188 



Phy&ics of the Soil. 



together and again compacted and reunited with the un- 

 stirred soil below. If this change does take place the 

 mulch is rendered less effective and a second stirring is 

 needed. 



FIG. 59. Showing: large cylinders for studying soil problems. 



The relative effectiveness of mulches stirred twice per 

 week, once per week, and once in two weeks, for a virgin 

 clay loam, in cylinders 52 inches deep and 18 inches in 

 diameter, standing in our plant house, as shown in Fig. 

 59, is given in the table which follows. 



