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1912] BRIGGS & SHANTZ—WILTING COEFFICIENT 23 
by Gatn,‘ Hetnricu,5 and more recently by Hepccock.® No 
quantitative correlation between the soil texture and the non- 
available moisture was established, and only in the case of a few 
soil types was the non-available moisture recorded. 
In field studies of soil moisture, determinations of the total 
water content can easily be made. The errors which enter into 
the determination of the wilting coefficient under field conditions 
are very great, due to the direct evaporation from the soil, local 
variation in soil texture, and non-uniform root distribution, com- 
bined with the difficulty of determining the exact wilting point 
when the roots occupy a large soil mass. Furthermore, it is only 
during periods of extreme drought that conditions are favorable 
for wilting coefficient determinations in the field. In view of 
these difficulties, it becomes important to ascertain whether the 
wilting coefficient can be determined by an indirect method based 
upon the relationship of the wilting coefficient to the moisture 
retentiveness of the soil as measured by physical methods. 
Accordingly we have compared the wilting coefficient with 
the moisture equivalent, the hygroscopic coefficient, the moisture 
holding capacity, and mechanical analysis for a series of soils 
ranging from sands to clays. In the wilting coefficient determina- 
tions Kubanka wheat (Grain Investigations no. 1440) has been 
used as an indicator. The results of these comparisons are given 
in the following sections: 
RELATION OF THE WILTING COEFFICIENT TO THE MOISTURE 
EQUIVALENT 
The moisture equivalent of the soil is the percentage of water 
which it can retain in opposition to a centrifugal force 1000 times 
that of gravity.7 In making the determinations the soils are 
4Gatn, E., Action de J’eau du sol sur la végétation. Rev. Gén. Botanique 
7°73- 1895. 
5’ Hemricu, R., Zweiter Bericht iiber die puger und Wirksamkeit des 
Lanérecaeae ea Versuchs-Station zu Rostock, 1894, p. 
6 Hepccocg, G. G., The relation of the water content of a soil to certain plants, 
principally mesophytes. Bot. Survey Nebraska. VI. Studies in the vegetation of 
the State II. 1902:5-79. 
7 a L. J. and McLane, J. W., The moisture equivalent of soils. U.S. 
Dept. A Bur. Soils, Bull. 45. 1907;-also, Moisture equivalent determinations 
and their claus Proc. Amer. Soc. Agronomy (1910) 2: 138-147. 1911 
