MUSHROOM GROWING IN THE UNITED STATES 15 



densation of moisture on the upper beds ; and a lack of sufficient heat 

 in the manure or insulation in the house walls to maintain the 

 desired temperatures. It is usually difficult to make floor beds 

 heat properly, and therefore it is advisable to raise them a few 

 inches or abandon them entirely. The tendency toward temperature 

 layering may be largely offset by running electric fans set vertically 

 or at an angle of 45° in the aisle during the heat. In most cases 

 the condensation of moisture on the surface of the top beds can 

 scarcely be avoided, but its harmful effect can be reduced by filling 

 the top beds with the driest manure and casing these beds with dry 

 soil. Houses that fail to heat up properly can usually be brought 

 up to a desirable temperature without excessive wetting or drying 

 out by a combination of live steam and hot water or steam radiation. 

 This practice has given satisfactory results in the Department of 

 Agriculture's experimental house during the seasons of 1928 to 1931, 

 inclusive. 



While the temperatures mentioned above are considered best by 

 many practical growers, the question of what is the most favorable 

 temperature is by no means settled. Theoretically the minimum air 

 temperature should be based on the thermal death points of insect 

 and fungus pests, and the maximum manure temperature should be 

 established by studies, under controlled conditions, of the effect 

 of the temperature during the final heat on the flora of the bed 

 and on the yield of mushrooms. The final answer to this question 

 will undoubtedly be a compromise between these two considerations. 

 In the meantime it would seem to be sound practice to follow the 

 lead of practical experience and avoid air temperatures lower than 

 120° and bed temperatures above 145° F. 



When mushrooms are grown in abandoned buildings the fore- 

 going conditions can often be obtained, but in old mines or caves 

 the air temperature can not be raised and the final heat can only 

 be approximated in the beds. The beds are usually made on the 

 floor (fig. 9) and more manure is used to prevent the temperature 

 from dropping too low during the period when the spawn is begin- 

 ning to run. With a deeper bed, 12 to 14 inches, the manure may 

 have a tendency to overheat and firefang a few days after the beds 

 are made. To prevent this the beds are sometimes packed by being 

 trampled with the feet over the entire surface. 



MANURE SUBSTITUTES AND SUPPLEMENTS 



Several years ago investigators at the Eothamsted Experiment 

 Station in England discovered that artificial manure comparing fa- 

 vorably in appearance and chemical composition with stable manure 

 could be made by composting straw or other material high in cellu- 

 lose with nitrogenous fertilizers. The essential features of their 

 process, which has been patented in the United States under patents 

 Nos. 1471979 and 1619679, are the addition of fertilizer to plant 

 refuse so as to add about three-quarters of a pound of nitrogen to 

 every 100 pounds of dry plant refuse, wetting the material and 

 adjusting the reaction to a slight alkalinity. As a result of these 

 investigations there arose a question whether compost suitable for 

 mushroom culture could be made by this process from straw, peat, or 

 other plant refuse. 



