14 



CIRCULAR 251, TJ. S. DEPARTMENT OP AGRICULTURE 



FINAL COMPOSTING IN THE BED 



A few of the larger growers run the manure into the house from 

 the ricks on a series of belt conveyors driven by electric motors 

 (fig. 8), but most of them use bushel baskets set in a row on long, 

 narrow cars which run on light, narrow-gauge tracks. The manure 

 is placed in the beds at the rate of 1 bushel to approximately 2 square 

 feet of bed space. If the compost is wet, or has approximately the 

 correct moisture content, it is allowed to lie in the beds loose or 

 only slightly packed during the heating process. If it is too dry 

 it is packed to help retain the moisture. 



A standard house is usually filled in one or two days; the house 

 is then sealed up tightly and the manure is allowed to go through 

 a final fermentation for a few days. High temperatures are gen- 

 erated inside the house by the manure and the whole procedure is 

 referred to as putting the manure through the " heat." This heat 

 serves three purposes: (1) It allows the grower to dry out the 



Figure 8. — Filling a mushroom house hy the use of helt conveyors 



manure if it is too wet; (2) it eradicates many harmful insects and 

 fungi which have been taken into the house with the manure; and 

 (3) it seems to bring about a healthier and more rapid run of 

 spawn, presumably because of a more favorable biological balance 

 or nutritional condition in the compost. 



The temperature usually begins to rise a few hours after the 

 house is closed and under favorable conditions continues to rise 

 slowly until the air temperature throughout the house reaches 120° 

 to 130° F. and the temperature of the manure in the beds is 130° 

 to 145°. These temperatures are maintained for 12 hours or, if the 

 compost is too wet, until the excess water is driven out. At the 

 peak heat calcium cyanide is usually dusted in the aisles or a small 

 amount of sulphur is burned in the house to kill any insects which 

 may be driven to the surface of the beds by the heat (p. 28). The 

 temperature is then lowered slowly to 75° for spawning. 



The principal difficulties encountered during the heat are : A tend- 

 ency for the temperature in the upper part of the house to run 10° 

 to 20° F. higher than that in the lower part; an excessive con- 



