56 



BULLETIN 835, IT. S. DEPARTMENT OF AGRICULTURE. 



of the experiment. This can be accounted for in two ways: First, 

 all evaporation could not be eliminated without liability of trapping 

 the air within the flume. Second, there is, as has been shown 

 previously, an increase in the percentage of moisture contained in 

 different portions of the flume with the age of the experiment. 



Table 41 gives the use of water by these flumes in equivalent depth 

 over an area equal to the cross section of the flumes. 



Table 40. — Water required 

 at various time* to ad- 

 vance moisture an aver- 

 age distance of 1 inch. 



Table 41. — Water removed 

 from tanks at various 

 times, in depth. 





Flume. 







Fiume. 



Number 

 of days. 









•Number 

 of days. 















70 



71 







70 



71 





c. c. 



C. C. 





Inches. 



fll'-Jicf, 



1 



259 



281 





1 



3.66 



3.66 



5- 



288 



291 





5 



7.32 



7.32 



10 



311 



310 





10 



10.37 



10.37 



15 



328 



321 





15 



12.81 



12.81 



20 



371 



326 





20 



15. 86 



1 1. 64 



30 



412 



333 





30 



20.13 



1 1. 69 



It is found that flume 70 used the equivalent of 20.13 inches of 

 water in 30 days, while the covered flume (71) used the equivalent of 

 17.69 inches or about 12| per cent less than the open flume. These 

 figures show that for the last ten days of the experiment the open 

 flume used 4.27 inches and the closed flume 3.05 inches or a little over 

 25 per cent less water than the open flume. These last figures would 

 represent the effect of evaporation. In other words, during the last 

 ten days of the experiment evaporation from the flume took care of 

 at least 25 per cent of the water furnished by the wick. 



EFFECT OF TEMPERATURE ON SOIL-MOISTURE CONDITIONS. 



As has been stated previously, a temperature at and below the 

 freezing point appears to have influenced to a marked extent the dis- 

 tribution of moisture within the flumes. Some few soil samples taken 

 from the flumes during the winter of 1916-17 gave results contrary 

 to what was to be expected. In the sampling of the flumes, two 

 samples were taken from each point of sample. The soil from the 

 top 5 inches was placed in one bottle and the soil from the bottom 

 5 inches in a second bottle and the moisture determined for each 

 separately. There are two basic reasons why the percentage of mois- 

 ture in the top samples should be less than that in the samples from 

 the bottom 5 inches. First, the sample from the upper 5 inches 



