220 



SOIL PHYSICS AND MANAGEMENT 



deficient in organic matter. Crayfish aid the downward movement 

 of water hy their burrows. 



7. Roots of plants penetrate the soil and later decay, leaving 

 passageways through which water may pass quite readily. 



Lysimeters or drain gages have been used for determining the 

 amount of percolation and evaporation. The longest and most 

 interesting records have been obtained at Rothamsted, England, 

 where records have been kept for 34 years. The gages consist of 

 masses of undisturbed soil of different depths enclosed' in cement 

 tanks with drainage outlets for measuring the percolation. The 

 soil is a flinty clay loam or heavy loam and is kept free from all 

 vegetation. 



Rainfall, Percolation and Evaporation 3 at Rothamsted, England, Average for 

 34 Years, 1871 to 1904 



Results for Years of Maximum and Minimum Rainfall 



It will be noted from the above table that the amount of perco- 

 lation varies but little for the different depths of soil. The average 

 percolation for tlie 20-inch deptli was 13.90 inches, while for the GO- 

 inch it was 13.79 inches. This shows that only 0.11 inch more water 

 was retained by the deeper soil. 



