WATER PENETRATION IN GUMBO SOILS. 11 
That this slow movement in the dry subsoil is due to the com- 
pacting of the wet soil above is further shown by laboratory experi- 
ments on dry soil under field conditions. It was found that where 
the soil was allowed to swell freely the water would move at least 
an inch in five minutes in the heaviest section of the soil. Since the 
rate of movement under field conditions is so much slower, there is 
no doubt that the compacting of the wet soil in the field is so great 
that it renders any movement of water through it almost impossible. 
Water movement in the dry subsoil is therefore limited by the rapid- 
ity with which the water can make its way through the wet soil above. 
SUMMARY. 
Water movement in the gumbo soils of the Belle Fourche Recla- 
mation Project may be summed up as follows: 
On a dry soil, penetration takes places rapidly to a depth of about 
2 feet because of the cracked condition of the soil near the surface. 
After the layer of easily penetrated soil becomes wet, it becomes 
so swollen and compact that it is nearly impervious, and further 
water movement is very slow. 
The fact that moisture can move only very slowly in the wet sur- 
face soil would make it necessary to run water over the soil for a very 
long time in order that any considerable portion might be absorbed. 
This is not practicable, for the experiment with a dry subsoil showed 
that water from the surface penetrated almost as deep in a few 
minutes as it did in 10 days, so that the increase in the amount of . 
moisture absorbed where the water stands for any considerable 
length of time over that taken in when the soil is simply covered 
would be so small as to be negligible. After a field has once been 
covered with water little benefit can result from having water con- 
tinue to stand on or flow over the soil. 
It is interesting to note the radical difference in water absorption 
between this soil and the sandy loam soil at Scottsbluff. The maxi- 
mum rate of absorption is obtained on the wet soil at Scottsbluff and 
on the dry soil on the Belle Fourche project. These diametric differ- 
ences apparently are due to the physical differences between the two 
soils and show clearly that a satisfactory practice on one type of soil 
may not be equally successful under other soil conditions. 
The results of these experiments and observations can easily be 
applied in field practice, and recommendations for methods and prac- 
tices may be based upon them. 
The following points relative to the application of water by irri- 
gation to these gumbo soils are clearly shown: 
(1) Water should be applied only when the surface is dry. 
(2) The quantity of water absorbed will depend upon the dryness and con- 
sequent cracked condition of the surface soil. 
