202 



Irrigation and Drainage 



these are much less than through the undisturbed soil, yet the 

 relative differences are nearly as large. That is to say, the soil 

 which, in the firm condition, has brought the largest amount of 

 water to the surface, has also, when its surface 1/2, 3 or 4 



Fig. 36. Method of measuring effectiveness of mulches. 



inches were converted into a mulch, permitted the largest losses 

 to take place ; while the soil having the slowest rate of loss 

 when the surface was firm has also given the least evaporation 

 through the several depths of mulches. 



If the losses per 100 days, expressed in inches, are brought 

 into contrast, they stand as shown below: 



No mulch 



INCHES 



Virgin clay loam 21.31 



Black marsh soil 5.19 



Difference 16.12 



1-inch 

 mulch 



INCHES 



11.13 

 3.12 



8.01 



2-inch 

 mulch 



INCHES 



8.65 

 2.38 



6.27 



3-inch 

 mulch 



INCHES 



7.85 

 2.27 



5.58 



4-inch 

 mulch 



INCHES 



7.81 

 2.23 



5.58 



It will be seen from this table that very wide differences 

 exist between the losses of moisture through mulches of like 



