VOLUME LXVII NUMBER 3 



THE 



Botanical Gazette 



MARCH igig 



RELATION OF MINIMUM MOISTURE CONTENT OF 

 SUBSOIL OF PRAIRIES TO HYGROSCOPIC 



COEFFICIENT^ 

 F. J. Alway, G. R. McDole, and R. S. Trumbull 



Introduction 



It has long been recognized that the maxima and minima 

 percentages of water found in well drained soils in the field are in 

 general roughly dependent upon the relative fineness of texture, 

 but very few data have been published in such form as to permit 

 of any attempt to compute the actual relations which these extremes 

 bear to the physical constants. In a previous paper (3) we have 

 reported laboratory experiments and field observations showing 

 that when loams, after rains sufficiently heavy to moisten them 

 thoroughly, are protected from losses by evaporation and tran- 

 spiration, they lose water by downward movement until the ratio 

 of moisture content to hygroscopic coefiicient reaches a value 

 between i . 8 and about 2.5; while with coarse sands the ratio is 

 as high as 6.0 or 7.0; and fine sands occupy an intermediate 

 position, the ratio rising with a decrease in hygroscopicity. 



While the maxima under field conditions are easily ascertainable 

 anywhere, it being necessary only to await heavy rains or to irrigate 

 a small area, the corresponding minima are developed only when a 

 very scanty rainfall or a prolonged absence of precipitation is 



' The work reported in this paper was carried out in 1907-1913, while the authors 

 were members of the staff of the Nebraska Agricultural Experiment Station. 



18s 



