24 



BULLETIN" 835, IT. S. DEPARTMENT OF AGRICULTURE. 



The figures within the small circles give in liters the quantity of 

 water removed from the tanks by the soil columns at the ends of 

 various periods of time. 



Table 11 gives the percentages of water used in 1, 3, 5, 10, 15, and 

 20 days of the total quantity used in 30 days. 



Table 11. — Water removed from tanks "by days expressed in percentages of 

 amount removed in 30 days. 









Flume. 







Number 

 of days. 

























20 



31 



50 



70 



90 





Per 



Per 



Per 



Per 



Per 





cent. 



cent. 



cent. 



cent. 



cent. 



1 



17 



22 



26 



18 



17 



3 



30 



36 



42 



30 



29 



5 



38 



42 



51 



36 



37 



10 



53 



58 



67 



52 



53 



15 



67 



70 



78 



64 



67 



20 



81 



81 



86 



79 



81 



30 



100 



100 



100 



100 



100 



Table 11 shows the relatively great use of water the first few 

 days of the experiment. In all cases more than one-half the total 

 quantity of water used in 30 days was used the first 10 daj T s or one- 

 third of the time. From 17 to 26 per cent of the total quantity used 

 in 30 days was used the first day and in two-thirds of the 30 days more 

 than 80 per cent of the water was used. The lighter the soil the 

 smaller the relative percentage of water used the first few days, and 

 the heavier the soil the greater the relative use of water during the 

 first few days. However, the lighter the soil the greater the total 

 quantity that will be used in long periods of time. This is the op- 

 posite of the conditions with the vertical flumes and is worthy of 

 note. The heavier the soil the less extended will be the wetted area 

 with the lapse of time, which condition is as would be expected. 

 That is, a sandy soil or a light soil will " sub " much farther in a 

 horizontal direction than a heavy soil. The results indicate also 

 that a heavy soil loses more water through evaporation when the soil 

 is 10 or more inches deep than a sandy soil. This can be accounted 

 for from the fact that the capillarity of the sandy soil is not suf- 

 ficiently great to keep the surface wetted to the optimum capillary 

 capacity for evaporation. It shows also the influence of gravity 

 even in these horizontal flumes 10 inches in depth. Table 12 gives the 

 percentage of the total distance moved and the percentage of the total 

 water used in 30 days for different periods of time. 



