72 



THE WATER-SUPPLYING POSTER OF THE SOIL 



state of the soil — as has been indicated by the studies of Cameron and 

 Gallagher^ — and if the optimum for this soil hes in the neighborhood 

 of 15 per cent of soil moisture, it is not surprising to find that the degree 

 of packing of the 20 per cent soil seems to determine in which of our 

 two categories it belongs. Following this suggestion, we may say, 

 tentatively at least, that those of our soils which were at or above the 

 optimum critical point in moisture content and were not firmly packed 

 failed to maintain a rate of supply to the osmometer, those below this 

 point, similarly packed, were able to maintain such a rate, and the 



Table 9. — Average hourly rates of absorption by osjnomeler A, operating against soi s of various 

 moisture contents, together mith corresponding mean rates for third and later hours. 



*Af ter hour 2. 



tBut there is a general fall in the rate to the end of the experiment. 



well-packed sample of the 20 per cent mixture behaved as though it 

 were below the critical point. How much truth there may be in this 

 generalization, and what may be its importance if true, must remain 

 for future investigation to bring out. 



Turning to the relative magnitudes of the absorption rates, as shown 

 in table 9, the initial average hourly rates are seen to give, generally, 

 an indication of the moisture content, as ought of course to be expected. 

 The peculiarly high initial rate shown by the first test of the 10 per cent 

 soil, as well as the near approach to agreement in the initial rates for 

 the 15 per cent soil and for the second test of the 10 per cent, are not 

 explainable from any information at hand. As shown in the heading 

 of table 7, a marked difference was apparent, as to packing, between 

 the two samples of the last-named soil mixture; but a priori con- 

 siderations would be out of place in this connection and we are unable 

 otherwise to discuss the matter without further experimentation. 



'Cameron, F. K., and F. E. Gallagher, Moisture content and physical condition of soils. 

 Dept. Agric, Bur. Soils Bull. 50. 1908. 



U. S. 



