a a ee 
WATER PENETRATION IN GUMBO SOILS. 3 
- these depths may be somewhat higher than in the first foot. The 
difference is not great, and as a whole the mechanical composition 
of the first 3 feet may be considered uniform. 
WATER CAPACITY OF THE GUMBO SOIL. 
The water-carrying capacity of this soil is high, and the minimum 
point to which crops can utilize the water is correspondingly high. 
The soil, when filled, will carry about 30 per cent of water, of which 
about 15 per cent is available for the use of crops. The character of 
the soil is such, however, that the crops do not root deeply, owing 
either to the lack of water in the lower depths or to the impervious 
nature of the soil. In spite, therefore, of the large quantity of 
water that can be obtained by the crop from the soil near the surface, 
the shallowness of feeding materially reduces the quantity of water 
actually available. 
PRODUCTIVITY OF THE GUMBO SOIL. 
The producing capacity of the soil is high. There is no evidence of 
a deficiency of any mineral element essential to crop production. 
When sufficient water is supplied, abundant crops are obtained. The 
high productive capacity of this soil is evidenced by the yields ob- 
tained on plats not irrigated in 1915, when the rainfall was unusually 
iavorable both in amount and in distribution. The average acre 
yields obtained were 72.2 bushels of barley, 36.2 bushels of winter 
wheat, 57.6 bushels of spring wheat, 125.6 bushels of oats, and 44.5 
tenes of corn. 
CHANGES IN THE VOLUME OF THE SOIL DUE TO WETTING AND 
DRYING. 
The large amount of clay present makes this soil subject to extreme 
changes in volume with changes in its water content. When the soil 
is wet it swells and compacts; when dried it shrinks and cracks. 
That the change in volume is great enough to cause a material 
change in physical structure is shown by the results of the follow- 
ing experiment, which was made for the purpose of obtaining a 
measure of this change. - 
The volume of oven-dried compact samples of soil was determined. 
These samples were then immersed in water and allowed to expand 
freely and the volume redetermined. The volume of the soil from 
the first foot increased 2.2 times. The volume of that from both the 
second and third feet increased 2.5 times. 
These changes in volume, due to variations in moisture content, 
result in the following structural differences: 
When dry this soil is usually covered with a natural mulch about 2 inches 
deep caused by the crumbling of the surface soil. Beneath this mulch is a 
layer of soil honeycombed with cracks. The number of these cracks and the 
