Dec. 6. 1915 Influence of Growth of Cowpeas on Soil Properties 445 



and should be an index to friability (Table IV). Wollny compared the 

 porosity of cores similarly taken by measuring the relative amounts of 

 water needed to fill the pore space, but the principle is the same in 

 both cases. 



Table IV. — Apparent specific gravity of soil under various treatments as determined on 

 October 15, IQI2 



Pint No. and treatment. 



Weight of soil. 



Average 



weight of 



core. 



Apparent 

 specific 

 gravity. 



D (unplowed; clean). . 

 E (unplowed; cowpeas) 

 F (plowed; cowpeas). . 

 F (plowed; shade) .... 

 G (plowed; clean). . . . 



Gtk. 

 I. 957 

 1,865 

 I, 720 

 I7740 

 1,635 



1,936 

 1,884 

 1,739 

 1,752 

 I-, 742 



^■33 

 1.26 

 I. 17 

 I. 18 

 I. 19 



Checking the results found by the Wollny method with those show^n 

 in Table III, the same ratio is found to hold in every case. This gives 

 strong assurance that the use of the compactness device, by means of 

 which the results of Table III were obtained, is an accurate method of 

 measuring soil friability, and, in that it is easily and rapidly made, a 

 very desirable one. 



Table V. — Percentage of 7noisture in the various experimental plots on October 15, igi2 



A study of the moisture in the soil at the close of the experiment, as 

 shown by Table V, reveals, as would be expected, that the plots in cow- 

 peas leave less moisture in the soil than do the un cropped plots kept 

 clean. However, this use of water is from below the second foot. Under 

 cowpeas the surface foot, as well as the second foot, contains as much 

 water as is found in the uncropped plots for the same depth. It would 

 seem, then, that the cowpea plant is a comparatively deep feeder and the 

 shade of its leaves serves as a blanket to prevent evaporation. This con- 

 clusion is again borne out by a study of the moisture content of the soil 

 under the artificial shade. 



Now, since only the moisture in the first foot could possibly affect the 

 degree of compactness or of looseness at any one time, a direct comparison 



