THE CONTROL OF SOIL MOISTURE 



277 



strated by Buckingham 1 in some experiments in which 

 arid climate conditions were created at the surface of a 

 capillary column forty-six inches in height. The soil 

 was a fine sandy loam. At first the loss of water under 

 the arid conditions was very rapid and exceeded that 

 under the humid conditions; but the rate of loss soon 

 dropped considerably below that of the humid column, 

 and continued to fall behind during the twenty days 

 of the experiment. The differences in this case were 

 due to self-mulching, a very common phenomenon of 

 arid land soils, particularly those of a loamy character. 

 This self-mulching is often seen in sands in humid 

 regions. The under layers of a sand pile are always 

 moist, due to the self-mulching tendencies of the sur- 

 face. The results of Buckingham are shown in the fol- 

 lowing curves : 



HUMID 



FIG. 44. Evaporation curves on a sandy loam under humid and arid 

 conditions. Self-mulching has occurred under the arid conditions 

 and a reduction in evaporation has resulted. 



ARID 



1 Buckingham, E. Studies on the Movement of Soil Mois- 

 ture. U. S. D. A., Bur. Soils, Bui. 38, pp. 18-24. 1907. 



