96 



BULLETIN K'-.it. U. S. DEPARTMENT OF AGRICULTURE. 



'abi e 1 Moisture equivalents in several types of soil in relation to capillary moisture 



and wilting coefficients. 



rip t ion of group. 



Mean Mean Ar „ an 



capil- mois- : x ™ Mean 



'ary ture ™* I ratio 



" lols - e ? m J a - cient. M ' E - /C 



ture. lent. 



■I \! i Nebra 



humus ii' 'i ovei 3 P. ct. 



21.82 



! Nebra 



■ to 



-43. 78 



humus 

 per 



maximum) 13.13 



ruo 



r oenl humus 20.47 



pruce); i 



r cenl humus 33.09 



ruo 



ni humus no. 13 



7u per cent silt 

 and clay, very little humus. 37.77 



'UpS 



Mean variation be- 

 roups 



P. ct. P. ct. 

 5.49 1-73 



19.24 



4.92 

 12.62 

 20.76 

 43.09 

 28.79 



6.99 



2.58 

 3.36 

 6.36 

 14.86 

 8.90 



0.253 



.407 



.377 

 .621 

 .632 

 -692 

 .762 



.533 

 1624 



Mean 

 varia- 

 tion. 



0.055 



.090 



.040 

 .042 

 .054 

 .077 



SB S 



0.320 



.357 



.530 

 .266 

 .307 

 .34S 

 .310 



0.035 



.028 



.038 

 .006 

 .030 

 .066 



.348 

 .0543 



.034 



Mean 

 Mian varia- 

 ratio tion 

 W.C. C. within 



group. 



0.080 



.152 



.200 

 .165 

 .193 

 .242 

 .236 



0.016 



.023 



.030 

 .014 

 .010 

 .051 



.181 

 ,0419 



.021 



1 . There are three outstanding facts in connection with 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 

 smallesl capacity for capillary water, a very weak hold on a large 

 pari 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 <»f only 2.90 per cent, but a moisture equivalent of 1.70 per 



mi . 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 fad 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 



