots. 
It is interesting to note that significant effects are indicated in 
tables 1 and 2, due to length of composting, amount of moisture in the 
bed, amount of dried blood added, and the interaction of length of 
composting with the amount of dried blood added. The data in table 
3 suggests a greater effect of the sulfate ion than of either potassium 
or calcium as indicated by the fact that the most significant treatment 
variance is due to interaction. It was clearly demonstrated by these 
and similar experiments that length of composting cannot be con- 
sidered as an independent variable in its effect upon mushroom yields 
because it is geared to other variables, such as the amount of nitrog- 
enous material in the compost. These influence the rate of conver- 
sion of certain materials in the compost to products of decomposition 
favorable to the mushroom as a source of energy for growth and fruit- 
ing in the presence of competing micro-organisms. Interactions of this 
kind are much more difficult to demonstrate by the outdoor com- 
posting system than by experiments employing controlled composting. 
