86 J. W. SHIVE AND B. E. LIVINGSTON 



Desert Laboratory and the latter from the experiment grounds 

 of that institution. The air dry soils were sifted through a wire 

 screen with openings 2 mm. in diameter, and a sufficient quaii- 

 tity of each was stored for use during the work. Plants were 

 grown in the clay loam and in two mixtures of this and sand, 

 one mixture containing equal parts by volume, and the other 

 one part by volume of loam and three parts of sand. The re- 

 quired volumes of the two original soils were measured in the air 

 dry condition, without any packing, as by jarring or tapping. 

 The mixtures, after having been made as uniform as possible, were 

 passed twice through a sieve before being used. Their moisture 

 holding capacities were determined by means of the method of 

 Hilgard/ which employs sheet metal pans with lateral walls 

 1 cm. high, the bottoms being perforated. The results are stated 

 in terms of percentage of dry weight. This method is the same 

 as that used by Briggs and Shantz and by Caldwell, and the water 

 holding powers dealt with in the present study should therefore 

 be comparable with the similar data given by those authors. 

 Table I presents these moisture holding capacities of the three 

 soils here used (these data being averages from six determinations, 

 which were in close agreement), together with then* respective 

 compositions in terms of the original sand and clay loam. 



The formula empirically derived by Briggs and Shantz {loc. cit. 

 (4) , page 68) , for expressing the relation between the moisture hold- 

 ing power of any soil and its water residue at permanent wilt- 

 ing of plants rooted therein, involves a decrease of the value 

 of the moisture holding power (expressed as per cent, of dry 

 weight) by the subtraction therefrom of a'Constant (21), and a 

 dividing of the remainder by another constant (2.90). The re- 

 sult is expressed as per cent, of dry weight of the soil and its 

 value should be practically identical, according to the experi- 

 ments and deductions of these writers, with that of the actual 

 soil moisture residue as derived from experimental permanent 

 wiltings, similarly expressed. The calculated moisture residues 



^ Hilgard, E. W., Soils, their formation, properties and composition. Page 209. 

 New York, 1911. 



