STUDIES ON THE RELATION OF THE NON- 
AVAILABLE WATER OF THE SOIL TO 
THE HYGROSCOPIC COEFFICIENT. 
BY F. J. ALWAY. 
INTRODUCTION. 
Tt is generally recognized that a mere statement of the total 
moisture content of a soil gives little or no information as to the 
amount of water which is available to plants growing upon that 
soil. To obtain such information it is necessary to first ascer- 
tain the nonavailable portion of the soil water. Sachs in 1859 
introduced the direct method for the determination of this — al- 
lowing plants to grow in flowerpots filled with the soil until they 
permanently wilted and then determining the amount of moisture 
remaining. At practically the same time Hilgard developed an 
indirect method — the determination of the hygroscopic coefficient 
of the soil, which consists in exposing a very thin layer of air- 
dry soil to an atmosphere saturated with water vapor and kept at 
a practically constant temperature until the maximum amount of 
hygroscopic moisture has been absorbed, after which the water 
content is determined. 
Notwithstanding the fact that the descriptions of both these 
methods were published over fifty years ago, almost all investi- 
gators who have occasion to make soil moisture determinations 
still publish their data in the form of percentages of total water. 
Tn field studies where the soil is exceptionally uniform such data 
may possess definite significance to the individual investigator 
well acquainted with the particular soil, but usually the data are 
meaningless to others and often are entirely misleading even to 
him who has made the moisture determinations. Such data do 
not permit of the recognition of a particular soil as either rela- 
tively moist or relatively dry; yet practically any farmer can rec- 
ognize a soil as either moist or dry by merely looking at it and feel- 
ing it. That most soil investigators have so long continued to 
follow a method which does not give as much useful information 
RESEARCH BUL. 3, AGR. EXP. STATION OF NEBR. 
