1912] BRIGGS & SHANTZ—WILTING COEFFICIENT 37 
which the relationships are based, were made with a soil column 
r cm. in height. The amount therefore is far in excess of that 
found in drained soils under field conditions. The relationships 
are expressed in the following formulae: 
Maximum available moisture= (wilting coefficient X1.9) +21 
Maximum available moisture = moisture equivalent +21 
Maximum available moisture= (hygroscopic coefficient X 2.8) +21 
Maximum available moisture= (0.02 sand+o. 23 silt+1.08 clay) +21 
Maximum available moisture= (moisture holding capacity Xo.65) +7 
The formulae show that difference in the maximum amount of 
available moisture that two soils are capable of holding is equal 
to the difference in their moisture equivalents; to 1.9 times the 
difference of their wilting coefficients; and to 2.8 times the differ- 
ence of their hygroscopic coefficients. 
Summary 
An investigation was made to determine whether the wilting 
coefficient of a soil can be computed from physical measurements 
of its moisture retentivity. A comparison of the wilting coefficient 
is made with the moisture equivalent, the hygroscopic coefficient, 
the moisture-holding capacity, and the mechanical analysis, for 
a series of soils ranging from sand to clay. From this comparison, 
a series of linear relationships is established, as expressed in the 
following equations, which form a means of computing the wilting 
coefficient when direct determinations are not feasible. 
moisture equivalent 
1.84 (10.007) 
hygroscopic coefficient 
0.68(1+0.018) 
moisture holding capacity—21 
2.90(1+0.021 
o.o1 sand+o. 12 silt+-o. 57 clay 
I+0.025 
The second term of the quantity within the brackets shows the 
probable error of the relationship in each case, and constitutes a 
measure of the relative accuracy of the different methods. 
U.S. DEPARTMENT OF AGRICULTURE 
BurEAv oF Piant INpustRY 
Wasurincton, D.C. 
Wilting coefficient = 
Wilting coefficient = 
Wilting coefficient 
Wilting coefficient 
