16 



T. Lyttleton Lyon and James A. Bizzell 



may these conditions be different in widely separated parts of the world, 

 but even in a given locality they change from time to time, or with different 

 soils, so that it is impossible to assign any definite ratio of percolate to 

 rainfall. The percolate is merely that part of the rainfall that is absorbed 

 by the soil and not returned to the atmosphere by evaporation from 

 the surface or by transpiration from plants. All the factors that affect 

 evaporation and transpiration therefore influence percolation, altho in 

 the opposite way. It is of interest, and perhaps may be useful, to know 

 how much of the rainfall passed thru the soil that remained bare for 

 five years and how much passed thru the planted soil, in order to compare 

 these figures with similar data obtained elsewhere. 



Percentage percolation of rainfall 



The figures for the flow from each of the lysimeter tanks, expressed 

 in liters for each month from May 1, 1910, to April 30, 1915, are given in 

 table 2 of the appendix (pages 93-94). The flow calculated to acre inches 

 annually for the same period is given in table 3 of the appendix (page 95). 

 These tables furnish the data from which may be found the average annual 

 percolation in inches from the unplanted soil and also from the soil on 

 which crops grew. This, together with the percentage percolation, is 

 stated in table 6. The rainfall during the five-years period averaged 

 31.14 inches annually. 



TABLE 6. Average Annual Percolation of Rainfall from Unplanted and from 



Planted Soil during Five-Years Period 



On the basis of these figures, about three-fourths of the rainfall 

 percolated thru the bare soil and one-half thru the cropped soil. As the 

 proportion of percolate depends on the character of the soil and on the 



i6 



