396 



Journal of Agricultural Research 



Vol. X, No. 8 



From the above studies, involving only coarse soils and giving discor- 

 dant results, no definite conclusions are to be drawn as to the effect of 

 the initial moistness upon the movement of water. 



NATURAL LOWER LIMIT OF MOISTURE IN THE SURFACE FOOT 



We wished the moisture content of the soils used in our experiments 

 to represent the lower limits naturally occurring in the surface foot in 

 regions of limited rainfall. The lierature furnishes almost no data upon 

 this subject, as a mere statement of the total moisture content is practi- 

 cally meaningless; it would be necessary to know the hygroscopic coef- 

 ficient or the moisture equivalent, together with the total water, or the 

 ratio of the last to one of the two constants. While the upper limit may 

 be ascertained by sampling very soon after a heavy rain or irrigation, 

 the lower limit in the field is to be found only after prolonged dry 

 weather; and even in a semiarid region there may occur several succes- 

 sive years when conditions of drouth are not severe enough to induce 

 the desired moisture conditions. From our field studies it would ap- 

 pear that in humid regions the moisture content of the whole surface 

 foot is but rarely reduced to the hygroscopic coefficient, while in the 

 semiarid regions this is not so unusual a phenomenon. In Tables IV 

 and V we report data obtained in southwestern Nebraska in the spring 

 of 1 91 1, a time exceptionally favorable for such a field study, as the 

 very dry crop season of the preceding year had been followed by a pe- 

 riod of seven months — September 26 to April 25 — in which the precipi- 

 tation was almost negligible, the total rain and snow fall at the four 

 places mentioned varying only from 0.85 to 3.45 inches (Table III). 



Table III. — Precipitation {in inches) at H. O. Ranch, Imperial, Wauneta, and McCook, 

 Nebr., during the autumn, winter, and spring of igio-ii, a period of unusual drouth 

 {Sept. 26, igio, to Apr. 27, jgii) 



During the last month of this dry period we took samples from the sur- 

 face foot of over 50 fields in the vicinity of the four meteorological sta- 



