96 
BULLETIN 1059, U. 
DEPARTMENT OF AGRICULTURE. 
Table 4. — Moisture equivalents in several types of soil in relation to capillary 
moisture and wilting coefficients. 
Description of group. 
Mean 
capil- 
lary 
mois- 
ture. 
Mean -. r „,„ 
mois- Mean M 
ture ^£8 ratio 
e ^ uiva " cient ^-E./C. 
lent. cient - 
Mean 
varia- 
tion. 
W. 
Mean Mean 
rat?? Mean Mean Varia " 
vr \r v aria- ratio tion 
p-'^- tion. W.C./C. within 
group. 
9 Michigan and Nebraska 
sands: humus not over 3 
per cent 
5 Michigan and Nebraska 
sands: humus 3 percent to 
21 per cent 
9 Pikes Peak gravels: humus 
2.1 per cent, clay 3.7 per 
cent (maximum i 
3 granitic loams (spruce); 3 
to 4 per cent humus 
3 granitic loams ('spruce); 4 
to 8 per cent humus 33.09 
4 granitic loams (spruce); S 
to 27 per cent humus 60. 13 
1 prairie clay: 70 per cent silt 
and clay, very little humus. 37. 77 
P.ct. 
21.82 
4o. 
13.13 
20.47 
P.ct. 
5.49 
19.24 
4.92 
P.ct. 
1.73 
2.58 
0. 2.53 
12.62 3.36 .621 
20.76 
3. 36 . 632 
43.09 14.86 
0. 055 
040 
042 
,054 
,077 
0. 320 0. 035 
28. 79 
,90 
,762 
.357 
.530 
.266 
.307 
.348 
.310 
.028 
,006 
,030 
0.080 
.152 
.200 
.165 
.193 
.242 
.236 
0.016 
.023 
.030 
.014 
.010 
.051 
Average of groups • .533 
Mean variation be- 
tween groups , ; i 1624 
,34S 
.0.543 
.034 
.181 
.0419 
1. There are three outstanding facts in connection Avith these data, 
clearly shown by the diagram. The first of these is that the two 
groups of sands show an extremely large proportion of the capillary 
water removable by the force of 100-gravity. and correspondingly 
low wilting coefficients. This speaks for the light hold which the 
sands have on their moisture, when even approaching saturation. 
2. The second conspicuous fact is that, with the exception of the 
granitic gravels, the wilting coefficients and moisture equivalents 
rise and fall somewhat proportionately. The gravels have the 
smallest capacity for capillary water, a very weak hold on a large 
part of it. and a strong hold on the remainder. This is partly caused 
by a small quantity of clay derived from the feldspar, but more 
largely to the fact that the feldspar is itself somewhat permeable. 
Coarse cleaned gravel of this type has been shown to have a capil- 
larity of only 2.90 per cent, but a moisture equivalent of 1.70 per 
cent. It seems likely that practically all of the latter would be non- 
available. 
3. Another important point to be noted is the very small amount 
of water removable from the prairie clay by the moderate centrifu- 
gal force, and the correspondingly high wilting coefficient. 
4. Finally, although the influence of humus is somewhat obscured 
by the fact that increasing amounts of it in one general soil type are 
usually accompanied by increasing amounts of silt and clay, it seems 
fairly certain that the humus does not yield up its moisture any too 
readily and that it may tend to make the wilting coefficient relatively 
high by preventing capillary movement to the roots. It must also 
