138 Journal of Agricultural Research voi. x, N0.3 



As a whole, then, figures 17, 18, and 19 indicate that water is gained 

 most rapidly during the first week by soils having about 8 per cent of 

 moisture. After the first week the gain increased uniformly with 

 decrease in initial percentage. 



The relatively small decrease in the attractive force for water with an 

 increase in initial content up to 8 per cent, together with the greater 

 ease with which moisture moves through the soil with an increase in 

 water content, allows the maximum movement in the first week in the 

 soil having 8.24 per cent. The slight gain in weight even for the first 

 week in the soils with more than 8 per cent of moisture seems to indicate 

 a marked decrease in the attractive force for water above this point. 



That this is true seems to be shown, because after the first week, 

 when the moisture content had risen somewhat, hardly any appreciable 

 gain was observed. In the soils having less than 8 per cent the resist- 

 ance of the dry soil to moisture movement prevented an equilibrium from 

 being established as soon as in the wetter ones. Consequently a con- 

 siderable movement will take place in the dry soil after the wet one has 

 apparently come to rest. It must be kept in mind that the source of 

 water was an unsaturated soil which itself has great water-holding power, 

 as pointed out by Briggs and McLane (6) and Bouyoucos (3). With 

 every loss of moisture from the source into the drier soil there is a stronger 

 resistance to the movement in the wet soil. Only soils with a very 

 great attractive force for water can draw water out of such a soil for any 

 length of time. 



Effect on Distribution with a Large Amount op Unsaturated Soil as the 

 Source of Moisture Supply 



In the fourth experiment on the effect of initial percentage on the move- 

 ment of soil moisture, columns of soil formed by filling eight sets of brass 

 tubes of three sections each with Greenville loam having 1.49, 3.27, 4.83, 

 10.21, 12.44, ^^^ 14.20 initial percentages were inserted to a depth of 

 about 4 inches into Greenville loam containing 30.45 per cent of water. 

 This wet soil was held in a moisture-proof wooden tub. The tubes of 

 soil were inserted horizontally through eight holes bored in the sides of 

 the tub. The apparatus presented the appearance of a wheel with the 

 hub as the source of moisture. The open ends of the tubes and the top 

 of the tub were carefully sealed to prevent all loss of water by evapora- 

 tion. The experiment lasted from May 24 until September 12, 1916, 

 when the tubes were removed and the moisture determined for each 

 2-inch section of the eight 24-inch tubes. 



Figure 20 gives the average moisture content for each of the eight 

 columns of soil. Scarcely more than a 2 per cent difference is found 

 between the highest and lowest moisture contents. The column of soil 

 originally having 4.83 per cent of moisture absorbed the most water, while 

 that with an initial percentage of 10.21 had the least. 



