400 Journal of Agricultural Research voi. x, no.s 



DOWNWARD MOVEMENT IN SOILS DIFFERING IN INITIAL WATER 



CONTENT 



EXPERIMENTS 



There were three subexperiments, which differed from one another 

 only in the initial moisture content of the soils, it being approximately 

 0.5, i.o, and 1.5 times the hygroscopic coefficient, respectively (Table 

 VII). The first would represent the lower limit of moisture in exposed 

 surface soils after a prolonged drouth during hot weather; the second 

 would correspond to the condition found just after a very heavy crop 

 had matured during warm, dry weather and so had had an opportunity 

 to exhaust fully the available soil moisture; while the last would repre- 

 sent that moisture content at which very shallow-rooted plants might 

 be expected to begin to suffer permanent wilting — the wilting coefficient 

 as defined by Briggs and Shantz (6, p. 9). 



All the soils mentioned in Table VI were used, with glass cylinders 

 14.24 inches (36.2 cm.) high and 3.07 inches (7.8 cm.) in internal diam- 

 eter. To bring the soil to the desired moisture content, a weighed 

 quantity of air-dried material, of which the moisture content had pre- 

 viously been determined, was placed upon a large sheet of oilcloth on 

 the floor of the mixing room, and while the mass was being shoveled 

 over, the calculated amount of water was added in small portions. 

 The whole was then mixed thoroughly, first by shoveling, then by 

 passing it twice through a swinging sieve of }i-\nch. mesh, and finally 

 by again shoveling, after which it was immediately placed in a large 

 covered can, allowed, to stand for several days, again passed through 

 the swinging sieve, returned to the can, and kept in it until transferred 

 to the cylinders. 



In filling the cylinders the soil was added very slowly with constant 

 tamping, care being taken to insure the firmness of that already in before 

 adding more. Blows as uniform as possible were delivered by means 

 of a tamper consisting of a 2 -inch rubber stopper on the end of a ^-inch 

 iron gas pipe 3 feet long. 



One inch of water was added to the surface of each of the cylinders. 

 In order to make the initial penetration of the water more uniform, 

 the cylinders were inverted in flat-bottomed metal trays, the desired 

 amount of water was added and was allowed to rise into the soil by 

 capillarity until all or nearly all had been absorbed, after which they 

 were placed right side up and covered to prevent evaporation. 



■ In each of the three experiments the water was applied to all the 

 cylinders at practically the same time, they having been filled and 

 inverted in the trays and the measured quantity of water required for 

 each placed beside it in a beaker. To facilitate the escape of the air 

 expelled by the entering water, a fine wire was placed under the edge 

 of the cylinder. Then the beakers were emptied into the trays as 



