6 BULLETIISr 447^ U. S. DEPARTMEjS^T OF AGRICULTURE. 



3 inches. In all of the tubes containing soil taken from below the 

 first 3 inches the water level fell less than one-eighth of an inch in 

 48 hours, and part of this was due to evaporation. 



The smallness of the tubes used may have caused some compact- 

 ing during the process of sampling; also the plat sampled was un- 

 doubtedly more compact than one that had not been continuously 

 fallowed. For this reason a part of the experiment was duplicated 

 on land that had been fallow for only a few months. Samples were 

 taken with tin cans 5 inches in diameter and with thin cutting edges. 

 By this means samples were taken from the surface and from depths 

 of 3 and 6 inches without any mechanical compacting of the soil in 

 sampling. The penetration in these cans was then studied in the 

 same way as in the brass tubes. Water passed through the surface 

 3 inches at the rate of 1 inch in two hours. For the other sections 

 the rate was at least as slow as in the brass tubes. Evidently the soil 

 in the brass tubes was not compacted enough to make any material 

 difference in the rate of penetration except in the surface section. 

 Even in this section the difference in the rate was probably due in 

 part to the fact that in the field the surface soil in the second plat 

 was considerably looser than in the first one sampled. 



The extreme slowness with which water passed into these sections 

 proves that water movement in a wet soil of this type in the field 

 is exceedingly slow. That this slowness is partly due to the natural 

 compacting of the soil by swelling is shown by a comparison of the 

 rate at which water moved through soil under natural conditions 

 with the rate at which it moved in a saturated soil that was allowed 

 to expand freely, as is shown in the first experiment. At any rate, 

 water movement in this soil when it is wet is so slow as to be prac- 

 tically negligible in field practice. 



PENETRATION OF WATER INTO DRY SOIL IN THE FIELD. 



The experiments alreadj^ described indicated that in this type of 

 soil a dry condition was most favorable for water movement. In 

 order to measure the maximum water penetration in the soil, a num- 

 ber of experiments were made on a plat that was extremely dry. The 

 plat was covered with a very thin dust mulch. Beneath the mulch 

 the soil was cracked into very small lumps to a depth of 15 inches; 

 below 15 inches it was very hard, dry, and compact. 



The first experiment in this series was made for the purpose of 

 determining the permeability of the soil at various depths. For this 

 purpose, borings 8 inches in diameter, extending below the surface to 

 depths of 6, 9, 12, 15, 18, 21, and 24 inches, were made. Two gallons 

 of water was then poured into each hole. A like quantity of water 

 was applied to an equal area at the surface by means of a tin can set 

 1 inch into the soil. 



