TIIK CONTROL OF SOIL MOISTURE 267 



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FIG. 43. Rainfall and percolation losses through a 40-inch soil column. 

 Lysimeter records, Rothamsted Experiment Station, England. 



It appears from these figures that about 50 per cent 

 of the rainfall in such a climate as that of England is 

 lost by percolation alone. It appears also that the loss 

 is much lower in summer than in winter, the ratio being 

 about one to three. Also, the longer the soil column, 

 the less is the percolation, due to the greater water- 

 holding capacity possessed by the longer column. 



187. Methods of checking loss by run-off and leaching. 

 - It must not be inferred that the soil is never in such 

 a condition that percolation, and even run-off, are not 

 advantageous. Often in winter the excess water may 

 be drained over the surface with no damage whatsoever. 

 Also, when the soil becomes filled with free water, either 

 in winter or in the growing season, drainage must 

 take place in order to establish optimum soil conditions. 

 The control of the free water of the soil may be brought 



