MUSHROOM GROWING IN THE UNITED STATES 13 



in the form of carbon dioxide, coincident with a lowering of the 

 water-holding capacity of the compost. 



The most desirable interval between turnings and the duration of 

 the composting period depend on the nature of the compost. 

 Weekly turnings are generally considered most satisfactory, but if 

 the manure is short a uniform compost may be obtained with inter- 

 vals of 10 days between turnings. In the Pennsylvania region, 

 where manure is shipped in by the carload, it usually has been 

 handled several times before the grower receives it. Under these 

 conditions a composting period of 25 to 35 days is generally suffi- 

 cient. This would include 10 days from the time of assembling to 

 the first turning and two or three turnings at weekly intervals. 

 When long manure is obtained fresh from the stables, six weeks may 

 be necessary with four or five turnings. In any case the real cri- 

 terion of the end of the composting period is the condition of the 

 compost. Well-composted manure is fairly uniform in color and 

 texture — a dark chocolate brown moderately speckled with white; 

 the straw is pliable enough to shear off readily when torn crossways ; 

 when squeezed the compost just moistens the hand without water 

 running out and at the same time is sufficiently moist and decomposed 

 to remain in a ball when so molded. When this condition is reached 

 the compost is ready for making beds and is taken into the house 

 about three days after the last turning. 



The Department of Agriculture is often requested to determine 

 whether samples of manure are suitable for mushroom culture, and 

 whether they are sufficiently composted to be ready for making beds. 

 Aside from detecting specific harmful material in the manure, no 

 laboratory procedure known can satisfactorily answer either ques- 

 tion. Often composts which are radically different in nutritional 

 value for the growth of mushrooms will have approximately the 

 same appearance and chemical analysis. When sufficient experi- 

 mental data have been accumulated, an approximate organic analysis, 

 or even a simple determination of the carbon-nitrogen ratio, or the 

 reaction (hydrogen-ion concentration) of the manure, may aid in 

 determining the proper degree of decomposition of the compost. At 

 present, however, not enough is known about the extent to which 

 these attributes are correlated with potential mushroom yield to 

 warrant substituting them for judgment based on the appearance and 

 feel of suitable compost. 



Inquiries for exact information on the optimum conditions for 

 fermentation of the compost and for methods of inducing the most 

 favorable bacterial flora are also received occasionally. Circum- 

 stantial evidence suggests that the type of microbial flora which 

 predominates during the composting period may have a profound 

 influence on the subsequent yield of mushrooms. Also, that in all 

 probability the predominating flora of the compost heap at a given 

 time is largely dependent on the variable factors of aeration, reac- 

 tion, moisture content, and temperature. Theoretically it should be 

 possible to determine and establish the optimum combination of 

 these factors. But no precise information is at present available, 

 and solution of the problem must await a considerable amount of 

 careful experimentation under controlled conditions. 



