10 



if such a soil were acid, it would be necessary to neutralize it with 

 ground limestone. 



In practice most growers would be well advised to select loam soils 

 of medium texture wherever possible and avoid the heavy clay loams. 

 In exceptional cases in which the grower is thoroughly familiar with 

 soil texture and the factors controlling physical conditions in soil, 

 it may be advisable to attempt to increase yields by experimenting 

 with soils of heavier texture. 



HEAT STERILIZATION pF SOIL 



During the past 5 years several growers in eastern Pennsylvania 

 have been steaming their casing soil to eradicate Mycogone. It is 

 generally known that steaming certain soils may be detrimental to 

 succeeding crops of higher plants. Therefore, preliminary experiments 

 were carried out to learn something of the effect on yield of mushrooms 

 of heating the casing soil at different temperatures. In the first 

 experiment, Keyport clay loam was divided into five portions. One 

 of these was placed in a layer 10 inches deep in an unused bed at the 

 top of the mushroom house and allowed to warm up during the "peak 

 heat," which was about 130° F. The other portions of soil were 

 placed in cotton sacks in a special heating chamber and raised to the 

 temperatures 150°, 170°, 190°, and 212°. The plots cased with 

 soils heated in the chamber yielded only half as much as those cased 

 with soil heated in the mushroom house at 130°. Similar results 

 were obtained in a subsequent experiment. In this experiment the 

 soil heated in cotton sacks was damaged in certain cases even when the 

 temperature did not exceed 135°. 



These experiments leave little doubt that serious loss in yield may 

 result from the heating of casing soil under certain conditions. This 

 question is being investigated further. Meanwhile a more critical 

 attitude should be assumed toward heat treatment of mushroom 

 casing soil than has been the case in the past. In some cases heat 

 treatment may be desirable and beneficial; in others it is clearly 

 harmful. 



SUMMARY 



Comparative tests indicate that casing practice may have a consider- 

 able influence on mushroom yields. 



The thickness of the soil was not an important factor. The cus- 

 tomary 1-inch casing seemed preferable. 



Two or three weeks after spawning seemed to be the best time for 

 casing. 



Soil approximately neutral in reaction gave better yields than very 

 acid soil or excessively alkaline soil. Ground limestone was found to 

 be more nearly foolproof and therefore preferable to hydrated lime for 

 neutralizing casing soil. 



In general, heavy soils yielded better than sandy soils. Clay loams 

 or even clays seemed preferable whenever their physical condition 

 was such that they did not puddle or cake on the bed. 



With the soil tested there was a noticeable reduction in yield as a 

 result of heat sterilization under certain conditions. 



