THE CONTROL OF SOIL-MOISTURE 



207 



1913 on a bare clay loam three feet deep are interesting as to 

 the light they afford regarding actual drainage losses in humid 

 regions : 



Table XXXIX 



PERCOLATION THROUGH A SLXTY-INCH COLUMN OF BARE CLAY 



LOAM. ROTHAMSTED EXPERIMENT STATION, ANNUAL 



AVERAGE OF 42 YEARS. 



It appears from these figures that the drainage loss is much 

 lower in summer than winter, the ratio being about one to 

 three. It is also to be noted that about 50 per cent, of the 

 rainfall in such a climate as England is lost by percolation 

 through a bare soil. This compares fairly well with Wollny's x 

 summary on eighteen soils in England, Switzerland, and Ger- 

 many. These soils, most of which were bare, showed a loss 

 of over 41 per cent, of the rainfall by drainage. 



Recent results, 2 due to variable conditions, are by no means 

 in agreement, ranging from a low to a very high percentage 

 loss of the rainfall. It seems fair to assume, however, that, 

 as soils are handled in humid regions, over half of the rain- 

 fall is lost by percolation and run-off combined. 



Percolation seems to be influenced, not only by the amount 



1 Wollny, E., Untersuchungen uber die Siclcerwassermengen in verscMe- 

 denen Bodenarten; Forsch. a. d. Gebiete d. Agri.-Physik., Band 11, 

 Seite 1-68, 1888. 



a For excellent review of literature see Lyon, T. L., and Bizzell, 

 J. A., Lysimeter Experiments ; Cornell Agr. Exp. Sta., Memoir 12, June, 

 1918. 



