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



lated from this formula agree with sufficient accuracy with the ob- 

 served values of y. 



Dr. Loughridge states that the limit of moisture movement was 

 reached at the end of 195 days at 50 inches. It is interesting to note 

 that the position of the moisture at the end of one year as calculated 

 from the formula would be 56.2 inches ; at 390 days, twice the time of 

 observation, 57 inches: two years at 66.2 inches; and three years, 72.9 

 inches, or only 22 inches above what it was at the end of 195 days. 



OPEN VERSUS COVERED FLUMES. 



The results obtained from the covered flumes are very similar to 

 those obtained from the flumes open on top to evaporation. "With one 

 or two exceptions the results with the covered flumes do not differ 

 materially from what could have been foreseen from the results with 

 the open flumes. The essential difference is one of degree, as would 

 have been expected. One striking exception is the fact that in every 

 instance of the 25 or 30 experiments the open flume has the more 

 rapid rate of movement of the moisture for the first one to five weeks 

 of the experiment, the difference in time depending upon the char- 

 acter of the soil. The heavier the soil and the longer the open flume 

 maintained the more rapid rate of movement of the moisture. The 

 more rapid rate of movement is maintained irrespective of evapora- 

 tion. This fact will be more clearly seen from the data submitted 

 below. There is, as would be expected, a small difference in the rela- 

 tive percentages of moisture contained in two flumes, and especially 

 is this difference noticeable in the upper layers of soil. 



Inasmuch as the results with the covered flumes differ only in de- 

 gree from those of the open flumes, it is not deemed that the sub- 

 mission of all the data and its discussion would add materially to the 

 value of this report. For that reason there will be discussed only 

 one covered flume in its relation to its comparable open flume. The 

 two flumes that will be presented in detail are the horizontal flumes 

 70 and 71 containing the soil from Upland. This is a gravel and 

 sand soil containing but little clay. The selection of this particu- 

 lar soil for presentation is merely for convenience, as the results 

 obtained by its use are similar to the results obtained from other soils; 

 figure 3 (p. 23) shows the curves representing the movement of 

 moisture in these two flumes. 



Table 38 gives the total movement of moisture in these two flumes 

 at the end of various periods of time. From this table it will be 

 observed that flume 70, which is open to evaporation, has the more 

 rapid rate of movement of the moisture up until the fifth clay. After 

 the fifth day flume 71. or the covered one, has a more extended move- 

 ment of the moisture and upon the thirtieth da t y this difference is 



