2 CIRCULAR 5 9, U. S. DEPARTMENT OE AGRICULTURE 



rather than the surface soil, which is still generally used in the United 

 States. Both heavy clays and sandy soils are usually avoided. 



In Germany, Passecker (7) recommends the use of a sandy loam 

 soil applied to a depth of an inch after the spawn has run from 10 days 

 to 2 weeks. He also suggests that only the lower layers of soil be used, 

 in order to avoid diseases resulting from contamination of the surface 

 soil. 



In the United States the practice of liming casing soil has evolved 

 in the last 15 years. In England the custom mentioned by Ware (12) of 

 mixing one half of a bushel of lime with each cubic yard of soil is 

 probably much older. Recent recommendations (6, 8, 10, 12), 

 specifying minimum, optimum, and maximum pH values are largely 

 based on a knowledge of the comparative-yield tests described in this 

 circular. 



As far as the writers are aware no replicated yield tests have been 

 previously recorded as a basis for casing-soil practice. In general 

 the criteria for selecting the casing soil and the methods used in 

 applying it are based largely on custom presumably derived from 

 numerous informal empirical tests. The material presented here is 

 the result of replicated field tests made to learn something of the 

 desirability of continuing or modifying certain of these practices. 



EXPERIMENTAL METHODS 



The yield tests were in all cases conducted at Arlington Experiment 

 Farm, Arlington, Va., and were made on plots 2 by 5 feet handled 

 uniformly according to standard practice except for the treatment 

 under consideration. In all tests except those recorded in table 2 the 

 plots were laid out in randomized blocks, using entire beds as rep- 

 licate blocks as suggested in an earlier paper (5). Most of the tests 

 were replicated five times. In the experiments recorded in tables 5 

 and 6, the yield was interfered with on one of the beds (blocks) by 

 some factor entirely irrelevant to the experiment, and because of this 

 an entire block was discarded, leaving only four replications. The 

 yields recorded are the sums of about 30 pickings for each crop. As a 

 rule the mushrooms were picked every 2 or 3 days and the beds con- 

 tinued bearing about 3 months. The recorded weights include the 

 weight of the stems in all experiments made subsequent to 1932. 

 Except where otherwise indicated the standard errors of the experi- 

 ments were calculated by the analysis of variance method. The 

 standard errors of the treatment means are attached to the tables as 

 footnotes wherever the variance due to the treatments was distinctly 

 greater than variance due to random error. 



THICKNESS OF CASING SOIL 



To test the relation of the thickness of casing soil to yield, an experi- 

 ment was made in which plots were cased to different depths but 

 otherwise were treated as nearly alike as possible. The mean yields 

 per square foot from the 15 plots were as follows: Beds cased 1 inch 

 yielded 1.6 pounds, beds cased V/ 2 inches yielded 1.5 pounds, and beds 

 cased 2 inches yielded 1.6 pounds. In a subsequent experiment 12 

 plots were cased 1 inch deep, and 12 comparable plots were cased 2 

 inches. The mean yields of these two series were nearly identical, 



